Packed Bed Reactor for Catalytic Cracking of Plasma Pyrolyzed Gas

IJSRD - International Journal for Scientific Research & Development| Vol. 1, Issue 4, 2013 | ISSN (online): 2321-0613
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Packed Bed Reactor for Catalytic Cracking of Plasma Pyrolyzed Gas
Nayak M. G1
Rana P.H2
Murugan P.V3
Dr. Nema S.K4
1,2,3,4
Department of Chemical Engineering
1, 2
Vishwakarma Government Engineering College, Chandkheda
3, 4
FCIPT division, Institute for plasma research, Gandhinagar
Abstract— Packed bed reactors play vital role in chemical
industries for obtaining valuable product, like steam
reforming of natural gas, ammonia synthesis, sulphuric acid
production, methanol synthesis, methanol oxidation,
butadiene production, styrene production. It is not only used
for production but also used in separation process like
adsorption, distillation and stripping section. Packed bed
reactors are work horse of the chemical and petroleum
industries. Its low cost, and simplicity makes it first choice
to any chemical processes. In our experimental work
vacuum residue is used as a feed which is pyrolyzed in the
primary chamber with the help of plasma into hydrogen and
hydrocarbon gases which is feed stream to the Ni catalyst
containing packed bed reactor called catalytic cracker. Ni
loading in the catalyst about 70 % is used to crack or
decompose lower molecular hydrocarbon in to hydrogen to
maximize the energy content per mass flow of gas steam
and also to minimize the carbon dioxide equivalent gases at
outlet of the reactor. Since cracking is surface phenomena so
the catalyst play important role in designing of reactor
shape. Parallel Catalytic packed bed with regeneration and
deactivation can be used for commercial production of clean
fuel.
Keywords: Vacuum residue, X ray analysis SEM of catalyst,
contact time, pressure drop, coking.
I. INTRODUCTION
Packed bed reactor employing Ni catalyst is the major
source of generation of hydrogen from hydrocarbon gases
present in plasma pyrolyzed [1,2]
gas. In industry steam
reforming, partial oxidation reaction are used for converting
hydrocarbon in to hydrogen and Carbon monoxide mixture
[3, 4]
. It is commonly called syngas. It is estimated that over
95 % of hydrogen generation from fossil fuel in which
major hydrogen production is by steam reforming of lighter
weight hydrocarbon like methane, ethane[5,6]
. This operation
involve filling nickel catalyst into tubes of shell and tube
type reactor and hot fluid supplied over the shell side to
provide heat necessary for steam reforming. Steam to
hydrocarbon ration is maintained around 2:1 depending
upon the hydrocarbon involve.
However in this operation we get the mixture of
hydrogen and carbon monoxide which is fed to shift
converter followed by purifier like Pressure swing
adsorption unit or cryogenic separation to get pure hydrogen
from the gas mixture. [7]
Since purification involves
additional space requirement as well as running and capital
cost, it is batter to think upon alternative approach.
Decomposition of methane, ethane or higher hydrocarbon is
one of the best alternatives as it produces hydrogen gas in
the product stream free from carbon monoxide, so this can
be used for fuel cell to generate electricity without any
purification. Carbon composition present in the hydrocarbon
gas is converted into carbon particle which is deposited over
the catalyst surface and gradually reduces efficiency of
decomposition. This carbon under SEM analysis shows
zigzag structure for methane, rolled fibre with entangled
cluster structure for ethylene and ethane over 5 % by weight
Ni on SiO2 at 673 K, performed by Kiyoshi otsuka and
coworkers [8]
. Filamentous carbon is also useful raw material
for its use in graphite electrode, to reduce metal oxide etc.
Catalyst bed can be regenerated by partial oxidation of
carbon into its oxide.
II. THEORY
The principal difference between reactor design calculations
involving homogeneous reactions and those involving fluid-
solid heterogeneous reactions is that for the latter, the
reaction takes place on the surface of the catalyst. The
reaction rate is based on mass of solid catalyst, W, rather
than on reactor volume, V[9]
. For cracking of gas in presence
of solid nickel catalyst the rate of formation of hydrogen or
rate of disappearance of hydrocarbons are denoted by
rH2’=molH2formed/(second. Gm of catalyst)
= -rH.C.’
= moles of hydrocarbon gases reacted/second. Gm of
catalyst
Assumption Involving packed Bed reactor design
There is no redial gradient in concentration of reaction
species.
Temperature of the reactor is constant or isothermal
operating condition.
Reaction rate is held constant.
III. PBR DERIVATION
General Balance on weight of catalyst is as under.[9]
In- out +Generation = Accumulation
FA,0 - FA + ∫ =
Fig (1): Packed bed reactor schematic diagram
At, Steady State
FA0-FA + ∫

(IJSRD/Vol. 1/Issue 4/2013/0010)
Differentiate with respect to W and rearrange
The Space time, tau, is obtained by dividing the reactor
volume by the volumetric flow rate entering the reactor:
τ=
Space time is the time necessary to process one volume of
reactor fluid at the entrance conditions.
Calculation steps
1) Analyzing gas composition at the inlet of reactor at
given temperature and pressure. It is done by Gas
chromatography analysis.
Sr. No. Component Volume %
1 Methane 14.08
2 Ethane 4.03
3 Propane 0.089
4 n-butane 0.0061
5 i-butane 0.015
6 Ethylene 0.9
7 Hydrocarbon 5
8 Nitrogen 38.1
9 Hydrogen 32.89
10 Carbon monoxide 4.89
Table (1): Gas composition at the inlet of reactor
For ideal gas volume percentage is equal to mole percentage
so next step is to find the compressibility factor z to
determine state of gas at given temperature and pressure.
2) Find compressibility factor for gas component.
In our experimental cracking work consist of hydrocarbon
gases mixture. Considering the non ideal behavior of the gas
component we need to introduce compressibility factor
which is denoted by Z.
It is denoted by
Z= P*V/n*R*T
Where P= pressure, in Kpa or mm Hg or mmWc
T = Temperature in Kelvin
V = Volumetric flow rate in m3
/hr
n = molar flow rate in mol/hr.
R =Universal gas constant =8.314 J/mol. K
If Z=1 for prevailing condition than gas behaves ideally,
otherwise it acts as a real gas. For ith
component its value is
Z i = Z0i + ωi*Z1i ------eq. 1
Value of Z0 and Z1 is obtained from table 1[10]
and table 2[10]
for given reduce T and P.
3) Molar flow rate of individual component can be
found by the following equation.
Fi,0 = P0 * υi,0 / Z* R* T0 ------eq. 2
4) Since compressibility factor for hydrocarbon gas is
nearer to 1 we can say gas behavior is ideal one and
total molar flow rate and mole fraction can be found by
following equation.
5) Ft,0 = ∑ Fi,0 -------eq. 3
6) Yi,0 =Fi,0/Ft,0 -------eq. 4
Table (2): Calculation of compressibility factor Z
Variable of our study are as follow.
1) Temperature
2) Volumetric flow rate of gas at inlet. Decomposition
reaction time for fixed temperature and volumetric flow
rate.
3) Weight of catalyst.
4) Concentration in Mol/m3 of gas at inlet can be
determined as follow.
Ci,0 = Fi,0/ υ,0 -----eq. 5
5) For given flow rate and temperature, pressure gas
individual component detail is completely determined
and presented in table 3.
CALCULATION OF MOLAR/MASS FLOWRATE OF GAS
AT INLET
P0 700 mm Hg
T0 823 K
Compon
ent
volu
metri
c
flow
rate
ϑa0
Molar flow
rate Fa0
mol/hr =
P0*ϑa0/Z*R
*T0
mol
fracti
on
Concent
ration
mol/m3
mass flow
rate ,inlet
gm/hr
CH4 0.141 1.920 0.141 1.920 30.727
C2H6 0.040 0.550 0.040 0.550 16.490
C3H8 0.001 0.012 0.001 0.012 0.534
n-C4H10 0.000 0.001 0.000 0.001 0.048
i-C4H10 0.000 0.002 0.000 0.002 0.119
C2H4 0.009 0.123 0.009 0.123 3.437
H.C. 0.050 0.682 0.050 0.682 58.650
N2 0.381 5.197 0.381 5.197 145.506
H2 0.329 4.486 0.329 4.486 8.972
CO 0.049 0.667 0.049 0.667 18.675
ϑ0 1.000 13.639 1 283.159
Table (3): Gas material balance data at the inlet of reactor
6) Reaction mechanism strongly suggests that operating
pressure should be as low as possible, because the
moles of product formed after the reaction is higher
than reactant. Considering 60 % conversion of 1m3/hr
Compon
ent
Tc Pc Pr Tr Vc Zc ω Z0 Z1
Methane
190.5
6
4.59
9
0.018
8
4.3
2
.09
8
.28
6
0.011
5
1.00
0
1.000
Ethane
305.3
2
4.87
2
0.017
7
2.6
9
.14
5
0.2
8
0.099
5
0.99
9
0.000
6
Propane
369.8
4
4.24
8
0.020
4
2.2
2
0.2
0.2
7
0.152
3
0.99
9
0.001
8
Butane
425.1
2
3.79
6
0.022
8
1.9
3
0.2
2
0.2
7
0.200
2
0.99
9
0.002
Pentane 475 3.5
0.024
7
1.7
3
0.2
9
0.2
7
0.25
0.99
9
0.002
Hexane 507.6
3.20
2
0.027
0
1.6
3
0.3
7
0.2
6
0.301
3
0.99
7
0.003
8

hydrocarbon into hydrogen and carbon at 823 K and
700 mm Hg pressure the hydrogen production and
concentration at the outlet can be found as
under:[11,12,13]
CH4  Cs + H2(g)
C2H62Cs + 3H2 CH4 + C + 2H2
C3H8 3C + 4H2  2C +CH4 + 3H2
C4H10 4C + 5H2  3C + CH4 + 4H2
C5H12 5C +6H2 4C +CH4 + 5H2
In general Hydrocarbon cracking or decomposition can be
expressed in term of
CnH2n+2  nC + (n+1)H2
For known volumetric flow rate Material balance across the
packed bed reactor for individual component is as under:-
Moles of i |inlet - Moles of i |outlet = Moles of ith component
converted.
Component
H2
produced
Mol/hr
C
produced
Mol/hr
H2
produced
gm/hr
C produced
gm/hr
CH4 2.3045 1.1523 4.6091 13.8272
C2H6 0.9894 0.6596 1.9788 7.9153
C3H8 0.0146 0.0146 0.0291 0.1748
n-C4H10 0.0025 0.0020 0.0050 0.0240
i-C4H10 0.0061 0.0049 0.0123 0.0589
C2H4 0.1473 0.1473 0.2946 1.7677
H.C. 2.8643 2.4551 5.7286 29.4614
N2 0.0000 0.0000 0.0000 0.0000
H2 0.0000 0.0000 0.0000 0.0000
CO 0.0000 0.0000 0.0000 0.0000
ϑ0 6.3288 4.4358 12.657 53.229
Table (4): Component converted inside the reactor
Moles of component, its concentration depend upon the
amount converted in the catalyst bed.
Since there is increase in the mole of product than reactant
we also have to determine two factor that is δi and εi for
individual component.
For Reaction A b/a B + c/a C
δi = b/a + c/a -1 ------eq. 6
εi = δi* yi,0 ------eq. 7
9) Concentration of reactant at the outlet of the reactor is
determined by the following formula
Ci= Ci,0*(1-X)/(1+εi*X)*p/p0 ------eq. 8
Or
C j = CT0 * (F j/ F T) * ( P / P0 ) * (T0/ T)
For given inlet volumetric flow rate of gas and conversion
value of δi and εi is as shown in table 5.
Component δi εi
Methane 2 0.2815
Ethane 4 0.1612
Ethylene 3 0.027
Propane 4 0.00356
Butane 8 0.027
Hexane 12 0.6
Table (5): δ and ε value of gas component.
Compon
ent
volum
etric
flow
rate
ϑa=Fa
*Z*R*
T/P
mol/m
3
Mola
r
flow
rate
mol/
hr
Fa=F
a0*(
1-X)
mol
fraction
Concen
tration
mol/m3
Ca=
Ca,0
*(1-
X)/(1
+εX)
*p/p
0
mol/
m3
ma
ss
flo
w
rat
e,o
utl
et
gm
/hr
Avg
mole
cular
weig
ht
gm/
mol
CH4 0.0616
0.768
2
0.0427 0.5324
0.532
4
12.
29
08
0.683
0
C2H6 0.0176
0.219
9
0.0122 0.1524
0.152
4
6.5
96
1
0.366
6
C3H8 0.0004
0.004
9
0.0003 0.0034
0.003
4
0.2
13
6
0.011
9
n-C4H10 0.0000
0.000
3
0.0000 0.0002
0.000
2
0.0
19
3
0.001
1
i-C4H10 0.0001
0.000
8
0.0000 0.0006
0.000
6
0.0
47
5
0.002
6
C2H4 0.0039
0.049
1
0.0027 0.0340
0.034
0
1.3
74
9
0.076
4
H.C. 0.0219
0.272
8
0.0152 0.1890
0.189
0
23.
46
00
1.303
7
N2 0.4167
5.196
7
0.2888 3.6014
3.601
4
14
5.5
06
5
8.086
2
H2 0.8672
10.81
48
0.6010 7.4948
7.494
8
21.
62
96
1.202
0
CO 0.0535
0.667
0
0.0371 0.4622
0.462
2
18.
67
52
1.037
8
ϑ(m3/hr) 1.4430
17.99
44
1.0000
22
9.8
13
5
12.77
14
Table (6): Component stream at the outlet of the reactor
Once the concentration of the gas at the outlet is known for
given condition we can either find the weight of catalyst
needed for given conversion provided that rate constant
value of each component is known or we can find the rate
constant for given weight of catalyst and conversion.
By using characteristics equation for packed bed reactor [9]
∑ -----eq. 9
Since decomposition of hydrocarbon lighter than gasoline
obey first order reaction rate law, we can estimate the rate
constant and activation energy as well as pre exponential
factor or the weight of catalyst for given conversion.
11) Ergun equation is used to calculate Pressure drop
calculation in porous bed. Ergun equation can be used for
laminar as well as turbulent flow in the packed bed.[9]
= * *[ + 1.75G] ----eq. 10
Where
P= pressure, lb/ft2
ф = Porosity= volume of void/total bed volume
1-ф = volume of solid/ total bed volume.
gc = 32.174 lbm.ft/s2
.lbf
Dp = diameter of particle in the bed, m

µ = viscosity of gas passing through the bed, lbm/ft.h(
kg/m.s)
z= length down the packed bed of pipe, ft.
u= superficial velocity= volumetric flow / cross sectional
area of pipe, ft/hr.
ρ=gas velocity, kg/m3
.
G= ρ*u = superficial mass velocity, kg/m2
.sec
Pressure drop in the across the bed is measured by u tube
manometer filled with water. Temperature of the gas inlet,
outlet and bed is measured by thermocouple.
Reactor based on the above design step is fabricated at the
workshop of the FCIPT division, Institute for plasma
research.
Fig (2): Reactor three dimensional drawing
Fig (3): Reactor plate three dimensional views
Reactor three dimensional drawing and its specification
drawing is shown in figure 1, 2 and 3 respectively.
Catalyst used for decomposition of hydrocarbon into
hydrogen is Ni catalyst found to contain 75 % of Ni as
measured by X-ray analysis.
Fig (4): Reactor design specification.

Fig (5): x ray analysis of Ni catalyst
SEM analysis of Ni catalyst is shown below.
Fig (6)
IV. CONCLUSION
Ni catalysis loaded packed bed reactor can be used to
maximize hydrogen generation from Ni catalyst. Vacuum
residue feed flow rate, Primary pyrolysis chamber
temperature, and pressure play important role in conversion
of hydrocarbon to hydrogen. By varying flow rate at given
temperature and pressure for a fixed catalyst weight
followed by measuring gas concentration at inlet and outlet
of reactor is useful to identify kinetics of the reaction as well
as to optimize the given reactor. Similarly by changing
temperature at constant pressure, volumetric flow rate and
fixed catalyst weight we can find the conversion as well as
effect of temperature on the conversion.
NomenclatureA.
Fi,0 = Molar flow rate of component i at reactor inlet.
Fi = Molar flow rate of component I at the reactor outlet.,
Ci,0 = Concentration of component I at reactor inlet.
Ci = Concentration of component I at reactor outlet.
τ = space time
υi,0 = Volumetric flow rate of ith
component at reactor inlet.
υi = Volumetric flow rate of ith component at reactor outlet.
T,0 = Temperature at reactor inlet.
T= Temperature at reactor outlet.
P,0= Pressure at reactor inlet.
P = Pressure at reactor outlet.
Z= Compressibility factor.
Pc = Critical pressure
Pr = Reduced pressure.
Tc= Critical temperature.
Tr = Reduced temperature.
ω= eccentricity factor.
R = Universal gas constant.
X= Conversion
δi = stoichiometric coefficient difference.
εi = Factional change in volume of gas per mole of ith
component reacted.
ACKNOWLEDGEMENT
FCIPT division, Institute for plasma research for providing
infrastructure and allow me to do my dissertation work.
REFERENCES
[1] Binhang Yan, Pengcheng Xu, Yong Jin, Yi Cheng,
Chemical Engineering Science, Volume 84, 24
December 2012, Pages 31-39
[2] M.G. Sobacchia, A.V. Savelieva, A.A. Fridmana :
Experimental assessment of a combined plasma
catalytic system for hydrogen production via partial
oxidation of
Hydrocarbon fuels , International Journal of Hydrogen
Energy 27 (2002) 635 – 642.
[3] Dissanayake , D. , Rosynek , M.P. ,Kharas , K.C.C. ,
and Lunsford , J.H. Partial oxidation of methane to
carbon monoxide and hydrogen over a nickel/alumina
catalyst . Journal of Catalysis , 1991 , 132 , 117 .
[4] Z. Khan, S. Yusup, M.M. Ahmad, V.S. Chok, Y.
Uemura, K. M. Sabil, Review on Hydrogen Production
Technologies in Malaysia , International Journal of
Engineering & Technology IJET-IJENS Vol:10 No:02
[5] Olga bicakova ,Pavel straka:The resources and methods
for hydrogen production, Acta Geodyn. Geomater., Vol.
7, No. 2 (158), , 2010, 175–188.
[6] Calin-Cristian Cormos, Hydrogen production from
fossil fuels with carbon capture and storage based on
chemical looping system, International Journal of
Hydrogen Energy, Volume 36, Issue 10, May 2011,
Pages 5960-5971.
[7] Hydrogen and syngas production and purification
technologies: Ke leu et. Al. Whiley publication,
AICHE.
[8] Kiyoshi otsuka , Yukio Shigeta, Sakae Takenaka,
Production of hydrogen from gasoline range alkanes
with reduced CO2 emission, International Journal of
Hydrogen Energy, Volume 27, Issue 1, January 2002,
Pages 11-18.
[9] Fogler H.S., “Isothermal reactor Design” Element of
chemical reaction engineering, 4th
edition.2009,p. 143-
147,175-182.
[10] Robert H. Perry: perry’s chemical engineers’ handbook
8th
, table 2-351 & 352page no : 2-500, 2-501.
[11] Sharif Hussein Sharif Zein. Abdul Rahman Mohamed.
and P. Sesha Talpa Sai , Kinetic Studies on Catalytic
Decomposition of Methane to Hydrogen and Carbon
over Ni/TiOz Catalyst , Ind. Eng. Chem. Res. 2004, 43.
4864-4870.
[12] Kiyoshi Otsuka, Shoji Kobayashi, Sakae Takenaka:
Catalytic decomposition of light alkanes, alkenes and
acetylene over Ni/SiO2 , Applied Catalysis A:
General 210 (2001) 371–379.
[13] Sakae Takenaka *, Kenji Kawashima, Hideki Matsune,
Masahiro Kishida: Production of CO-free hydrogen
through the decomposition of LPG and kerosene over
Ni-based catalysts , Applied Catalysis A: General 321
(2007) 165–174.

Packed Bed Reactor for Catalytic Cracking of Plasma Pyrolyzed Gas

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Packed Bed Reactor for Catalytic Cracking of Plasma Pyrolyzed Gas