preparation of hetrocatalyst from rice husk

BAHIR DAR INSTITUTE OF TECHNOLOGY
SCHOOL OF CHEMICAL AND FOOD ENGINEERING
PREPARATION AND CHARACTERIZATION OF ZEOLITE USING SILICA
FROM RICE HUSK ASH
PREPARED BY:-
MULUGETA ADUGNA
TESFAYE ALAMIREW
SUMMITED TO:-
NIGUS GABBIYE (PHD)

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Acknowledgment
.We wish to express our sincere thanks and deep gratitude to our teacher Dr.Nigus
Gabbiye for his invaluable guidance, constant encouragement, inspiration and assistant
throughout this project.
Our great appreciation is also given to Ato Addis for all his help especially in performing
the ICP analysis and DSC analysis. We would also like to acknowledge laboratory
assistances in the research and organic laboratory, where the majority of the experiment
work was completed.

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TABLE OF CONTENT
1. Introduction...................................................................................... 6
1.1 Introduction to the zeolites catalyst .................................................................... 6
1.2 Catalyst and catalysis........................................................................................... 6
2. Literature Review of the Zeolite Catalysts.......................................... 9
2.1 History of zeolites ................................................................................................ 9
2.2 Uses of zeolites .................................................................................................. 10
2.3 Structures of zeolites ......................................................................................... 11
2.4 Catalytic properties of zeolites ........................................................................... 13
2.4.1 Catalytic activity of zeolites............................................................................... 13
2.4.2 Catalytic selectivity of zeolites........................................................................... 15
3. Limitations....................................................................................... 18
4. Objective of project ......................................................................... 19
5. Methodology ................................................................................... 20
5.1 introduction of zeolite preparation......................................................................... 20
5.2 Experimental work .................................................................................................. 21
5.2.1 Extraction of silcon dioxide from rice husk.......................................................... 21
5.2.2 Preparation of the zeolites catalyst ..................................................................... 23
5.2.3 Preparation of zinc impregnated zeolite.............................................................. 26
6. characterization of prepared zeolite type y catalyst......................... 29
6.1 inductively coupled plasma (ICP) analysis ........................................................... 29
6.2 Differential scanning calorimetry analyses ............................................................. 30
6.3 Point of zero charge ................................................................................................ 32
6.4 PH ............................................................................................................................ 33
6.5 Performance evalution of prepared zeolite catalyst .............................................. 34
7. Conclusion ....................................................................................... 36
8 recommendations............................................................................. 37
Reference ............................................................................................ 38

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LIST OF FIGURE
Figure 2.1 Tetrahedral units for the zeolite structures................................12
Figure 2.2 Formation of the hydroxyl bridge in the zeolite framework.......14
Figure 2.3 Reversible formations of the classical Lewis and Brönsted acid
sites............................................................................................................14
Figure 2.4 Reactant selectivity...................................................................16
Figure 2.4 (B) Product selectivity ................................................................17
Figure 2.5 (C) Restricted transition-state selectivity ..................................17
Figure 5.1. Flow Chart of the Synthesis of Faujasite Type Y–Zeolite Catalyst
...................................................................................................................25
LIST OF PICTURES
Picture 1: prepared Sodium Aluminate......................................................18
Picture 2: washed rice husk with distilled water.........................................22
Pic3: washed rice husk before boiled .........................................................22
Pic5: dried in oven for about 24 hr .............................................................22
Figure:-6 prepared NaYzeolite....................................................................26
Pic: 7 impregnated zeolites with zinc solutions ..........................................28
Picture:8 zinc promoted zeolites after calcination......................................28

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Abstract
This project was conducted how to prepare and characterize the NaY –type zeolite
prepared locally from rice husk (which considered as a type of agricultural waste that is
difficult to discard) which is used as source of silca, and also the experiment studied on
the removal of one divalent zinc [Zn+2
] ions from solutions by wet impregnation process
using our prepared NaY-type zeolites as an adsorbent material. We try to characterize the
catalyst by ICP techniques to know about the composition of Aluminum , silicon and
zinic impregnated to this support. The Si/Al ratio is around 2.28. we also conduct DSC to
know the specific heat, enthalpy & some physical characterization like pH of our
catalyst.

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1. Introduction
1.1 Introduction to the zeolites catalyst
This project is conducted to study the preparation and characterization of zeolites
from silicon dioxide that is extracted from rice husk, which is often considered as a solid
waste from rice milling, contains approximately 70% of organic compounds and 30% of
hydrate silica (SiO2). In general, the rice husk can be used as a cheap energy source
through combustion, generate heat or electric power or for other purposes as low value
material such as adsorption of heavy metals, synthesis of different types of zeolites and
also to produce metallurgical silicon.
Zeolites as a type of porous material have become important for catalytic
processing, either in the cracking of crude oil distillate for fuel manufacture or in the
conversion of crude oil fractions to gasoline in the presence of hydrogen in hydro
cracking processes. In chemical and petrochemical industries, zeolites have the ability to
act as catalysts for the chemical reactions, which occur inside the internal channels, and
to modify the products. Thus, the petroleum industry is the most significant consumer
of zeolites-based catalysts [7]. Adding the catalyst diminishes decomposition
temperature and promotes decomposition speed, hence makes a chemical process more
efficient and reduces pollution by saving energy while minimizing unnecessary products
and by-products.
Nevertheless zeolites have special catalytic properties; only a few types of zeolites
have the required physical and chemical specifications to act as catalysts, namely acidity,
thermal stability and pores sizes large enough to allow reactant molecules ready access to
their surface. Of these zeolites, the Y-type is still the main cracking component of
today’s catalyst, which presents as an excellent model for stud [9].
1.2 Catalyst and catalysis
Generally, the process by which a catalyst affects a reaction, speeds up or slows
down, is called catalysis, and a catalyst can be either heterogeneous or homogeneous
with bio-catalysts (enzymatic) are often seen as a separate group. A catalyst is defined

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as any substance “organic, synthetic, or metal” that works to accelerate a chemical
reaction by reducing its activation energy (Ea) without affecting in any way the
possibilities for this reaction within a chemical system. In fact, these possibilities
described in terms of thermodynamics by means of the Gibbs free energy of the
materials involved in the reaction – the reaction proceeds spontaneously if ∆G < 0 and
vice versa. However, heterogeneous catalysis is the common attractive method for
activating reactions that are thermodynamically possible but which occur at a very slow
rate because of their chemical kinetics.
Since heterogeneous catalysis is a surface “interface phenomenon”, the catalysts
need a large surface area often expressed in m2
.g-1
to provide a sufficiently high
activity. The highly porous structures of zeolites, containing a three dimensional
network of channels, make them ideal as industrial catalysts, especially as it is possible
to modify their porosities and activities to selectivity minimize as much as possible the
formation of by-products. Therefore, this kind of catalyst is utilized to realize a
maximum conversion of the feedstock by increasing the rate of reaction. In addition, the
catalyst must has a good thermal stability (i.e. temperature at which it decomposes upon
heating at a constant rate) and is highly resistance to chemical agents during catalysis [5,
4, 3].
Moreover, zeolite catalyst has a high diffusivity – an important physical property
required for a commercially successful operation, which characterizes the ability of
fluids to diffuse throughout the zeolite structure. As such, the mass transfer of the
reactants to the active sites is increased, making possible the use of higher space
velocities of hydrocarbons often expressed in time-1
and lower residence times in the
reactor chamber. Additionally, most recent zeolitic or molecular sieve catalysts, as
they are also known, have a good hardness and are able to resist attrition and abrasion,
meaning that each catalyst particle is able to hold its shape. The choice of catalyst for
any specific purpose is depending on the operating conditions, feedstock, product
demands and the cost of process [6].
Theoretically, the overall reaction that takes place throughout the active sites on
the catalyst’s surface follow a five-step mechanism ,
These stages are: –
1- Thermal decomposition, generally after the transport of reactants from the
homogeneous phase (i.e gaseous or liquid) to the zeolite surface.

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2- Primary catalytic reaction following absorption of reactants on specific
sites of the surface so as to produce the intermediate chemisorbed species.
3- Secondary reactions between primary products in the sorbed phase.
4- Desorption of the products from the sorbed phase to release the sites.
5- Removal of the products from the catalyst surface into the homogeneous
phase, and accumulation of polymerizable products from further reaction
by their adsorption on the surface of the catalyst as coke.
Catalyst poisoning is a problem in all reactions, but the generation of coke as a by-
product is the most significant problem. The deposition of coke by occupying active
catalytic sites leads to reduce catalyst activity, thereby reducing the products yield
with deactivation occurring in two discrete ways: 1) pore blockage which prevents
the access of reactant molecules to the whole segments of zeolite pores, and 2) site
coverage caused by poisoning the zeolite acid sites. The acidity of zeolite is generated
by aluminium ions, which can be present in the zeolite framework or as extra
framework aluminium (EFAl) species. It is possible to increase the catalyst life by
means of decreasing its sensitivity to the effects of coking, however a proper
regeneration treatment is required to burn off all the coke in an oxygen rich dry
atmosphere [10].
.

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2. Literature Review of the Zeolite Catalysts
2.1 History of zeolites
Previously, the content of rice husk ash at different combustion temperatures has
been studied. The white ash that was obtained from combustion is generally 10-15% of
the total dry weight of rice husk. The water content may affect the combustion
temperature and the rice husk that has been treated with hot-water and some steam-
explosion processes give a lower level of metallic impurities. When the rice husk is
leached with mineral acid and calcined in oven, white powder rice husk silica (RHS) is
obtained. The RHS with high silica purity is suitable as a silica source for the production
of inorganic materials such as silicon carbide and silicon nitride. In a research field
related to catalysis, RHS was used as a silica source for the synthesis of micro-porous
materials such as zeolites and meso-porous silica. Rice husk was successfully used as a
silica source for the synthesis of type Y-zeolite in sodium form (NaY). In this study, a
low coast agricultural waste, which is Rice Husk was used as a raw material to synthesis
type Y-zeolite and the using of this prepared zeolite in the removal of zinc ion (Zn+2)
from solution. The remaining samples of type Y-zeolite after treating with aqueous
solutions containing zinc ion (Zn+2) was tested as a zinc promoted type Y-zeolite
catalyst and compared this catalyst with normally type Y-zeolite catalyst prepared from
rice husk only (without treatment with zinc ion (Zn+2).
The history of zeolites began in 1756 when the first zeolite mineral was discovered.
Zeolites originate in cavities inside rocks, as they are produced due to chemical
reactions within the volcanic magma. Axel F. Cronstedt, a Swedish mineralogist who
derived the term from two classical Greek words “zeo” and “lithos”, which mean, “to
boil” and “a stone”, first used the word “zeolite”. In addition, the name “boiling stone”
was also used because of the bubbles that zeolites release when heated in blowpipes
under high temperatures [13].

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Some of the more fundamental properties of zeolites were established over a period
of 130 years beginning in 1840, when Damour reported that zeolites had undergone
reversible dehydration with no apparent change in the transparency of the crystal form,
and in 1858 Eichhorn observed the reversibility of ion exchange on zeolite minerals. In
1930, Taylor and Pauling determined the crystal structure of the zeolites and showed
evidence of the presence of cavities in these structures; soon after in 1932 McBain
established the term “molecular sieve” to describe the porous solid materials, and the
ability of zeolite structure to act as sieves on a molecular scale. In 1945 Barrer – the
father of zeolite science in the United Kingdom; reported the first classification of
zeolite minerals based on the size and the rate of molecules absorbed: rapidly, slowly
or not significantly at room temperature. In the early 1950s, Milton and Breck
discovered the commercially vital synthetic zeolites A, P, X and Y. These zeolites
were synthesized from readily available raw materials. At that time, only aluminium-
rich zeolites could be synthesised. In 1967, Wadlinger and his co-workers introduced
the first silica- rich forms of zeolite beta (BEA). To date over 197 zeolite framework
types with an array of physical and chemical properties have been synthesized. Infact,
these are used to great effect in a wide range of industrial processes and it is always
important to know the specific type of zeolite one is using in order to assure that it
is appropriate for one's need [11,9].
2.2 Uses of zeolites
The larger-pore zeolite structures of type (Y) are often used in catalytic cracking
and hydro cracking processes in the petroleum industry, and are also used in catalytic
degradation of polymer wastes for recycling processes, which gives rise to an
increase in the recovery yield of gasoline-range hydrocarbons as the elementary
compositions between plastics and petroleum fractions are similar [6].

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In contrast, the smaller-pore zeolite structures of type (A) are employed to
selectively separate small molecules e.g.; H2S, H2O from organic molecules, and is
often used in the separation of light normal from branched paraffins, because the
latter (iso-alkanes) are slightly larger than the former. The type (A) zeolite may also
be used to aid the elimination of traces of sulphur compounds. Other industrial
applications of zeolites include the removal of potentially harmful organics or ions
from water, where natural zeolites are employed as ion exchangers, aiding the removal
of NH4
+ from wastewater, and also as builders in Laundry detergents to remove Ca2+
and Mg2+,here by softening the washing liquid.In addition, they are used as absorption
agents, and in membrane synthesis, and soil treatment processes for agriculture, and
also as modifiers in electrochemical processes, as well as in the nuclear industry or the
removal of radioactive species. Given the wide spread uses of zeolites, it is important to
consider the implications on health, and as such selective zeolites have been certified as
safe for human consumption – this includes e.g. Clinoptilolite (HEU), which is the most
abundant natural zeolite used as a good adsorbent in sulfar dioxide, SO2, removal [11,8].
2.3 Structures of zeolites
Zeolites are generally defined as crystalline alumina-silicates, and may be found as
natural minerals that are extensively mined in many parts of the world; however most
pure zeolites used in industrial processes are produced synthetically. Commonly, the
alumina-silicate framework of zeolites consists of alumina (AlO4)5-
and silica (SiO4)4-
tetrahedral units and their corners link all of these tetrahedral units together. Since
silicon has a valance of four and aluminum a valance of only three, the AlO4
tetrahedron carries a net negative charge. Accordingly, a positive extra-framework cation
such as sodium (Na+
) is incorporated as a charge counter-balance, and that gives the
zeolite its ion exchange characteristic. Furthermore, Lowenstein’s rule states that (four
Si atoms can surround each Al atom, while up to four Al atoms can surround the Si
atom), with oxygen bridges joining the Al and Si atoms such that no two aluminum
atoms bond to the same oxygen atom. This accounts for the fact that the zeolite LTA has
the lowest possible value of the Si/Al ratio [5].

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With the oxygen atoms distributed throughout the zeolite network, a rich variety
of beautiful three-dimensional structures may be found. The two types of tetrahedral
units can be arranged in a variety of ways and presented in different ratios – including
the faujasite type zeolite, for instance, which is characterised by interconnected voids
bounded by supercages with a diameter of 1.3 nm that can host cations and water
molecule. As such water moves freely inside the structure, but the zeolite framework
remains rigid. Figure 2.1 shows a tetrahedral structure that consists of a Si or Al atom.
The oxygen at each tetrahedral corner is connected with another tetrahedron by straight
lines that schematically represent the T-O-T bridges. These tetrahedrons are called
primary-building units (PBUs) and combine to shape the secondary- building units or
SBUs that give rise to the unique topology. As soon as SBUs are linked together, the
sodalite like in zeolite Y or any other geometrical shapes can
.
Figure 2.1 Tetrahedral units for the zeolite structures [5].
Since zeolites are microporous structures, each zeolite topology has a typical pore
opening, dependent on the size of the oxygen ring that defines the pore (i.e. the size of
the SBU). Thus, a description of a zeolite structure always relates with a description of
the pore openings and the dimensionality of the channel system within. Their unique
porous properties make zeolite consumption increases to a global market of several
million tonnes per annum.
According to the international union of pure and applied chemistry (IUPAC), the
classification is as follows; Micropores: dp ≤ 2 nm, Mesopores: 2 nm, < dp ≤ 50 nm
and Macropores: dp > 50 nm, with dp being the pore diameter. In these pores, the
dissolved organic molecules with appropriate sizes to fit into the catalyst pores are
adsorbed during the reaction.
As a general rule, zeolites structures have important properties and these

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properties are summarized in the following points :
 Stability of the crystal structure when dehydrated (i.e. the removal
of water from the zeolite crystals) – this is common of many types
of zeolites with dehydration occurring at temperatures below 400 °C.
 Adsorption of gases, vapour and other molecules inside the
microporous channels, because they are large enough to allow the
passage of guest species. In additional to a large void volume, a low
density and uniform molecular sized channels characterize the
majority types of the zeolite materials.
 A variety of other physical properties such as electrical
conductivity, cation exchange and catalytic properties [5, 4]
2.4 Catalytic properties of zeolites
Zeolites can operate both as ion-exchange materials and also reversible
adsorption systems for water or small organic molecules, with a potential capacity
of more than 25% of the framework weight; however the two most significant
properties for zeolites are acidity and porosity. The acidity of a zeolite is usually
responsible for the catalytic activity of catalysts, whilst the porosity is responsible
for the catalytic selectivity during the reactions. These catalytic properties can be
modified to provide enhanced flexibility across a range of applications [14].
2.4.1 Catalytic activity of zeolites
Zeolites are mostly employed as acid catalysts, with the catalytic activities
of zeolites attributed to the generation of strong acidic sites on their surfaces.
Electron pair acceptors or Lewis acid sites (L) and proton donor or Brönsted acid
sites (B), are both found in zeolites with the former resulting from the rupturing of
hydroxyl bridges between aluminium and silicon atoms in the framework, and the
latter resulting from the hydroxyl bridge that forms as shown in Figure 2.2. The
Brönsted acid site is formed when the negatively chared aluminium framework is
Counter-balanced by proton (H+
), such that it is necessary to replace the cations
present in the freshly synthesized zeolite with protons, for instance by substitution
of sodium ion (Na+
) with an ammonium ion (NH+
4). A high temperature calcining
process is then required to drive off the ammonia and leave a protonated form of

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the zeolite. In other circumstances where the zeolite is not protonated, a trigonally
coordinated Al-atom possessing a vacant orbital is produced that can accept an
electron pair and acts as a Lewis acid site [1,8].
Figure 2.2 Formation of the hydroxyl bridge in the zeolite framework [1].
Steaming modification may be used to increase the lattice Si/Al ratio of a zeolite by
means of removing different fractions of framework Al-atoms, where heating of
Brönsted acid sites causes dehydroxylation with the formation of an electron acceptor
“Lewis acid sites” at high temperatures, and fixation of water leads to some of the (L)
sites changing into (B) sites as shown in the Figure2.3. The rate of change is
proportional to the temperature used in the process – it increases with the increasing of
temperature [10].
Figure 2.3 Reversible formations of the classical Lewis and Brönsted acid
sites [10-11].

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This process is followed by the ejection of aluminium species (AlO+
) from the lattice
positions into cationic positions. Alternatively, water vapour used during the steaming
process can provide support to the oxygen atoms within the framework by increasing
their abilities to bond with the migrating silica species from other parts of the crystal and
causing the formation of new Si-O-Si bonds, in order to re-occupy the created vacancies
by these silicon atoms – such a structure tends to shrink under stabilization. The activity
of a zeolite catalyst may be defined by: (a) the strength of acidity, (b) the acid sites
density, and (c) the accessibility of the bridging hydroxyl groups, which act as Brönsted
acid sites. Undoubtedly, a decrease in the number of Al-atoms in the framework “high
Si/Al ratio” causes a decrease in the density of Brönsted acidity of a zeolite, but may
also increase the single acid site “proton donor” strength. By decreasing the Al content,
the charge density of anions “hydroxyl groups within the framework” decreases and
leads to less intense interaction of OH-groups whitin the framework, thereby increasing
the ease of proton transfer from the surface site to the adsorbed base. Thus, the overall
catalytic activity of a zeolite can be enhanced [10, 11].
It should be noted that stronger Brönsted acidic sites are present in highly
crystalline zeolite structures and that such structures have greater activity than the non-
crystalline type with same chemical composition. The impact of this is that
crystallization time is considered as a major parameter in the hydrothermal synthesis
process.
Whilst it would be expected that stronger acid sites would be foremost in the
catalyst selection process, this is not always true – especially in the cases of processes
such as cracking or hydrocracking where weak interactions are as a rule preferred,
assuming there is sufficient strength to catalyze the reaction. This is because the use of
zeolite catalyst with much stronger acid sites leads to easy deactivation it due to rapid
deposition of coke or poisoning with impurities [10].
2.4.2 Catalytic selectivity of zeolites
A catalyzed chemical reaction frequently takes place within the zeolite pores,
internal channels or cavities, and therefore there are size restrictions on the reactants,
products, or transition states intermediates. The maximum free pore diameters must thus

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significantly influence the shape-selectivity phenomenon.
Usually, shape selective catalysis is applied either to increase yields of a preferred
product or to hinder undesirable reactions, and the desire for precise control over
selectivity means that the heterogeneous catalysis is more favourable than the
homogeneous one for cracking reactions, since the pore size depends on the type of
cation present within the zeolite framework – e.g. a monovalent cation such as
potassium or sodium reduces the actual pore size of zeolite-A to below 0.4 nm.
However, the pores enlarge slightly at higher temperatures, which can then allow the
diffusion of molecules into or out-of the channel systems throughout the reaction. Whilst
there are many factors impacting shape selectivity, the zeolite frameworks may be
modified for specific applications, for instance, the uniform micropores in Y-type
zeolites provide excellent catalytic selectivity opportunities, as the faujasite type zeolites
have a regular opening large enough to accommodate molecules commonly found in gas
or oil refining operations [1, 13].
The desire to increase the porous properties of more siliceous zeolites has led to the
development of high surface area mesoporous materials, with extra- porosity of zeolites
such as ZSM-5 being created by desilication methodology. This involves the removal of
silicon from the framework, accordingly decreasing the lattice Si/Al ratio.
Weisz and Csiscery have shown that zeolite shape-selectivity can be divided into three
main categories, described with mechanisms shown in Figure 2.4 A, B and C:
A- Reactant selectivity: This arises when some of the reactant molecules
are too large to enter the zeolite channel system and products are only
formed from those molecules that are able to diffuse through the
Catalyst pores.
Figure 2.4 Reactant selectivity [1].

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B- Product selectivity: This arises when some of the product molecules
created inside the channel systems are too large to transport out of the
zeolite structure. They either deactivate the catalyst or are converted
by cracking to less bulky molecules, which then escape from catalyst
pores.
Figure 2.4 (B) Product selectivity [1] .
.
C- Restricted transition-state selectivity: This arises when some transition state
molecules are too large to form in the zeolite channels or cavities because those
molecules would require more space than available.
Both reactant and product molecules are prevented from dispersing through the
pores and only the possible product molecules from the
transition states are produced in the void space.
Figure 2.5 (C) Restricted transition-state selectivity [1]

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3. Limitations
The first problem we encounter is Unavailability of chemicals like Sodium Aluminate
Oxide (NaAlO2) which is used as a raw material for preparation of feed stock gel. But we
try to prepare this chemical in our laboratory from Sodium Hydroxide and Aluminium
oxide.
Chemical reaction
2NaOH(s) +Al2O3(s) 2NaAlO2(s) + H2O(l)
By using stochiometric balance
80 gm NaOH=102 gm Al2O3 80gm NaOH=164 gm NaAlO2
10 gm NaOH=? 10 gm NaOH=?
Therefore 10 gm of NaOH is reacting with 12.75 gm of Al2O3 and gives 20.50 gm of NaAlO2.
The above reaction is takes place using magnetic stirrer at room temperature. The reaction
is exothermic. After the reaction takes place we separate the product from water by
filtration, and then dry it at room temperature.
Picture 1: prepared Sodium Aluminate
Secondly Unavailability of chemicals like n-heptane which is used for performance
evaluation of our catalyst as catalytic cracking materials. But we try to use hexane as
catalytic cracking materials.
H2O
NaAlO2

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4. Objective of project
This project is essentially focused on the synthesis and characterization of Y-type zeolite
catalytic properties for the cracking of a long chain hydrocarbon into its derivative
components on a lab scale,. In view of that, the aim of the present study can be
summarized as follows;
General objective
 Synthesis of Na-Y zeolites form from silicon dioxide which extracted from rice
husk and aluminum source
Specific objective
 Analysis of the synthesized Y-samples by means of the most common
characterization techniques (i.e. ICP, DSC, TGA and BET) to investigate their
properties and establish the correlations between the achieved results from these
characterizations.
 Impregnate the synthesized NaY zeolites with zinc
 The final aim of the present study was catalytic cracking of n-heptanes (nC7) over
the selected Y-catalysts in order to assess the effectiveness of the catalyst...

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5. Methodology
5.1 introduction of zeolite preparation
In this project we have gathered and analyzed data from different sources. The
major data are collected by doing experiments, different books, observation we were
give conclusion, recommendation and possible solution that we understood from the
information samples.
In general zeolites can be synthesized from a reaction mixture containing silica,
alumina, alkali hydroxide and water. The nucleation and crystal growth are the two
most essential steps in zeolites crystallization, with nucleation taking place during the
induction period within complex chemical reactions. In fact, the induction time is a point
on the crystallization curve, where the conversion of amorphous material into crystalline
product begins
For the duration of the induction period, reorganization of the amorphous alumina-
silica “intermediate” gel takes place, and a number of small crystalline nuclei are formed
as the zeolites synthesis mixture is heated. The nucleation mechanisms in liquid-solid
systems can be divided into primary and secondary nucleation stages, where the former
is an important part in the zeolite synthesis system, and is itself divided into
homogeneous and heterogeneous nucleation. Homogeneous nucleation occurs only
within the solution, and after the amorphous gel “extraneous materials” appears, the
interface between the gel phase and liquid phase playing a significant part for the
heterogeneous nucleation to take place. Briefly, the amorphous materials in the
primary amorphous phase “initial gel” develops during heating and convert into the
secondary amorphous phase “equilibrated gel”, nuclei gradually form and are
transformed to the crystalline zeolite product.
In addition, the rate of crystallization mechanism may be increased by the use of
elevated temperature and aging (i.e. adding seed crystals to a crystallization system),
where a combination of the two leads to proceed the mechanism more quicker than in

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the non-aged case, due to a significant increase in the available
Surface area for crystal growth and nucleation of new crystals [12, 15]
5.2 Experimental work
In order to prepare zeolite we followed the following pre preparation steps
5.2.1 Extraction of silcon dioxide from rice husk
Materials needed
 Teflon Baker
 Pyrex Baker
 Balance
 Magnetic stirrer
 droplet
 heater
 Oven
 furnace
 Sulphuric acid
 Sodium hydroxide
 Aluminium oxide
 Sodium hydroxide
 Zinc chloride
 Sodium Aluminate Oxide
 Husk
 Distilled water
The procedure that we follow to extract silcon dioxide from rice husk were as follows
Rice husk was collected from Woreta fields in the Southern of Gonder.
 The husk was washed three times with distilled water. Excess distilled water was
used to remove the soluble materials present in the rice husk bringing from field.

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Picture 2: washed rice husk with distilled water
 Boiled to remove color and other fine impurities may be found in the rice husk
Pic3: washed rice husk before boiled Pic4: color removal after
boiled
 And then dried at 105°C for 24 hours. When the rice husk was heated at 105°C
in an oven, most of the water had been removed from the rice husk while the
second major mass loss of about 45-65% was attributed to the breakdown of
cellulose constituent char, which is a carbonaceous residue.
Pic5: dried in oven for about 24 hr
 The rice husk was treated with 10% sulfuric acid (H2SO4) for 24 hours for
preliminary removing all impurities. Until now we are try to remove the impurities.
 . Dry rice husk were sieved to eliminate residual rice and clay particles and also
They were well washed with double distilled water, filtered, dried in air, and
calcined at 750°C for 6 h

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 12 g of calcined were then subjected for dissolution in sodium hydroxide NaOH
(4 M) followed by boiling at 90°C for 12 h.
 Concentrated hydrochloric acid (HCl (37%)) was then added to the
aforementioned base dissolved rice hask for complete precipitation. So the rice
husk were filtered, washed with excess distilled water to be freeing from
chloride ions and finally dried in an oven at 120°C for 6 h
At this stage all hydrated silcon dioxide wich was found in rice husk is extracted
5.2.2 Preparation of the zeolites catalyst
In general zeolites can be synthesized from a reaction mixture containing
silica, alumina, alkali hydroxide and water, So, Faujasite type Y–zeolites could
be synthesized using silicon dioxide which is extracted from rice husk as a silica
source.
Seed gel preparation
 A 500 ml Teflon beaker containing a magnetic stirrer was washed with
deionized water.
 Sodium hydroxide of 1.6616 g was added slowly to deionized water
and stir until clear and homogenous solution appeared for about 5
minutes.
 The aqueous solution of sodium hydroxide was ready for the
preparation of seed gel. The gel was prepared according to the
following molar chemical composition
1.67 Na2O:0.1 Al2O3: 1 SiO2: 5 H2O
Feed stock gel preparation
 Two milliliter aqueous solution of sodium hydroxide was added to 0.7515g
sodium aluminate oxide until a homogenous mixture was formed.
 1.5361g rice husk was added separately to 5.5 ml sodium hydroxide aqueous
until homogenously mixed.

24
 Both of the preparations were heated under vigorous stirring to obtain a
homogenous mixture.
 The sample was aged for 24 hours at room temperature in the Teflon bottle.
 The aluminate and silicate solutions were mixed together in the polypropylene
beaker, subsequently stirred for 2 hours with the purpose of making it
completely homogenized.
This combined solution was used as the feed stock gel. The flow chart of the process is
shown in figure 5.1

25
Figure 5.1. Flow Chart of the Synthesis of Faujasite Type Y–Zeolite Catalyst

26
Figure:-6 prepared NaYzeolite
5.2.3 Preparation of zinc impregnated zeolite
We impregnate our prepared sample zeolite in order to know the ability to adsorb
zinc ions from solutions that contains zinc even though this experiment is done in
adsorption units.Zinc impregnated zeolites is used as catalyst for cracking of n-alkanes
hydrocarbons especially for n-heptanes

27
We impregnate our prepared zeolite with zinc ion as follows
the experiments were carried out using simulated synthesis aqueous
solutions of (Zn+2)ions.1000 mg/l stock solution of (Zn+2) ions was
prepared by dissolving suitable amount of zinc sulfate (ZnSO4) in one
liter of double distilled water
All solutions using in the experiments were prepared by diluting the
stock solution with distilled water to the desired concentrations for the
experimental work of this investigation. The (Zn+2) ions concentrations
were measured using ICP
Then we were impregnate half of the prepared zeolite using prepared
solutions as shown on the picture below

28
Pic: 7 impregnated zeolites with zinc solutions
After impregnation we calcined the sample at 300 O
C
Picture:8 zinc promoted zeolites after calcination
zeolite
Zinc solutions

29
6. characterization of prepared zeolite type y catalyst
In general, the characterization of a zeolite catalyst has to provide information
about structure and morphology, the chemical composition, the ability to sorb and retain
molecules and the ability to chemically convert these molecules. Information on the
structural, chemical and catalytic characteristics of zeolites is essential for deriving
relations between their chemical and physicochemical properties on the one side and the
sorptive and catalytic properties on the other. Such relations are of high importance, as
they allow the rational development of sorbents, catalyst and advanced structural
materials. In this project, zeolite was synthesized from silcon dioxide of rice husk. The
main uses are as an adsorbent material to adsorb divalent zinc (Zn+2) ions from
simulated aqueous solution and use the remaining samples as a catalyst for n-
heptane isomerization, thus only characterizations with respect to these applications
are being dealt with in depth. There are many characterization techniques but the
important ones in this study are inductive coupled plasma (ICP), Differential
scanning calorimetry (DSC) and determination of BET surface area and pore volume of
prepared zeolite catalysts.
6.1 inductively coupled plasma (ICP) analysis
In order to identify and/or determine the concentration of the atomic and molecular
species present in a chemical composition, an analytical spectroscopy technique can
commonly be used such as ICP-AES – inductively coupled plasma, atomic emission
spectrometry. It is fundamentally a type of emission spectroscopy widely employed to
detect the traces of metals within the sample, which can identify each element from the
wavelength of its electro- magnetic radiation. The atoms or the molecules in accordance
with their electronic structures frequently emit certain wavelengths of photons when
transmitting from an excited state to a lower energy state. As a result, raising the
intensity of this emission refers to an increase of concentration of metal within the
sample. Consequently, the composition of the sample can be determined.
The procedure that we followed for the analysis is as follows

30
Determination of silcon concentration
Before the analysis with the ICP proceed we had prepared the following samples
 Prepared of standard solution using 100gm of silica gel in 1L of distilled water
 Prepared our samples using sodium hydroxide in order to digest 10gm of zeolite
samples.
So the ICP result showed as the concentration of silcon in the samples is [Si] = 5
571.30 X mg/l
Determination of Aluminium concentration
 Prepared of standard solution using 100gm of Aluminium nitrate in 1L of
distilled water
 Prepared our samples using hydrochloric acid in order to digest 10gm of
zeolite samples.
So the ICP result showed as the concentration of Aluminium in the samples is
[Al] =2 438.665X mg/l
So from above result si/Al ratio is 2.28
Determination of zinc concentration
 Prepared of standard solution using 100gm of zinc sulphate in 1L of distilled
water
 Prepared our samples using Sulphuric acid in order to digest 10gm of zeolite
samples.
So the ICP result showed as the concentration of zincin the samples is [Zn] = 887.71 X
mg/l
6.2 Differential scanning calorimetry analyses
The word calorimeter is derived from the Latin word calore, which means heat, and
Calorimetry is a science deals with the heat of chemical reactions or heat capacity
measurements from physical changes. In the project, differential scanning calorimetry
DSC is used to investigate the enthalpies of transitions during the calcination step. The
DSC-instrument can mostly be utilized to investigate the thermo physical properties of
polymers and to study oxidation or other chemical reactions.

31
Procedure used in analyses is as follows
About 10 mg of zeolite sample and 10mg of zinc impregnated sample was charged
into a hermetically sealed aluminium sample pan and weighed before and after the seal –
with a second pan and lid used as a reference chamber. The sample and the reference
were then placed on the heat flux dish “thermoelectric disc”, which can generate a tightly
controlled heat flux. (Heat flux (q/t) can be expressed in terms of change of heat (q) vs.
change of time (t) , and both the sample and reference are maintained at the same
temperature (T) and heating rate (∆T/t) during the experiment. Thus, whether the heat
capacity (Cp) of the sample (i.e. the amount of heat required to raise the temperature of
the sample by one degree, J.°C-1
) or the enthalpy (∆H) can be calculated as follows :
(q/t)/(ΔT)= q/ΔT= CP=ʃdq= ʃCPdT=ΔH
Generally, more or less heat must flow to the sample inside the DSC-instrument
depending on whether the applied process is exothermic or endothermic. The enthalpy
is expressed by the following equation , with instrument error in DSC typically ± (0.5 -
1) ºC:
H  K.A (3.16)
Where:-
∆H is the enthalpy of transition (J.g-1
), which measures the heat
content. Changes of state or phase of matter are also accompanied
by enthalpy changes, and if ∆H is positive, the reaction is
endothermic such as in a melting process – heat is absorbed by the
system. In contrast, if ∆H is negative, the reaction is exothermic such
as in a freezing process – heat is desorbed from the system.
K is the calorimetric constant, which is actually varies from
instrument to instrument and can be determined by analyzing a
well-characterised sample with known enthalpies of transition (i.e.
well-defined heat capacity over the range of temperatures). Indium
(In), a very soft metal as a reference with a value of K about
1.0780 was used for this purpose, and
A is the area under the peaks that are reflected in the DSC plot [11, 4,
10].
What we had seen from the result DSC result is the enthalpy, the specific
heat flow of the NaY zeolite is better than zinc promoted zeolites.

32
6.3 Point of zero charge
The zero point of charge is a fundamental description of a mineral surface, and is more
or less the point where the total concentration of surface anionic sites is equal to the total
concentration of surface cationic sites, and most (but not all) of the sites are as the neutral
hydroxide.
At pH values above the ZPC, the surface has a net negative or anionic charge, and the
surface would participate in cation attraction, and cation exchange reactions.At pH values
below the ZPC, the surface has a net positive charge, and the surface will attract anions,
and participate in anion exchange reactions
We followed the following procedure in order to know point of zero charge
Mix 0.2gm of our sample with 0.2gm of sodium nitrate in 30ml of distilled water
Then titrate our sample with sodium hydroxide and nitric acid
Finally plot a graph PH versus change in PH.
∆pH=pH measured-pH initial
pH 1.21 1.34 1.41 1.76 1.99 10.83 11.17 11.4 11.70
∆pH -9.19 9.06 -8.99 -8.64 -8.41 0.43 0.77 1 1.3
Table 1: point of zero charge of zeolite catalyst.
Graph 1: point of zero charge of zeolite catalyst.
-10
-8
-6
-4
-2
0
2
1 1.21 1.34 1.41 1.76 1.99 10.83 11.17 11.7 11.7
∆pH
∆pH

33
pH 1.16 1.30 1.47 1.67 2.05 11.52 11.87 12.10 12.25 12.35
∆pH -8.78 -8.64 8.47 -8.27 -7.89 1.58 1.93 2.16 2.31 2.41
Table 2: point of zero charge of Zinc impregnated catalyst.
.
Graph 2: point of zero charge of Zinc impregnated catalyst.
So from graph point of zero charge of zeolite is and for impregnated zink also______
6.4 PH
The pH scale measures how acidic or basic a substance is. It ranges from 0 to 14. A
pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic.
We checkered the PH of our sample as follows
 Dissolve 10mg of our sample in distilled water
 Then we measure the PH
The PH meters showed as
PH of zeolites is around 10.40 and PH of zinc impregnated is around 9.94
-10
-8
-6
-4
-2
0
2
4
1 1.16 1.3 1.47 1.67 2 2.05 11 11.5211.87 12 12.1 12.2512.35
∆pH
∆pH

34
6.5 Performance evalution of prepared zeolite catalyst
We try to evaluate our sample activity performance in the following two methods
1. Activity Test of Synthesized Type NaY– Zeolite
The activity test of our sampled is
The activity of our sample Na Y–zeolite prepared was studied by
applying removal of (Zn+2) ions.
The (Zn+2) ions removal from solution was carried out in a laboratory
by using of wet impregnated. Then the outlet samples collected and
tested by inductive coupled plasma equipment to find the remaining
concentration of (Zn+2) ions.
. (Zn+2) ions removal was calculated from the equation:
[Zn+2
]0 – [Zn+2
]
R%= _____________
[Zn+2
]0
Where: [Zn+2]o and[Zn+2] are initial and residual divalent zinc (Zn+2)ion concentration
and where R is removal respectively from ICP result
[Zn+2
]0 =12803.04mg/L and [Zn+2
]0 – [Zn+2
] = 887.71 mg/Concentration
adsorbed zinc by zeolite
R%= 887.71/12803.04
R%== 0.695%
Even though the result is very small it showed as our prepared zeolite sampled has an abilityto
2. Activity Test of zinc promoted Synthesized Type Y– Zeolite
The zinc promoted type Y zeolite catalyst activity was studied by applying n- heptane
catalytic cracking reaction.
But we couldn’t work this activity test because of the following reasons
Since the catalytic cracking reaction is takes place under high temperature
between 4000
c-5000
c and the experiments of catalytic cracking were performed in
an experimental fluidized bed unit. The unit consists of n-heptane storage tank, gas

35
flow meter, dosing pump, evaporator, condenser/separator, cooler with appropriate
control, and power supply box. due to these difficulties we couldntt work
experiments in our laboratory
gas chromatography device (GC) that is found in our research lab is not
worked due to an availability of standard solutions since A sample of
gaseous product after cracking was collected and then analyzed by gas
chromatography device (GC),

36
7. Conclusion
Zeolites as a type of porous material have become important for catalytic
processing. Nevertheless zeolites have special catalytic properties; only a few types of
zeolites have the required physical and chemical specifications to act as catalysts,
namely acidity, thermal stability and pores sizes large enough to allow reactant
molecules ready access to their surface. In general zeolites can be synthesized from
a reaction mixture containing silica, alumina, alkali hydroxide and water, So, zeolites
could be synthesized using silicon dioxide which is extracted from rice husk as a silica
source. Then we impregnate our prepared sample zeolite in order to know the ability to
adsorb zinc ions from solutions that contains zinc. So the ICP result showed as the
concentration of zinc in the samples is [Zn] = 887.71 X mg/l, concentration of
Aluminium in the samples is [Al] =2 438.665X mg/l and concentration of silcon in the
samples is [Si] = 5 571.30 X mg/l. the Si/Al ratio is 2.28.
We also characterize the specific heat and enthalpy of catalyst support and Zn
impregnated catalyst by using DSC.

37
8 recommendations
In the future, in order to modify the catalytic properties of zeolite-Y catalysts.
Investigation of the catalytic performance of the nheptane cracking reaction at 450 ºC of
zeolite catalysts produced and deactivation time. Characterization techniques like BET,
TGA and GC will be performed to know more about the physical and chemical
characteristics of zeolite and to modify it. Some chemicals are not easily available, so one
have to collect all necessary chemicals before doing his/her experiment. The Si/Al ratio
can be modified to better catalyst property by adjusting it.Post-synthesis modification of
zeolites may be achieved using techniques such as de-alumination or de-silication and
have been developed in an attempt to improve several operational properties

38
Reference
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2- R.M. Barrer. Zeolites and Clay Minerals as Sorbents and Molecular Sieves.
London-New York: Academic Press, Inc, 1978.
3- R. Szostak. Molecular Sieves (principles of synthesis and identification). New
York-USA: Van Nostrand Reinhold, 1989.
4- R.M. Milton. Commercial Development of Molecular Sieve Technology.
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