![carbon utilization technologies is the mineralization process which is classified into
two types: in situ and ex situ mineralization. Mineral trapping or in situ mineraliza-
tion is underground geological sequestration where a fraction of injected CO2 reacts
with alkaline rocks in the target formation and it forms solid carbonate species. In ex
situ mineralization, CO2 reaction takes place in an industrial process. The final
product obtained by this technology can store CO2 for a long time.
2 R. Mahmoudi Kouhi et al.
Fig. 1.1 Carbon utilization categories and products
The most important challenges facing carbon utilization technologies are high
energy consumption, long-term effects, and the cost of raw materials required.
Economic issues regarding different methods, durability over time, and insufficient
maturity of the technologies are the other issues that should be considered. One of
the most important advantages of using carbon utilization is its ability to be used in
sectors that are responsible for around 53% of carbon dioxide emitted into the air
(Fig. 1.2). The usage of alternative fuels leads to a reduction in carbon emissions in
the transport and electricity and heat sectors. In addition, the construction and
industrial sectors reduce their carbon emissions through the manufacturing of car-
bonates from industrial wastes. Utilization approaches have the potential to reduce
about one-fifth of the emissions necessary in the industrial sectors. It is the only
option for significantly reducing direct emissions from other industrial point sources,
and it will play a significant role in reducing CO2 emissions from fossil fuel–based
power plants. It is estimated that the use of carbon utilization will help cut CO2
emissions by up to 32% by 2050. Up to 2060, industrial operations may accumulate
more than 28 Gt of CO2, with the chemical, steel, and cement subsectors accounting
for the majority of this [2].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-15-320.jpg)
![1 Carbon Utilization Technologies & Methods 3
Fig. 1.2 Gross estimate of greenhouse gas emissions by various segments. (Modified after [1])
1.2 CCS Versus CCU
Carbon capture and storage (CCS) and carbon capture and utilization (CCU) refer to
technologies that capture CO2. In CCS methods, CO2 is permanently stored while
the major purpose of CCU is to convert it into valuable products such as fuels and
chemicals. Both CCS and CCU are based on carbon capture, but the difference is
what happens after the capture phase. Figure 1.3 shows the scope of each of these
technologies’ effects, as well as their similarities. As can be observed, the method of
in situ mineralization is the borders between the usage of CCU and CCS technolo-
gies, implying that these two approaches can be classed in both.
1.3 Fuels and Chemicals
The main source of energy used in current energy systems is fossil fuels, which result
in the generation of large amounts of carbon dioxide when used in transportation and
industry. Therefore, it is necessary to find alternatives for them. Carbon dioxide
conversion into fuels and chemicals reduces greenhouse gas emissions and depen-
dence on petrochemicals. The utilization of CO2 as a feedstock for fuel synthesis as
well as chemicals has shown many potential environmental and economic benefits.
Several industries, including fuel cells, power plants, and transportation, can utilize
the produced fuel. CO2 is a thermodynamically stable molecule; thus in order to
utilize it and produce high fuel yields, a lot of heat and catalyst inventory must be](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-16-320.jpg)
![applied. Carbon dioxide can be utilized to produce energy carriers and transportation
fuels such as methane, methanol, formic acid, dimethyl ether, carbon monoxide or
synthesis gas (syngas), and Fischer-Tropsch fuels. In addition to synthetic fuels, it is
also possible to produce various chemicals such as urea, polymers, formic acid,
salicylic acid, acyclic carbonates, cyclic carbonates, and fine chemicals such as
biotin using carbon dioxide. Table 1.1 summarizes some chemicals and fuels that
are currently being manufactured industrially from CO2.
4 R. Mahmoudi Kouhi et al.
Fig. 1.3 The relations of CCU and CCS technologies
Table 1.1 Main chemicals and fuels that are now manufactured from CO2 on a worldwide scale
[3, 4]
Product
Production
(Mt/year)
CO2 utilization
(tCO2/t product)
Technology readiness
level
Methane 1100–1500 2.750 CO2 methanation: 7
Methanol 65.00 1.373 Hydrogenation of CO2:
8–9
Formic acid 1.00 0.956 Electrochemical reduc-
tion of CO2: 6
Dimethyl ether 11.40 1.911 1–3
Liquid fuels – 2.6 5–9
Urea 180.00 0.735 9
Salicylic acid 0.17 0.319 9
Polycarbonate 5.00 0.173 9
Polyurethane 15.00 0.300 8–9
Cyclic
carbonates
Ethylene
carbonate
0.20 0.499 4–5
Propylene
carbonate
0.20 0.431
Dimethyl carbonate 1.60 1.466 8–9](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-17-320.jpg)
![þ þ ð Þ
1 Carbon Utilization Technologies & Methods 5
1.3.1 Methane Production
One of the most significant energy sources is methane (CH4), which is mostly
obtained from natural gas, a fossil fuel source with relatively low costs, and is
used to generate heat, power, and value-added chemicals [5]. CO2 methanation
has recently attracted considerable interest, due to its use in Power-to-Gas (PtG)
technology and the upgrading of biogas [6]. In order to effectively incorporate
renewable energy sources, such as wind and solar energy, into the current energy
mix, PtG processes are viewed as a potential and intriguing solution [7]. In this
technology, hydrogen generated from surplus renewable energy is chemically
changed into methane, which can be stored and transported using the already-
existing, highly developed natural gas infrastructure, by reacting with CO2 [6].
Among the several PtM techniques already in use, catalytic CO2 hydrogenation
(methanation) has received the most attention, and demonstration units are already in
operation in a number of nations [5]. At the beginning of the twentieth century,
Sabatier and Senderens conducted the first studies of the methanation reaction, also
known as the Sabatier reaction. Through this reaction, CO2 and H2 are converted into
CH4 and H2O (Eq. 1.1) [8].
CO2 þ 4H2 → CH4 þ 2H2O, ΔH = - 165 kJ:mol- 1
ð1:1Þ
Due to the exothermic nature of this reaction, products with low temperature and
high pressure are preferred in terms of thermodynamics [8]. CO2 hydrogenation can
be thought of as a result of combining reverse water gas shift (RWGS) reaction and
CO hydrogenation (Eqs. 1.2 and 1.3) [9].
CO2 þ H2 → CO þ H2O, ΔH0
r = 41:2 kJ:mol- 1
ð1:2Þ
CO 3H2 → CH4 H2O, ΔH0
r = - 206:3 kJ:mol- 1
1:3
Reactors for methanation might be either biological or catalytic (Fig. 1.4).
Methanogenic microorganisms function as biocatalysts in biological methanation
[9]. A biogas plant’s fermenter or a separate bioreactor can be used to conduct this
process [10].
Metals from group VIII of the periodic table catalyze the methanation reaction.
Ru was shown to be the most active metal catalyst, followed by Fe, Ni, and Co. Ni is
typically chosen as the active component because of its high selectivity and reactiv-
ity, and because it is reasonably priced [11]. Despite having advantages over Ni
systems, Ru catalysts are more expensive. Given the low cost and wide availability
of methane from natural gas, hydrogenation of CO2 to methane is not now feasible
on a big scale and is not anticipated to be in the near future. Furthermore, methane
has a significantly lower economic value than the conversion of CO2 into a variety of
other compounds [12].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-18-320.jpg)
![6 R. Mahmoudi Kouhi et al.
Fig. 1.4 Concepts for reactors that produce substitute natural gas [9]
The electrochemical reduction of CO2 is another potential method for producing
methane from CO2. This technique is still being validated in the lab. However, recent
results have emphasized the attractive characteristics of this path [5]. Currently, only
copper is capable of catalyzing the conversion of CO2 into hydrocarbons, particu-
larly methane, in an aqueous solution. Higher overpotentials, low activity, and poor
product selectivity are problems with conventional Cu electrodes [13]. To create
catalysts with improved methane selectivity, more research is still required.
1.3.2 Methanol Production
The most basic liquid hydrocarbon that can be used as a fuel, a hydrogen carrier, or a
feedstock for creating more intricate chemical compounds is methanol (CH3OH)
[14]. Formaldehyde, acetic acid, dimethyl ether (DME), and methyl tertiary-butyl
ether (MTBE) are the primary chemical derivatives of methanol [15]. The methanol-
to-olefins process creates light olefins like ethylene and propylene, which can be
utilized to make polymers and hydrocarbon fuels. Additionally, methanol is
converted into dimethyl carbonate in supercritical CO2, which is a helpful interme-
diary for derivatives utilized in polycarbonates and polyurethanes [16].
According to Eq. (1.4), syngas, which has a CO/H2 mixture, is being used to
create methanol on an industrial scale. Currently, syngas (mixture of CO and H2)
produced mostly from natural gas reforming is transformed into methanol at tem-
peratures between 250 and 300 °C and pressures between 5 and 10 MPa, using a
CuO/ZnO/Al2O3 catalyst [15, 17].
CO þ 2H2 → CH3OH, ΔH = - 90:6 kJ:mol- 1
ð1:4Þ
Currently, a little amount of CO2 (up to 30%) is typically added to the syngas.
The energy balance and methanol yield both considerably increase with the addition
of CO2 to the CO/H2 feed. Syngas is low in hydrogen and high in carbon oxides
(CO and CO2). The CO in syngas is transformed to CO2 via the water-gas shift](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-19-320.jpg)
![þ þ ð Þ
(WGS) reaction to increase its H2 content and promote methanol synthesis
(Eq. 1.5) [16].
1 Carbon Utilization Technologies & Methods 7
CO þ H2O → CO2 þ H2, ΔH0
298 = - 41:2 kJ mol- 1
ð1:5Þ
The catalytic hydrogenation process shown in Eq. (1.6) is the most direct method
for producing methanol from CO2 and involves the production of H2 using water
electrolysis, ideally with the use of renewable energy, and the subsequent combina-
tion with CO2 waste streams to create methanol, which is known as the Power-to-
Methanol process. This process involves the RWGS (Eq. 1.7) as a secondary
reaction and is less exothermic than the syngas-based approach. RWGS reaction is
regarded unfavorable since it consumes H2 and reduces the yield of methanol
synthesis. It was discovered that the rate of the direct methanol synthesis from
CO2 was inhibited by the water produced as a byproduct. [5, 15, 16].
CO2 þ 3H2 → CH3OH þ H2O, ΔH = - 49:5 kJ:mol- 1
ð1:6Þ
CO2 H2 → CO H2O, ΔH0
r = 41:2 kJ:mol- 1
1:7
Hydrogenation of carbon dioxide to methanol is an efficient CO2 utilization
technique and is considered an effective sustainable development strategy. This
method is technically comparable to the production of methanol from syngas for
industrial use [16]. If direct hydrogenation of CO2 to methanol is replaced with
methanol production from syngas, improved catalysts are greatly needed [12]. In
comparison to conventional synthesis, this method has a better water footprint, but
still lacks competitive economic viability [4].
The electrochemical reduction of CO2 using protons and electrons as a source of
H2 is another method for producing methanol. Due to its complicated kinetics, this
reaction requires efficient electrocatalysts. One of the most effective materials for the
electrochemical conversion of CO2 into alcohols, including methanol, has been
recognized to be copper or copper-based electrodes. In order to improve the elec-
trochemical CO2 reduction to CH3OH, the usage of copper alloys has also been
studied. Cu-Zn mixed oxides make up the majority of commercial catalysts used
today to produce methanol, demonstrating the metals’ synergistic influence on
methanol synthesis [5, 12].
1.3.3 Dimethyl Ether (DME) Production
The simplest ether is dimethyl ether (DME), which has the chemical formula
CH3OCH3. DME has physical properties similar to liquefied petroleum gases
(LPG) such as propane and butane. DME has been marketed as a diesel substitute
since the mid-1990s. With a high cetane number (55-60), DME has several desirable](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-20-320.jpg)
![ð Þ
þ þ ð Þ
þ þ ð Þ
ð Þ
characteristics over conventional fuels, including very low emissions of pollutants
(SOx, NOx, CO, and particulate matter) [18, 19].
8 R. Mahmoudi Kouhi et al.
Indirect synthesis (two-stage) and direct synthesis from syngas (single-stage) are
typically the two methods used to produce DME. In the single-stage method, DME is
prepared directly from syngas in a single reactor [20]. Fixed-bed reactors have been
used for the majority of theoretical studies on single-step DME production [21]. In
the two-step process, syngas is first transformed into methanol (Eq. 1.8), which is
then dehydrated to produce dimethyl ether (Eq. 1.9). Zeolites and Al2O3, in partic-
ular, have been suggested as acid catalysts for the dehydration of methanol to DME
[22]. In a reactor, WGS reaction can occur concurrently (Eq. 1.10) [19].
Methanol synthesis : CO þ 2H2 → CH3OH, ΔH = - 90:6 kJ:mol- 1
ð1:8Þ
Methanol dehydration : 2CH3OH → CH3OHCH3 þ H2O, ΔH =
- 23:41 kJ:mol- 1
1:9
WGS : CO H2O → CO2 H2, ΔH0
298 = - 41:2 kJ mol- 1
1:10
While the current technologies for both methods rely on fossil-based syngas,
which again causes environmental issues, recent studies examine the possibility of
replacing syngas with CO2/H2 feed (Eqs. 1.11 to 1.13) [22].
CO2 hydrogenetion : CO2 þ 3H2 → CH3OH þ H2O, ΔH =
- 49:5 kJ:mol- 1
ð1:11Þ
RWGS : CO2 H2 → CO H2O, ΔH0
r = 41:2 kJ:mol- 1
1:12
Methanol dehydration : 2CH3OH → CH3OHCH3 þ H2O, ΔH =
- 23:41 kJ:mol- 1
1:13
The direct synthesis of DME from concentrated CO2 and H2 has lately gained
attention due to the growing interest in CO2 capture and valorization. The synthesis
of methanol is a recognized thermodynamically limited process. As a result, using
methanol immediately to create DME via a direct method has the advantageous
effect of pushing the equilibrium toward higher conversions. Because of the water
forming in greater quantities and the consequently more stringent thermodynamic
constraints, the CO2 to DME process is more difficult than the syngas method and
hence necessitates focused attention. A strategy that has been introduced to solve this
problem is the in situ removal of water produced in all individual reactions using a
membrane reactor [22].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-21-320.jpg)
![þ þ ð Þ
ð Þ þ ð Þ ð Þ ð Þ
ð Þ
1 Carbon Utilization Technologies & Methods 9
1.3.4 Formic Acid Production
Formic acid (HCOOH) serves as a platform for chemical energy storage in addition
to being a valuable chemical that is frequently used as a preservative and
antibacterial agent. Through its decomposition to CO2 and H2 and potential for
reversible transition back to formic acid, this acid is a known hydrogen storage
component [18]. Formic acid and its salts have a wide range of uses, including as a
starting chemical for esters, alcohols, or medicinal products, as well as in the
production of textiles, leather, and dyes and as a cleaning or disinfection
solution [23].
Formic acid is produced industrially most frequently via a two-step process: In
the first step, methyl formate is generated from methanol and CO (Eq. 1.14), and in
the second step, methyl formate is hydrolyzed into formic acid (Eq. 1.15). The
second step is thermodynamically unfavorable [5].
CH3OH þ CO → CH3COOH, ΔHr = - 29 kJ:mol- 1
ð1:14Þ
CH3COOH H2O → HCO2H CH3OH, ΔHr = 16:3 kJ:mol- 1
1:15
Also, formic acid can be produced through the hydrogenation of carbon dioxide
(Eq. 1.16). As a result of the conversion of gases into liquids during this process, the
reaction is entropically unfavorable. The reaction is therefore exergonic in the
aqueous phase and endergonic in the gas phase. However, when the reaction is
carried out in the aqueous phase, the presence of the solvent can change the reaction
thermodynamics and makes it slightly exergonic (Eq. 1.17). By employing additives,
such as specific bases like ammonia (Eq. 1.18) and triethylamine, the equilibrium
can be changed in favor of the product. Carbonates, bicarbonates, and hydroxides are
frequently used for the reaction in water [24, 25].
CO2 g
ð Þ þ H2 g
ð Þ → HCO2H l
ð Þ, ΔG0
298K = 32:9 kJ:mol- 1
ð1:16Þ
CO2 aq H2 aq → HCO2H aq , ΔG0
298K = - 4 kJ:mol- 1
1:17
CO2 g
ð Þ þ H2 g
ð Þ þ NH3 aq
ð Þ → HCO-
2 aq
ð Þ þ NHþ
4 aq
ð Þ, ΔG0
298K =
- 9:5 kJ:mol- 1
1:18
Numerous homogeneous and heterogeneous catalysts have been developed for
CO2 hydrogenation to formic acid on a lab scale. Transition metal complexes,
especially those based on Ir and Ru, have been used in a tremendous amount of
attempts, and the results are very remarkable. To become potentially practical, these
catalysts require further improvements in selectivity to formic acid and stability.
Heterogeneous catalysts, on the other hand, are less studied for this reaction;
however, recently the number of examples has notably increased. The heterogeneous
catalysts are characterized as follows, with clear practical advantages for continuous](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-22-320.jpg)
![þ þ ð Þ
operation and product separation: heterogenized molecular catalysts and
unsupported and supported bulk/nanometal catalysts [18].
10 R. Mahmoudi Kouhi et al.
Because of the high market value and widespread use of formic acid, direct
electrochemical reduction of carbon dioxide to this substance has emerged as a
viable option. This procedure involves supplying electricity to an electrolytic cell.
An electrolyte cell is made up of an anode and a cathode with catalyst-coated
surfaces, as well as an electrolyte(s) that allows ions to be transferred between the
electrodes. Eqs. (1.19) and (1.20) show half-reactions that take place at the anode
and cathode of an electrolytic cell set up to make formic acid from CO2.
Cathode : CO þ 4Hþ
þ 4e-
→ 2HCOOH ð1:19Þ
Anode : 2H2O → O2 4Hþ
4e-
1:20
The typical operating conditions of this process are ambient temperature and
pressure, which is one of its main advantages. However, the primary hurdles for the
development of this method are significant overpotentials and limited product
selectivity. Various catalysts based on Co, Pb, Pd, Sn, and In metal-free nitrogen-
doped carbon materials have been reported for this process over the last few decades
[4, 5, 26].
1.3.5 Carbon Monoxide – Syngas Production
Carbon monoxide (CO) is an important chemical product precursor (Fig. 1.5)
[27]. Synthesis gas, also known as syngas, is a gaseous fuel mixture of carbon
monoxide and hydrogen that is fed to a number of industrial processes, including the
direct DME (dimethyl ether) synthesis, the Fischer-Tropsch (F-T) synthesis, the
ammonia synthesis, the methanol synthesis, the power and heat generation
Fig. 1.5 Applications and principal derivatives of carbon monoxide [27]](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-23-320.jpg)
![processes, and the SNG (substitute natural gas) synthesis [28]. Due to its superior
efficiency than the direct conversion technologies now in use, syngas remains the
industrially favored technology for the indirect conversion of natural gas into higher-
value chemicals and fuels for the time being. Although almost any raw material
containing carbon can be utilized to produce H2/CO mixtures, natural gas, liquid
hydrocarbon sources, solid fossil carbon sources like coal or lignite, or raw materials
obtained from renewable sources are now the most preferred sources [29]. Methane/
natural gas is the most extensively utilized raw material for synthesis gas due to its
availability, gas composition, and inexpensive cost [30].
1 Carbon Utilization Technologies & Methods 11
Steam methane reforming (SMR), dry methane reforming (DRM), autothermal
reforming (ATR), partial oxidation (POX), bireforming (BR), tri-reforming (TR),
and combined reforming (CR) have traditionally been used to produce syngas from
fossil-based natural gas and coal [28]. When methane is used to create syngas, the
process involves the employment of an oxidizing agent that oxidizes methane to
carbon monoxide while also creating hydrogen in a ratio that varies depending on the
oxidant type. Carbon dioxide is able to function as an oxidizing agent through a
procedure called dry reforming [31]. Because DRM is a highly endothermic reaction
(Eq. 1.21), equilibrium conversion to syngas must occur at extremely high
temperatures [32].
CH4 þ CO2 → 2CO þ 2H2, ΔH0
298 = 248 kJ mol- 1
ð1:21Þ
The methane dry reforming process is the most endothermic reaction when
compared to SMR and ATR [33]. DRM yields syngas with a H2 to CO ratio that
is more compatible with some downstream synthesis processes, such as Fischer-
Tropsch synthesis [17].
Due to the difficulty in developing catalysts with a long life-span on stream at a
low price acceptable for profit-oriented commercialization, despite its economic and
environmental potential, DRM is still in its infancy [34]. The formation of coke and
sintering, which quickly deactivate the catalysts, is the main obstacle inhibiting the
widespread use of DRM in the industry [32]. It is expected that coke will deposit on
the reforming catalyst due to high working temperatures, which increase the molec-
ular energy enough to split the C-H bonds in methane [33]. In order to be used on a
large scale in industrial applications, the ideal DRM catalyst must be extremely
stable and have better resistance to coke formation. Numerous experiments using
supported metal catalysts and noble (ruthenium, rhodium, platinum, palladium, and
iridium) and non-noble metals (nickel and cobalt) have been conducted [32].
The dry reforming reaction equilibrium is usually influenced by the
co-occurrence of the RWGS reaction (Eq. 1.22) [30].
CO2 þ H2 → CO þ H2O, ΔH0
298 = 41:2 kJ mol- 1
ð1:22Þ
The H2/CO molar ratio is decreased as a result of the RWGS reaction by
consuming H2 [35]. It is an endothermic reaction, so formation of CO is favored at](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-24-320.jpg)
![þ
ð Þ þ þ ð Þ
þ þ ð Þ
high temperatures [36]. Only in the presence of a suitable and sustainable source of
hydrogen and thermal energy at the proper temperature level the RWGS reaction will
be commercially attractive as a source for syngas [29]. For this reaction, a variety of
heterogeneous catalysts have been utilized, including systems based on copper, iron,
or ceria (Cerium (IV) oxide). However, in general, they have low thermal stability,
and methane commonly forms as an unfavorable byproduct [12]. In designing a
suitable catalyst for the RWGS reaction, criteria of high activity and high CO
selectivity should be considered [36].
12 R. Mahmoudi Kouhi et al.
The direct electrolysis of carbon dioxide to carbon monoxide and oxygen is
another method for producing CO from carbon dioxide [37]. Three electrolysis
techniques are used in this procedure: solid oxide electrolysis at high temperature,
molten carbonate electrolysis, and low temperature electrolysis using a solution-
phase or gas diffusion electrolysis cell. The only CO2 electrolysis method that is
nearing commercialization is high-temperature electrolysis in solid oxide cells [38].
1.3.6 Liquid Hydrocarbons Production (Fischer-Tropsch)
A good substitute for storing renewable energy is liquid hydrocarbons. They are the
main source of energy for use in aviation and transportation [20]. Carbon dioxide can
also be converted to hydrocarbons through Fischer-Tropsch (FT) and methanol
pathways. For the FT pathway, the intermediate product is CO (or a synthesis
gas), while for the methanol pathway, it is methanol [39]. There are three steps in
both pathways [17]:
• Using renewable electricity to electrolyze water to produce hydrogen.
• Conversion of CO2 to an intermediate product, methanol or CO.
• Liquid hydrocarbon synthesis, followed by improvement or conversion to the
desired fuel.
Synthesis gas can be converted into a variety of products, including synthetic
fuels, lubricants, and petrochemicals, using the FT process [40]. In the Fischer-
Tropsch pathway, RWGS reaction (Eq. 1.23) is used to produce syngas, which is
then converted to liquid hydrocarbons via the Fischer-Tropsch reaction [39]. Syn-
thesis of alkanes, as the main products of FT processes, alkenes, and alcohols are
given in Eqs. (1.24) through (1.26) [4]. Ni, Fe, and Cu catalysts can be used in the
RWGS reaction; also, Co, Fe, and Ru catalysts can be used in the Fischer-Tropsch
synthesis, respectively [39].
CO2 þ H2 → CO þ H2O ð1:23Þ
2n 1 H2 nCO → CnH2nþ2 nH2O 1:24
2nH2 nCO → CnH2n nH2O 1:25](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-25-320.jpg)
![þ þ ð Þ ð Þ
þ þ ð Þ
1 Carbon Utilization Technologies & Methods 13
2nH2 nCO → CnH2nþ2O n - 1 H2O 1:26
In the methanol pathway, CO2 and H2 react over a metallic catalyst to produce
methanol, which is then converted into other hydrocarbons over acidic catalysts
[39]. Through a series of reactions, including DME synthesis, olefin synthesis,
oligomerization, and hydrotreating, methanol is transformed into gasoline, diesel,
and kerosene [17].
Currently, methanol is generated from synthesis gas using a Cu-ZnO-Al2O3
catalyst (Eq. 1.27). Recent research efforts have concentrated on the development
of catalysts that support the direct conversion of CO2 to methanol (Eq. 1.28). It is
vital to utilize a very selective catalyst for this reaction because it is favored at low
temperatures and high pressure and can yield a variety of byproducts [39].
CO þ 2H2 → CH3OH, ΔH298k
r = - 90:6 kJ:mol- 1
ð1:27Þ
CO2 3H2 → CH3OH H2O, ΔH298k
r = - 49:5 kJ:mol- 1
1:28
Another way to create fuel-like hydrocarbons that can be used in the current
infrastructure is through electroreduction of CO2 [41]. There are a number of
systems that can produce products with new carbon-carbon bonds, even though
the reduction of CO2 to C1 feedstocks such CO, methane, formic acid, or methanol is
the process that occurs most frequently [12]. Although the Faradaic efficiency is still
low due to H2O dissociation to H2, Cu-based electrodes are perfectly suitable in
activating CO2 [41]. As mentioned above, the electroreduction of CO2 to value-
added compounds shows promise, but is still far from commercialization due to the
high overpotential of this reaction and the low activity of the currently available
catalysts [42].
1.3.7 Urea Production
Another non-toxic product made from carbon dioxide is urea (CH4N2O). Liquid and
solid fertilizers, urea-formaldehyde resins used to manufacture adhesives and
binders, melamine for resins, livestock feeds, NOx control from boilers and furnaces,
and a variety of chemical applications are all the uses of urea [43].
Reforming natural gas to produce ammonia and carbon dioxide is the most widely
used process for producing urea [44]. The production of urea results from the
reaction of carbon dioxide and ammonia at a temperature between 185 and 190 °C
and a pressure between 180 and 200 atm. Two equilibrium reactions known as
Basaroff reactions with incomplete reactants conversion are involved in this process:
Ammonium carbamate (H2N-COONH4) is generated in the first stage by the fast
and exothermic reaction of liquid ammonia with gaseous CO2 at high temperature
and pressure (Eq. 1.29). In the next step, ammonium carbamate decomposes slowly](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-26-320.jpg)
![þ ð Þ
and endothermically into urea and water using the heat produced by previous
reaction (Eq. 1.30) [45, 46].
14 R. Mahmoudi Kouhi et al.
Fig. 1.6 Urea derivatives
synthesis from amine and
CO2 [47]
2NH3 þ CO2 → NH2COONH4, ΔH = - 117 kJ:mol- 1
ð1:29Þ
NH2COONH4 → NH2CONH2 H2O, ΔH = 15:5 kJ:mol- 1
1:30
The use of CO2 in the synthesis of urea derivatives has received a lot of interest.
Anti-cancer agents, plastic additives, gasoline antioxidants, agricultural pesticides,
dyes, medicines, gasoline antioxidants, and corrosion inhibitors are just a few uses
for urea derivatives. The traditional process for producing urea derivatives includes
the reaction of amines with phosgene, carbon monoxide, or isocyanate, which has
serious toxicological and environmental issues. One of the main aims of Green
Chemistry nowadays is to replace these dangerous reagents in chemical processes.
As a result, there has been a significant advancement in the production of urea
derivatives through the reaction of amines with CO2 either with or without the use of
a dehydrating agent, using basic ionic liquids or base catalysts [47–49] (Fig. 1.6).
1.3.8 Polymers
A unique class of chemicals known as polymers is employed in the manufacturing
process for plastics and resins. Polymers, such as polyurethanes and polycarbonates,
are adaptable materials with several practical uses, including those in the electrical
and electronic industries, the automobile sector, packaging, the medical industry,
personal care goods, and the construction [50]. Up until this point, the primary raw
materials used in the manufacturing of polymers were petrochemicals[51]. However,
the chemical industry is under pressure to discover practical substitutes for the
manufacture of renewable chemicals and polymers due to the depletion of fossil
fuels and the legal demand for sustainable and renewable plastics under the circular
economy [50]. As a raw material for the synthesis of polymers, CO2 can partially
replace petrochemicals. One example is the copolymerization of epoxides with CO2
to create polycarbonates [17]. As potential, more environmentally acceptable raw
materials for plastics, CO2-based polymers have received a lot of industrial interest
[52]. Additionally, using CO2 to produce different biodegradable polymers is seen to
be a cost-effective strategy from an economic perspective [20]. There are two
chemical methods for including CO2 in the production of polymers: direct and
indirect methods. Both strategies have been shown to be feasible and possible
[48, 49].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-27-320.jpg)
![1 Carbon Utilization Technologies & Methods 15
1.3.8.1 The Direct Method
The direct method produces high CO2 content polymers such as polycarbonates,
polyols, polyurethanes, polyureas, and polyesters by using CO2 as a monomer in
combination with proper reagents and catalysts [12].
1.3.8.1.1 Polycarbonates (PCs) from CO2
Aromatic PCs are utilized as engineering plastics in automobiles, electrical and
electronic equipment, and construction because of their great impact resistance,
stiffness, toughness, superior thermal stability, transparency, and flame retardancy.
The toxic and destructive phosgene reaction with 1,2-diol is the traditional method
for producing polycarbonates. The copolymerization of epoxides, such as propylene
oxide, cyclohexene oxide, vinyl oxide, ethylene oxide, and styrene oxide and CO2, is
an alternate method for the selective production of PCs. This process is the most
promising application of CO2. In general, transition metals or metals from the main
group of elements, such as cobalt, zinc, chromium, magnesium, and aluminum, are
used as homogeneous or heterogeneous catalysts for the copolymerization of CO2
and epoxides. Compared to heterogeneous catalysts, homogeneous catalysts are
more active and selective. Current CO2 copolymerization research focuses on the
development of catalysts for the production of polymers with tailored properties and
derived from renewable epoxides such as limonene oxide, cyclohexadiene oxide,
and α-pinene oxide [17, 51].
1.3.8.1.2 Polyurethanes (PUs) from CO2
Polyurethanes (PUs), one of the most significant polymers, are used in a variety of
products in daily life, including adhesives, sealants, coatings, elastomers and foams,
heart valves, and cardiovascular catheters. They are manufactured commercially
using polyaddition of diisocyanates with di- or polyols. Establishing isocyanate-free
production methods has received recent attention in the field of PUs; CO2 can play a
significant role in this vital transition. When CO2 reacts with cyclic amines like
aziridines and azetidines or the N-analogs of epoxides, PUs can be produced [50].
1.3.8.1.3 Polyureas (PUA) from CO2
Polyureas (PUAs) are polymers with urea linkages built into their backbone. They
are used as linings, joint sealants, and microcapsules among other things in a variety
of industries, including the building industry, the automobile industry, household
products, and marine-related technology. PUAs are created commercially by the
polyaddition process utilizing the reagents diisocyanate and diamine. These](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-28-320.jpg)
![polymers can be made via non-isocyanate methods using CO2-sourced (a)cyclic
carbonates or urea, or direct CO2 copolymerizing with diamines [50].
16 R. Mahmoudi Kouhi et al.
1.3.8.2 The Indirect Method
The indirect method involves converting CO2 into a different monomer, such as
methanol, ethylene, carbon monoxide, organic carbonates, dimethyl carbonate, or
urea, which enables the synthesis of a wide range of polymers with a variety of
controlled and specified properties. Additionally, CO2 can be used to create chemical
building blocks for polymer synthesis, specifically urea. This makes it possible to
create a variety of thermosetting polymers, including Melamine-Formaldehyde
(MF) and Urea-Formaldehyde (UF) resins, as well as commercial plastics like
Polyoxymethylene (POM) or Polymethylmethacrylate (PMMA) [51].
1.3.9 Other Chemicals
In addition to urea and polymers, the production of other chemicals, such as salicylic
acid, inorganic and organic carbonates, fine chemicals such as biotin, etc., is possible
by utilizing carbon dioxide. Acyclic (linear) carbonates (e.g., dimethyl
carbonate [DMC], diethyl carbonate [DEC], diallyl carbonate [DAC], and diphenyl
carbonate [DPC]) and cyclic carbonates (e.g., ethylene carbonate [EC], cyclohexene
carbonate [CC], propylene carbonate [PC], and styrene carbonate [SC]) make up the
majority of the organic carbonates class [53]. CO2 and two equivalents of an alcohol,
such as methanol, can be used to produce linear carbonates directly. Linear carbon-
ates are used as solvents, reagents (for alkylation or acylation reactions), and
gasoline additives. The cyclic carbonates can be produced by reacting CO2 with a
cyclic ether (e.g., an epoxide) or a diol. They are used as monomers for polymers,
components of special materials, and also in the synthesis of hydroxyesters and
hydroxyamines [45, 53].
1.3.10 Beverage and Food Industry
Food production is possible using CO2 that is captured for CCU. The principal
applications for food-grade CO2 at the moment are the creation of carbonated
beverages, deoxygenated water, milk products, and food preservation. In addition
to serving as a carbonating agent for the creation of champagne, alcoholic drinks,
and soft drinks, carbon dioxide can also be utilized as a preservative, packing gas,
and flavor solvent. Potential CO2 merchant markets in the US require between 3.2
and 4.0 million metric tons of CO2 annually for food processing and between 1.6 and
2.4 million metric tons of CO2 annually for carbonated beverages. CO2 is utilized to](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-29-320.jpg)
![prevent food from oxidizing. Although N2 gas is frequently used to prevent oxida-
tion, CO2 and N2 together are preferable for antioxidative food packaging. Addi-
tionally, antibacterial behavior of CO2 has been demonstrated in a variety of
literature. Food freshness is preserved as a result, extending its shelf life [20, 52, 54].
1 Carbon Utilization Technologies & Methods 17
Fig. 1.7 Typical food items obtained through SFE [52]
Mechanical refrigeration is mostly employed during transportation and storage in
traditional food preservation. However, liquid carbon dioxide, dry ice (i.e., the solid
form of CO2), and modified atmosphere packaging (MAP) technologies are more
frequently employed for refrigeration of foods that need freeze drying (dehydration).
CO2 is frequently used as a flushing gas in MAP. Because of its high solubility in
food matrices, the presence of carbon dioxide in the atmosphere package may reduce
the pressure or volume of package, so balancing the pressure between the inside and
outside of the package. To prevent high CO2 dissolution into foods, the CO2-based
MAP strategy should be implemented with extreme professionalism in accordance
with food attributes and operational requirements. High levels of dissolved CO2
cause packaging to collapse and produce products with a poor texture and flavor
[20, 52].
Supercritical fluid extraction (SFE) technology is a method for utilizing CO2 in
flavors as well as coffee decaffeination, which is advantageous for the separation and
extraction of heat-sensitive, volatile, and oxidizable components. Compared to
traditional separation methods, this method has several advantages, including
non-toxicity, non-corrosiveness, and chemical stability of the extraction agent in
SFE, as well as its reusability after decompression, controllability of SFE extraction
capability by adjusting the main operating factors, and providing better permeability
compared to other solvent approaches. Due to the aforementioned benefits, super-
critical CO2 extraction (SCE) technology is preferred in the food processing indus-
try. As seen in Fig. 1.7, this technology is currently used widely in daily life [52].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-30-320.jpg)
![18 R. Mahmoudi Kouhi et al.
1.4 Biological Conversion
The utilization of microorganisms to produce a variety of products is known as
biological conversion of CO2. In some circumstances, the emerging field of synthetic
biology has the potential to improve biological systems. Microorganisms such as
algae, cyanobacteria, and β-Proteobacteria take up CO2 and convert it into a variety
of valuable compounds during biological CO2 conversion. Some of these products
could be large-scale bulk chemicals like ethylene and ethanol. More high-value
chemicals, such as medicines, nutrition, cosmetics, and fragrances, can also be
produced; while low in volume, these items may give a more cost-competitive
route than traditional industrial synthesis routes [55]. In this part, we look at the
microorganisms utilized in biological conversion and the products they produce.
1.4.1 Microorganisms
In this section, we look at the key microorganisms used in biological conversion like
algae, cyanobacteria, and β-Proteobacteria that have received the most interest and
could potentially be turned into industrial-scale bioprocesses.
1.4.1.1 Algae
Algae are a wide category of aquatic eukaryotic organisms that can do photosyn-
thesis. Its primary habitats include moist, wooded places, still waters, lakes, and
pools. Algae are commonly classified into two types based on their size and shape:
macroalgae and microalgae. Similar to kelps, algae are composed of many cells that
join together to form structures such as roots and stems, as well as the leaves of more
mature plants. The great majority of microalgae or microscopic photosynthetic
creatures are present in unicellular form and can be found in a wide range of
environments. Microalgae are regarded to be one of the earth’s oldest life forms.
They can thrive in a number of natural habitats, including freshwater, brackish water,
and seawater and can adapt to a variety of high temperatures and pH levels. On the
basis of their habitats and physical characteristics, microalgal species can also be
categorized further. These groups include euglenoids, diatoms, green algae
(Chlorophyceae), red algae (Rhodophyceae), yellow-green algae (Xanthophyceae),
golden algae (Chrysophyceae), and Chlorophyceae (green algae) [56].
The Calvin-Benson-Bassham (CBB) cycle allows algae to utilize CO2. The CBB
cycle, in fact, is an essential biological mechanism for converting CO2 from the
atmosphere to organic matter. The main enzyme for CO2 fixation in this cycle is
ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Aside from the CBB
cycle, nature has identified five other carbon fixation mechanisms, the most efficient
of which is the reductive acetyl-CoA process under anaerobic conditions [57]. For](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-31-320.jpg)
![their ability to fix inorganic carbon, both macro- and microalgae are investigated and
utilized. Their potential is attributed to their widespread distribution (especially in
moist conditions), high biomass capability, rapid CO2 uptake and utilization, and,
most crucially, their ability to make secondary products with high commercial value
from biomass. The most industrially important component of algal biomass is lipid,
which is used to make secondary goods such as biofuels and lubricants. To maxi-
mize the value of algal carbon capture and utilization, it is critical to select high lipid-
producing strains and optimize growing parameters such as light, temperature, and
pH [58].
1 Carbon Utilization Technologies & Methods 19
1.4.1.2 Cyanobacteria
Cyanobacteria (or blue-green algae) are phylogenetically a group of Gram-negative
photosynthetic prokaryotes having widespread distribution ranging from hot springs
to the Antarctic and Arctic regions. The role of cyanobacteria in nitrogen fixation
and in the maintenance of the fertility of rice is well documented. [59] Additionally,
they are believed to have contributed to the early rise in atmospheric O2 and the
lowering of CO2 around 2.3 billion years ago. 20–30% of Earth’s primary photo-
synthetic productivity is accounted for by cyanobacteria, which convert solar energy
into chemical energy stored in biomass at a rate of 450 TW [60, 61]. RuBisCO,
which catalyzes the same reaction as in the CBB cycle in algae, is in charge of the
carbon utilization in cyanobacteria. Due to their simpler structure than algae,
cyanobacteria are more effective in fixing carbon from the atmosphere. However,
they cannot produce the same amount of biomass [58, 62].
1.4.1.3 β-Proteobacteria
β-Proteobacteria are a class of Gram-negative bacteria, and one of the eight classes of
the phylum Pseudomonadota. Ralstonia Eutropha H16 is a Gram-negative
lithoautotrophic bacterium from the Proteobacteria-subclass. It is a common inhab-
itant of freshwater and soil biotopes and is highly adapted to survive in environments
with intermittent anoxia [63]. R.Eutropha lives on hydrogen (H2) as its only energy
source when there are no organic materials present, fixing CO2 through the CBB
cycle. In addition, it is capable of utilizing a wide array of carbon sources for growth
and polymer biosynthesis, including sugars, organic acids, fatty acids, and CO2. The
biggest advantage of working with R.Eutropha is the ability to store carbon within its
cytoplasm in the form of polyhydroxyalkanoates (PHAs), also known as
bio-plastics. Genetic engineering, on the other hand, can be utilized to create poly-
mers of varying lengths. R.Eeutropha is also sought after for its various carbon
utilization routes and biocompatibility in the production of pharmaceutical
chemicals [58, 64].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-32-320.jpg)
![20 R. Mahmoudi Kouhi et al.
1.4.1.4 Other Microorganisms
Other microorganisms, in addition to those mentioned, have the ability to absorb
carbon and produce fuel and other valuable industrial substances. For example,
acetogenic bacteria such as Clostridium autoethanogenum have the ability to grow
and convert CO2 and CO into low-carbon fuels and chemicals like ethanol, acetone,
and butanol [65]. Besides that, there are many microorganisms from an archaeal
domain that can fix carbon dioxide through CO2 fixing pathways [66].
1.4.2 Bio-Based Products
In this part, we will discuss the three main products of the biological conversion
method: bio-plastics, biofuels, and bio-alcohols. Producing these products and
attempting to improve each process, as well as discovering useful new products,
might serve as a road map for future research.
1.4.2.1 Bioplastics
Bioplastics are plastics derived in whole or in part from biological material.
Bioplastics differ from biodegradable plastics, which are readily decomposed by
microorganisms. Polyhydroxyalkoanates (PHAs) can be synthesized by microbes
with the polymer accumulating in the microbes’ cells during growth [55]. Packaging,
food services, agriculture and horticulture, consumer electronics, and other indus-
tries are all using bioplastics. About 2.42 million tons of bioplastics were produced
globally in 2021, with nearly 48% (1.15 million tons) of that volume going to the
packaging market, which is the largest market for bioplastics (Fig. 1.8).[67].
Fig. 1.8 Global production capacity of bioplastics in 2021 by marketing segment [67]](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-33-320.jpg)
![1 Carbon Utilization Technologies & Methods 21
Fig. 1.9 Biofuel production from microalgae and two side products (Organic fertilizers, Bio-based
chemicals). (Modified after [68])
1.4.2.2 Biofuels
Microalgae have been tested as a viable feedstock for biofuel generation in the
current era due to its high energy content, rapid growth rate, low-cost culture
methods, and significant ability for CO2 fixation and O2 addition to the environment.
Biofuel has gained significant attention as an alternative fuel in recent years due to its
capacity to adapt with gasoline for a maximum 85% blend without engine modifi-
cation. As a result, academics and environmentalists are constantly questioning the
suitability of various alternatives for biofuel. Figure 1.9 depicts the various forms of
biofuels produced from microalgae; additionally, bio-based chemicals and
bio-fertilizers are available as byproducts alongside biofuels [68].
1.4.2.3 Bio-Alcohols
Alcohols produced from biological resources or biomass are known as bio-alcohols.
Bioethanol, the most common and extensively produced bio-alcohol, is an important
alternative fuel for spark ignition engines. As ethanol has a poor energy density
(70% that of gasoline) and is corrosive to current engine technology and fuel
infrastructure, its use as a replacement for conventional gasoline is called into
question. It also rapidly absorbs water, resulting in separation and dilution in the
storage tank. Isopropanol can be produced biologically. It can be used to supplement](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-34-320.jpg)
![Organisms Advantages Disadvantages
gasoline. It is also used to esterify fat for biodiesel production instead of methanol,
which lowers its tendency to crystallize at low temperatures [58, 69].
22 R. Mahmoudi Kouhi et al.
Table 1.2 Benefits, drawbacks, and products produced by microorganisms [58]
Bio-
based
products
Algae Wide distribution
Fast growing
Fast CO2 uptake
High cellular lipid content
High-value byproducts
Light requirement
Water requirement
Large amount of
phosphorousRequired as a
fertilizer
Bio-plas-
tics
Biofuels
Cyanobacteria Simple cultivation
Higher photosynthetic levels
Higher growth rates
Capability to produce a
wideRange of fuels
Temperature, pH, and
lightIntensity affect productivity
Increasing the operating cost
ofCell cultivation due to agitation
Bio-
alcohols
β-Proteobacteria Aerobic
microorganisms’Easier culti-
vation
Diverse carbon sourcesAnd
carbon utilization pathways
Natural ability to store carbon
Availability of genetic modi-
fication tools
Under development gas
fermentation
Bio-plas-
tics
Bio-
alcohols
Table 1.2 lists the advantages, disadvantages, and products generated by all three
microorganisms: algae, cyanobacteria, and proteobacteria.
1.5 Carbon Mineralization
Carbon mineralization is a natural process that occurs when CO2 reacts with metal
cations to generate carbonate minerals, with calcium and magnesium being the most
attractive metals. The CO2 is permanently eliminated from the atmosphere after
being trapped in the permanent and nontoxic state of the carbonate minerals.
Mineralization methods are generally classified into two types: in situ and ex situ.
In situ mineralization or mineral trapping involves injecting CO2 into geological
formations containing alkaline minerals in order to promote natural carbon miner-
alization over time. Ex situ mineralization occurs when CO2-bearing gases react with
alkaline mine tailings or industrial wastes on the earth’s surface in an industrial
process. These approaches can also provide a low-cost way to reduce greenhouse gas
emissions.
In general, the degree of mineral carbonation is determined by available CO2
dissolved in solution, available alkalinity in solution, and chemical conditions that
promote available alkalinity via mineral dissolution and carbonate precipitation
[70]. Mineral carbonation products are stable solids that limit the possibility of](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-35-320.jpg)
![CO2 emission back into the atmosphere. According to IPCC Special Report on
Carbon dioxide Capture and Storage, the fraction of carbon dioxide stored by
mineral carbonation retained after 1000 years in in situ mineralization is almost
expected to be 100%. As a result, the need for monitoring disposal sites will be
minimized [71]. Carbonation reactions that mineralize CO2 are exothermic, so it
does not require energy inputs, which means these spontaneous reactions generate
heat. On the other side, mineralization processes happen very slowly and might take
hundreds of years. This issue has to be resolved, especially with the ex situ
mineralization approach, which calls for various energy-intensive pre-treatment
procedures like grinding and heating [72, 73].
1 Carbon Utilization Technologies & Methods 23
The mineralization potential capacity of resources due to the presence of appro-
priate geological formations and industrial wastes is virtually limitless. Ultramafic
and mafic rocks like peridotite and basalt are more suited due to their high concen-
tration of metals like magnesium and calcium compared to intermediate and felsic
rocks like diorite and granite, which are made up of inert minerals like silicon
dioxide. Basaltic rocks are the most feasible formation to store CO2 as they make
up most of the ocean floor, over 70% of the earth’s surface, and more than 5% of the
continents [73]. In addition, alkaline solid wastes such as iron/steel slags, coal-fired
products, fuel combustion products, mineral processing wastes, incinerator residues,
cement/concrete wastes, and pulp/paper mill wastes exist in Gt-Size for mineralized
construction materials [74, 75]. Mineral carbonation technologies generally store
between 10,000 and 1000,000 Gt of total carbon. In contrast, the estimated carbon
production in 100 years is roughly 2300 Gt. Despite this enormous potential, large-
scale carbon mineralization has not yet been implemented owing to the absence of
information on mineral concentrations, compositions, and volumes at specific geo-
logic resource locations [76, 77].
1.5.1 In-Situ Mineralization
The process of injecting CO2 into geological formations containing alkaline minerals
to enhance natural carbon mineralization over time is known as in situ mineralization
or mineral trapping. In situ mineralization requires subsurface rocks rich in suitable
alkaline minerals (magnesium and calcium), which can react with CO2. Injection in
gaseous, liquid, or supercritical forms into underground reservoirs is the three
storage options for CO2. In these systems, four types of trapping mechanisms are
considerable for CO2 utilization: Hydrodynamic trapping refers to CO2 trapping as
supercritical fluid or gas under a low-permeability caprock. Residual trapping refers
to trapping CO2 in tiny pores. Solubility trapping relates to the dissolution of CO2 in
the formation fluid. Finally, mineral trapping refers to the incorporation of CO2 in a
stable mineral phase via reactions with mineral and organic matter in the formation.
As storage proceeds from structural to mineral trapping, CO2 becomes more immo-
bile, enhancing storage safety and lowering reliance on cap rock effectiveness
(Fig. 1.10) [71, 73, 78].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-36-320.jpg)
![24 R. Mahmoudi Kouhi et al.
Fig. 1.10 Physical and geochemical trapping is used to ensure storage security. The physical
process of residual CO2 trapping and the geochemical processes of solubility trapping and mineral
trapping, increase with time. The left-hand panel, typical sedimentary reservoir, right-hand panel,
peridotite reservoir [70, 71]
Sedimentary basins are capable of implementing in situ mineralization. In these
formations, the porosity and permeability of the target formation are essential factors
in injectivity, while solution chemistry, temperature, and pH are crucial factors in
carbonate formation potential [79]. However, this approach faces some significant
problems. Low rock reactivity due to the lack of silicate-bound divalent metals
required for carbonate production is the major challenge; the risk of returning CO2
to the surface is also present, as the majority of the injected CO2 will most likely
remain in the gaseous, liquid, or supercritical phase for an extended period
[71, 73]. As a result, several CCS approaches have been developed to overcome
the constraints of sedimentary injection. The most important one is the injection of
CO2 into mafic or ultramafic lithologies that have large concentrations of divalent
cations like Ca2+
, Mg2+
, and Fe2+
in order to promote fast mineralization to calcite
(CaCO3), dolomite (CaMg(CO3)2), magnesite (MgCO3), or siderite (FeCO3)
[73, 80, 81]. Figure 1.11 depicts the mafic (basaltic), ultramafic, and sedimentary
reservoirs accessible for carbon mineralization. Although mafic rocks are more
plentiful in size, ultramafic rocks can react faster with CO2 due to their more
significant concentration of reactive minerals. Additionally, large-scale facilities
and pilot projects for CO2 sequestration across the globe are visible [72].
1.5.1.1 Challenges and Risks
Regardless of ex situ methods, in situ mineralization should be regularly monitored
as it may confront some challenges and risks that must be addressed. Since direct
sampling of mineralization is too complex and expensive, quick indirect monitoring](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-37-320.jpg)
![appears feasible and cost-effective. Leakage from wellbores or non-sealed fractures
in the caprock and pressure buildup in the reservoir that may result in caprock
hydraulic fracturing are significant risks [72]. Also, contamination of drinking
water aquifers as supercritical CO2 is buoyant in the subsurface and can travel
upwards in the presence of an open pathway, such as a transmissive fault. Further-
more, injecting fluids underground can trigger earthquakes by increasing pore fluid
pressure and changing rock volume, allowing faults to move [70, 76].
1 Carbon Utilization Technologies & Methods 25
Fig. 1.11 Map of CO2 sequestration facilities, pilot projects, and long-term storage potential in
geological formations [72]
All these risks can be avoided by monitoring CO2 plume migration, pressure in
and above the reservoir, induced seismicity, the degree of secondary trapping
mechanisms, leakage into groundwater, and the chemistry of freshwater aquifers
near the CO2 reservoir and leakage to the atmosphere. In terms of human health,
utilizing best practices and managing operations to reduce the likelihood of worker
injury, uncontrolled CO2 emissions, and fugitive emissions are also crucial [70, 72].
1.5.1.2 Pros and Cons
Compared to ex situ mineralization, in situ mineralization has several benefits. The
first and most important are the readily available, vast rock “reservoirs” that may be
used to absorb CO2 and reduce its effects on the environment. These reservoirs may
also be found all over the globe, as seen in Fig. 1.11. This approach is more
advantageous regarding costs and energy since, despite ex situ mineralization, no
pre-treatment activities are required. Finally, because of the large-scale projects that
may be performed using this approach, the foundation of government and big](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-38-320.jpg)
![þ þ þ ð Þ ð Þ
industries are conceivable. On the other hand, there are some disadvantages to this
approach: the first and the major one is the slow kinetics of reactions, as carbon
mineralization may take up to hundreds of years depending on the formation types
and CO2 injection. Moreover, infrastructure needs are prohibitive since reservoirs
might be located distant from waste and CO2 sources. That is why more extraordi-
nary engineering efforts and advanced technologies are necessary. Furthermore,
CO2 leakage into the atmosphere or ground water is always possible. Thus, the
entire system should be regularly monitored to prevent these potential risks.
26 R. Mahmoudi Kouhi et al.
1.5.1.3 In Situ Projects
The CarbFix experiment in Iceland and the Wallula Project in Washington State are
the two projects that have shown in situ mineralization of CO2 in basaltic formations.
In both experiments, thick sequences of basaltic lavas were extensively characterized
regarding composition, structure, and hydrology before injecting CO2-rich fluids to
test storage in pore space and produce solid carbonate minerals.
1.5.1.3.1 CarbFix
The CarbFix Pilot Project is an academic-industrial collaboration that has created an
innovative method for safely and permanently capturing CO2 and H2S from emis-
sion sources and storing it as stable carbonate minerals in the subsurface basalts by
imitating and speeding up the natural process of carbon mineralization. With this
method, CO2 and other acid gases may be captured and stored as stable mineral
phases for less than $25 per ton [82]. It involves a combined program consisting of a
CO2 pilot gas separation plant, CO2 injection pilot test, laboratory-based experi-
ments, studying of natural analogs, and numerical modeling. Following CO2 injec-
tion into aquifers, it will dissolve and acidify the formation water before dissociating
into bicarbonate and carbonate ions via the following reaction (Eq. 1.31) [83]:
CO2 aq
ð Þ þ H2O $ H2CO3 $ HCO-
3 þ Hþ
$ CO2 -
3 þ 2Hþ
ð1:31Þ
The subsurface injection of carbonated water causes it to react with the Ca and
Mg found in the rock. Rocks often include calcium and magnesium as oxides.
However, since many rocks, like basalt, include silicate minerals of these elements
(like forsterite and anorthite), some example reactions may be as follows (Eqs. 1.32
through 1.34) [83, 84]:
Ca, Mg
ð Þ2þ
þ C2O þ H2O → Ca, Mg
ð ÞCO3 þ 2Hþ
ð1:32Þ
Mg2SiO4 4Hþ
→ 2Mg2þ
2H2O SiO2 aq 1:33](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-39-320.jpg)
![þ þ þ ð Þ ð Þ
1 Carbon Utilization Technologies & Methods 27
Fig. 1.12 (a) The field-scale, in situ basalt-carbonation pilot plant in Hellisheidi, Iceland [84], (b)
Core from CarbFix site. (Source: CarbFix project, Orkuveita Reykjavikur)
CaAl2Si2O8 2Hþ
H2O → Ca2þ
Al2Si2O5 OH 4 1:34
The CO2 gas injection site is located in southwest Iceland, about 3 km south of the
Hellisheidi geothermal power plant above subsurface basalts formations. (Fig. 1.12)
The power plant has a CO2 generation capability of around 60,000 tons per year. A
treatment facility separates the primary gases generated, which include CO2 and
H2S. The H2S is separated and injected back into the geothermal reservoir, while the
CO2 (98% CO2, 2% H2S) is transported through a 3 km long pipeline to the CO2
injection location. The CO2 injected into the storage formation entirely dissolves in
water, resulting in a single fluid phase entering the storage formation. CO2 at 25 bar
and groundwater are injected together. Carbon dioxide is transported to a depth of
500 meters by injected groundwater, where it enters the target storage formation
totally dissolved. Under these circumstances, CO2-charged water reacts with basaltic
minerals, increasing pH and alkalinity. Given that the amount of water necessary to
completely dissolve CO2 varies on the temperature and partial pressure of CO2, the
total dissolution of CO2 at the CarbFix site takes 22 tons of H2O per ton of CO2 [83].
By utilizing tracers such as trifluormethylsulfur pentafluoride (SF5CF3), acid red
dye (amidorhodamine G), and radiocarbon (14
C), the mineralization of the injected
gases has been demonstrated and is being tracked by sampling fluids from wells
close to the injection spot. The injection well is filled with known quantities of CO2
and tracers. The assessment of CO2 mineralization by mass balance calculations is
made possible by measured tracer concentration and chemical composition in
monitoring wells. Utilizing various isotopes, the mineralization has also been quan-
tified. According to monitoring results, more than 95% of the subsurface CO2
injections mineralized within a year, and almost all of the H2S injections mineralized
within 4 months after injection. Furthermore, the injected radioactive carbon tracer
was found in the carbonates that precipitated on the pump and inside of the
monitoring well pipes. This finding demonstrated that carbon dioxide may be](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-40-320.jpg)
![quickly and permanently trapped in basaltic bedrock, consequently lowering green-
house gas emissions [85].
28 R. Mahmoudi Kouhi et al.
The new project CarbFix2 builds upon the success of the original CarbFix
project, which was funded by the EU’s seventh Framework Program. It is a com-
prehensive project consisting of [86]:
• Development of the technology to perform the CarbFix geological carbon storage
method using seawater injection into submarine rocks
• Reducing the cost of the entire CCS chain
• Impure CO2 capture and co-injection into the subsurface
• Integration of the CarbFix method with novel direct air capture technology
The goal of the CarbFix2 project was to make the CarbFix geological storage
solution both commercially feasible with a full CCS chain and transportable across
Europe.
1.5.1.3.2 Wallula Project
The Wallula Project in Washington State, the world’s first continental flood basalt
sequestration, was conducted in 2013 by the Pacific Northwest National Laboratory
(PNNL) of the U.S. Department of Energy Big Sky Regional Carbon Sequestration
Partnership to examine the viability of safely and permanently storing CO2 in basalt
formations. By injecting 1000 metric tons of supercritical CO2 into a natural basalt
formation in the Columbia River Basalt Group at 830–890 m depth, PNNL
researchers started a field demonstration of carbon storage. Prior to drilling, site
appropriateness was evaluated by collecting, processing, and analyzing a four-mile,
five-line, three-component seismic swath that was processed as a single data-dense
line. Results from 2 years of post-injection monitoring, including a long-term
sampling of water retrieved from the injection zone, shallow groundwater and soil
gas monitoring, and PSInSAR, [87] revealed the formation of new carbonate
minerals as a result of CO2 injection. Nodules of calcium, iron, magnesium, and
manganese carbonate mineral ankerite (Ca(Fe, Mg, Mn)(CO3)2) were detected in
vesicles throughout the cores. Additional carbon isotope research confirmed the
nodules to be chemically unique from basalt’s naturally occurring carbonates and
to be in direct accordance with the isotopic signature of injected CO2. At the top of
the injection zone, there was unmineralized CO2 that was still present beneath the
caprock, showing that not all of the CO2 had mineralized (Fig. 1.13). Results from
modeling show that within 2 years, mineralization sequestered almost 60% of the
CO2 that was injected. However, it is uncertain what will happen to the remaining
CO2 because no leaks have been identified. According to the experimental results,
carbonates only occupied around 4% of the reservoir accessible pore space, giving it
a significant amount of storage capacity [76, 88].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-41-320.jpg)
![ð Þ þ ð Þ ð Þ þ ð Þ þ ð Þ ð Þ
ð Þ þ ð Þ ð Þ þ ð Þ ð Þ
30 R. Mahmoudi Kouhi et al.
1.5.2.1.1 Direct Carbonation
The process of direct carbonation is separated into two parts: direct gas-solid
carbonation and aqueous mineral carbonation. The direct gas-solid carbonation
process is the simplest method. The potential of this method for heat recovery at
high temperatures reduces energy consumption and improves viability. Unfortu-
nately, this approach has fundamental difficulties, including a slow reaction rate, and
is applicable only for refined and unusual materials such as calcium and magnesium
oxides and hydroxides. High temperatures and pressures (between 100 and 150 bar)
are recommended as a remedy to this issue, although this approach may decrease the
process overall efficiency due to the significant amount of energy needed. The direct
gas-solid reaction of olivine serves as an illustration of this process (Eq. 1.35)
[71, 89].
Mg2SiO4 s
ð Þ þ 2CO2 g
ð Þ → 2MgCO3 s
ð Þ þ SiO2 s
ð Þ ð1:35Þ
On the other hand, aqueous mineral carbonation is the most commonly studied ex
situ mineral carbonation route, and it was one of the first that was investigated on a
small scale [90]. The carbonic acid pathway technique comprises CO2 interacting
with olivine or serpentine in an aqueous solution at high pressure (100–159 bar).
This process involves dissolving CO2 in water, where it dissolves into bicarbonate
and H+
, producing a pH of around 5.0 to 5.5 at high CO2 pressure. If we use the
previous aqueous carbonation process as an example, the reactions are as follows
(Eqs. (1.36) though 1.38) [89]:
CO2 g
ð Þ þ H2O l
ð Þ → H2CO3 aq
ð Þ → Hþ
aq
ð Þ þ HCO-
3 aq
ð Þ ð1:36Þ
Mg2SiO4 s 4Hþ
aq → 2Mg2þ
aq SiO2 s 2H2O l 1:37
Mg2þ
aq HCO-
3 aq → MgCO3 s Hþ
aq 1:38
Mg2+
is released by H+
in the second reaction, and in the third reaction, it reacts
with bicarbonate to form magnesium carbonate, which subsequently precipitates. As
with the prior method, raising the temperature and pressure can enhance the reaction
rate. Furthermore, pre-treatment methods such as crushing and heating can be used
to improve carbonate conversions and acceptable reaction rates; however, it should
be noted that the use of these techniques, despite improving the process, increases
energy consumption, resulting in a reduction in stored carbon [91].
1.5.2.1.2 Indirect Carbonation
Since direct methods for unrefined solid materials are ineffective, there is a strong
need for alternative methods like indirect mineral carbonation that are more energy
efficient and cost-effective acids or other solvents are used in this multi-stage process](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-43-320.jpg)
![ð Þ þ ð Þ ð Þ ð Þ þ ð Þ ð Þ
ð Þ ð Þ þ ð Þ ð Þ þ ð Þ ð Þ
þ ð Þ ð Þ
to extract reactive components from minerals. The extracted components then react
with CO2 in either an aqueous or a gaseous phase. Indirect carbonation, like direct
methods, can be divided into some categories.
1 Carbon Utilization Technologies & Methods 31
The first method that we discuss here is direct gas-solid carbonation. In order to
improve the conversion rate, the mineral could first be converted into an oxide or
hydroxide and subsequently carbonated. The direct gas-solid carbonation of cal-
cium/magnesium oxides/hydroxides proceeds much faster than the gas-solid car-
bonation of calcium/magnesium silicates, although a high temperature and CO2
pressure are required. As a result, in the first stage of this method, which typically
occurs in a fluidized bed, alkaline earth metals in the silicate form are changed into
oxide or hydroxide form. Following this reaction with CO2, the products of this step
react with CO2 and precipitate as stable carbonates (Eqs. 1.39 through 1.41) [92]:
Mg2SiO4 s
ð Þ þ 4HCl g
ð Þ → 2MgCl2 aq
ð Þ þ 2H2O l
ð Þ þ SiO2 s
ð Þ ð1:39Þ
MgCl2 aq 2H2O l → Mg OH 2 s 2HCl aq 1:40
Mg OH 2 s CO2 g → MgCO3 s H2O l 1:41
In addition to the procedure mentioned above, using various acids such as acetic
acid and hydrochloric acid is also frequent. The goal of applying these acids is to
maximize Ca and Mg ion leaching while ensuring selective leaching. Because acetic
acid is more acidic than ammonium chloride, it has a higher calcium ion leaching
ratio [93]. The use of acetic acid as an extractant has a major side effect of lowering
the pH of the leachate. Alkali must be used to stimulate the carbonation reaction in
order to fix this problem [94]. As seen in the reactions below (Eqs. 1.42 and 1.43),
divalent magnesium is separated in the first stage of the magnesium silicate reaction
with acetic acid and is then ready to react with carbon dioxide gas in the next stage:
MgSiO3 s
ð Þ þ 2CH3COOH aq
ð Þ → Mg2þ
aq
ð Þ þ 2CH3COO-
aq
ð Þ
þ SiO2 s
ð Þ þ H2O l
ð Þ ð1:42Þ
Mg2þ
aq
ð Þ þ 2CH3COO-
aq
ð Þ þ H2O l
ð Þ þ CO2 g
ð Þ → MgCO3 s
ð Þ
2CH3COOH aq 1:43
Ammonium chloride is a kind of strong acid and weak alkali salt. For the leaching
reaction using ammonium chloride, the solution shows alkalinity as the reaction
proceeds because of the generation of ammonia. Noteworthy, the alkalinity of the
solution promotes the dissolution of CO2 in the precipitation reaction. At the same
time, the leachate using ammonium chloride has a strong pH-buffer ability, because
an ammonia buffer solution is formed in it. Ammonium chloride is regarded as an
ideal recyclable solvent because it can be regenerated in the carbonation reaction
stage. As the carbonation reaction proceeds, NH4Cl is regenerated, which makes it
recyclable for the leaching reaction [93]. As shown in the reaction below (Eqs. 1.44
and 1.45), in addition to the formation of magnesium carbonate at the end of the](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-44-320.jpg)
![ð Þ
reaction, ammonium chloride is also generated, saving the consumption of this acid
throughout the cycle:
32 R. Mahmoudi Kouhi et al.
2MgSiO3 s
ð Þ þ 4NH4Cl aq
ð Þ → 2MgCl2 aq
ð Þ þ 4NH3 g
ð Þ þ 2H2O l
ð Þ þ SiO2 s
ð Þ
ð1:44Þ
2MgCl2 aq
ð Þ þ 4NH3 g
ð Þ þ 2CO2 g
ð Þ þ 2H2O l
ð Þ → 2MgCO3 s
ð Þ þ 4NH4Cl aq
ð Þ
1:45
Other solvents commonly used in indirect carbonation include ammonium sul-
fate, citric acid, hydrochloric acid, sulfuric acid, and others. In relation to the use of
solvent, it is important to note that, despite improvements in the reaction rate and
overall efficiency, if these materials are not recovered, there is a risk of serious
environmental damage, particularly to the local ground water and soil, so all aspects
of using these materials must be considered.
1.5.2.2 Feedstocks
The feedstocks needed for the ex situ reaction with CO2, depending on where they
come from, can be categorized into three main groups: natural minerals, mine
tailings, and industrial waste. The three cases are further discussed in the following
sections.
1.5.2.2.1 Natural Minerals
Natural minerals such as wollastonite (CaSiO3) and forsterite (Mg2SiO4) are con-
sidered suitable for mineralization owing to the presence of alkaline earth elements
such as Ca and Mg. Although alkali metals like Na and K have the capacity to react
with CO2 and capture it, they are less frequently utilized as an efficient raw material
due to the strong reactivity of their final product, particularly in water. Additionally,
iron can be a useful source due to its abundance in the ground and its great capacity
to react with CO2 and produce siderite (FeCO3), but its usage is not cost-effective
due to the high value of metal. Natural minerals suited for CO2 reactions are
classified into two types: natural calcium silicates such as wollastonite (CaSiO3)
and natural magnesium silicates such as olivine (Mg2SiO4) and serpentine
(Mg3Si2O5(OH)4). Compared to magnesium silicate, minerals in the first category –
natural calcium minerals like wollastonite – have a quicker reaction rate and a wider
range of industrial applications. However, the widespread availability of magnesium
silicates in a variety of forms, including dunites, serpentinites, and peridotites, has
made them a dependable source for producing stable carbonates [95]. The most
important reactions between natural minerals and CO2 that result in stable carbonate
are shown below (Eqs. 1.46 to 1.48):](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-45-320.jpg)
![34 R. Mahmoudi Kouhi et al.
Fig. 1.14 Estimate of tailings and waste rock produced in relation to ore production and worldwide
proportion of tailings per commodity in 2016 [96]
Each year, the amount of tailings generated, particularly in open pit mines,
increases significantly due to a drop in the grade of extractable rocks. Only in
2016, nearly 9 billion tons of tailings from metal and mineral extraction were
generated, creating challenges, especially in the field of maintenance and prevention
of harmful environmental effects. It should be emphasized that copper, gold, iron,
and coal accounted for the majority of this tailings, with 46, 21, 9, and 8%,
respectively (Fig. 1.14) [96].
Nickel and asbestos are the primary sources of ultramafic tailings. Manufacturing
sites can be used in carbon sequestration of each of these tailings, which is a
combination of much unique magnesium and calcium-containing compounds, and
their dissolving rate and reactivity are related to their composition. As a result of
these characteristics, four unique patterns of CO2 reactivity in ultramafic tailings
may be imagined [76]:
• Fast carbonation of the magnesium hydroxide mineral like brucite
• Fast absorption of CO2 by hydrotalcite minerals
• Fast cation exchange reactions of swelling clays
• Relatively slow dissolution of calcium and magnesium silicate
Nickel Tailings
Nickel is mined from two different types of deposits: nickel-rich laterite generated
by weathering of ultramafic rocks in tropical regions containing garnierite
(Ni-silicate) and from Ni-sulfide concentrations in mafic igneous rocks, primarily
pentlandite. Despite the high costs of employing nickel tailings, because of the high
MgO content, it is possible to integrate extraction and CO2 separation using inno-
vative methods. Furthermore, ultramafic deposits of nickel support stabilization of
chrysolite asbestos and decrease the environmental impact of these tailings [95]. In
2011, the world’s nickel resources were projected to be 296 million tons (Fig. 1.15).
This quantity is divided into 178 million tons for nickel laterite deposits and
118 million tons for nickel sulfide resources. Australia has the most considerable](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-47-320.jpg)
![nickel resources than any other country, with 31 million tons of laterite resources and
11 million tons of sulfide resources. Indonesia and South Africa are in the next
places with reserves of 33 million tons [97]. The abundance of nickel deposits and
their distribution across continents allow this material to be employed as one of the
essential resources in lowering existing carbon and reaching zero-carbon technolo-
gies in related sectors. There are difficulties in extracting nickel from low-grade
ultramafic deposits. Serpentine minerals are typically found in ultramafic ores. These
ores have low recoveries because of the difficulty in dispersing and effectively
rejecting them. For instance, during the first five years of operation at Mt. Keith,
Australia, nickel recovery from ores containing 0.58% Ni and 40% MgO was only
60% [91].
1 Carbon Utilization Technologies & Methods 35
Fig. 1.15 Laterite and sulfide nickel deposits in several countries in 2011(numbers are in KT).
(Modified after [97])
Asbestos Tailings
Asbestos is a naturally occurring category of fibrous materials. There are six types of
asbestos that have been discovered; they come from the amphibole and serpentine
mineral groups. White asbestos, often known as chrysotile (Mg3(Si2O5)(OH)4), is
the kind of asbestos that is most frequently found in veins in serpentine rock
formations. Where serpentine is mined for chrysotile asbestos, the tailings often
include considerable residual asbestos and may be categorized as hazardous. These
tailings would be great feed for mineral carbonation because not only has size
reduction occurred, but when chrysotile is carbonated, the asbestiform character of
minerals is removed and it is highly environmentally beneficial as asbestos can cause
cancer of the lung, cancer of the larynx, and certain gastrointestinal cancers. Glob-
ally, 4 Mt. of asbestos is produced, each ton producing 20 tons of tailings. Because
of the high quantities of MgO (40%) found in these tailings, they would constitute an
excellent source of mineral carbonation [95, 98]. Despite the benefits that may be
obtained from the carbonization of asbestos, the world’s extraction of this material is
significantly declining owing to its environmental concerns, making it impossible to](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-48-320.jpg)
![CaO MgO Al2O3 SiO2 Fe2O3 TiO2 MnO Cr2O3 Others
– – –
utilize asbestos as a viable feedstock for carbonization and mitigating global
warming in the long term.
36 R. Mahmoudi Kouhi et al.
1.5.2.2.3 Industrial Wastes
This section investigates the use of industrial waste as a raw material in the
mineralization process. Because of the existence of considerable amounts of alkaline
earth metals, such as calcium and magnesium, the tailings of the steel, cement, and
coal sectors have the most potential when compared to other industries. Addition-
ally, residues from aluminum manufacturing facilities, such as red mud, can be
utilized for carbon sequestration. Because of the rising need for the availability of
more products connected to these industries, it is conceivable to broadly employ
these raw materials to reduce environmental consequences. The fact that industrial
wastes, as opposed to mineral tailings, are situated close to point sources of CO2
emission, decreases the cost of the process and also improves the likelihood that
these products will react and create stable carbonate minerals. As a consequence, in
addition to capturing carbon from the atmosphere, the approach has been proposed
to manage unstable industrial wastes for disposal in compliance with safety regula-
tions, as well as their reuse.
Steel Slag
Steel slag is a waste product produced during the manufacturing of steel. It is
massively produced during the steelmaking process utilizing electric arc furnaces.
Steel slag can be produced when iron ore is smelted in a basic oxygen furnace. These
slags are mostly used as aggregate replacement in construction applications such as
granular foundations, embankments, engineered fill, highway shoulders, and hot mix
asphalt pavement.
Steel slags are generally classified into four types: blast furnace slag (BF), basic
oxygen furnace slag (BOF), electric arc furnace slag (EAF), and ladle furnace slag
(LF). Table 1.3 shows the most common components of these four categories. CaO,
MgO, Al2O3, SiO2, and Fe2O3 are the basic chemical compositions of slag. The
chemical compositions of different slags vary substantially; CaO % in BF and LF
slag is the highest, followed by BOF and EAF slag. Each slag has a roughly equal
Table 1.3 Most common chemical compositions of four slag categories [93]
Components slag
type
BF slag 42.67 8.57 13.21 29.41 0.37 1.49 0.40 0.001 3.879
BOF slag 42.43 9.15 3.03 12.00 26.74 0.48 2.85 0.22 3.10
EAF slag 32.30 5.01 2.74 28.83 23.53 1.06 2.40 0.11 4.02
LF slag 50.50 11.90 18.60 12.90 1.60 4.50](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-49-320.jpg)
![MgO concentration. BF slag includes more SiO2 and Al2O3, but BOF and EAF slag
have more Fe2O3 [93].
1 Carbon Utilization Technologies & Methods 37
Fig. 1.16 The emission reduction potential of legacy and future iron and steelmaking slag by way
of CO2 mineralization [99]
Steelmaking activities emit considerable amounts of CO2 (6–7% of total CO2
emissions globally; 0.28–1 ton of CO2/ton of steel produced). In addition, 315–420
Mt./y of slag is generated annually, according to estimates, although specific slag
production numbers are not available [91]. Currently, slag-based CO2 mineralization
has the potential to cut emissions by 268 Mt. CO2/y. Legacy slag has an 8.2 GtCO2
mineralization potential, despite being frequently bonded in building material
(Fig. 1.16) [99].
Although steel slag has been employed in various industrial-scale applications,
there are still limitations associated with this technology. The most pressing issues
that must be addressed are a lack of steel slag due to their widespread use in other
industries, an increase in energy and economic costs while optimizing process
parameters, limitations of reaction kinetics, minimizing environmental impacts,
and a drastic difference in compositions for each waste unit, which makes it
impossible to use a particular method on a global scale [76, 100].
Red Mud
Red mud, usually referred to as bauxite residue, is a byproduct of the Bayer process,
which extracts alumina from bauxite ore. It is composed of a mixture of solid and
metallic oxides and contains compounds like Fe2O3, Al2O3, TiO2, CaO, SiO2, and
Na2O. Annually, 70 million tons of red mud is generated, 1.0–1.5 t for each ton of
alumina produced [91]. Red mud includes toxic heavy metals, and its high alkalinity
makes it exceedingly corrosive and harmful to soil, water, land, air, and living forms,
posing a significant disposal challenge. Although around 4 million tons of red clay is
employed annually in the cement, iron, and road construction sector, this amount
remains relatively small in comparison to the enormous rate of production.](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-50-320.jpg)
![Therefore, attempts to discover new applications for this hazardous waste must be
continued.
38 R. Mahmoudi Kouhi et al.
Red mud can hold up to 0.01% of CO2 emissions from fossil fuels globally,
assuming they have a 5% CO2 uptake. This equals to 3.5 Mt. of CO2 every year. This
amount of red mud created has the potential to prevent up to 0.01% of worldwide
CO2 emissions caused by fossil fuels [91, 95]. Various methods have been used for
the neutralization of red mud by adding liquid carbon dioxide, saline brines or
seawater, Ca and Mg-rich brines, soluble Ca and Mg salts, acidic water from mine
tailings, fly ash, and carbon dioxide gas [101]. Despite all the benefits of adopting it,
there are several issues that must be addressed in its deployment. The most signif-
icant issue in applying this technology on a large scale is the development of used
devices with high capacity and low energy costs. The usage of this approach may
assist in mitigating climate change effects and reduce the environmental problems
associated with wastes if the aforementioned issues are resolved.
Coal Ash
Coal ash, also known as coal combustion residuals or CCRs, is largely created by the
combustion of coal in coal-fired power plants. This ash contains a number of
byproducts produced from the burning of coal, including fly ash, bottom ash, boiler
slag, and clinker. When fine coal is burnt, a fine, powdery silica substance known as
fly ash is produced. Bottom ash, on the other hand, is a larger coarse ash particle that
accumulates at the bottom of a coal furnace because it is too big to be removed by
smokestacks. Fly ash and bottom ash make up the majority of coal ash, making up
85–95 weight percent and 5–15 weight percent of all generated ash, respectively
[95]. India, China, and the United States are now the greatest producers of fly ash,
whereas nations such as the Netherlands, Italy, and Denmark have the highest
utilization rates of produced coal fly ash (CFA) (Fig. 1.17) [102].
0
20
40
60
80
100
120
CFA Production CFA Utilization(%)
Fig. 1.17 Production and utilization of CFA across the globe. (Modified after [102])](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-51-320.jpg)
![1 Carbon Utilization Technologies & Methods 39
Fly ash is applied in a variety of fields, including construction, as a cheap
adsorbent for the removal of organic compounds, flue gas, and metals, lightweight
aggregate, mine backfill, road sub-base, and zeolite synthesis, which is on the agenda
to address environmental issues associated to fly ash [103, 104].
One of the primary benefits of employing fly ash for carbonation is the absence of
pre-treatment activities, which are energy-intensive and can destabilize the entire
process. This lack of necessity is due to highly fine granulation, which gives a high
amount of material for reaction with CO2 gas. Despite this significant property, the
relatively low quantity of alkaline earth metals such as calcium and magnesium in
these tailings limits their ability to be used for carbonation on a wide scale and at a
cheap cost. This makes fly ash with a high lime concentration one of the most
desirable raw materials for mineralization. These carbonation processes produce
cement solids, which may be utilized to manufacture concrete. China is one of the
most significant producers of these raw materials in the world, producing 100 million
tons of fly ash each year, around half of that is used as a raw material for processes in
other industries. However, as the country’s rate of construction declines, there will
soon be less demand for fly ash in concrete and paving, highlighting the need to find
new applications for the material. In addition to aiding in the capture of carbon
dioxide that has been released into the atmosphere, carbonation may be used in this
situation to convert fly ash from a serious environmental threat into a less hazardous
substance. These environmental effects include the accumulation of heavy metals
like lead and arsenic, as well as ash particles in the air, which decrease air quality and
expose people to these poisons through inhalation [76].
Cement
Cement – a fine powdered substance – is the most significant building material. It is a
binding agent that sets and hardens to keep building components like stones, bricks,
and tiles together. It is made mostly of limestone, sand or clay, bauxite, and iron ore;
however, it can also contain other materials including shells, chalk, marl, shale, clay,
blast furnace slag, and slate. There are different types of cement for different
construction works and ordinary Portland cement (OPC) is the most commonly
used type of cement in the world. Annual global cement production is 2.8 GT, with a
projected growth to 4.0 GT in near future [91]. Cement manufacturing is the energy
and carbon-intensive industry. The cement industry contributes approximately 5%
of the global man-made carbon dioxide (CO2) emissions and is thus becoming the
second largest CO2 contributor in the industry after power plants [105].
Numerous strategies have been suggested and put into practice to minimize the
carbon emissions associated with the production of enormous quantity of cement
globally and the constantly rising demand for this essential commodity. The utili-
zation of supplementary cementitious materials, electric or hydrogen-fired kilns,
point source carbon capture during cement manufacturing, and carbon mineraliza-
tion are all examples. If these strategies are extensively implemented, the idea of
attaining a carbon-neutral program for this industry is not far-fetched. The employ-
ment of three techniques – mixing carbonation (injecting pure CO2 during concrete](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-52-320.jpg)
![mixing), carbonation curing (changing water or steam with pure CO2 during
processing), and the creation of synthetic aggregates (reaction of CO2 with alkaline
feedstock containing calcium and/or magnesium, including recycled concrete and a
variety of industrial wastes) – is more effective when it comes to the strategy of
carbon mineralization for cement [76]. By increasing the strength of concrete during
production, carbonation can reduce the amount of cement needed overall, reducing
carbon intensity and feedstock costs.
40 R. Mahmoudi Kouhi et al.
The cement industry also produces a significant amount of wastes, such as cement
kiln dust (CKD) and cement bypass dust (CBD). In fact, for every 100 tons of
cement, 15–20 tons of CKD is produced. Cement waste is very reactive due to its
fine particle size and high CaO content (20-60%). CKD generally contains 38–48%
CaO, but because it also contains 46–57% CaCO3, a substantial portion of it is
already carbonated. CBD, on the other hand, has fewer carbonates than CKD. As a
result, they have a high inclination to store CO2 (0.5 ton CO2 per ton CBD)
[95]. Many factors, including the significant amount of usable raw materials, the
simplicity of using raw materials due to the absence of energy-intensive pretreatment
processes like crushing, and the high potential for CO2 reaction, have led researchers
to consider the uptake and mineralization of carbon by cement wastes.
1.5.2.3 Application and Products
The final products of mineral carbonation are numerous and can be utilized in
various fields; our goal in this section is to review these products and their uses in
various industries. The construction industry uses most the application of silica and
carbonate materials, whereas cement and the resulting material, i.e., concrete, are
manufactured on a Gt scale globally every year, and a substantial portion of the
energy and carbon emitted into the atmosphere is the result of this massive volume of
manufacturing. Other important environmentally friendly applications of these
materials include use as materials in the process of mine rehabilitation and use as
materials to reduce water and soil pollution with the possibility of adjusting the pH,
assisting in the deposit of fine-grained tailings, and precipitating heavy metals.
1.5.2.3.1 Calcite and Magnesite Applications
Calcite is a carbonation product produced by a mineral carbonation process that uses
inorganic wastes and natural rock sources such as wollastonite. The construction
industry is mineral carbonation’s key consumer of calcium carbonate. Calcite is also
used as ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC)
in a range of industrial processes. PCC is pulverized limestone that ranges in particle
size from a few millimeters to several microns. Also, the most important no-value
use for the carbonates from mineral carbonation would be in mine reclamation
projects, because of the massive amount of carbonates (Gt of magnesium carbonate)
that would be produced if the mineral carbonation technology was effectively](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-53-320.jpg)
![implemented. When it comes to magnesite, approximately 98% of it is converted to
magnesia for conventional uses such as refractories. As a result, magnesite currently
has a limited number of non-CO2 emitting applications, such as precipitated mag-
nesium carbonate or agricultural applications. Magnesite can be used as a building
material; however, there is currently no market for it. Since the market is small,
mineral carbonation magnesite is likely to be reused in large quantities for low-value
applications such as land restoration programs [77].
1 Carbon Utilization Technologies & Methods 41
Fig. 1.18 Summary of the possible carbon mineralization product applications. (Modified after
[77])
1.5.2.3.2 Silica Applications
Mineral carbonation can produce silica byproducts as an amorphous phase, which
might be utilized in the construction industry as a pozzolanic cement substitute
material or as a filler. More than half of the electronic silicon raw materials marketed
globally are produced in Norway. This demonstrates that mineral carbonation
feedstocks are theoretically suitable for the production of high-purity silica and
existing processing technologies may be used to post-process the mineralization
by-products. As the electrical properties of these materials are so sensitive to
impurities, it is improbable that these products can achieve such a level of purity
without further post-processing [77, 106].
The applications of mineral carbonation products that do not contain calcination
can be divided into three categories: low-end high-volume, high-end low-volume,
and silica. Figure 1.18 shows the summary of the possible carbon mineralization
product applications by this type of classification [77].](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-54-320.jpg)
![criminals, and saw her safe at the door of her flat in the Avenue
Parmentier.
When Baron Cederström was seeking local colour for his
painting "The Maréchale in the Café,"[1] he drove down with his
wife to a meeting in the Rue d'Angoulême. As they approached the
hall, the Baroness caught sight of some of the faces and took fright.
[1] This painting is now in the picture gallery of Stockholm. The artist, as is well
known, afterwards married Madame Patti.
"Go back, go back!" she shouted to the coachman.
The Baron tried in vain to reassure her.
"Give me my salts!" she cried, feeling as if she would faint. "I
never saw such faces in my life. They are all murderers and
brigands." To Catherine, who came out to welcome her, she
exclaimed, "I am sure the good God won't send you to Purgatory, for
you have it here!"
"You have nothing to fear," was the answer; "I am here every
night." But as the Baroness was led up to the front seats, she still
cast scared looks at the people she passed.
Some of the politically dangerous classes did give trouble for a
time. Knives were displayed and some blood was shed. An excited
sergeant of police declared one night that half the cut-throats of
Paris were in that hall, and by order of the authorities it was closed.
Soon, however, the meetings were again in full swing, and when
Catherine's eldest brother Bramwell, her comrade in many an English
campaign, paid her a flying visit three months after she left home,
he was delighted with all that he saw. "The meetings," he wrote,](https://image.slidesharecdn.com/28747487-250519112730-4d12970d/85/Carbon-Capture-Utilization-And-Storage-Technologies-1st-Edition-Ali-Ahmadian-75-320.jpg)
Carbon Capture Utilization And Storage Technologies 1st Edition Ali Ahmadian
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- 5. Green Energy andTechnology Ali Ahmadian Ali Elkamel Ali Almansoori Editors Carbon Capture, Utilization, and Storage Technologies Towards More Sustainable Cities
- 6. Green Energy and Technology
- 7. Climate change, environmental impact and the limited natural resources urge scien- tific research and novel technical solutions. The monograph series Green Energy and Technology serves as a publishing platform for scientific and technological approaches to “green”—i.e. environmentally friendly and sustainable—technolo- gies. While a focus lies on energy and power supply, it also covers "green" solutions in industrial engineering and engineering design. Green Energy and Technology addresses researchers, advanced students, technical consultants as well as decision makers in industries and politics. Hence, the level of presentation spans from instructional to highly technical. **Indexed in Scopus**. **Indexed in Ei Compendex**.
- 8. Ali Ahmadian • Ali Elkamel • Ali Almansoori Editors Carbon Capture, Utilization, and Storage Technologies Towards More Sustainable Cities
- 9. Editors Ali Ahmadian Department of Electrical Engineering University of Bonab Bonab, Iran Department of Chemical Engineering University of Waterloo Waterloo, ON, Canada Ali Elkamel Department of Chemical Engineering University of Waterloo Waterloo, ON, Canada Department of Chemical Engineering Khalifa University Abu Dhabi, United Arab Emirates Ali Almansoori Department of Chemical Engineering Khalifa University Abu Dhabi, United Arab Emirates ISSN 1865-3529 ISSN 1865-3537 (electronic) Green Energy and Technology ISBN 978-3-031-46589-5 ISBN 978-3-031-46590-1 (eBook) https://doi.org/10.1007/978-3-031-46590-1 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.
- 10. Preface Despite the consideration of alternative energy resources and increasing the energy efficiency in the systems to decrease the amount of CO2 emissions, the cumulative rate of CO2 in the atmosphere needs to be decreased to limit the detrimental effects of climate change. Therefore, regardless of the extension of clean and more efficient energy systems, carbon-removing technologies need to be implemented. Carbon Capture, Utilization, and Storage (CCUS) is a novel technology that captures CO2 from facilities including power plants, the transportation systems, and industrial sectors. The CCUS technologies can deliver ‘negative emissions’ by removing CO2 directly from the atmosphere or from biomass-based energy and storing the CO2. Therefore, CCUS technologies need to be implemented in the smart sustainable cities. This book is an attempt to bring together the experts from the different disciplines related to carbon capture, utilization, and storage process and its impact on sustain- able cities development. It contains eight chapters in which numerous researchers and experts from academia and industries are collaborated. The breakdown of the chapters is as follows: • Chapter 1 describes the important fuels and chemicals and the synthesis methods of each. The use of carbon dioxide in the beverage and food industry is therefore considered. Moreover, the two types of carbon mineralization – in situ and ex situ, which are thought to be the most recent and efficient techniques for carbon utilization – are covered and the applications, products, challenges and risks of each of these techniques are clearly discussed. • Chapter 2 evaluates the capabilities of CO2 detection satellites as objective, independent, potential, low-cost and external data sources for monitoring CO2 emissions from human activities. • Chapter 3 discusses a much more general framework which allows different capacities for the booster stations. Furthermore, the boosters can be installed at any location, depending on pressure losses along the pipeline. v
- 11. • Chapter 4 reviews the concept of Power-to-X technologies and the electrification of the chemical industry. • Chapter 5 provides an overview of machine learning concepts and general model architectures in the context of post-combustion carbon capture. Also, this chapter presents and compares different machine learning models within the field of absorption-based carbon capture. The strengths and limitation of the strategies used in the creation of past models are discussed. • Chapter 6 presents a design and optimization framework for a tidal power generation plant in the Bay of Fundy, Canada, in order to reduce the operation’s cost and emission pollution. • Chapter 7 presents a systematic framework to integrate renewable energy tech- nologies for the oil and gas industry focusing on solar energy use to meet hydrogen requirements of the crude oil upgrading process for bitumen feedstock in tar sands processing. • Chapter 8 represents a comprehensive review on CO2 monitoring satellites. vi Preface The editors of the book warmly thank all the contributors for their valuable works. Also, we would like to thank the respected reviewers who improved the quality of the book by the valuable and important comments. Waterloo, ON, Canada Ali Ahmadian Waterloo, ON, Canada Ali Elkamel Abu Dhabi, United Arab Emirates Ali Almansoori
- 12. Contents 1 Carbon Utilization Technologies & Methods . . . . . . . . . . . . . . . . . . . 1 Reza Mahmoudi Kouhi, Mohammad Milad Jebrailvand Moghaddam, Faramarz Doulati Ardejani, Aida Mirheydari, Soroush Maghsoudy, Fereshte Gholizadeh, and Behrooz Ghobadipour 2 The Potential of CO2 Satellite Monitoring for Climate Governance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Fereshte Gholizadeh, Behrooz Ghobadipour, Faramarz Doulati Ardejani, Mahshad Rezaee, Aida Mirheydari, Soroush Maghsoudy, Reza Mahmoudi Kouhi, and Mohammad Milad Jebrailvand Moghaddam 3 CO2 Transportation Facilities: Economic Optimization Using Genetic Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Farzad Hourfar, Mohamed Mazhar Laljee, Ali Ahmadian, Hedia Fgaier, Ali Elkamel, and Yuri Leonenko 4 Power-to-X and Electrification of Chemical Industry . . . . . . . . . . . . 115 Kelly Wen Yee Chung, Sara Dechant, Young Kim, Ali Ahmadian, and Ali Elkamel 5 Machine Learning Models for Absorption-Based Post-combustion Carbon Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Fatima Ghiasi, Ali Ahmadian, Kourosh Zanganeh, Ahmed Shafeen, and Ali Elkamel 6 Design and Optimization of a Tidal Power Generation Plant in the Bay of Fundy, Canada . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Reagan McKinney, Claudia Nashmi, Arash Rafat, Ali Ahmadian, and Ali Elkamel vii
- 13. viii Contents 7 Renewable Energy Integration for Energy-Intensive Industry to Reduce the Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 Cheng Seong Khor, Ali Ahmadian, Ali Almansoori, and Ali Elkamel 8 A Review on CO2 Monitoring Satellites . . . . . . . . . . . . . . . . . . . . . . . 213 Steve Houang, Andres Espitia, Shawn Pang, Joshua Cox, Ali Ahmadian, and Ali Elkamel Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
- 14. Chapter 1 Carbon Utilization Technologies & Methods Reza Mahmoudi Kouhi, Mohammad Milad Jebrailvand Moghaddam, Faramarz Doulati Ardejani, Aida Mirheydari, Soroush Maghsoudy, Fereshte Gholizadeh, and Behrooz Ghobadipour 1.1 Introduction Carbon utilization is the process of using captured CO2 as a resource to make value- added products, and it is also an important aspect of climate mitigation. Generally, there are three categories carbon utilization technologies can be divided into: chem- ical technologies, biological technologies, and mineralization processes (Fig. 1.1). CO2 is utilized in chemical processes to produce polymers as well as organic compounds such as acyclic carbonates and cyclic carbonates. The production of energy carriers and transportation fuels such as methanol opens more opportunities for the capturing of CO2. Liquid fuels are not considered long-term alternatives since they ultimately burn out. In biological technology, microorganisms like algae, cyanobacteria, and proteobacteria are utilized to convert CO2 into a range of useful chemicals, such as ethylene and ethanol. High-value chemicals may also be pro- duced in the pharmaceutical and food sectors. In the approach like chemical methods, CO2 is not permanently stored, as it is released back into the atmosphere when the biofuel is burned. But the fuel is a carbon-free product since first it captures carbon from the atmosphere before entering it again by burning. The third group of R. Mahmoudi Kouhi · M. M. Jebrailvand Moghaddam · F. Doulati Ardejani (✉) · A. Mirheydari · S. Maghsoudy · F. Gholizadeh School of Mining, College of Engineering, University of Tehran, Tehran, Iran Climate Change Group, Mine Environment & Hydrogeology Research Laboratory (MEHR Lab.), University of Tehran, Tehran, Iran e-mail: reza_mahmoudi@ut.ac.ir; milad.jebrailvand@ut.ac.ir; fdoulati@ut.ac.ir; aida.mirheidari@ut.ac.ir; s.maghsoudy@ut.ac.ir; fereshtegholizade@ut.ac.ir B. Ghobadipour Climate Change Group, Mine Environment & Hydrogeology Research Laboratory (MEHR Lab.), University of Tehran, Tehran, Iran School of Civil Engineering, Iran University of Science & Technology, Tehran, Iran © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Ahmadian et al. (eds.), Carbon Capture, Utilization, and Storage Technologies, Green Energy and Technology, https://doi.org/10.1007/978-3-031-46590-1_1 1
- 15. carbon utilization technologies is the mineralization process which is classified into two types: in situ and ex situ mineralization. Mineral trapping or in situ mineraliza- tion is underground geological sequestration where a fraction of injected CO2 reacts with alkaline rocks in the target formation and it forms solid carbonate species. In ex situ mineralization, CO2 reaction takes place in an industrial process. The final product obtained by this technology can store CO2 for a long time. 2 R. Mahmoudi Kouhi et al. Fig. 1.1 Carbon utilization categories and products The most important challenges facing carbon utilization technologies are high energy consumption, long-term effects, and the cost of raw materials required. Economic issues regarding different methods, durability over time, and insufficient maturity of the technologies are the other issues that should be considered. One of the most important advantages of using carbon utilization is its ability to be used in sectors that are responsible for around 53% of carbon dioxide emitted into the air (Fig. 1.2). The usage of alternative fuels leads to a reduction in carbon emissions in the transport and electricity and heat sectors. In addition, the construction and industrial sectors reduce their carbon emissions through the manufacturing of car- bonates from industrial wastes. Utilization approaches have the potential to reduce about one-fifth of the emissions necessary in the industrial sectors. It is the only option for significantly reducing direct emissions from other industrial point sources, and it will play a significant role in reducing CO2 emissions from fossil fuel–based power plants. It is estimated that the use of carbon utilization will help cut CO2 emissions by up to 32% by 2050. Up to 2060, industrial operations may accumulate more than 28 Gt of CO2, with the chemical, steel, and cement subsectors accounting for the majority of this [2].
- 16. 1 Carbon Utilization Technologies & Methods 3 Fig. 1.2 Gross estimate of greenhouse gas emissions by various segments. (Modified after [1]) 1.2 CCS Versus CCU Carbon capture and storage (CCS) and carbon capture and utilization (CCU) refer to technologies that capture CO2. In CCS methods, CO2 is permanently stored while the major purpose of CCU is to convert it into valuable products such as fuels and chemicals. Both CCS and CCU are based on carbon capture, but the difference is what happens after the capture phase. Figure 1.3 shows the scope of each of these technologies’ effects, as well as their similarities. As can be observed, the method of in situ mineralization is the borders between the usage of CCU and CCS technolo- gies, implying that these two approaches can be classed in both. 1.3 Fuels and Chemicals The main source of energy used in current energy systems is fossil fuels, which result in the generation of large amounts of carbon dioxide when used in transportation and industry. Therefore, it is necessary to find alternatives for them. Carbon dioxide conversion into fuels and chemicals reduces greenhouse gas emissions and depen- dence on petrochemicals. The utilization of CO2 as a feedstock for fuel synthesis as well as chemicals has shown many potential environmental and economic benefits. Several industries, including fuel cells, power plants, and transportation, can utilize the produced fuel. CO2 is a thermodynamically stable molecule; thus in order to utilize it and produce high fuel yields, a lot of heat and catalyst inventory must be
- 17. applied. Carbon dioxide can be utilized to produce energy carriers and transportation fuels such as methane, methanol, formic acid, dimethyl ether, carbon monoxide or synthesis gas (syngas), and Fischer-Tropsch fuels. In addition to synthetic fuels, it is also possible to produce various chemicals such as urea, polymers, formic acid, salicylic acid, acyclic carbonates, cyclic carbonates, and fine chemicals such as biotin using carbon dioxide. Table 1.1 summarizes some chemicals and fuels that are currently being manufactured industrially from CO2. 4 R. Mahmoudi Kouhi et al. Fig. 1.3 The relations of CCU and CCS technologies Table 1.1 Main chemicals and fuels that are now manufactured from CO2 on a worldwide scale [3, 4] Product Production (Mt/year) CO2 utilization (tCO2/t product) Technology readiness level Methane 1100–1500 2.750 CO2 methanation: 7 Methanol 65.00 1.373 Hydrogenation of CO2: 8–9 Formic acid 1.00 0.956 Electrochemical reduc- tion of CO2: 6 Dimethyl ether 11.40 1.911 1–3 Liquid fuels – 2.6 5–9 Urea 180.00 0.735 9 Salicylic acid 0.17 0.319 9 Polycarbonate 5.00 0.173 9 Polyurethane 15.00 0.300 8–9 Cyclic carbonates Ethylene carbonate 0.20 0.499 4–5 Propylene carbonate 0.20 0.431 Dimethyl carbonate 1.60 1.466 8–9
- 18. þ þ ð Þ 1 Carbon Utilization Technologies & Methods 5 1.3.1 Methane Production One of the most significant energy sources is methane (CH4), which is mostly obtained from natural gas, a fossil fuel source with relatively low costs, and is used to generate heat, power, and value-added chemicals [5]. CO2 methanation has recently attracted considerable interest, due to its use in Power-to-Gas (PtG) technology and the upgrading of biogas [6]. In order to effectively incorporate renewable energy sources, such as wind and solar energy, into the current energy mix, PtG processes are viewed as a potential and intriguing solution [7]. In this technology, hydrogen generated from surplus renewable energy is chemically changed into methane, which can be stored and transported using the already- existing, highly developed natural gas infrastructure, by reacting with CO2 [6]. Among the several PtM techniques already in use, catalytic CO2 hydrogenation (methanation) has received the most attention, and demonstration units are already in operation in a number of nations [5]. At the beginning of the twentieth century, Sabatier and Senderens conducted the first studies of the methanation reaction, also known as the Sabatier reaction. Through this reaction, CO2 and H2 are converted into CH4 and H2O (Eq. 1.1) [8]. CO2 þ 4H2 → CH4 þ 2H2O, ΔH = - 165 kJ:mol- 1 ð1:1Þ Due to the exothermic nature of this reaction, products with low temperature and high pressure are preferred in terms of thermodynamics [8]. CO2 hydrogenation can be thought of as a result of combining reverse water gas shift (RWGS) reaction and CO hydrogenation (Eqs. 1.2 and 1.3) [9]. CO2 þ H2 → CO þ H2O, ΔH0 r = 41:2 kJ:mol- 1 ð1:2Þ CO 3H2 → CH4 H2O, ΔH0 r = - 206:3 kJ:mol- 1 1:3 Reactors for methanation might be either biological or catalytic (Fig. 1.4). Methanogenic microorganisms function as biocatalysts in biological methanation [9]. A biogas plant’s fermenter or a separate bioreactor can be used to conduct this process [10]. Metals from group VIII of the periodic table catalyze the methanation reaction. Ru was shown to be the most active metal catalyst, followed by Fe, Ni, and Co. Ni is typically chosen as the active component because of its high selectivity and reactiv- ity, and because it is reasonably priced [11]. Despite having advantages over Ni systems, Ru catalysts are more expensive. Given the low cost and wide availability of methane from natural gas, hydrogenation of CO2 to methane is not now feasible on a big scale and is not anticipated to be in the near future. Furthermore, methane has a significantly lower economic value than the conversion of CO2 into a variety of other compounds [12].
- 19. 6 R. Mahmoudi Kouhi et al. Fig. 1.4 Concepts for reactors that produce substitute natural gas [9] The electrochemical reduction of CO2 is another potential method for producing methane from CO2. This technique is still being validated in the lab. However, recent results have emphasized the attractive characteristics of this path [5]. Currently, only copper is capable of catalyzing the conversion of CO2 into hydrocarbons, particu- larly methane, in an aqueous solution. Higher overpotentials, low activity, and poor product selectivity are problems with conventional Cu electrodes [13]. To create catalysts with improved methane selectivity, more research is still required. 1.3.2 Methanol Production The most basic liquid hydrocarbon that can be used as a fuel, a hydrogen carrier, or a feedstock for creating more intricate chemical compounds is methanol (CH3OH) [14]. Formaldehyde, acetic acid, dimethyl ether (DME), and methyl tertiary-butyl ether (MTBE) are the primary chemical derivatives of methanol [15]. The methanol- to-olefins process creates light olefins like ethylene and propylene, which can be utilized to make polymers and hydrocarbon fuels. Additionally, methanol is converted into dimethyl carbonate in supercritical CO2, which is a helpful interme- diary for derivatives utilized in polycarbonates and polyurethanes [16]. According to Eq. (1.4), syngas, which has a CO/H2 mixture, is being used to create methanol on an industrial scale. Currently, syngas (mixture of CO and H2) produced mostly from natural gas reforming is transformed into methanol at tem- peratures between 250 and 300 °C and pressures between 5 and 10 MPa, using a CuO/ZnO/Al2O3 catalyst [15, 17]. CO þ 2H2 → CH3OH, ΔH = - 90:6 kJ:mol- 1 ð1:4Þ Currently, a little amount of CO2 (up to 30%) is typically added to the syngas. The energy balance and methanol yield both considerably increase with the addition of CO2 to the CO/H2 feed. Syngas is low in hydrogen and high in carbon oxides (CO and CO2). The CO in syngas is transformed to CO2 via the water-gas shift
- 20. þ þ ð Þ (WGS) reaction to increase its H2 content and promote methanol synthesis (Eq. 1.5) [16]. 1 Carbon Utilization Technologies & Methods 7 CO þ H2O → CO2 þ H2, ΔH0 298 = - 41:2 kJ mol- 1 ð1:5Þ The catalytic hydrogenation process shown in Eq. (1.6) is the most direct method for producing methanol from CO2 and involves the production of H2 using water electrolysis, ideally with the use of renewable energy, and the subsequent combina- tion with CO2 waste streams to create methanol, which is known as the Power-to- Methanol process. This process involves the RWGS (Eq. 1.7) as a secondary reaction and is less exothermic than the syngas-based approach. RWGS reaction is regarded unfavorable since it consumes H2 and reduces the yield of methanol synthesis. It was discovered that the rate of the direct methanol synthesis from CO2 was inhibited by the water produced as a byproduct. [5, 15, 16]. CO2 þ 3H2 → CH3OH þ H2O, ΔH = - 49:5 kJ:mol- 1 ð1:6Þ CO2 H2 → CO H2O, ΔH0 r = 41:2 kJ:mol- 1 1:7 Hydrogenation of carbon dioxide to methanol is an efficient CO2 utilization technique and is considered an effective sustainable development strategy. This method is technically comparable to the production of methanol from syngas for industrial use [16]. If direct hydrogenation of CO2 to methanol is replaced with methanol production from syngas, improved catalysts are greatly needed [12]. In comparison to conventional synthesis, this method has a better water footprint, but still lacks competitive economic viability [4]. The electrochemical reduction of CO2 using protons and electrons as a source of H2 is another method for producing methanol. Due to its complicated kinetics, this reaction requires efficient electrocatalysts. One of the most effective materials for the electrochemical conversion of CO2 into alcohols, including methanol, has been recognized to be copper or copper-based electrodes. In order to improve the elec- trochemical CO2 reduction to CH3OH, the usage of copper alloys has also been studied. Cu-Zn mixed oxides make up the majority of commercial catalysts used today to produce methanol, demonstrating the metals’ synergistic influence on methanol synthesis [5, 12]. 1.3.3 Dimethyl Ether (DME) Production The simplest ether is dimethyl ether (DME), which has the chemical formula CH3OCH3. DME has physical properties similar to liquefied petroleum gases (LPG) such as propane and butane. DME has been marketed as a diesel substitute since the mid-1990s. With a high cetane number (55-60), DME has several desirable
- 21. ð Þ þ þ ð Þ þ þ ð Þ ð Þ characteristics over conventional fuels, including very low emissions of pollutants (SOx, NOx, CO, and particulate matter) [18, 19]. 8 R. Mahmoudi Kouhi et al. Indirect synthesis (two-stage) and direct synthesis from syngas (single-stage) are typically the two methods used to produce DME. In the single-stage method, DME is prepared directly from syngas in a single reactor [20]. Fixed-bed reactors have been used for the majority of theoretical studies on single-step DME production [21]. In the two-step process, syngas is first transformed into methanol (Eq. 1.8), which is then dehydrated to produce dimethyl ether (Eq. 1.9). Zeolites and Al2O3, in partic- ular, have been suggested as acid catalysts for the dehydration of methanol to DME [22]. In a reactor, WGS reaction can occur concurrently (Eq. 1.10) [19]. Methanol synthesis : CO þ 2H2 → CH3OH, ΔH = - 90:6 kJ:mol- 1 ð1:8Þ Methanol dehydration : 2CH3OH → CH3OHCH3 þ H2O, ΔH = - 23:41 kJ:mol- 1 1:9 WGS : CO H2O → CO2 H2, ΔH0 298 = - 41:2 kJ mol- 1 1:10 While the current technologies for both methods rely on fossil-based syngas, which again causes environmental issues, recent studies examine the possibility of replacing syngas with CO2/H2 feed (Eqs. 1.11 to 1.13) [22]. CO2 hydrogenetion : CO2 þ 3H2 → CH3OH þ H2O, ΔH = - 49:5 kJ:mol- 1 ð1:11Þ RWGS : CO2 H2 → CO H2O, ΔH0 r = 41:2 kJ:mol- 1 1:12 Methanol dehydration : 2CH3OH → CH3OHCH3 þ H2O, ΔH = - 23:41 kJ:mol- 1 1:13 The direct synthesis of DME from concentrated CO2 and H2 has lately gained attention due to the growing interest in CO2 capture and valorization. The synthesis of methanol is a recognized thermodynamically limited process. As a result, using methanol immediately to create DME via a direct method has the advantageous effect of pushing the equilibrium toward higher conversions. Because of the water forming in greater quantities and the consequently more stringent thermodynamic constraints, the CO2 to DME process is more difficult than the syngas method and hence necessitates focused attention. A strategy that has been introduced to solve this problem is the in situ removal of water produced in all individual reactions using a membrane reactor [22].
- 22. þ þ ð Þ ð Þ þ ð Þ ð Þ ð Þ ð Þ 1 Carbon Utilization Technologies & Methods 9 1.3.4 Formic Acid Production Formic acid (HCOOH) serves as a platform for chemical energy storage in addition to being a valuable chemical that is frequently used as a preservative and antibacterial agent. Through its decomposition to CO2 and H2 and potential for reversible transition back to formic acid, this acid is a known hydrogen storage component [18]. Formic acid and its salts have a wide range of uses, including as a starting chemical for esters, alcohols, or medicinal products, as well as in the production of textiles, leather, and dyes and as a cleaning or disinfection solution [23]. Formic acid is produced industrially most frequently via a two-step process: In the first step, methyl formate is generated from methanol and CO (Eq. 1.14), and in the second step, methyl formate is hydrolyzed into formic acid (Eq. 1.15). The second step is thermodynamically unfavorable [5]. CH3OH þ CO → CH3COOH, ΔHr = - 29 kJ:mol- 1 ð1:14Þ CH3COOH H2O → HCO2H CH3OH, ΔHr = 16:3 kJ:mol- 1 1:15 Also, formic acid can be produced through the hydrogenation of carbon dioxide (Eq. 1.16). As a result of the conversion of gases into liquids during this process, the reaction is entropically unfavorable. The reaction is therefore exergonic in the aqueous phase and endergonic in the gas phase. However, when the reaction is carried out in the aqueous phase, the presence of the solvent can change the reaction thermodynamics and makes it slightly exergonic (Eq. 1.17). By employing additives, such as specific bases like ammonia (Eq. 1.18) and triethylamine, the equilibrium can be changed in favor of the product. Carbonates, bicarbonates, and hydroxides are frequently used for the reaction in water [24, 25]. CO2 g ð Þ þ H2 g ð Þ → HCO2H l ð Þ, ΔG0 298K = 32:9 kJ:mol- 1 ð1:16Þ CO2 aq H2 aq → HCO2H aq , ΔG0 298K = - 4 kJ:mol- 1 1:17 CO2 g ð Þ þ H2 g ð Þ þ NH3 aq ð Þ → HCO- 2 aq ð Þ þ NHþ 4 aq ð Þ, ΔG0 298K = - 9:5 kJ:mol- 1 1:18 Numerous homogeneous and heterogeneous catalysts have been developed for CO2 hydrogenation to formic acid on a lab scale. Transition metal complexes, especially those based on Ir and Ru, have been used in a tremendous amount of attempts, and the results are very remarkable. To become potentially practical, these catalysts require further improvements in selectivity to formic acid and stability. Heterogeneous catalysts, on the other hand, are less studied for this reaction; however, recently the number of examples has notably increased. The heterogeneous catalysts are characterized as follows, with clear practical advantages for continuous
- 23. þ þ ð Þ operation and product separation: heterogenized molecular catalysts and unsupported and supported bulk/nanometal catalysts [18]. 10 R. Mahmoudi Kouhi et al. Because of the high market value and widespread use of formic acid, direct electrochemical reduction of carbon dioxide to this substance has emerged as a viable option. This procedure involves supplying electricity to an electrolytic cell. An electrolyte cell is made up of an anode and a cathode with catalyst-coated surfaces, as well as an electrolyte(s) that allows ions to be transferred between the electrodes. Eqs. (1.19) and (1.20) show half-reactions that take place at the anode and cathode of an electrolytic cell set up to make formic acid from CO2. Cathode : CO þ 4Hþ þ 4e- → 2HCOOH ð1:19Þ Anode : 2H2O → O2 4Hþ 4e- 1:20 The typical operating conditions of this process are ambient temperature and pressure, which is one of its main advantages. However, the primary hurdles for the development of this method are significant overpotentials and limited product selectivity. Various catalysts based on Co, Pb, Pd, Sn, and In metal-free nitrogen- doped carbon materials have been reported for this process over the last few decades [4, 5, 26]. 1.3.5 Carbon Monoxide – Syngas Production Carbon monoxide (CO) is an important chemical product precursor (Fig. 1.5) [27]. Synthesis gas, also known as syngas, is a gaseous fuel mixture of carbon monoxide and hydrogen that is fed to a number of industrial processes, including the direct DME (dimethyl ether) synthesis, the Fischer-Tropsch (F-T) synthesis, the ammonia synthesis, the methanol synthesis, the power and heat generation Fig. 1.5 Applications and principal derivatives of carbon monoxide [27]
- 24. processes, and the SNG (substitute natural gas) synthesis [28]. Due to its superior efficiency than the direct conversion technologies now in use, syngas remains the industrially favored technology for the indirect conversion of natural gas into higher- value chemicals and fuels for the time being. Although almost any raw material containing carbon can be utilized to produce H2/CO mixtures, natural gas, liquid hydrocarbon sources, solid fossil carbon sources like coal or lignite, or raw materials obtained from renewable sources are now the most preferred sources [29]. Methane/ natural gas is the most extensively utilized raw material for synthesis gas due to its availability, gas composition, and inexpensive cost [30]. 1 Carbon Utilization Technologies & Methods 11 Steam methane reforming (SMR), dry methane reforming (DRM), autothermal reforming (ATR), partial oxidation (POX), bireforming (BR), tri-reforming (TR), and combined reforming (CR) have traditionally been used to produce syngas from fossil-based natural gas and coal [28]. When methane is used to create syngas, the process involves the employment of an oxidizing agent that oxidizes methane to carbon monoxide while also creating hydrogen in a ratio that varies depending on the oxidant type. Carbon dioxide is able to function as an oxidizing agent through a procedure called dry reforming [31]. Because DRM is a highly endothermic reaction (Eq. 1.21), equilibrium conversion to syngas must occur at extremely high temperatures [32]. CH4 þ CO2 → 2CO þ 2H2, ΔH0 298 = 248 kJ mol- 1 ð1:21Þ The methane dry reforming process is the most endothermic reaction when compared to SMR and ATR [33]. DRM yields syngas with a H2 to CO ratio that is more compatible with some downstream synthesis processes, such as Fischer- Tropsch synthesis [17]. Due to the difficulty in developing catalysts with a long life-span on stream at a low price acceptable for profit-oriented commercialization, despite its economic and environmental potential, DRM is still in its infancy [34]. The formation of coke and sintering, which quickly deactivate the catalysts, is the main obstacle inhibiting the widespread use of DRM in the industry [32]. It is expected that coke will deposit on the reforming catalyst due to high working temperatures, which increase the molec- ular energy enough to split the C-H bonds in methane [33]. In order to be used on a large scale in industrial applications, the ideal DRM catalyst must be extremely stable and have better resistance to coke formation. Numerous experiments using supported metal catalysts and noble (ruthenium, rhodium, platinum, palladium, and iridium) and non-noble metals (nickel and cobalt) have been conducted [32]. The dry reforming reaction equilibrium is usually influenced by the co-occurrence of the RWGS reaction (Eq. 1.22) [30]. CO2 þ H2 → CO þ H2O, ΔH0 298 = 41:2 kJ mol- 1 ð1:22Þ The H2/CO molar ratio is decreased as a result of the RWGS reaction by consuming H2 [35]. It is an endothermic reaction, so formation of CO is favored at
- 25. þ ð Þ þ þ ð Þ þ þ ð Þ high temperatures [36]. Only in the presence of a suitable and sustainable source of hydrogen and thermal energy at the proper temperature level the RWGS reaction will be commercially attractive as a source for syngas [29]. For this reaction, a variety of heterogeneous catalysts have been utilized, including systems based on copper, iron, or ceria (Cerium (IV) oxide). However, in general, they have low thermal stability, and methane commonly forms as an unfavorable byproduct [12]. In designing a suitable catalyst for the RWGS reaction, criteria of high activity and high CO selectivity should be considered [36]. 12 R. Mahmoudi Kouhi et al. The direct electrolysis of carbon dioxide to carbon monoxide and oxygen is another method for producing CO from carbon dioxide [37]. Three electrolysis techniques are used in this procedure: solid oxide electrolysis at high temperature, molten carbonate electrolysis, and low temperature electrolysis using a solution- phase or gas diffusion electrolysis cell. The only CO2 electrolysis method that is nearing commercialization is high-temperature electrolysis in solid oxide cells [38]. 1.3.6 Liquid Hydrocarbons Production (Fischer-Tropsch) A good substitute for storing renewable energy is liquid hydrocarbons. They are the main source of energy for use in aviation and transportation [20]. Carbon dioxide can also be converted to hydrocarbons through Fischer-Tropsch (FT) and methanol pathways. For the FT pathway, the intermediate product is CO (or a synthesis gas), while for the methanol pathway, it is methanol [39]. There are three steps in both pathways [17]: • Using renewable electricity to electrolyze water to produce hydrogen. • Conversion of CO2 to an intermediate product, methanol or CO. • Liquid hydrocarbon synthesis, followed by improvement or conversion to the desired fuel. Synthesis gas can be converted into a variety of products, including synthetic fuels, lubricants, and petrochemicals, using the FT process [40]. In the Fischer- Tropsch pathway, RWGS reaction (Eq. 1.23) is used to produce syngas, which is then converted to liquid hydrocarbons via the Fischer-Tropsch reaction [39]. Syn- thesis of alkanes, as the main products of FT processes, alkenes, and alcohols are given in Eqs. (1.24) through (1.26) [4]. Ni, Fe, and Cu catalysts can be used in the RWGS reaction; also, Co, Fe, and Ru catalysts can be used in the Fischer-Tropsch synthesis, respectively [39]. CO2 þ H2 → CO þ H2O ð1:23Þ 2n 1 H2 nCO → CnH2nþ2 nH2O 1:24 2nH2 nCO → CnH2n nH2O 1:25
- 26. þ þ ð Þ ð Þ þ þ ð Þ 1 Carbon Utilization Technologies & Methods 13 2nH2 nCO → CnH2nþ2O n - 1 H2O 1:26 In the methanol pathway, CO2 and H2 react over a metallic catalyst to produce methanol, which is then converted into other hydrocarbons over acidic catalysts [39]. Through a series of reactions, including DME synthesis, olefin synthesis, oligomerization, and hydrotreating, methanol is transformed into gasoline, diesel, and kerosene [17]. Currently, methanol is generated from synthesis gas using a Cu-ZnO-Al2O3 catalyst (Eq. 1.27). Recent research efforts have concentrated on the development of catalysts that support the direct conversion of CO2 to methanol (Eq. 1.28). It is vital to utilize a very selective catalyst for this reaction because it is favored at low temperatures and high pressure and can yield a variety of byproducts [39]. CO þ 2H2 → CH3OH, ΔH298k r = - 90:6 kJ:mol- 1 ð1:27Þ CO2 3H2 → CH3OH H2O, ΔH298k r = - 49:5 kJ:mol- 1 1:28 Another way to create fuel-like hydrocarbons that can be used in the current infrastructure is through electroreduction of CO2 [41]. There are a number of systems that can produce products with new carbon-carbon bonds, even though the reduction of CO2 to C1 feedstocks such CO, methane, formic acid, or methanol is the process that occurs most frequently [12]. Although the Faradaic efficiency is still low due to H2O dissociation to H2, Cu-based electrodes are perfectly suitable in activating CO2 [41]. As mentioned above, the electroreduction of CO2 to value- added compounds shows promise, but is still far from commercialization due to the high overpotential of this reaction and the low activity of the currently available catalysts [42]. 1.3.7 Urea Production Another non-toxic product made from carbon dioxide is urea (CH4N2O). Liquid and solid fertilizers, urea-formaldehyde resins used to manufacture adhesives and binders, melamine for resins, livestock feeds, NOx control from boilers and furnaces, and a variety of chemical applications are all the uses of urea [43]. Reforming natural gas to produce ammonia and carbon dioxide is the most widely used process for producing urea [44]. The production of urea results from the reaction of carbon dioxide and ammonia at a temperature between 185 and 190 °C and a pressure between 180 and 200 atm. Two equilibrium reactions known as Basaroff reactions with incomplete reactants conversion are involved in this process: Ammonium carbamate (H2N-COONH4) is generated in the first stage by the fast and exothermic reaction of liquid ammonia with gaseous CO2 at high temperature and pressure (Eq. 1.29). In the next step, ammonium carbamate decomposes slowly
- 27. þ ð Þ and endothermically into urea and water using the heat produced by previous reaction (Eq. 1.30) [45, 46]. 14 R. Mahmoudi Kouhi et al. Fig. 1.6 Urea derivatives synthesis from amine and CO2 [47] 2NH3 þ CO2 → NH2COONH4, ΔH = - 117 kJ:mol- 1 ð1:29Þ NH2COONH4 → NH2CONH2 H2O, ΔH = 15:5 kJ:mol- 1 1:30 The use of CO2 in the synthesis of urea derivatives has received a lot of interest. Anti-cancer agents, plastic additives, gasoline antioxidants, agricultural pesticides, dyes, medicines, gasoline antioxidants, and corrosion inhibitors are just a few uses for urea derivatives. The traditional process for producing urea derivatives includes the reaction of amines with phosgene, carbon monoxide, or isocyanate, which has serious toxicological and environmental issues. One of the main aims of Green Chemistry nowadays is to replace these dangerous reagents in chemical processes. As a result, there has been a significant advancement in the production of urea derivatives through the reaction of amines with CO2 either with or without the use of a dehydrating agent, using basic ionic liquids or base catalysts [47–49] (Fig. 1.6). 1.3.8 Polymers A unique class of chemicals known as polymers is employed in the manufacturing process for plastics and resins. Polymers, such as polyurethanes and polycarbonates, are adaptable materials with several practical uses, including those in the electrical and electronic industries, the automobile sector, packaging, the medical industry, personal care goods, and the construction [50]. Up until this point, the primary raw materials used in the manufacturing of polymers were petrochemicals[51]. However, the chemical industry is under pressure to discover practical substitutes for the manufacture of renewable chemicals and polymers due to the depletion of fossil fuels and the legal demand for sustainable and renewable plastics under the circular economy [50]. As a raw material for the synthesis of polymers, CO2 can partially replace petrochemicals. One example is the copolymerization of epoxides with CO2 to create polycarbonates [17]. As potential, more environmentally acceptable raw materials for plastics, CO2-based polymers have received a lot of industrial interest [52]. Additionally, using CO2 to produce different biodegradable polymers is seen to be a cost-effective strategy from an economic perspective [20]. There are two chemical methods for including CO2 in the production of polymers: direct and indirect methods. Both strategies have been shown to be feasible and possible [48, 49].
- 28. 1 Carbon Utilization Technologies & Methods 15 1.3.8.1 The Direct Method The direct method produces high CO2 content polymers such as polycarbonates, polyols, polyurethanes, polyureas, and polyesters by using CO2 as a monomer in combination with proper reagents and catalysts [12]. 1.3.8.1.1 Polycarbonates (PCs) from CO2 Aromatic PCs are utilized as engineering plastics in automobiles, electrical and electronic equipment, and construction because of their great impact resistance, stiffness, toughness, superior thermal stability, transparency, and flame retardancy. The toxic and destructive phosgene reaction with 1,2-diol is the traditional method for producing polycarbonates. The copolymerization of epoxides, such as propylene oxide, cyclohexene oxide, vinyl oxide, ethylene oxide, and styrene oxide and CO2, is an alternate method for the selective production of PCs. This process is the most promising application of CO2. In general, transition metals or metals from the main group of elements, such as cobalt, zinc, chromium, magnesium, and aluminum, are used as homogeneous or heterogeneous catalysts for the copolymerization of CO2 and epoxides. Compared to heterogeneous catalysts, homogeneous catalysts are more active and selective. Current CO2 copolymerization research focuses on the development of catalysts for the production of polymers with tailored properties and derived from renewable epoxides such as limonene oxide, cyclohexadiene oxide, and α-pinene oxide [17, 51]. 1.3.8.1.2 Polyurethanes (PUs) from CO2 Polyurethanes (PUs), one of the most significant polymers, are used in a variety of products in daily life, including adhesives, sealants, coatings, elastomers and foams, heart valves, and cardiovascular catheters. They are manufactured commercially using polyaddition of diisocyanates with di- or polyols. Establishing isocyanate-free production methods has received recent attention in the field of PUs; CO2 can play a significant role in this vital transition. When CO2 reacts with cyclic amines like aziridines and azetidines or the N-analogs of epoxides, PUs can be produced [50]. 1.3.8.1.3 Polyureas (PUA) from CO2 Polyureas (PUAs) are polymers with urea linkages built into their backbone. They are used as linings, joint sealants, and microcapsules among other things in a variety of industries, including the building industry, the automobile industry, household products, and marine-related technology. PUAs are created commercially by the polyaddition process utilizing the reagents diisocyanate and diamine. These
- 29. polymers can be made via non-isocyanate methods using CO2-sourced (a)cyclic carbonates or urea, or direct CO2 copolymerizing with diamines [50]. 16 R. Mahmoudi Kouhi et al. 1.3.8.2 The Indirect Method The indirect method involves converting CO2 into a different monomer, such as methanol, ethylene, carbon monoxide, organic carbonates, dimethyl carbonate, or urea, which enables the synthesis of a wide range of polymers with a variety of controlled and specified properties. Additionally, CO2 can be used to create chemical building blocks for polymer synthesis, specifically urea. This makes it possible to create a variety of thermosetting polymers, including Melamine-Formaldehyde (MF) and Urea-Formaldehyde (UF) resins, as well as commercial plastics like Polyoxymethylene (POM) or Polymethylmethacrylate (PMMA) [51]. 1.3.9 Other Chemicals In addition to urea and polymers, the production of other chemicals, such as salicylic acid, inorganic and organic carbonates, fine chemicals such as biotin, etc., is possible by utilizing carbon dioxide. Acyclic (linear) carbonates (e.g., dimethyl carbonate [DMC], diethyl carbonate [DEC], diallyl carbonate [DAC], and diphenyl carbonate [DPC]) and cyclic carbonates (e.g., ethylene carbonate [EC], cyclohexene carbonate [CC], propylene carbonate [PC], and styrene carbonate [SC]) make up the majority of the organic carbonates class [53]. CO2 and two equivalents of an alcohol, such as methanol, can be used to produce linear carbonates directly. Linear carbon- ates are used as solvents, reagents (for alkylation or acylation reactions), and gasoline additives. The cyclic carbonates can be produced by reacting CO2 with a cyclic ether (e.g., an epoxide) or a diol. They are used as monomers for polymers, components of special materials, and also in the synthesis of hydroxyesters and hydroxyamines [45, 53]. 1.3.10 Beverage and Food Industry Food production is possible using CO2 that is captured for CCU. The principal applications for food-grade CO2 at the moment are the creation of carbonated beverages, deoxygenated water, milk products, and food preservation. In addition to serving as a carbonating agent for the creation of champagne, alcoholic drinks, and soft drinks, carbon dioxide can also be utilized as a preservative, packing gas, and flavor solvent. Potential CO2 merchant markets in the US require between 3.2 and 4.0 million metric tons of CO2 annually for food processing and between 1.6 and 2.4 million metric tons of CO2 annually for carbonated beverages. CO2 is utilized to
- 30. prevent food from oxidizing. Although N2 gas is frequently used to prevent oxida- tion, CO2 and N2 together are preferable for antioxidative food packaging. Addi- tionally, antibacterial behavior of CO2 has been demonstrated in a variety of literature. Food freshness is preserved as a result, extending its shelf life [20, 52, 54]. 1 Carbon Utilization Technologies & Methods 17 Fig. 1.7 Typical food items obtained through SFE [52] Mechanical refrigeration is mostly employed during transportation and storage in traditional food preservation. However, liquid carbon dioxide, dry ice (i.e., the solid form of CO2), and modified atmosphere packaging (MAP) technologies are more frequently employed for refrigeration of foods that need freeze drying (dehydration). CO2 is frequently used as a flushing gas in MAP. Because of its high solubility in food matrices, the presence of carbon dioxide in the atmosphere package may reduce the pressure or volume of package, so balancing the pressure between the inside and outside of the package. To prevent high CO2 dissolution into foods, the CO2-based MAP strategy should be implemented with extreme professionalism in accordance with food attributes and operational requirements. High levels of dissolved CO2 cause packaging to collapse and produce products with a poor texture and flavor [20, 52]. Supercritical fluid extraction (SFE) technology is a method for utilizing CO2 in flavors as well as coffee decaffeination, which is advantageous for the separation and extraction of heat-sensitive, volatile, and oxidizable components. Compared to traditional separation methods, this method has several advantages, including non-toxicity, non-corrosiveness, and chemical stability of the extraction agent in SFE, as well as its reusability after decompression, controllability of SFE extraction capability by adjusting the main operating factors, and providing better permeability compared to other solvent approaches. Due to the aforementioned benefits, super- critical CO2 extraction (SCE) technology is preferred in the food processing indus- try. As seen in Fig. 1.7, this technology is currently used widely in daily life [52].
- 31. 18 R. Mahmoudi Kouhi et al. 1.4 Biological Conversion The utilization of microorganisms to produce a variety of products is known as biological conversion of CO2. In some circumstances, the emerging field of synthetic biology has the potential to improve biological systems. Microorganisms such as algae, cyanobacteria, and β-Proteobacteria take up CO2 and convert it into a variety of valuable compounds during biological CO2 conversion. Some of these products could be large-scale bulk chemicals like ethylene and ethanol. More high-value chemicals, such as medicines, nutrition, cosmetics, and fragrances, can also be produced; while low in volume, these items may give a more cost-competitive route than traditional industrial synthesis routes [55]. In this part, we look at the microorganisms utilized in biological conversion and the products they produce. 1.4.1 Microorganisms In this section, we look at the key microorganisms used in biological conversion like algae, cyanobacteria, and β-Proteobacteria that have received the most interest and could potentially be turned into industrial-scale bioprocesses. 1.4.1.1 Algae Algae are a wide category of aquatic eukaryotic organisms that can do photosyn- thesis. Its primary habitats include moist, wooded places, still waters, lakes, and pools. Algae are commonly classified into two types based on their size and shape: macroalgae and microalgae. Similar to kelps, algae are composed of many cells that join together to form structures such as roots and stems, as well as the leaves of more mature plants. The great majority of microalgae or microscopic photosynthetic creatures are present in unicellular form and can be found in a wide range of environments. Microalgae are regarded to be one of the earth’s oldest life forms. They can thrive in a number of natural habitats, including freshwater, brackish water, and seawater and can adapt to a variety of high temperatures and pH levels. On the basis of their habitats and physical characteristics, microalgal species can also be categorized further. These groups include euglenoids, diatoms, green algae (Chlorophyceae), red algae (Rhodophyceae), yellow-green algae (Xanthophyceae), golden algae (Chrysophyceae), and Chlorophyceae (green algae) [56]. The Calvin-Benson-Bassham (CBB) cycle allows algae to utilize CO2. The CBB cycle, in fact, is an essential biological mechanism for converting CO2 from the atmosphere to organic matter. The main enzyme for CO2 fixation in this cycle is ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Aside from the CBB cycle, nature has identified five other carbon fixation mechanisms, the most efficient of which is the reductive acetyl-CoA process under anaerobic conditions [57]. For
- 32. their ability to fix inorganic carbon, both macro- and microalgae are investigated and utilized. Their potential is attributed to their widespread distribution (especially in moist conditions), high biomass capability, rapid CO2 uptake and utilization, and, most crucially, their ability to make secondary products with high commercial value from biomass. The most industrially important component of algal biomass is lipid, which is used to make secondary goods such as biofuels and lubricants. To maxi- mize the value of algal carbon capture and utilization, it is critical to select high lipid- producing strains and optimize growing parameters such as light, temperature, and pH [58]. 1 Carbon Utilization Technologies & Methods 19 1.4.1.2 Cyanobacteria Cyanobacteria (or blue-green algae) are phylogenetically a group of Gram-negative photosynthetic prokaryotes having widespread distribution ranging from hot springs to the Antarctic and Arctic regions. The role of cyanobacteria in nitrogen fixation and in the maintenance of the fertility of rice is well documented. [59] Additionally, they are believed to have contributed to the early rise in atmospheric O2 and the lowering of CO2 around 2.3 billion years ago. 20–30% of Earth’s primary photo- synthetic productivity is accounted for by cyanobacteria, which convert solar energy into chemical energy stored in biomass at a rate of 450 TW [60, 61]. RuBisCO, which catalyzes the same reaction as in the CBB cycle in algae, is in charge of the carbon utilization in cyanobacteria. Due to their simpler structure than algae, cyanobacteria are more effective in fixing carbon from the atmosphere. However, they cannot produce the same amount of biomass [58, 62]. 1.4.1.3 β-Proteobacteria β-Proteobacteria are a class of Gram-negative bacteria, and one of the eight classes of the phylum Pseudomonadota. Ralstonia Eutropha H16 is a Gram-negative lithoautotrophic bacterium from the Proteobacteria-subclass. It is a common inhab- itant of freshwater and soil biotopes and is highly adapted to survive in environments with intermittent anoxia [63]. R.Eutropha lives on hydrogen (H2) as its only energy source when there are no organic materials present, fixing CO2 through the CBB cycle. In addition, it is capable of utilizing a wide array of carbon sources for growth and polymer biosynthesis, including sugars, organic acids, fatty acids, and CO2. The biggest advantage of working with R.Eutropha is the ability to store carbon within its cytoplasm in the form of polyhydroxyalkanoates (PHAs), also known as bio-plastics. Genetic engineering, on the other hand, can be utilized to create poly- mers of varying lengths. R.Eeutropha is also sought after for its various carbon utilization routes and biocompatibility in the production of pharmaceutical chemicals [58, 64].
- 33. 20 R. Mahmoudi Kouhi et al. 1.4.1.4 Other Microorganisms Other microorganisms, in addition to those mentioned, have the ability to absorb carbon and produce fuel and other valuable industrial substances. For example, acetogenic bacteria such as Clostridium autoethanogenum have the ability to grow and convert CO2 and CO into low-carbon fuels and chemicals like ethanol, acetone, and butanol [65]. Besides that, there are many microorganisms from an archaeal domain that can fix carbon dioxide through CO2 fixing pathways [66]. 1.4.2 Bio-Based Products In this part, we will discuss the three main products of the biological conversion method: bio-plastics, biofuels, and bio-alcohols. Producing these products and attempting to improve each process, as well as discovering useful new products, might serve as a road map for future research. 1.4.2.1 Bioplastics Bioplastics are plastics derived in whole or in part from biological material. Bioplastics differ from biodegradable plastics, which are readily decomposed by microorganisms. Polyhydroxyalkoanates (PHAs) can be synthesized by microbes with the polymer accumulating in the microbes’ cells during growth [55]. Packaging, food services, agriculture and horticulture, consumer electronics, and other indus- tries are all using bioplastics. About 2.42 million tons of bioplastics were produced globally in 2021, with nearly 48% (1.15 million tons) of that volume going to the packaging market, which is the largest market for bioplastics (Fig. 1.8).[67]. Fig. 1.8 Global production capacity of bioplastics in 2021 by marketing segment [67]
- 34. 1 Carbon Utilization Technologies & Methods 21 Fig. 1.9 Biofuel production from microalgae and two side products (Organic fertilizers, Bio-based chemicals). (Modified after [68]) 1.4.2.2 Biofuels Microalgae have been tested as a viable feedstock for biofuel generation in the current era due to its high energy content, rapid growth rate, low-cost culture methods, and significant ability for CO2 fixation and O2 addition to the environment. Biofuel has gained significant attention as an alternative fuel in recent years due to its capacity to adapt with gasoline for a maximum 85% blend without engine modifi- cation. As a result, academics and environmentalists are constantly questioning the suitability of various alternatives for biofuel. Figure 1.9 depicts the various forms of biofuels produced from microalgae; additionally, bio-based chemicals and bio-fertilizers are available as byproducts alongside biofuels [68]. 1.4.2.3 Bio-Alcohols Alcohols produced from biological resources or biomass are known as bio-alcohols. Bioethanol, the most common and extensively produced bio-alcohol, is an important alternative fuel for spark ignition engines. As ethanol has a poor energy density (70% that of gasoline) and is corrosive to current engine technology and fuel infrastructure, its use as a replacement for conventional gasoline is called into question. It also rapidly absorbs water, resulting in separation and dilution in the storage tank. Isopropanol can be produced biologically. It can be used to supplement
- 35. Organisms Advantages Disadvantages gasoline. It is also used to esterify fat for biodiesel production instead of methanol, which lowers its tendency to crystallize at low temperatures [58, 69]. 22 R. Mahmoudi Kouhi et al. Table 1.2 Benefits, drawbacks, and products produced by microorganisms [58] Bio- based products Algae Wide distribution Fast growing Fast CO2 uptake High cellular lipid content High-value byproducts Light requirement Water requirement Large amount of phosphorousRequired as a fertilizer Bio-plas- tics Biofuels Cyanobacteria Simple cultivation Higher photosynthetic levels Higher growth rates Capability to produce a wideRange of fuels Temperature, pH, and lightIntensity affect productivity Increasing the operating cost ofCell cultivation due to agitation Bio- alcohols β-Proteobacteria Aerobic microorganisms’Easier culti- vation Diverse carbon sourcesAnd carbon utilization pathways Natural ability to store carbon Availability of genetic modi- fication tools Under development gas fermentation Bio-plas- tics Bio- alcohols Table 1.2 lists the advantages, disadvantages, and products generated by all three microorganisms: algae, cyanobacteria, and proteobacteria. 1.5 Carbon Mineralization Carbon mineralization is a natural process that occurs when CO2 reacts with metal cations to generate carbonate minerals, with calcium and magnesium being the most attractive metals. The CO2 is permanently eliminated from the atmosphere after being trapped in the permanent and nontoxic state of the carbonate minerals. Mineralization methods are generally classified into two types: in situ and ex situ. In situ mineralization or mineral trapping involves injecting CO2 into geological formations containing alkaline minerals in order to promote natural carbon miner- alization over time. Ex situ mineralization occurs when CO2-bearing gases react with alkaline mine tailings or industrial wastes on the earth’s surface in an industrial process. These approaches can also provide a low-cost way to reduce greenhouse gas emissions. In general, the degree of mineral carbonation is determined by available CO2 dissolved in solution, available alkalinity in solution, and chemical conditions that promote available alkalinity via mineral dissolution and carbonate precipitation [70]. Mineral carbonation products are stable solids that limit the possibility of
- 36. CO2 emission back into the atmosphere. According to IPCC Special Report on Carbon dioxide Capture and Storage, the fraction of carbon dioxide stored by mineral carbonation retained after 1000 years in in situ mineralization is almost expected to be 100%. As a result, the need for monitoring disposal sites will be minimized [71]. Carbonation reactions that mineralize CO2 are exothermic, so it does not require energy inputs, which means these spontaneous reactions generate heat. On the other side, mineralization processes happen very slowly and might take hundreds of years. This issue has to be resolved, especially with the ex situ mineralization approach, which calls for various energy-intensive pre-treatment procedures like grinding and heating [72, 73]. 1 Carbon Utilization Technologies & Methods 23 The mineralization potential capacity of resources due to the presence of appro- priate geological formations and industrial wastes is virtually limitless. Ultramafic and mafic rocks like peridotite and basalt are more suited due to their high concen- tration of metals like magnesium and calcium compared to intermediate and felsic rocks like diorite and granite, which are made up of inert minerals like silicon dioxide. Basaltic rocks are the most feasible formation to store CO2 as they make up most of the ocean floor, over 70% of the earth’s surface, and more than 5% of the continents [73]. In addition, alkaline solid wastes such as iron/steel slags, coal-fired products, fuel combustion products, mineral processing wastes, incinerator residues, cement/concrete wastes, and pulp/paper mill wastes exist in Gt-Size for mineralized construction materials [74, 75]. Mineral carbonation technologies generally store between 10,000 and 1000,000 Gt of total carbon. In contrast, the estimated carbon production in 100 years is roughly 2300 Gt. Despite this enormous potential, large- scale carbon mineralization has not yet been implemented owing to the absence of information on mineral concentrations, compositions, and volumes at specific geo- logic resource locations [76, 77]. 1.5.1 In-Situ Mineralization The process of injecting CO2 into geological formations containing alkaline minerals to enhance natural carbon mineralization over time is known as in situ mineralization or mineral trapping. In situ mineralization requires subsurface rocks rich in suitable alkaline minerals (magnesium and calcium), which can react with CO2. Injection in gaseous, liquid, or supercritical forms into underground reservoirs is the three storage options for CO2. In these systems, four types of trapping mechanisms are considerable for CO2 utilization: Hydrodynamic trapping refers to CO2 trapping as supercritical fluid or gas under a low-permeability caprock. Residual trapping refers to trapping CO2 in tiny pores. Solubility trapping relates to the dissolution of CO2 in the formation fluid. Finally, mineral trapping refers to the incorporation of CO2 in a stable mineral phase via reactions with mineral and organic matter in the formation. As storage proceeds from structural to mineral trapping, CO2 becomes more immo- bile, enhancing storage safety and lowering reliance on cap rock effectiveness (Fig. 1.10) [71, 73, 78].
- 37. 24 R. Mahmoudi Kouhi et al. Fig. 1.10 Physical and geochemical trapping is used to ensure storage security. The physical process of residual CO2 trapping and the geochemical processes of solubility trapping and mineral trapping, increase with time. The left-hand panel, typical sedimentary reservoir, right-hand panel, peridotite reservoir [70, 71] Sedimentary basins are capable of implementing in situ mineralization. In these formations, the porosity and permeability of the target formation are essential factors in injectivity, while solution chemistry, temperature, and pH are crucial factors in carbonate formation potential [79]. However, this approach faces some significant problems. Low rock reactivity due to the lack of silicate-bound divalent metals required for carbonate production is the major challenge; the risk of returning CO2 to the surface is also present, as the majority of the injected CO2 will most likely remain in the gaseous, liquid, or supercritical phase for an extended period [71, 73]. As a result, several CCS approaches have been developed to overcome the constraints of sedimentary injection. The most important one is the injection of CO2 into mafic or ultramafic lithologies that have large concentrations of divalent cations like Ca2+ , Mg2+ , and Fe2+ in order to promote fast mineralization to calcite (CaCO3), dolomite (CaMg(CO3)2), magnesite (MgCO3), or siderite (FeCO3) [73, 80, 81]. Figure 1.11 depicts the mafic (basaltic), ultramafic, and sedimentary reservoirs accessible for carbon mineralization. Although mafic rocks are more plentiful in size, ultramafic rocks can react faster with CO2 due to their more significant concentration of reactive minerals. Additionally, large-scale facilities and pilot projects for CO2 sequestration across the globe are visible [72]. 1.5.1.1 Challenges and Risks Regardless of ex situ methods, in situ mineralization should be regularly monitored as it may confront some challenges and risks that must be addressed. Since direct sampling of mineralization is too complex and expensive, quick indirect monitoring
- 38. appears feasible and cost-effective. Leakage from wellbores or non-sealed fractures in the caprock and pressure buildup in the reservoir that may result in caprock hydraulic fracturing are significant risks [72]. Also, contamination of drinking water aquifers as supercritical CO2 is buoyant in the subsurface and can travel upwards in the presence of an open pathway, such as a transmissive fault. Further- more, injecting fluids underground can trigger earthquakes by increasing pore fluid pressure and changing rock volume, allowing faults to move [70, 76]. 1 Carbon Utilization Technologies & Methods 25 Fig. 1.11 Map of CO2 sequestration facilities, pilot projects, and long-term storage potential in geological formations [72] All these risks can be avoided by monitoring CO2 plume migration, pressure in and above the reservoir, induced seismicity, the degree of secondary trapping mechanisms, leakage into groundwater, and the chemistry of freshwater aquifers near the CO2 reservoir and leakage to the atmosphere. In terms of human health, utilizing best practices and managing operations to reduce the likelihood of worker injury, uncontrolled CO2 emissions, and fugitive emissions are also crucial [70, 72]. 1.5.1.2 Pros and Cons Compared to ex situ mineralization, in situ mineralization has several benefits. The first and most important are the readily available, vast rock “reservoirs” that may be used to absorb CO2 and reduce its effects on the environment. These reservoirs may also be found all over the globe, as seen in Fig. 1.11. This approach is more advantageous regarding costs and energy since, despite ex situ mineralization, no pre-treatment activities are required. Finally, because of the large-scale projects that may be performed using this approach, the foundation of government and big
- 39. þ þ þ ð Þ ð Þ industries are conceivable. On the other hand, there are some disadvantages to this approach: the first and the major one is the slow kinetics of reactions, as carbon mineralization may take up to hundreds of years depending on the formation types and CO2 injection. Moreover, infrastructure needs are prohibitive since reservoirs might be located distant from waste and CO2 sources. That is why more extraordi- nary engineering efforts and advanced technologies are necessary. Furthermore, CO2 leakage into the atmosphere or ground water is always possible. Thus, the entire system should be regularly monitored to prevent these potential risks. 26 R. Mahmoudi Kouhi et al. 1.5.1.3 In Situ Projects The CarbFix experiment in Iceland and the Wallula Project in Washington State are the two projects that have shown in situ mineralization of CO2 in basaltic formations. In both experiments, thick sequences of basaltic lavas were extensively characterized regarding composition, structure, and hydrology before injecting CO2-rich fluids to test storage in pore space and produce solid carbonate minerals. 1.5.1.3.1 CarbFix The CarbFix Pilot Project is an academic-industrial collaboration that has created an innovative method for safely and permanently capturing CO2 and H2S from emis- sion sources and storing it as stable carbonate minerals in the subsurface basalts by imitating and speeding up the natural process of carbon mineralization. With this method, CO2 and other acid gases may be captured and stored as stable mineral phases for less than $25 per ton [82]. It involves a combined program consisting of a CO2 pilot gas separation plant, CO2 injection pilot test, laboratory-based experi- ments, studying of natural analogs, and numerical modeling. Following CO2 injec- tion into aquifers, it will dissolve and acidify the formation water before dissociating into bicarbonate and carbonate ions via the following reaction (Eq. 1.31) [83]: CO2 aq ð Þ þ H2O $ H2CO3 $ HCO- 3 þ Hþ $ CO2 - 3 þ 2Hþ ð1:31Þ The subsurface injection of carbonated water causes it to react with the Ca and Mg found in the rock. Rocks often include calcium and magnesium as oxides. However, since many rocks, like basalt, include silicate minerals of these elements (like forsterite and anorthite), some example reactions may be as follows (Eqs. 1.32 through 1.34) [83, 84]: Ca, Mg ð Þ2þ þ C2O þ H2O → Ca, Mg ð ÞCO3 þ 2Hþ ð1:32Þ Mg2SiO4 4Hþ → 2Mg2þ 2H2O SiO2 aq 1:33
- 40. þ þ þ ð Þ ð Þ 1 Carbon Utilization Technologies & Methods 27 Fig. 1.12 (a) The field-scale, in situ basalt-carbonation pilot plant in Hellisheidi, Iceland [84], (b) Core from CarbFix site. (Source: CarbFix project, Orkuveita Reykjavikur) CaAl2Si2O8 2Hþ H2O → Ca2þ Al2Si2O5 OH 4 1:34 The CO2 gas injection site is located in southwest Iceland, about 3 km south of the Hellisheidi geothermal power plant above subsurface basalts formations. (Fig. 1.12) The power plant has a CO2 generation capability of around 60,000 tons per year. A treatment facility separates the primary gases generated, which include CO2 and H2S. The H2S is separated and injected back into the geothermal reservoir, while the CO2 (98% CO2, 2% H2S) is transported through a 3 km long pipeline to the CO2 injection location. The CO2 injected into the storage formation entirely dissolves in water, resulting in a single fluid phase entering the storage formation. CO2 at 25 bar and groundwater are injected together. Carbon dioxide is transported to a depth of 500 meters by injected groundwater, where it enters the target storage formation totally dissolved. Under these circumstances, CO2-charged water reacts with basaltic minerals, increasing pH and alkalinity. Given that the amount of water necessary to completely dissolve CO2 varies on the temperature and partial pressure of CO2, the total dissolution of CO2 at the CarbFix site takes 22 tons of H2O per ton of CO2 [83]. By utilizing tracers such as trifluormethylsulfur pentafluoride (SF5CF3), acid red dye (amidorhodamine G), and radiocarbon (14 C), the mineralization of the injected gases has been demonstrated and is being tracked by sampling fluids from wells close to the injection spot. The injection well is filled with known quantities of CO2 and tracers. The assessment of CO2 mineralization by mass balance calculations is made possible by measured tracer concentration and chemical composition in monitoring wells. Utilizing various isotopes, the mineralization has also been quan- tified. According to monitoring results, more than 95% of the subsurface CO2 injections mineralized within a year, and almost all of the H2S injections mineralized within 4 months after injection. Furthermore, the injected radioactive carbon tracer was found in the carbonates that precipitated on the pump and inside of the monitoring well pipes. This finding demonstrated that carbon dioxide may be
- 41. quickly and permanently trapped in basaltic bedrock, consequently lowering green- house gas emissions [85]. 28 R. Mahmoudi Kouhi et al. The new project CarbFix2 builds upon the success of the original CarbFix project, which was funded by the EU’s seventh Framework Program. It is a com- prehensive project consisting of [86]: • Development of the technology to perform the CarbFix geological carbon storage method using seawater injection into submarine rocks • Reducing the cost of the entire CCS chain • Impure CO2 capture and co-injection into the subsurface • Integration of the CarbFix method with novel direct air capture technology The goal of the CarbFix2 project was to make the CarbFix geological storage solution both commercially feasible with a full CCS chain and transportable across Europe. 1.5.1.3.2 Wallula Project The Wallula Project in Washington State, the world’s first continental flood basalt sequestration, was conducted in 2013 by the Pacific Northwest National Laboratory (PNNL) of the U.S. Department of Energy Big Sky Regional Carbon Sequestration Partnership to examine the viability of safely and permanently storing CO2 in basalt formations. By injecting 1000 metric tons of supercritical CO2 into a natural basalt formation in the Columbia River Basalt Group at 830–890 m depth, PNNL researchers started a field demonstration of carbon storage. Prior to drilling, site appropriateness was evaluated by collecting, processing, and analyzing a four-mile, five-line, three-component seismic swath that was processed as a single data-dense line. Results from 2 years of post-injection monitoring, including a long-term sampling of water retrieved from the injection zone, shallow groundwater and soil gas monitoring, and PSInSAR, [87] revealed the formation of new carbonate minerals as a result of CO2 injection. Nodules of calcium, iron, magnesium, and manganese carbonate mineral ankerite (Ca(Fe, Mg, Mn)(CO3)2) were detected in vesicles throughout the cores. Additional carbon isotope research confirmed the nodules to be chemically unique from basalt’s naturally occurring carbonates and to be in direct accordance with the isotopic signature of injected CO2. At the top of the injection zone, there was unmineralized CO2 that was still present beneath the caprock, showing that not all of the CO2 had mineralized (Fig. 1.13). Results from modeling show that within 2 years, mineralization sequestered almost 60% of the CO2 that was injected. However, it is uncertain what will happen to the remaining CO2 because no leaks have been identified. According to the experimental results, carbonates only occupied around 4% of the reservoir accessible pore space, giving it a significant amount of storage capacity [76, 88].
- 42. 1 Carbon Utilization Technologies & Methods 29 Fig. 1.13 (a) Schematic representation of the Wallula Project and location of Ankerite nodules forming in the deep subsurface and (b) calcium carbonate nodules. (Source: Odeta Qafoku | PNNL) 1.5.2 Ex Situ Mineralization Ex situ mineralization takes place when CO2-bearing gases in an industrial process interact with natural minerals, alkaline mine tailings, or industrial wastes on the earth’s surface. The source material, which is frequently an alkaline earth metal silicate, is transformed into the metal’s carbonate as a result of this reaction. The finished product, depending on the type of raw material, may be valuable and utilized as feed in downstream industries. One of the most significant advantages of this technology is waste management, which results in the production of a valuable product with fewer environmental problems after the reaction of hazardous wastes from industries such as iron and cement, which can damage water, soil, and even atmosphere. The proximity of some of these raw materials to point sources of CO2, the size of the available tailings, which eliminates the need for energy-intensive processes, and the faster reaction time are some additional benefits of this method over the in situ method, in addition to the cases already mentioned. On the other hand, there are significant obstacles to this technology that must be addressed as quickly as feasible, such as the high cost per kilo of carbon captured when compared to the in situ method. Furthermore, while some carbon mineralization products have commercial value, the low value of other production materials is not yet convincing to invest in this technology, and as a result, despite the enormous potential of the raw materials, employing this approach on a large scale is not common in the globe. 1.5.2.1 Ex Situ Sequestration Routes Carbonation studies have identified several ways for performing ex situ CO2 seques- tration, which are classed as direct carbonation and indirect carbonation. Each of these two approaches will be discussed more below.
- 43. ð Þ þ ð Þ ð Þ þ ð Þ þ ð Þ ð Þ ð Þ þ ð Þ ð Þ þ ð Þ ð Þ 30 R. Mahmoudi Kouhi et al. 1.5.2.1.1 Direct Carbonation The process of direct carbonation is separated into two parts: direct gas-solid carbonation and aqueous mineral carbonation. The direct gas-solid carbonation process is the simplest method. The potential of this method for heat recovery at high temperatures reduces energy consumption and improves viability. Unfortu- nately, this approach has fundamental difficulties, including a slow reaction rate, and is applicable only for refined and unusual materials such as calcium and magnesium oxides and hydroxides. High temperatures and pressures (between 100 and 150 bar) are recommended as a remedy to this issue, although this approach may decrease the process overall efficiency due to the significant amount of energy needed. The direct gas-solid reaction of olivine serves as an illustration of this process (Eq. 1.35) [71, 89]. Mg2SiO4 s ð Þ þ 2CO2 g ð Þ → 2MgCO3 s ð Þ þ SiO2 s ð Þ ð1:35Þ On the other hand, aqueous mineral carbonation is the most commonly studied ex situ mineral carbonation route, and it was one of the first that was investigated on a small scale [90]. The carbonic acid pathway technique comprises CO2 interacting with olivine or serpentine in an aqueous solution at high pressure (100–159 bar). This process involves dissolving CO2 in water, where it dissolves into bicarbonate and H+ , producing a pH of around 5.0 to 5.5 at high CO2 pressure. If we use the previous aqueous carbonation process as an example, the reactions are as follows (Eqs. (1.36) though 1.38) [89]: CO2 g ð Þ þ H2O l ð Þ → H2CO3 aq ð Þ → Hþ aq ð Þ þ HCO- 3 aq ð Þ ð1:36Þ Mg2SiO4 s 4Hþ aq → 2Mg2þ aq SiO2 s 2H2O l 1:37 Mg2þ aq HCO- 3 aq → MgCO3 s Hþ aq 1:38 Mg2+ is released by H+ in the second reaction, and in the third reaction, it reacts with bicarbonate to form magnesium carbonate, which subsequently precipitates. As with the prior method, raising the temperature and pressure can enhance the reaction rate. Furthermore, pre-treatment methods such as crushing and heating can be used to improve carbonate conversions and acceptable reaction rates; however, it should be noted that the use of these techniques, despite improving the process, increases energy consumption, resulting in a reduction in stored carbon [91]. 1.5.2.1.2 Indirect Carbonation Since direct methods for unrefined solid materials are ineffective, there is a strong need for alternative methods like indirect mineral carbonation that are more energy efficient and cost-effective acids or other solvents are used in this multi-stage process
- 44. ð Þ þ ð Þ ð Þ ð Þ þ ð Þ ð Þ ð Þ ð Þ þ ð Þ ð Þ þ ð Þ ð Þ þ ð Þ ð Þ to extract reactive components from minerals. The extracted components then react with CO2 in either an aqueous or a gaseous phase. Indirect carbonation, like direct methods, can be divided into some categories. 1 Carbon Utilization Technologies & Methods 31 The first method that we discuss here is direct gas-solid carbonation. In order to improve the conversion rate, the mineral could first be converted into an oxide or hydroxide and subsequently carbonated. The direct gas-solid carbonation of cal- cium/magnesium oxides/hydroxides proceeds much faster than the gas-solid car- bonation of calcium/magnesium silicates, although a high temperature and CO2 pressure are required. As a result, in the first stage of this method, which typically occurs in a fluidized bed, alkaline earth metals in the silicate form are changed into oxide or hydroxide form. Following this reaction with CO2, the products of this step react with CO2 and precipitate as stable carbonates (Eqs. 1.39 through 1.41) [92]: Mg2SiO4 s ð Þ þ 4HCl g ð Þ → 2MgCl2 aq ð Þ þ 2H2O l ð Þ þ SiO2 s ð Þ ð1:39Þ MgCl2 aq 2H2O l → Mg OH 2 s 2HCl aq 1:40 Mg OH 2 s CO2 g → MgCO3 s H2O l 1:41 In addition to the procedure mentioned above, using various acids such as acetic acid and hydrochloric acid is also frequent. The goal of applying these acids is to maximize Ca and Mg ion leaching while ensuring selective leaching. Because acetic acid is more acidic than ammonium chloride, it has a higher calcium ion leaching ratio [93]. The use of acetic acid as an extractant has a major side effect of lowering the pH of the leachate. Alkali must be used to stimulate the carbonation reaction in order to fix this problem [94]. As seen in the reactions below (Eqs. 1.42 and 1.43), divalent magnesium is separated in the first stage of the magnesium silicate reaction with acetic acid and is then ready to react with carbon dioxide gas in the next stage: MgSiO3 s ð Þ þ 2CH3COOH aq ð Þ → Mg2þ aq ð Þ þ 2CH3COO- aq ð Þ þ SiO2 s ð Þ þ H2O l ð Þ ð1:42Þ Mg2þ aq ð Þ þ 2CH3COO- aq ð Þ þ H2O l ð Þ þ CO2 g ð Þ → MgCO3 s ð Þ 2CH3COOH aq 1:43 Ammonium chloride is a kind of strong acid and weak alkali salt. For the leaching reaction using ammonium chloride, the solution shows alkalinity as the reaction proceeds because of the generation of ammonia. Noteworthy, the alkalinity of the solution promotes the dissolution of CO2 in the precipitation reaction. At the same time, the leachate using ammonium chloride has a strong pH-buffer ability, because an ammonia buffer solution is formed in it. Ammonium chloride is regarded as an ideal recyclable solvent because it can be regenerated in the carbonation reaction stage. As the carbonation reaction proceeds, NH4Cl is regenerated, which makes it recyclable for the leaching reaction [93]. As shown in the reaction below (Eqs. 1.44 and 1.45), in addition to the formation of magnesium carbonate at the end of the
- 45. ð Þ reaction, ammonium chloride is also generated, saving the consumption of this acid throughout the cycle: 32 R. Mahmoudi Kouhi et al. 2MgSiO3 s ð Þ þ 4NH4Cl aq ð Þ → 2MgCl2 aq ð Þ þ 4NH3 g ð Þ þ 2H2O l ð Þ þ SiO2 s ð Þ ð1:44Þ 2MgCl2 aq ð Þ þ 4NH3 g ð Þ þ 2CO2 g ð Þ þ 2H2O l ð Þ → 2MgCO3 s ð Þ þ 4NH4Cl aq ð Þ 1:45 Other solvents commonly used in indirect carbonation include ammonium sul- fate, citric acid, hydrochloric acid, sulfuric acid, and others. In relation to the use of solvent, it is important to note that, despite improvements in the reaction rate and overall efficiency, if these materials are not recovered, there is a risk of serious environmental damage, particularly to the local ground water and soil, so all aspects of using these materials must be considered. 1.5.2.2 Feedstocks The feedstocks needed for the ex situ reaction with CO2, depending on where they come from, can be categorized into three main groups: natural minerals, mine tailings, and industrial waste. The three cases are further discussed in the following sections. 1.5.2.2.1 Natural Minerals Natural minerals such as wollastonite (CaSiO3) and forsterite (Mg2SiO4) are con- sidered suitable for mineralization owing to the presence of alkaline earth elements such as Ca and Mg. Although alkali metals like Na and K have the capacity to react with CO2 and capture it, they are less frequently utilized as an efficient raw material due to the strong reactivity of their final product, particularly in water. Additionally, iron can be a useful source due to its abundance in the ground and its great capacity to react with CO2 and produce siderite (FeCO3), but its usage is not cost-effective due to the high value of metal. Natural minerals suited for CO2 reactions are classified into two types: natural calcium silicates such as wollastonite (CaSiO3) and natural magnesium silicates such as olivine (Mg2SiO4) and serpentine (Mg3Si2O5(OH)4). Compared to magnesium silicate, minerals in the first category – natural calcium minerals like wollastonite – have a quicker reaction rate and a wider range of industrial applications. However, the widespread availability of magnesium silicates in a variety of forms, including dunites, serpentinites, and peridotites, has made them a dependable source for producing stable carbonates [95]. The most important reactions between natural minerals and CO2 that result in stable carbonate are shown below (Eqs. 1.46 to 1.48):
- 46. þ þ ð Þ ð Þ þ þ þ ð Þ 1 Carbon Utilization Technologies & Methods 33 Wollastonite : CaSiO3 þ CO2 → CaCO3 þ SiO2 ð1:46Þ Olivine : Mg2SiO4 2CO2 → 2MgCO3 SiO2 1:47 Serpentine : Mg3Si2O5 OH 4 3CO2 → 3MgCO3 2SiO2 2H2O 1:48 One of the most significant benefits of employing natural minerals for carbon mineralization is the abundant availability of these materials on a huge scale when compared to alternative sources such as industrial wastes. However, the unprocessed nature of these materials and the requirement for pre-treatment procedures like grinding and crushing to create an effective surface area are some important draw- backs of this approach. Furthermore, the necessity for transportation due to the sources’ considerable distance from CO2 point sources raises the price and lessens the appeal of this strategy. 1.5.2.2.2 Mine Tailings Mine tailings are the byproducts of mineral processing operations. These tailings are a slurry of pulverized rock, as well as water and chemical reagents left over after processing. Their phase and chemical compositions vary depending on the charac- teristics of source rocks and the mineral processing procedures they have experi- enced. Mining tailings have always been seen as having little or no financial value. But the utilization of mining tailings has advanced to a new level as a result of recent technological advancements and new demands that have emerged across many industries. This new approach has been made most appealing by the reactivity and alkalinity of mineral tailings, which has found application in processes like acid neutralization (for example, use in reducing the environmental effects of acid mine drainage), reducing carbon in the atmosphere (as one of the environmental priorities of the twenty-first century) and long-term immobilization of environmentally haz- ardous metal. Due to the presence of reactive elements like Ca and Mg, the utilization of ultramafic mineral tailings offers the possibility of eliminating millions of tons of CO2. In addition, the large amount of reactive surface area observed in crushed tailings is appropriate for reacting with CO2. This eliminates the need for an energy-intensive operation such as crushing (compared to the use of natural and raw minerals). The likelihood of getting these tailings will grow day by day as a result of the rise in demand in the mining industry in the upcoming years. This makes things simpler for heavy industry companies to employ these materials to decrease environmental pollution, especially in order to meet zero-carbon targets. However, there are also significant issues that require adequate attention, such as energy-intensive pre-treat- ments like heat treatment, and chemical activation with reagents. Furthermore, due to the placement of mine tailings in remote areas, one of the limits that challenge the use of this technology is the necessity to transport them.
- 47. 34 R. Mahmoudi Kouhi et al. Fig. 1.14 Estimate of tailings and waste rock produced in relation to ore production and worldwide proportion of tailings per commodity in 2016 [96] Each year, the amount of tailings generated, particularly in open pit mines, increases significantly due to a drop in the grade of extractable rocks. Only in 2016, nearly 9 billion tons of tailings from metal and mineral extraction were generated, creating challenges, especially in the field of maintenance and prevention of harmful environmental effects. It should be emphasized that copper, gold, iron, and coal accounted for the majority of this tailings, with 46, 21, 9, and 8%, respectively (Fig. 1.14) [96]. Nickel and asbestos are the primary sources of ultramafic tailings. Manufacturing sites can be used in carbon sequestration of each of these tailings, which is a combination of much unique magnesium and calcium-containing compounds, and their dissolving rate and reactivity are related to their composition. As a result of these characteristics, four unique patterns of CO2 reactivity in ultramafic tailings may be imagined [76]: • Fast carbonation of the magnesium hydroxide mineral like brucite • Fast absorption of CO2 by hydrotalcite minerals • Fast cation exchange reactions of swelling clays • Relatively slow dissolution of calcium and magnesium silicate Nickel Tailings Nickel is mined from two different types of deposits: nickel-rich laterite generated by weathering of ultramafic rocks in tropical regions containing garnierite (Ni-silicate) and from Ni-sulfide concentrations in mafic igneous rocks, primarily pentlandite. Despite the high costs of employing nickel tailings, because of the high MgO content, it is possible to integrate extraction and CO2 separation using inno- vative methods. Furthermore, ultramafic deposits of nickel support stabilization of chrysolite asbestos and decrease the environmental impact of these tailings [95]. In 2011, the world’s nickel resources were projected to be 296 million tons (Fig. 1.15). This quantity is divided into 178 million tons for nickel laterite deposits and 118 million tons for nickel sulfide resources. Australia has the most considerable
- 48. nickel resources than any other country, with 31 million tons of laterite resources and 11 million tons of sulfide resources. Indonesia and South Africa are in the next places with reserves of 33 million tons [97]. The abundance of nickel deposits and their distribution across continents allow this material to be employed as one of the essential resources in lowering existing carbon and reaching zero-carbon technolo- gies in related sectors. There are difficulties in extracting nickel from low-grade ultramafic deposits. Serpentine minerals are typically found in ultramafic ores. These ores have low recoveries because of the difficulty in dispersing and effectively rejecting them. For instance, during the first five years of operation at Mt. Keith, Australia, nickel recovery from ores containing 0.58% Ni and 40% MgO was only 60% [91]. 1 Carbon Utilization Technologies & Methods 35 Fig. 1.15 Laterite and sulfide nickel deposits in several countries in 2011(numbers are in KT). (Modified after [97]) Asbestos Tailings Asbestos is a naturally occurring category of fibrous materials. There are six types of asbestos that have been discovered; they come from the amphibole and serpentine mineral groups. White asbestos, often known as chrysotile (Mg3(Si2O5)(OH)4), is the kind of asbestos that is most frequently found in veins in serpentine rock formations. Where serpentine is mined for chrysotile asbestos, the tailings often include considerable residual asbestos and may be categorized as hazardous. These tailings would be great feed for mineral carbonation because not only has size reduction occurred, but when chrysotile is carbonated, the asbestiform character of minerals is removed and it is highly environmentally beneficial as asbestos can cause cancer of the lung, cancer of the larynx, and certain gastrointestinal cancers. Glob- ally, 4 Mt. of asbestos is produced, each ton producing 20 tons of tailings. Because of the high quantities of MgO (40%) found in these tailings, they would constitute an excellent source of mineral carbonation [95, 98]. Despite the benefits that may be obtained from the carbonization of asbestos, the world’s extraction of this material is significantly declining owing to its environmental concerns, making it impossible to
- 49. CaO MgO Al2O3 SiO2 Fe2O3 TiO2 MnO Cr2O3 Others – – – utilize asbestos as a viable feedstock for carbonization and mitigating global warming in the long term. 36 R. Mahmoudi Kouhi et al. 1.5.2.2.3 Industrial Wastes This section investigates the use of industrial waste as a raw material in the mineralization process. Because of the existence of considerable amounts of alkaline earth metals, such as calcium and magnesium, the tailings of the steel, cement, and coal sectors have the most potential when compared to other industries. Addition- ally, residues from aluminum manufacturing facilities, such as red mud, can be utilized for carbon sequestration. Because of the rising need for the availability of more products connected to these industries, it is conceivable to broadly employ these raw materials to reduce environmental consequences. The fact that industrial wastes, as opposed to mineral tailings, are situated close to point sources of CO2 emission, decreases the cost of the process and also improves the likelihood that these products will react and create stable carbonate minerals. As a consequence, in addition to capturing carbon from the atmosphere, the approach has been proposed to manage unstable industrial wastes for disposal in compliance with safety regula- tions, as well as their reuse. Steel Slag Steel slag is a waste product produced during the manufacturing of steel. It is massively produced during the steelmaking process utilizing electric arc furnaces. Steel slag can be produced when iron ore is smelted in a basic oxygen furnace. These slags are mostly used as aggregate replacement in construction applications such as granular foundations, embankments, engineered fill, highway shoulders, and hot mix asphalt pavement. Steel slags are generally classified into four types: blast furnace slag (BF), basic oxygen furnace slag (BOF), electric arc furnace slag (EAF), and ladle furnace slag (LF). Table 1.3 shows the most common components of these four categories. CaO, MgO, Al2O3, SiO2, and Fe2O3 are the basic chemical compositions of slag. The chemical compositions of different slags vary substantially; CaO % in BF and LF slag is the highest, followed by BOF and EAF slag. Each slag has a roughly equal Table 1.3 Most common chemical compositions of four slag categories [93] Components slag type BF slag 42.67 8.57 13.21 29.41 0.37 1.49 0.40 0.001 3.879 BOF slag 42.43 9.15 3.03 12.00 26.74 0.48 2.85 0.22 3.10 EAF slag 32.30 5.01 2.74 28.83 23.53 1.06 2.40 0.11 4.02 LF slag 50.50 11.90 18.60 12.90 1.60 4.50
- 50. MgO concentration. BF slag includes more SiO2 and Al2O3, but BOF and EAF slag have more Fe2O3 [93]. 1 Carbon Utilization Technologies & Methods 37 Fig. 1.16 The emission reduction potential of legacy and future iron and steelmaking slag by way of CO2 mineralization [99] Steelmaking activities emit considerable amounts of CO2 (6–7% of total CO2 emissions globally; 0.28–1 ton of CO2/ton of steel produced). In addition, 315–420 Mt./y of slag is generated annually, according to estimates, although specific slag production numbers are not available [91]. Currently, slag-based CO2 mineralization has the potential to cut emissions by 268 Mt. CO2/y. Legacy slag has an 8.2 GtCO2 mineralization potential, despite being frequently bonded in building material (Fig. 1.16) [99]. Although steel slag has been employed in various industrial-scale applications, there are still limitations associated with this technology. The most pressing issues that must be addressed are a lack of steel slag due to their widespread use in other industries, an increase in energy and economic costs while optimizing process parameters, limitations of reaction kinetics, minimizing environmental impacts, and a drastic difference in compositions for each waste unit, which makes it impossible to use a particular method on a global scale [76, 100]. Red Mud Red mud, usually referred to as bauxite residue, is a byproduct of the Bayer process, which extracts alumina from bauxite ore. It is composed of a mixture of solid and metallic oxides and contains compounds like Fe2O3, Al2O3, TiO2, CaO, SiO2, and Na2O. Annually, 70 million tons of red mud is generated, 1.0–1.5 t for each ton of alumina produced [91]. Red mud includes toxic heavy metals, and its high alkalinity makes it exceedingly corrosive and harmful to soil, water, land, air, and living forms, posing a significant disposal challenge. Although around 4 million tons of red clay is employed annually in the cement, iron, and road construction sector, this amount remains relatively small in comparison to the enormous rate of production.
- 51. Therefore, attempts to discover new applications for this hazardous waste must be continued. 38 R. Mahmoudi Kouhi et al. Red mud can hold up to 0.01% of CO2 emissions from fossil fuels globally, assuming they have a 5% CO2 uptake. This equals to 3.5 Mt. of CO2 every year. This amount of red mud created has the potential to prevent up to 0.01% of worldwide CO2 emissions caused by fossil fuels [91, 95]. Various methods have been used for the neutralization of red mud by adding liquid carbon dioxide, saline brines or seawater, Ca and Mg-rich brines, soluble Ca and Mg salts, acidic water from mine tailings, fly ash, and carbon dioxide gas [101]. Despite all the benefits of adopting it, there are several issues that must be addressed in its deployment. The most signif- icant issue in applying this technology on a large scale is the development of used devices with high capacity and low energy costs. The usage of this approach may assist in mitigating climate change effects and reduce the environmental problems associated with wastes if the aforementioned issues are resolved. Coal Ash Coal ash, also known as coal combustion residuals or CCRs, is largely created by the combustion of coal in coal-fired power plants. This ash contains a number of byproducts produced from the burning of coal, including fly ash, bottom ash, boiler slag, and clinker. When fine coal is burnt, a fine, powdery silica substance known as fly ash is produced. Bottom ash, on the other hand, is a larger coarse ash particle that accumulates at the bottom of a coal furnace because it is too big to be removed by smokestacks. Fly ash and bottom ash make up the majority of coal ash, making up 85–95 weight percent and 5–15 weight percent of all generated ash, respectively [95]. India, China, and the United States are now the greatest producers of fly ash, whereas nations such as the Netherlands, Italy, and Denmark have the highest utilization rates of produced coal fly ash (CFA) (Fig. 1.17) [102]. 0 20 40 60 80 100 120 CFA Production CFA Utilization(%) Fig. 1.17 Production and utilization of CFA across the globe. (Modified after [102])
- 52. 1 Carbon Utilization Technologies & Methods 39 Fly ash is applied in a variety of fields, including construction, as a cheap adsorbent for the removal of organic compounds, flue gas, and metals, lightweight aggregate, mine backfill, road sub-base, and zeolite synthesis, which is on the agenda to address environmental issues associated to fly ash [103, 104]. One of the primary benefits of employing fly ash for carbonation is the absence of pre-treatment activities, which are energy-intensive and can destabilize the entire process. This lack of necessity is due to highly fine granulation, which gives a high amount of material for reaction with CO2 gas. Despite this significant property, the relatively low quantity of alkaline earth metals such as calcium and magnesium in these tailings limits their ability to be used for carbonation on a wide scale and at a cheap cost. This makes fly ash with a high lime concentration one of the most desirable raw materials for mineralization. These carbonation processes produce cement solids, which may be utilized to manufacture concrete. China is one of the most significant producers of these raw materials in the world, producing 100 million tons of fly ash each year, around half of that is used as a raw material for processes in other industries. However, as the country’s rate of construction declines, there will soon be less demand for fly ash in concrete and paving, highlighting the need to find new applications for the material. In addition to aiding in the capture of carbon dioxide that has been released into the atmosphere, carbonation may be used in this situation to convert fly ash from a serious environmental threat into a less hazardous substance. These environmental effects include the accumulation of heavy metals like lead and arsenic, as well as ash particles in the air, which decrease air quality and expose people to these poisons through inhalation [76]. Cement Cement – a fine powdered substance – is the most significant building material. It is a binding agent that sets and hardens to keep building components like stones, bricks, and tiles together. It is made mostly of limestone, sand or clay, bauxite, and iron ore; however, it can also contain other materials including shells, chalk, marl, shale, clay, blast furnace slag, and slate. There are different types of cement for different construction works and ordinary Portland cement (OPC) is the most commonly used type of cement in the world. Annual global cement production is 2.8 GT, with a projected growth to 4.0 GT in near future [91]. Cement manufacturing is the energy and carbon-intensive industry. The cement industry contributes approximately 5% of the global man-made carbon dioxide (CO2) emissions and is thus becoming the second largest CO2 contributor in the industry after power plants [105]. Numerous strategies have been suggested and put into practice to minimize the carbon emissions associated with the production of enormous quantity of cement globally and the constantly rising demand for this essential commodity. The utili- zation of supplementary cementitious materials, electric or hydrogen-fired kilns, point source carbon capture during cement manufacturing, and carbon mineraliza- tion are all examples. If these strategies are extensively implemented, the idea of attaining a carbon-neutral program for this industry is not far-fetched. The employ- ment of three techniques – mixing carbonation (injecting pure CO2 during concrete
- 53. mixing), carbonation curing (changing water or steam with pure CO2 during processing), and the creation of synthetic aggregates (reaction of CO2 with alkaline feedstock containing calcium and/or magnesium, including recycled concrete and a variety of industrial wastes) – is more effective when it comes to the strategy of carbon mineralization for cement [76]. By increasing the strength of concrete during production, carbonation can reduce the amount of cement needed overall, reducing carbon intensity and feedstock costs. 40 R. Mahmoudi Kouhi et al. The cement industry also produces a significant amount of wastes, such as cement kiln dust (CKD) and cement bypass dust (CBD). In fact, for every 100 tons of cement, 15–20 tons of CKD is produced. Cement waste is very reactive due to its fine particle size and high CaO content (20-60%). CKD generally contains 38–48% CaO, but because it also contains 46–57% CaCO3, a substantial portion of it is already carbonated. CBD, on the other hand, has fewer carbonates than CKD. As a result, they have a high inclination to store CO2 (0.5 ton CO2 per ton CBD) [95]. Many factors, including the significant amount of usable raw materials, the simplicity of using raw materials due to the absence of energy-intensive pretreatment processes like crushing, and the high potential for CO2 reaction, have led researchers to consider the uptake and mineralization of carbon by cement wastes. 1.5.2.3 Application and Products The final products of mineral carbonation are numerous and can be utilized in various fields; our goal in this section is to review these products and their uses in various industries. The construction industry uses most the application of silica and carbonate materials, whereas cement and the resulting material, i.e., concrete, are manufactured on a Gt scale globally every year, and a substantial portion of the energy and carbon emitted into the atmosphere is the result of this massive volume of manufacturing. Other important environmentally friendly applications of these materials include use as materials in the process of mine rehabilitation and use as materials to reduce water and soil pollution with the possibility of adjusting the pH, assisting in the deposit of fine-grained tailings, and precipitating heavy metals. 1.5.2.3.1 Calcite and Magnesite Applications Calcite is a carbonation product produced by a mineral carbonation process that uses inorganic wastes and natural rock sources such as wollastonite. The construction industry is mineral carbonation’s key consumer of calcium carbonate. Calcite is also used as ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC) in a range of industrial processes. PCC is pulverized limestone that ranges in particle size from a few millimeters to several microns. Also, the most important no-value use for the carbonates from mineral carbonation would be in mine reclamation projects, because of the massive amount of carbonates (Gt of magnesium carbonate) that would be produced if the mineral carbonation technology was effectively
- 54. implemented. When it comes to magnesite, approximately 98% of it is converted to magnesia for conventional uses such as refractories. As a result, magnesite currently has a limited number of non-CO2 emitting applications, such as precipitated mag- nesium carbonate or agricultural applications. Magnesite can be used as a building material; however, there is currently no market for it. Since the market is small, mineral carbonation magnesite is likely to be reused in large quantities for low-value applications such as land restoration programs [77]. 1 Carbon Utilization Technologies & Methods 41 Fig. 1.18 Summary of the possible carbon mineralization product applications. (Modified after [77]) 1.5.2.3.2 Silica Applications Mineral carbonation can produce silica byproducts as an amorphous phase, which might be utilized in the construction industry as a pozzolanic cement substitute material or as a filler. More than half of the electronic silicon raw materials marketed globally are produced in Norway. This demonstrates that mineral carbonation feedstocks are theoretically suitable for the production of high-purity silica and existing processing technologies may be used to post-process the mineralization by-products. As the electrical properties of these materials are so sensitive to impurities, it is improbable that these products can achieve such a level of purity without further post-processing [77, 106]. The applications of mineral carbonation products that do not contain calcination can be divided into three categories: low-end high-volume, high-end low-volume, and silica. Figure 1.18 shows the summary of the possible carbon mineralization product applications by this type of classification [77].
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- 56. converted Potman. This young man was a leader in petty and mischievous annoyances. The genuineness of his conversion was evidenced by his giving up the public-house work to seek more honourable employment." From Middlesbro' (1878): "Miss Booth visited us for five days, and many blood-bought souls have been blessed and saved. Her first Sunday with us was a day of power, and it will not be soon forgotten by those present. It was a grand sight to see a large hall filled to the door with anxious hearers, while hundreds went away; but the grandest sight of all was to see old and young flocking to the penitent form." From Leicester: "Miss Booth's services may be summarised in the statement that she had twenty-two souls the first Sunday evening, and increasing victory thereafter right on to the end." At Whitby there was a six weeks' campaign, organised by Captain Cadman. On the first Sunday "the large hall, which holds three thousand, was well filled, and in the after service many souls were brought to Jesus." On the second Sunday "Miss Booth was listened to with breathless attention. In the after service we drew the net to land, having a multitude of fishes, and among them we found we had caught a fox-hunter, a dog-fancier, drunkards, a Roman Catholic, and many others. In the week-night services souls were saved every night. The proprietor of the hall had got some large bills out announcing 'Troupe of Arctic Skaters in the Congress Hall for a week,' but he put them off by telling them it was no use coming, as all the town was being evangelised." The concluding services "drew great crowds from all parts of town and country, rich and poor, until the hall was so filled that there was no standing room." In a Consecration meeting, "After Miss Booth's address we
- 57. formed a large ring in the centre of the hall, which brought the power down upon us; hundreds looked on with astonishment and tears in their eyes, whilst others gave themselves wholly to God.... Ministers, like Nicodemus of old, came to see by what power these miracles were wrought, and, going back to their congregations, resolved to serve God better, and to preach the gospel more faithfully in the future." From Leeds: "Miss Booth in the Circus. A glorious month. Hard- hearted sinners broken down. Best of all, our own people have been getting blessedly near to God. On Sunday mornings love feasts from nine to ten.... It would be impossible to give even an outline of the various and glorious cases of conversion that have come under our notice through the month which is past. For truly Christ has been bringing to His fold rich and poor, young and old." From Cardiff: "The question, 'Does this work stand?' received a magnificent reply on Sunday. The crowds who filled the Stuart Hall, to hear Miss Booth, were the largest any one can remember seeing during all the four years of the Mission's history there." From King's Lynn: "Miss Booth's Mission. The town has had a royal visit from the Lord of Lords and King of Kings. There has been a great awakening, and trembling, and turning to the Lord. Whole families have been saved, and whole courts have sought salvation. Our holiness meeting will never be forgotten.... The work here rolls on gloriously. Not only in Lynn but for miles round the town it is well known that a marvellous work has been done and is still going forward." All these battles and victories were naturally followed by the General with intense interest, and as often as it was possible he was at his daughter's side. Mrs. Booth joined them when they were
- 58. opening a campaign together at Stockton-on-Tees, and sent her impressions to a friend. "Pa and Katie had a blessed beginning yesterday. Theatre crowded at night, and fifteen cases. I heard Katie for the first time since we were at Cardiff. I was astonished at the advance she had made. I wish you had been there, I think you would have been as pleased as I was. It was sweet, tender, forcible, and Divine. I could only adore and weep. She looked like an angel, and the people were melted, and spellbound like children." The General began to call her his "Blücher," for she helped to win many a hard-fought battle which he might otherwise have lost. When the rowdies threatened to take the upper hand at a meeting, he would say, "Put on Katie, she's our last card; if she fails we'll close the meeting." "I remember," wrote her eldest brother, "a striking instance of this occurring in a certain northern town on a Sunday night. A crowd assembled at the doors of the theatre, composed of the lowest and roughest of the town, who, overpowering the doorkeepers, pressed into the building and took complete possession of one of the galleries, so that by the time the remainder of the theatre was occupied this portion of it represented a scene more like a crowded tap-room than the gallery of what was for the moment a place of worship. Rows of men sat smoking and spitting, others were talking and laughing aloud, while many with hats on were standing in the aisles and passages, bandying to and fro jokes and criticisms of the coarsest character. All this continued with little intermission during the opening exercises, and the more timid among us had practically given up hope about the meeting, when Miss Booth rose, and standing in front of the little table just before the footlights,
- 59. commenced to sing, with such feeling and unction as it is impossible to describe with pen and ink, 'The rocks and the mountains will all flee away. And you will need a hiding-place that day.' There was instantaneous silence over the whole house; after singing two or three stanzas, she stopped and announced her text, 'Let me die the death of the righteous and let my last end be like His.' While she did so nearly every head in the gallery was uncovered, and within fifteen minutes both she and every one of the fifteen hundred people present were completely absorbed in her subject, and for forty minutes no one stirred or spoke among that unruly crowd, until she made her concluding appeal, and called for volunteers to begin the new life of righteousness, when a great big navvy-looking man rose up, and in the midst of the throng in the gallery exclaimed, 'I'll make one!' He was followed by thirty others that night."
- 60. CATHERINE BOOTH (From a portrait by Edward Clifford, exhibited at the Royal Academy and presented to Mrs. Booth)
- 61. Well might the General's hopes regarding the young soul-winner be high and confident. "Papa," wrote Mrs. Booth, "says he felt very proud of her the other day as she walked by his side at the head of a procession with an immense crowd at their heels. He turned to her and said, 'Ah, my lass, you shall wear a crown by-and-by.'" With what desires and prayers the mother of this Wunderkind followed such a career is indicated by her letters. "Oh, it seems to me that if I were in your place—young—no cares or anxieties—with such a start, such influence, and such a prospect, I should not be able to contain myself for joy. I should indeed aspire to be 'the bride of the Lamb,' and to follow Him in conflict for the salvation of poor, lost and miserable man.... I don't want you to make any vows (unless, indeed, the Spirit leads you to do so), but I want you to set your mind and heart on winning souls, and to leave everything else with the Lord. When you do this you will be happy—oh, so happy! Your soul will then find perfect rest. The Lord grant it you, my dear child.... I have been 'careful about many things.' I want you to care only for the one thing.... Look forward, my child, into eternity—on, and ON, and ON. You are to live for ever. This is only the infancy of existence—the school-days, the time. Then is the grand, great, glorious eternal harvest." Whatever gifts were the dower of the young evangelist, she refused to regard herself as different in God's sight from the poorest and meanest of sinners. If God loved her, He loved all with an equal love. That conviction was the motive-power of all her evangelism. A limited atonement was to her unthinkable. How often she has made vast audiences sing her father's great hymn, "O boundless salvation, so full and so free!" When she was conducting a remarkable
- 62. campaign in Portsmouth, she found herself one day among a number of the ministers of the town, one of whom in his admiration of her and her work persisted in calling her one of the elect. This led to an animated discussion on election. Katie listened for a while, but lost patience at last, and, rising, delivered herself thus: "I am not one of the elect, and I don't want to be. I would rather be with the poor devils outside than with you inside." Having discharged this bombshell she flew upstairs to her mother. "Oh!" she cried, "what have I done?" When she repeated what she had said, her mother, whose laugh was always hearty, screamed with delight. Election as commonly taught was rank poison to the Mother of the Army. The doctrine that God has out of His mere good pleasure elected some to eternal life made her wild with indignation. When her son Bramwell was staying for a time in Scotland, she wrote him: "It seems a peculiarity of the awful doctrine of Calvinism that it makes those who hold it far more interested in and anxious about its propagation than about the diminution of sin and the salvation of souls.... It may be God will bless your sling and stone to deliver His servant out of the paw of this bear of hell—Calvinism." One naturally asks what became of Catherine's education all this time. On this subject also Mrs. Booth held strong views. When her daughter was sixteen she wrote to her: "You must not think that we do not rightly value education, or that we are indifferent on the subject. We have denied ourselves the common necessaries of life to give you the best in our power, and I think this has proved that we put a right value on it. But we put God and righteousness first and education second, and if I had life to begin over again I should be
- 63. still more particular.... I would like you to learn to put your thoughts together forcibly and well, to think logically and clearly, to speak powerfully, i.e. with good but simple language, and to write legibly and well, which will have more to do with your usefulness than half the useful knowledge you would have to spend your time over at College." When the principal of a Ladies' College, who had attended Mrs. Booth's meetings and been blessed, offered to receive Catherine and educate her gratuitously, Mrs. Booth, after visiting the College and breathing the atmosphere of the place, declined the tempting offer with thanks. Some will, of course, be disposed to question the wisdom of the mother's decision. It should not be impossible to combine the noblest learning with the most fervent faith. Yet every discipline must be judged by its fruits. How many Catherine Booths have hitherto been produced by Newnham and Girton? Long after Catherine the second had left her home-land, she continued to receive letters from her English converts, and when, after many years, she resumed her evangelistic work in England, people whom she had never seen and never heard of before would come and tell her that they had been saved through her mission at this or that place. All these testimonies were like bells ringing in her soul. One out of many may be resounded. Writing to Paris in 1896, Henry Howard, now the Chief of Staff in the Army, said: "I have certainly never forgotten your Ilkeston campaign of sixteen years ago, when God made your soul a messenger to my soul. You led me towards an open door which I am pleased to remember I went in at,
- 64. and during these many years your own share in my life's transformation has often been the subject of grateful praise." CHAPTER III THE SECRET OF EVANGELISM After many victories at home, William and Catherine Booth began to look abroad. They realised that "the field is the world," and they longed to commence operations on the Continent. In the summer of 1881, with high hopes and some natural fears, they dedicated their eldest daughter to France. In giving her they gave their best. Delicate girl though she was, she had become one of the greatest spiritual forces in England. She swayed vast multitudes by something higher than mere eloquence. Wherever she went revivals broke out and hundreds were converted. There was a pathos and a power in her appeals which made them irresistible. At the time of her departure she received many letters from friends whom she had spiritually helped, and who realised how much they would miss her in England. Nowhere had she done more good, nowhere could her absence create a greater blank, than in her own home. Her sister Eva wrote: "I cannot bear the thought that you are gone. You have always understood me. I hope one day to be of some use to you, in return for all you have done for me." And her brother Herbert wrote her: "You cannot know how much I felt your leaving. The blow came so suddenly. You were gone. Only God and myself know how much I had lost in you. I can truthfully say that
- 65. you have been everything to me, and if it had not been for you I should never have been where and what I am spiritually at present. God bless you a thousand thousand times. Oh! how I long to be of some little service to you after all you have been to me.... Thousands upon thousands of true, loving hearts are bearing you up at the Eternal throne, mine among them. You have a chance that men of the past would have given their blood for, and that the very angels in Heaven covet." There was no Entente Cordiale in those days, and at the thought of parting with Katie, and letting her go to live in the slums of Paris, Mrs. Booth confessed that she "felt unutterable things." In a letter to a friend she wrote: "The papers I read on the state of Society in Paris make me shudder, and I see all the dangers to which our darling will be exposed!" But if her fears were great, her faith was greater. Asked by Lady Cairns how she dared to send a girl so young and unprotected into such surroundings, she answered, "Her innocence is her strength, and Katie knows the Lord." And if Katie herself was asked to define Christianity, she answered, "Christianity is heroism!" For a girl of this spirit, was there, after all, anything so formidable in the French people? Was there not rather a pre- established harmony between her and the pleasant land of France, as her remarkable predilection for the French language already seemed to indicate? Is any nation in the world so chivalrous as the French? any nation so sensitive to the charm of manner, the magnetic power of personality? any nation—in spite of all its hatred of clericalism—gifted with so infallible a sense of the beauty of true holiness? Courage, camarade!
- 66. What were the ideas with which Catherine began her work in Paris? What was her plan of campaign? How did she hope to conquer? On these points let us listen to herself. "I saw," she says, "that the bridge to France was—making the French people believe in me. That is what the Protestants do not understand. They preach the Bible, they write books, they offer tracts. But that does not do the work. 'Curse your bibles, your books, your tracts!' cry the French. I have seen thousands of testaments given away to very little purpose. I have seen them torn up to light cigars. And the conviction that took shape in my mind was that, unless I could inspire faith in me, there was no hope. Only if Jesus is lifted up in flesh and blood, will He to-day draw all men to Him. If I cannot give Him, I shall fail. France has not waited till now for religion, for preaching, for eloquence. Something more is needed. 'I that speak unto thee am He'—there is a sense in which the world is waiting for that to-day. You may say that this leads to fanaticism, to all sorts of error; and yet I always come back to it. Christ's primary idea, His means of saving the world, is, after all, personality. The face, the character, the life of Jesus is to be seen in men and women. This is the bridge to the seething masses who believe in nothing, who hate religion, who cry 'Down with Jesus Christ!' What sympathy I felt with them as I listened to their angry cries against something which they had never really seen or known. They shout 'Jesuits,' but they have never seen Jesus. Could they but see Him, they would still 'receive Him gladly.' It is the priests' religion that has made them bitter. 'Money to be baptised! Money to be married! Money to be buried!' was what I heard them mutter. Ah! they are quick to recognise the comedian in religion, and equally quick to recognise the real thing.
- 67. France is more sensitive to disinterested love than any nation I have ever known. France will never accept a religion without sacrifice. "These were the convictions with which I began the work in Paris, and, if I had to begin it over again to-day, I would go on the same lines. When I knew what I had to do, my mind was at rest. I said, 'We will lay ourselves out for them; they shall know where we live, they can watch us day and night, they shall see what we do and judge us.' And the wonderful thing in those first years of our work in France and Switzerland was the flame. We lighted it all along the line. Wherever we went we brought the fire with us, we fanned it, we communicated it. We could not help doing so, because it was in us, and that was what made us sufferers. The fire had to be burning in us day and night. That is our symbol—the fire, the fire! Seigneur, ce que mon coeur réclame, C'est le Feu ... Le seul secret de la Victoire, C'est le Feu. We all know what the fire is. It warms and it burns; it scorches the Pharisees and makes the cowards fly. But the poor, tempted, unhappy world knows by whom it is kindled, and says: 'I know Thee who Thou art—the Holy One of God!' "That was what filled the halls at Havre and Rouen, Nîmes and Bordeaux, Brussels and Liège. We personified Some One, and that was the attraction. I have not the insufferable conceit to suppose that it was anything in me that drew them. What am I? Dust and ashes. But if you have the fire, it draws, it melts; it consumes all
- 68. selfishness; it makes you love as He loves; it gives you a heart of steel to yourself, and the tenderest of hearts to others; it gives you eyes to see what no one else sees, to hear what others have never given themselves the trouble to listen to. And men rush to you because you are what you are; you are as He was in the world; you have His sympathy, His Divine love, His Divine patience. Therefore He gives you the victory over the world; and what is money, what are houses, lands, anything, compared with that? "This was the one attraction. When I went to France I said to Christ: 'I in You and You in me!' and many a time in confronting a laughing, scoffing crowd, single-handed, I have said, 'You and I are enough for them. I won't fail You, and You won't fail me.' That is something of which we have only touched the fringe. That is a truth almost hermetically sealed. It would be sacrilege, it would be desecration, it would be wrong, unfair, unjust if Divine power were given on any other terms than absolute self-abandonment. When I went to France I said to Jesus, 'I will suffer anything if You will give me the keys.' And if I am asked what was the secret of our power in France, I answer: First, love; second, love; third, love. And if you ask how to get it, I answer: First, by sacrifice; second, by sacrifice; third, by sacrifice. Christ loved us passionately, and loves to be loved passionately. He gives Himself to those who love Him passionately. And the world has yet to see what can be done on these lines." CHAPTER IV CHRIST IN PARIS
- 69. In the early spring of 1881 Captain Catherine Booth and her intrepid lieutenants, Florence Soper, Adelaide Cox and Elizabeth Clark, who enjoyed the privilege of her example and training, began life in Paris. Later on they were joined by Ruth Patrick, Lucy Johns and others. Soon after they were joined by the General's youngest son, Herbert Booth, who is proud of having received his first black eye in assisting his sister during those early fights, and Arthur Sydney Clibborn, who lived a life of unparalleled devotion and heroism, and later became the Maréchale's husband. Years before Canon Barnett and his band of Oxford men were attracted to Whitechapel, these fresh young English girls settled in a similar quarter of the French capital. What quixotic impulses carried them thither? They had no social or political ideals to realise. They had not been persuaded that altruism is better than egoism, that the enthusiasm of humanity is nobler than the pursuit of pleasure or the love of culture. They were not weary of the conventions of society and seeking a new sensation in slumming. They were not playing at soldiers. But they, too, had their dreams and visions. They loved Christ, and they wished to see Christ victorious in Paris. Coming into a wilderness of poverty, squalor and vice, they dared to believe that they could make the desert to rejoice and blossom as the rose. They had the faith which laughs at impossibilities. The first letter Catherine received from her father after she set foot in France breathed tender affection and ardent hope. "Oh, my heart does yearn over you! How could you fear for a single moment that you would be any less near and dear to me on account of your brave going forth to a land of strangers to help me in the great purpose and struggle of my life? My darling, you are nearer and
- 70. dearer than ever.... France is hanging on you to an extent fearful to contemplate, and you must regard your health, seeing that we cannot go on without you. We shall anxiously await information as to when you make a start. Everybody who has heard you and knows you feels the fullest confidence in the result. Nevertheless I shall be glad for you to get to work, seeing that I know you won't be easy in your mind until you have seen a few French sinners smashed up at the penitent form." With her own hand Catherine raised the flag at Rue d'Angoulême 66, in Belleville. Here was a hall for six hundred, situated in a court approached by a narrow street. The bulk of the audience that gathered there night after night were of the artisan class. Some were young men of a lower type, and from these came what disturbance there was. The French sense of humour is keen, and there were many lively sallies at the expense of the speakers and singers on the platform. Every false accent, every wrong idiom, every unexpected utterance or gesture was received with an outburst of laughter. But the mirth was superficial, and the expression on the faces of the tired men, harassed women, and pale children was one of settled melancholy. Catherine instinctively felt that what they needed was a gospel of joy; certainly not the preaching of hell, for did they not live in hell? These toiling sisters and brothers were the multitudes on whom Jesus had compassion. Meetings were held night after night, and for six months the Capitaine was never absent except on Saturdays. Those were days of fight, and she fought, to use her own phrase, like a tiger. She had to fight first her own heart. She knew her capacity, and God had done great things through her in England. The change from an
- 71. audience of five thousand spellbound hearers in the circus of Leeds to a handful of gibing ouvriers in the Belleville quarter of Paris was indeed a clashing antithesis. A fortnight passed without a single penitent, and Catherine was all the time so ill that it was doubtful if she would be able to remain in the field. That fortnight was probably one of the supreme trials of her faith. The work appeared so hopeless! There was nothing to see. But for the Capitaine faith meant going on. It meant saying to her heart, "You may suffer, you may bleed, you may break, but you shall go on." She went on, believing, praying, fighting, and at last the tide of battle turned. The beginning of what proved a memorable meeting was more than usually unpromising. One of the tormentors, a terrible woman, known as "the devil's wife," excelled herself that night. She was of immense size, and used to stand in the hall with arms akimbo and sleeves rolled up above the elbows, and with one wink of her eye would set everybody screaming and yelling. On this occasion there was not a thing that she did not turn to ridicule. The fun grew fast and furious, and some of the audience got up and began to dance. The meeting seemed to be lost; but by a master-stroke the leader turned defeat into victory. Through the din she cried, "Mes amis! I will give you twenty minutes to dance, if you will then give me twenty minutes to speak. Are you agreed?" A tall, dark, handsome ouvrier, in a blue blouse, who had been a ringleader in the disturbances, jumped up and said, "Citizens, it is only fair play;" and they all agreed. So they had their dance, and at the end of the appointed time the ouvrier, standing with watch in hand, cried, "Time up, citizens; it is the Capitaine's turn!" The bargain was kept. Everybody sat down, and an extraordinary silence filled the place.
- 72. Not for twenty, but for an hour and twenty minutes the leader had the meeting in the hollow of her hand. When the audience filed out, the tall ouvrier remained behind, and Catherine went down to where he was sitting in the back of the hall. With his chiselled face and firm-set mouth, he looked like a man who could have seen one burned alive without moving a muscle. "Thank you," said the Capitaine, "you have helped me to-night. Have you understood what I have been saying?" "I believe that you believe what you say." "Oh! of course I believe." "Well, I was not sure before." With a sigh he added, "Have you time to listen?" "Yes, certainly." It was midnight and they were alone. As he began in softest tones to tell the story of his inner life, she felt the delicacy of the soul that is hidden under the roughest exterior. He said, "I had the happiest home in all Paris. I married the woman I loved, and after twelve months a little boy came to our home. Three weeks after, my wife lost her reason, and now she is in an asylum. But there was still my little boy. He was a beautiful child. We ate together, slept together, walked and talked together. He was all the world to me. He was the first to greet me in the morning, and the first to welcome me in the evening when I came home from work. This went on till the sixth year struck, and then...." His lips twitched, and he turned his face away. His hearer softly said, "He died." He gave a scarcely perceptible nod, and smothered a groan. "And then," he continued, "I went to the devil. Before the open grave in the Père Lachaise
- 73. cemetery, with hundreds of my comrades about me, I lifted my hand to heaven and cried, 'If there be a God, let Him strike me dead!'" "But He did not strike you dead?" "No." "He is very gentle and patient with us all. And now you have come here to-night. Does it not seem to you a strange thing that you out of all the millions of France, and I out of all the millions of England should be all alone together here at midnight? How do you account for it? Isn't it because God thought of you, and loves you? ... Do you ever pray?" "I pray? Oh, never! Perhaps I prayed as a child, but never now." "But I pray," said the Capitaine, and, kneeling down, she prayed a double prayer, for herself as well as for him. She wanted this man's salvation for her own sake and the work's sake. For weeks she had been fighting and praying for a break, and she felt as if on the issue of this wrestling for a single soul depended the whole future of the work in France. While she prayed for his salvation from sin she was silently praying for her own deliverance from doubt and fear and discouragement. And both prayers were heard. When she opened her eyes, she saw his face bathed in tears. She knew that his heart was melted, and she spoke to him of the love of God. "But I have hated Him. I have hated religion; I have come here to mock you; I have called you Jesuits." "Yet God loves you." "But why did He allow my wife to lose her reason? Why did He take my child if He is love?" "I cannot answer these questions. You will know why one day. But I know He loves you."
- 74. "Is it possible that He can forgive a poor sinner like me?" "It is certain." Émile was won. Some nights afterward he gave his testimony, and for seven years he always stood by the Maréchale. He was her best helper. When he used to get up to speak, there was immediate attention. "Citizens," he would say, "you all know me. You have heard me many times. This God whom I once hated I now love, and I want to speak to you about Him." After this, conversions became frequent. The mercy-seat was rarely empty. One of the first French songs of Catherine's composition contained the most curious idioms: Quand je suis souffrant, Entendez mon cri, etc. —Donnez moi Jesus. But she sang it with such feeling that it was the means of the conversion of a clever young governess, who became one of her most devoted officers. Then another striking conquest was made. One night a rough fellow, partly drunk, approached the Capitaine and said a vile word to her in the hearing of "the devil's wife," who dealt him a blow that sent him reeling across the hall crying, "You dare not touch her, she is too pure for us!" (Elle est trop pure pour nous!) Catherine rushed between them and stopped the fight. Thus "la femme du diable" was won, and from that time she got two or three others to join her in forming Catherine's bodyguard, who nightly escorted her and her comrades through the Rue d'Allemagne, which was a haunt of
- 75. criminals, and saw her safe at the door of her flat in the Avenue Parmentier. When Baron Cederström was seeking local colour for his painting "The Maréchale in the Café,"[1] he drove down with his wife to a meeting in the Rue d'Angoulême. As they approached the hall, the Baroness caught sight of some of the faces and took fright. [1] This painting is now in the picture gallery of Stockholm. The artist, as is well known, afterwards married Madame Patti. "Go back, go back!" she shouted to the coachman. The Baron tried in vain to reassure her. "Give me my salts!" she cried, feeling as if she would faint. "I never saw such faces in my life. They are all murderers and brigands." To Catherine, who came out to welcome her, she exclaimed, "I am sure the good God won't send you to Purgatory, for you have it here!" "You have nothing to fear," was the answer; "I am here every night." But as the Baroness was led up to the front seats, she still cast scared looks at the people she passed. Some of the politically dangerous classes did give trouble for a time. Knives were displayed and some blood was shed. An excited sergeant of police declared one night that half the cut-throats of Paris were in that hall, and by order of the authorities it was closed. Soon, however, the meetings were again in full swing, and when Catherine's eldest brother Bramwell, her comrade in many an English campaign, paid her a flying visit three months after she left home, he was delighted with all that he saw. "The meetings," he wrote,
- 76. "are held every night. The congregations vary from 150 to 400.... On Sunday, at three, I attended the testimony meeting, which is only for converts and friends. About seventy were present. Miss Booth took the centre, and gathered round her a little company. I cannot describe that meeting. When I heard those French converts singing that first hymn, 'Nearer to heaven, nearer to heaven,' I wept for joy, and during the season of prayer which followed my heart overflowed. Here, using another tongue, among a strange people, almost alone, this little band have trusted the Lord and triumphed.... Then testimonies were invited.... I wept and rejoiced, and wept again. I glorified God. Had I not heard these seventeen people speak in their own language of God's saving power in Paris during those few weeks! I require all who read this to rejoice. I believe they will. Remember how great a task it is to awaken the conscience before Christ can be offered; to convince of sin as well as of righteousness; to call to repentence as well as faith.... On the following night 300 were present.... Miss Booth stepped off the platform as she concluded her address, and came down, as so many of us have seen her come down at home, into the midst of the people. Her closing appeal seemed to go through them. Many were deeply moved. Some of those sitting at the back, who had evidently come largely for fun, quailed before one's very eyes, and seemed subdued and softened. God was working." Later in the year the new headquarters on the Quai de Valmy were opened. Here there was a hall for 1200. No other form of religion could draw such an assembly of the lowest class of Parisians as nightly met in it. The men came in their blouses, kept their caps on their heads, and—except that they abstained from smoking, in
- 77. obedience to a notice at the door—behaved with the freedom and ease of a music-hall audience. But the earnest way in which most of those present joined in the hymns proved that they were not mere spectators, and it was astonishing that many rough, unkempt, and even brutal-looking men soon learned to sing heartily without using the book. There were a hundred converts in the first year and another five hundred in the second. Paris herself began to testify that a good work had been begun in her midst. On the way to and from the hall in the Rue d'Angoulême Catherine, who by this time had begun to be endearingly known as the Maréchale, the highest military title in France, used often to meet a priest, to whom she always said "Bon jour, mon père." One day he paused and said, "Madame la Maréchale, I want to tell you that since you began your work in this quarter the moral atmosphere of the whole place has changed. I meet the fruits everywhere, and I can tell better than you what you are doing." She felt that God sent her that word of encouragement. One of her letters of this time indicates what kind of impression her work was making. "There is a man," she wrote, "who has attended our meetings most regularly. He listens with breathless attention, and sometimes the tears flow down his cheeks. He was visited, and sent me 70 francs for our work, with a message that he desired to see me. I saw him, and he gave me 80 more, with the words 'Sauvez la jeunesse'! ('Save the young!') I found him very dark and hopeless about himself.... The next week he again called me aside in the hall, put 50 francs into my hand, saying he hoped soon we should have a hall in every quarter of Paris. 'Save the young people!' he again said. I said 'Yes, but I want to see you
- 78. saved.' 'That will come,' he said, and left the hall. Last Sunday afternoon, I noticed him weeping in a corner of the hall, as our young people were witnessing for Jesus, and, after the services, he asked if he might speak to me for two minutes; this time he handed me 60 francs, telling me to go on praying for him. He has lived a bad life and is troubled with the thought of the past." It began to be commonly believed that the Maréchale could work certain kinds of miracles. A woman who had attended the meetings, and been blessed in her soul, became convinced that the English lady had power to cast out devils, and one day she brought a neighbour to the physician of souls, introducing her with the remark, "She has not only one but seven devils." The new-comer had a frightful face. She was so drunken, immoral and violent that nobody could live with her. Yet she, too, had a soul. The Maréchale made her get down on her knees, put both her hands on her head, and prayed that the devils might all be cast out. "She's now another woman," was the testimony soon after borne by all her neighbours. One of the surest indications of the success of the work in Paris is found in the fact that, before the end of the first year there was a general demand for a newspaper corresponding in some degree to the English War Cry. That was a memorable day on which the Maréchale and her officers sat in their Avenue Parmentier flat, like a coterie of Fleet Street journalists, gravely discussing their new venture. It was indicative of the holy simplicity of the editor-in-chief that she thought at first of changing The War Cry into Amour. She did not realise the sensation which the cry "Amour, un sou!" would have created in the Boulevards. Her proposal was overruled, but her second suggestion, to call the paper En Avant, was received with
- 79. acclamation. This was a real inspiration. The paper duly appeared in the beginning of 1882, and has gone on successfully ever since. The shouting of its name in the streets set all the world and his wife a- thinking and a-talking. What if the Man of Nazareth is after all far ahead of our modern philosophers and statesmen, and if this handful of English girls is come to lead us all forward to true liberty, equality and fraternity? The reports of the work in France were received with feelings of gratitude at home. To "My dear Kittens"—a family pet-name—her brother Bramwell wrote: "We are more than satisfied with your progress. The General says that so far as he can judge your rate of advance in making people is greater than his own was at the beginning. I am sure you ought to feel only the liveliest confidence and greatest encouragement all the time." And to "My darling Blücher" the General himself wrote, "I appreciate and admire and daily thank God for your courage and love and endurance. God will and must bless you. We pray for you. I feel I live over again in you. We all send you our heartiest greetings and our most tender affection. Look up. Don't forget my sympathy. Don't trouble to answer my scrawls. I never like to see your handwriting because I know it means your poor back. Remember me to all your comrades." "I feel I live over again in you." The thought was evidently habitual in the General's mind. "He bids me tell you," wrote Emma, "that you are his second self." The resemblance was physical as well as spiritual. With her tall figure, her chiselled face, her aquiline nose, her penetrating blue eyes, Catherine became, as time went on, more and more strikingly like her father. One of her sons, who saw her
- 80. stooping over the General the day before he died, said that the two pallid faces were like facsimiles in marble. CHAPTER V FREEDOM TO WORSHIP GOD In the autumn of 1883 the Maréchale suddenly leapt into fame as a latter-day Portia, brilliantly and successfully pleading in a Swiss law- court, before the eyes of Europe, the sacred cause of civil and religious liberty. The land of Tell, the oldest of modern republics, has always been regarded as a shrine of freedom. It has shown itself hospitable to all kinds of ideas, even the newest, the strangest, the most anti-Christian, the most anti-social. There is a natural affinity between free England and free Switzerland. "Two Voices are there; one is of the sea, One of the mountains; each a mighty Voice: In both from age to age thou didst rejoice; They were thy chosen music, Liberty." In the "Treaty of Friendship" between Great Britain and Switzerland, drawn up in 1855, it was agreed that "the subjects and citizens of either of the two contracting parties shall, provided they conform to the laws of the country, be at liberty, with their families, to enter, establish themselves, reside and remain in any part of the territories
- 81. of the other." Yet the presence of a few English evangelists in Switzerland evoked a storm of persecution in which the first principles of religious liberty were as much violated as ever they had been in the days of the Huguenots. When the Maréchale and some comrades accepted an urgent invitation to Switzerland, she little thought that she would be the heroine of an historical trial. She went to preach the gospel. She observed the laws of the land, and respected the religious susceptibilities of its people. When she entered Geneva, she published only one poster, and that after it had been duly visé; she allowed no processions, banners or brass bands in the streets. Her only crime was that she sought to gain the ears of those who never entered a place of worship, and that she marvellously succeeded. If good order was not always maintained at her meetings, it was not her fault, but that of the authorities who refused to do their duty. History repeats itself. As in ancient Thessalonica during the visit of St. Paul, so in modern Geneva, some citizens, "moved with jealousy, took unto themselves certain vile fellows of the rabble, and gathering a crowd set the city on an uproar." The ringleaders of the disturbance were paid by noted traffickers in vice, who were themselves often seen in the meetings inciting the audience to riot. One of the first converts, a student, confessed that he had got twenty francs a night, and as much whisky as he could drink, to make a row. The Department of Justice and Police chanced at that time to have as its president a Councillor of State, M. Heridier, who thought it right not to punish the offenders but to banish their victims. In a sitting of the Grand Council he said, "We have been petitioned to call
- 82. out a company of gendarmerie to protect these foreigners, and to prevent brawls and rows. I will not consent to take such a step. There are already eight police agents in these places every evening who have a very hard time of it.... These agents might be doing more useful work elsewhere, and I am just about to withdraw them." That meant handing over the strangers to the tender mercies of the mob. It was a gross breach of the laws of hospitality and chivalry as well as of the constitution of a free country. The city of Calvin did not know the day of its visitation. The Maréchale and her comrades began their meetings in the Casino on December 22, 1882. The hall was crowded, and soon there was raging a great battle between the powers of light and darkness. A disturbance had evidently been organised. A band of students in coloured caps, who had come early and taken possession of the front of the galleries and other prominent positions, were on their worst behaviour. The first hymn was interrupted by cries and ribald songs, and the prayer which followed was almost drowned. But the Maréchale was never more calm and confident than when facing such music. At every slight lull in the storm, she uttered, in clear, penetrating tones, some pointed words which pierced many a heart. Within an hour she not only had subdued her audience but was inviting those who desired salvation to come forward to the penitent form. Scoffers of half an hour ago left their places, trembling under the sense of guilt, and as they knelt down the Maréchale sang, in soft notes, the hymn: Reviens, reviens, pauvre pécheur, Ton Père encore t'attend;
- 83. Veux-tu languir loin du bonheur, Et pécher plus longtemps? O! reviens à ton Sauveur, Reviens ce soir, Il veut te recevoir, Reviens à ton Sauveur! A strange influence stole over the meeting, hushing the crowd into profound silence, and the Spirit did His work in many hearts. The Maréchale conducted a similar service the following night, and on Christmas Eve she faced an audience of 3000 in the Salle de la Reformation. Its composition was entirely to her mind, for she was never so inspired with divine pity and power as when she was confronting the worst elements of a town. The theatres, the cabarets, the dancing saloons, the drinking dens, and the rendezvous of prostitution had poured their contents into the hall. Socialists who had found refuge in Geneva—men of many nationalities—came en masse. A large part of the audience were so entirely strangers to the idea of worship or of a Divine Being, that the sound of prayer called forth loud derisive laughter, with questions and cries of surprise and scorn. But the soldiers of Christ, clad in armour of light, were more than a match for the powers of darkness. Many a winged word found its mark, and the after-meeting in the smaller hall, into which three hundred were crowded, was pervaded by a death-like stillness, in which many sought and found salvation. Some of the ringleaders of the disturbance had pushed their way into this room; but they
- 84. remained perfectly quiet, evidently subdued and over-awed, with an expression on their faces of intense interest, which showed that they felt they were in presence of a reality in religion which they had not before encountered. The Maréchale sang her own hymn "Je viens à Toi, dans ma misère," and many joined in the chorus: Ote tous mes péchés! Agneau de Dieu, je viens a Toi, Ote tous mes péchés. One of those who were melted by the words wrote: "I was like the demoniac of Gadara. I may say I was possessed; I was chained for fifteen years to a frightful life.... It was then that you came. I was at first astonished; then remorse seized me. Then followed a frightful torment in my soul—a real hell. I resolved to put an end to it one way or another. Yet I thought I would go and hear you once more. I had been in darkness and anguish since the day of the first meeting. No word had I been able to recall of that day's teaching, except the words of the sacred song 'Ote tous mes péchés' (Take all my sins away). These sounded in my heart and brain through the day and the sleepless night—these and these only. Bowed down with grief and despair, again I came to the Reformation Hall, and to the after- meeting. The first sounds which fell on my ear were again those very words, 'Ote tous mes péchés,' and then you spoke on the words, 'Though your sins be as scarlet, they shall be white as snow'; you seemed to speak to me alone, to regard me alone—and I felt it was God who had sent me there to hear those words."
- 85. Hundreds of such letters were written. Evidence came from all sides of blessing received in many homes, of wild sons reclaimed, of drunkards and vicious men transformed by the power of God, of light and joy brought into families over which a cloud had hung. Not only anarchists and prodigals, but students of theology and the children of pastors had their lives transformed. In a meeting for women only, at which 3000 were present, the daughter of Pastor Napoleon Roussel began the new life. Her brother had been one of the converts in the first meeting in the Reformation Hall. Mlle. Roussel was to be the Maréchale's secretary for five years, and accompany her in a great American tour. A divinity student who attended a "night with Jesus" on New Year's Eve, wrote: "I passed a long night of watch, which I shall never forget. Since then I am ever happy, and can say 'Glory to God' every hour of the day." But as the tide of Divine blessing rose, the tide of human hatred also rose, and in the beginning of February the "exercises" of the Army were by Cantonal decree forbidden. A week later, the Maréchale, with a young companion, Miss Maud Charlesworth, now Mrs. Gen. Ballington Booth, was expelled from the Canton of Geneva. During her six weeks in the city she had been used to bring about probably the greatest revival which it had witnessed since the days of the Reformers. One of the most eminent lawyers of Geneva, Edmond Pictet, who had himself been greatly blessed during those stirring weeks, helped her to draw up an Appeal (Recours) to the Grand Council. He found, however, that she needed but little help, and often remarked that with the warm heart of an evangelist she combined the lucid intelligence of an advocate. When the Council of State had deputed
- 86. two or three of its members to hear her on the subject of her Appeal, she came back to Geneva under a safe-conduct to meet them. In the course of the interview, at which the British Consul in the city was present, the leading Councillor said, "You are a young woman; it is not in accordance with our ideas and customs that young women should appear in public. We are scandalised (froissés) by it." The rejoinder which he received was so remarkable a defence of "the Prophesying of Women" that we give it in full. "Listen to me, I beg of you, sir. It is contrary, you tell me, to your sense of what is right and becoming that young women should preach the Gospel. Now, if Miss Charlesworth and I had come to Geneva to act in one of your theatres, I have no doubt we should have met with sympathy and approval from your public. We could have sung and danced on your stage; we could have dressed in a manner very different from, and much less modest than, that in which you see us dressed; we could have appeared before a miscellaneous audience, men and women, young and old, and of every class; members of the Grand Council, M. Herdier himself and others, would have come to see us act; we should have got money; Geneva would have paid ungrudgingly in that case; and you would all have sat and approved; you would have clapped your hands and cheered us; you would have brought your wives and daughters to see us, and they also would have applauded. There would have been nothing to froisser you, no immorality in all that, according to your ideas and customs. The noise (bruit) we should have thus made would not have caused our expulsion. But when women come to try and save some of the forty or fifty thousand of your miserable, scoffing, irreligious population who never enter any place of worship,
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