Carbon dioxide reforming of methane in porous and dense membrane reactors:
Thermodynamic equilibrium approach
Tung Chun Yaw and Nor Aishah Saidina Amin*
Chemical Engineering Department, Faculty of Chemical and Natural Resources Engineering
Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia
Abstract
Carbon dioxide reforming of methane is one of the most promising processes to
convert methane and carbon dioxide, both well known as greenhouse contributors, to
syngas. During the last decades, extensive efforts have been conducted to investigate
the performance of catalytic reactors to produce high yield and selectivity of the
syngas. Despite all the considerable efforts, this process is still not commercially
viable due to its high endothermic reversibility nature, which requires high operating
temperature (~ 1000K). Besides, the occurrence of reverse water gas shift side
reaction further reduces the process efficiency. Nevertheless, removal of the
product(s) from the reaction zone with a membrane will shift the reaction
equilibrium, and consequently increases the reactant conversion and product yield at
lower operating temperatures. A thermodynamic tool based on the method of
“Lagrange’s undetermined multipliers” is used to evaluate the equilibrium
performance of CORM in porous and dense membrane reactor in the temperature
range of 700–1200K. Thermodynamic equilibrium analysis has indicated that
application of membrane reactor is able to enhance the performance of high
endothermic reversible reaction (CORM) in terms of conversion, products yield and
syngas ratio. However, when the temperatures exceed higher than 1000K, the
advantages of membrane reactor turn to be less significant. In addition, dense
membrane reactor has shown better performance than porous membrane reactor when
both membranes operate at the same permeability. Nonetheless, if the hydrogen
selectivity is not the key factor for designing membrane reactor, utilization of porous
membrane is more applicable for CORM process due to its higher permeability
nature.
Keywords: carbon dioxide, methane, membrane reactor, syngas, permeability
1. Introduction
The carbon dioxide reforming of methane (CORM) to synthesis gas (equation
(1)) is an important topic of current catalytic researches. The chemical method of
utilization of greenhouse gases, CO2 reforming of CH4 not only eliminates them but
also yields lower H2/CO molar ratio syngas (a mixture of H2 and CO) which is a
preferable feedstock for Fischer-Tropsch synthesis of liquid hydrocarbons [1,2].
During the past decades, the CORM process has received much attention and efforts
_____________________________________________________________________
* Corresponding author. Tel: 07-5535588;Fax: 07-5581463E-mail address: r-aishah@utm.my
have been focused on development of catalysts which show high activity towards
synthesis gas formation [3-12]. However, CORM using conventional catalytic
methods often has two serious problems [13]: (a) it is an intensively endothermic
reaction consuming much energy; (b) the catalysts used are inclined to deactivate due
to coke deposition on the catalytic surface.
CH4 + CO2 ' 2CO + 2H2
∆Hº298K = 247 kJ/mol
(1)
Furthermore, the reversibility nature of CORM imposes a limit, determined by
thermodynamic equilibria, on the conversion and yields of CO and H2 that are well
below commercially acceptable level, unless the reaction temperature is very high
(>1000K). The higher reaction temperature and higher energy consumption are the
main disadvantages of this process in industry application. Besides, the occurrence of
Reverse Water Gas Shift (RWGS) side reaction (equation (2)) also causes the
reduction of H2 selectivity which further lowers the syngas ratio to less than unity.
Equilibrium conversions in such thermodynamically limited reactions can be
overcome by preferentially removal of one or more of the products from the reaction
system [14-16]. According to Le Chatelier’s principle, CH4 and CO2 conversion and
products yield in the CORM process will increase if both products of the reaction (or
preferentially only one of them: H2) could be selectively removed from the reaction
system. Thus, the equilibrium limitations of a conventional reactor can be
circumvented. Besides, the H2 selectivity might also increase if H2 is continuously
removed from the reaction zone due to the suppression of the RWGS side reaction.
H2 + CO2 ' H2O + CO
∆Hº298K = 41 kJ/mol
(2)
In recent years, membrane reactors have been increasingly studied in this
process as a mean to overcome such equilibrium limitations. A membrane reactor in
which the permselective characteristic of the membrane is used to remove product
from the reaction zone as it is formed, can be beneficial to an equilibrium-limited
process by allowing higher one-pass reactor conversions to be achieved and/or by
decreasing reaction temperature if it is endothermic. The application of a membrane
reactor to high temperature heterogeneous gas phase reaction requires thermally and
chemically stable inorganic membranes. These membranes are classified into two
groups according to the separation mechanisms [17,18]: (a) porous membranes (PM)
mainly made of ceramic; (b) dense metallic membranes (DM).
In designing of an efficient membrane, there are at least two key parameters
that determine its effectiveness: permeability and selectivity. Dense membranes offer
the highest selectivity for H2 via metal hydride formation and a solution-diffusion
transport process but their efficiency is reduced because of their low permeability and
the low flux of permeated gas. As long as the selectivity is not the major factor in the
membrane design, research on membrane reactors preferably utilize porous
membranes which give higher values of permeability at the expense of selectivity
[19,20].
Most investigations in this reaction have centered on the use of dense Pd or
Pd/Ag membranes [17,21,22]. These membranes, while exhibiting excellent
selectivity toward hydrogen, suffer from the relatively low H2 permeability and
susceptible to poisoning by sulfur and coke. To avoid these difficulties, other
investigators have used porous ceramic membranes [23-25] which exhibit better
mechanical and thermal stability but allow gases other than hydrogen to permeate
through the membrane [26].
The present study investigates the concept of using a membrane reactor to
enhance the conversion of methane and yield of syngas during CORM.
Thermodynamic equilibrium conversions of methane and carbon dioxide to syngas
have been analyzed in a porous as well as dense membrane reactor. The performance
of the membrane reactor was evaluated by comparing the data from these two types of
reactors.
2. Calculation of equilibrium composition
Carbon dioxide reforming of methane is a multiple reaction network. Besides
the methane reforming with carbon dioxide to produce syngas, there are several
series-parallel side reactions which involve the reactions between reactants and
products. These side reactions include RWGS (equation (2)) and other equations
shown in equations (3) and (4).
CH4 + H2O ' CO + 3H2
CH4 + 2H2O ' CO2 + 4H2
∆Hº298K = 225.4 kJ/mol
∆Hº298K = 165 kJ/mol
(3)
(4)
Based on all the reactions involved, five gas species, CH4, CO2, CO, H2, and
H2O, which are assumed to be ideal gases are considered in this paper for
simplification.
The total Gibbs energy of a single-phase system with specified temperature T
and pressure P, (Gt)T,P is a function of the composition of all gases in the system, as
shown in equation (5).
(Gt)T,P = g(n1, n2, n3,…, nN)
(5)
At equilibrium condition, the total Gibbs energy of the system has its
minimum value. To find the set of ni’s which minimizes (Gt)T,P, subject to the
constraints of the material balances, the standard of this type of problems was based
on the method of Lagrange’s undetermined multipliers. The procedure for gas-phase
reactions was described by Smith et al. [27]. In this paper, the equilibrium
composition at 700–1200 K at 1 atm of a gas-phase system, which contain species
CH4, CO2, CO, H2, and H2O were calculated. In the initial state, CH4 to CO2 was set
to a ratio of 1:1. By applying Lagrange’s undetermined multipliers method for total
Gibbs free energy minimization, the following equations need to be solved
simultaneously:
λk
∆G°fi
+ ln( yiΦiP / IiP°) + ∑
aik = 0
RT
k RT
Ak
( k = 1,2,…,w)
∑ yiaik = n
i
(i = 1,2,…,N)
(6)
(7)
and
∑y = 1
(8)
i
i
where N
w
∆G° fi
R
T
yi
Φi
P
Ii
P°
λk
aik
Ak
n
= total number of species comprising the system
= total number of elements comprising the system
= the standard Gibbs-energy change of formation for species i.
= universal gas constant.
= system temperature
= mole fraction of species i at equilibrium condition.
= fugacity coefficient of species i in solution. If we assume the
assumption of ideal gases is justified in all cases, the Φi are all unity
= system pressure
= the number of isomers of species i.
= pressure in the standard state, in this case, is 1 bar.
= Lagrange multiplier of element k.
= the number of atoms of the kth element presents in each molecule of
chemical species i.
= total number of atomic masses of the kth element in the system, as
determined by the initial constitution of the system.
= total number of mole at equilibrium condition.
When this method is applied to membrane reactor, the permeation of H2, CO,
CO2 and CH4 is taken into consideration. The amount of elements removed from the
reaction system is deducted from the right hand side of equation (7). The H2
permeability (H2 removed from the system divided by total H2 formed) was set from 0
(non-membrane) to 0.5 (very high permeability). Other gas permeabilities for porous
membrane are based on the Knudsen selectivities from literatures [23, 28].
Since there were 5 species and 3 elements (C, H, and O) in the system, a total
of 9 equations (5 for equation (6), 3 for equation (7) and 1 for equation (8)) had to be
solved simultaneously in order to calculate the 9 unknowns in the formulae (mole
fraction of 5 species, Lagrange multiplier of 3 elements and total number of mole).
All calculations were done by using Mathcad 2000 Professional software. Values of
calculated ∆G° fi that were used in the calculation were given by Gurvich et al. [29].
The thermodynamic equilibrium amount of each species in terms of mole was
calculated by multiplying yi with n. Finally, the reactants conversion and products
yield were calculated by using the following equations:
Methane conversion, X CH 4 :
=
nCH 4 (in) − nCH 4 (out)
nCH 4 (in)
× 100%
(9)
Carbon dioxide conversion, X CO 2 :
=
nCO2(in) − nCO2(out)
nCO2(in)
× 100%
(10)
Carbon monoxide yield, YCO:
nCO(out)
× 100%
=
nCH 4 (in) + nCO2 (in)
(11)
Hydrogen yield, YH 2 :
=
2 × n H 2 (out)
4 × nCH 4 (in)
× 100%
(12)
× 100%
(13)
Hydrogen yield, YH 2O :
=
2 × n H 2O(out)
4 × nCH 4 (in)
3. Results and discussion
The influences of H2 permeation on CH4 and CO2 conversion for both porous
and dense membrane reactors are presented in Fig. 1. The results indicated that CO2
conversion is higher than CH4 conversion at all temperatures. This is due to the
occurrence of RWGS side reaction together with CORM process in which CO2 will
react with H2 formed to produce water and CO. Besides, the CH4 conversion is found
to approach CO2 conversion as the temperature increases because of the high
endothermic nature of CORM process and the less favorable RWGS reaction at high
temperature.
When membrane reactor is applied in this process, the results illustrated that
CH4 conversion increases with the increment of H2 permeation while the CO2
conversion only increases slightly. This has proven that preferential removal of H2
using membrane reactor is able to increase the reactants (more noteworthy for CH4)
conversion. Furthermore, a relatively small increment of CO2 conversion than CH4
conversion also proves that the introduction of membrane reactor is able to suppress
the RWGS side reaction. As both CH4 and CO2 conversions are tend to be equivalent,
according to the reaction stoichiometric, the side reactions will be suppressed.
Fig. 1 also illustrates that increment in syngas formation is mainly depends on
the reaction temperatures. This increment of syngas yield is due to the high
endothermic nature of CORM process. On the other hand, H2 yield (formed from
CH4) is always less than CO yield (formed from CO2), which has the same agreement
with CH4 and CO2 conversions. This difference is also due to the occurrence of
RWGS side reaction. In order to improve the H2 yield, utilization of membrane
reactors with high H2 permeation rate is needed. Nevertheless, application of
membrane reactor did not show significant improvement of CO yield due to the
suppression of RWGS.
Another interesting finding from Fig. 1 reveals that at temperature 900K, both
H2 and CO yield show greater increment (~ 12%) than other temperatures as H2
permeation increase from 0 (non-membrane) to 0.5 (very high membrane
permeability). In addition, when the temperature increases over 1000K, the advantage
of membrane reactor turn out to be less significant as the products yield already
achieved >90%.
For comparison between porous and dense membrane reactor, it is interesting
to observe that dense membrane reactor shows relatively better performance at same
H2 permeation for all temperatures. In other words, dense membrane reactor shows
better applicability than porous membrane reactor for CORM process. However, it is
important to realize that this conclusion is based on the assumption that both type of
membrane reactors operate at the same H2 permeation. Nonetheless, it should be
remembered that dense membranes have higher selectivity but lower permeability
nature than porous membranes. As depicted in Fig. 1, porous membranes show better
performance when its permeability is at least 10% higher than dense membranes.
Hence, porous membrane reactors should be more applicable compared to dense
membrane reactors.
(a)12
(b)35
Pre ce ntage (%)
Pre ce ntage (%)
10
8
6
4
30
25
20
2
0
15
0
0.1
0.2
0.3
0.4
0.5
(c)70
0
0.1
0.2
0.3
0.4
0.5
0.2
0.3
0.4
0.5
0.2
0.3
0.4
0.5
(d)9 0
Pre ce ntage (%)
Pre ce ntage (%)
65
60
55
50
85
80
45
75
40
0
0.1
0.2
0.3
0.4
0
0.5
(e)
(f)
100
100
Pre ce ntage (%)
98
Pre ce ntage (%)
0.1
96
94
92
99
98
97
96
90
0
0.1
Precentage
(%)
35
30
25
20
15
0
0.2
0.3
H 2 Pe rme ation
0.4
0.5
CH4 Conversion (PM)
CO2 Conversion (PM)
H2 Yield (PM)
Permeation
0.3
0.4
CO0.1YieldH20.2
(PM)
0
0.1
H 2 Pe rme ation
CH4 Conversion (DM)
CO2 Conversion (DM)
H2 Yield (DM)
0.5 CO Yield (DM)
Figure 1: Comparisons between porous (PM) and dense (DM) membrane reactors at temperatures
(a) 700K, (b) 800K, (c) 900K, (d) 1000K, (e) 1100K, and (f) 1200K.
7
6
6
5
5
H 2 O Yie ld (%)
H 2 O Yie ld (%)
7
4
3
2
700K
800K
4
900K
3
1000K
2
1100K
1200K
1
1
0
0
0
0.1
0.2
0.3
0.4
H 2 Pe rme abilty
0.5
0
0.1
0.2
0.3
0.4
0.5
H 2 Pe rme abilty
Figure 2: Equilibrium water yield as a function of temperature and H2 permeation for
(a) porous membrane and (b) dense membrane
The only side product from CORM process is water, which is formed through
RWGS side reaction. From Fig. 2, it is found that water formation is strongly depends
on the operating temperatures and H2 permeation. The reduction of water formation as
temperature increases is due to unfavorable RWGS reaction nature at high operating
temperature. Besides, the decreasing trend of water formation when H2 permeation
increases also shows that H2 removal from reaction zone using membrane reactor is
able to hinder RWGS side reaction.
Another important parameter that determines the performance of CORM
process is the ratio of syngas production. According to the reaction stoichiometric,
syngas ratio produced should be unity. However, due to the occurrence of undesirable
side reactions, the syngas ratio is found to be less than unity. Hence, it is important to
utilize membrane reactor with the purpose of increasing the syngas ratio. Table 1
summarizes that total syngas ratio in CORM process is strongly depends on
membrane permeability and operating temperatures. The total syngas ratio is found
lower than the desirable level when the temperature is less than 1000K for
conventional reactors (hydrogen permeation is 0). However, introduction of
membrane reactor is able to increase the total syngas ratios. In addition, utilization of
membrane reactor with higher hydrogen permeability can further improve the total
syngas ratio. Nonetheless, when the temperature increases over 1000K, the advantage
of membrane reactor on syngas ratios becomes less significant.
TABLE 1
Effect of H2 permeation and temperature on total syngas ratio for porous and dense membrane
reactor
Permeation
0
0.1
0.2
0.3
0.4
0.5
700 K
PM
DM
0.44
0.44
0.47
0.48
0.51
0.51
0.54
0.55
0.57
0.60
0.63
0.66
800 K
PM
DM
0.61
0.61
0.63
0.64
0.66
0.67
0.70
0.71
0.73
0.75
0.77
0.79
900 K
PM
DM
0.78
0.78
0.80
0.80
0.82
0.82
0.84
0.85
0.86
0.87
0.89
0.90
1000 K
PM
DM
0.90
0.90
0.91
0.91
0.92
0.93
0.94
0.94
0.94
0.95
0.96
0.96
1100 K
PM
DM
0.96
0.96
0.97
0.97
0.97
0.97
0.98
0.98
0.98
0.98
0.98
0.98
1200 K
PM DM
0.99 0.99
0.99 0.99
0.99 0.99
0.99 0.99
0.99 0.99
0.99 0.99
(a)
1
0.9
H2/CO Ratio
0.8
0.7
0.6
0.5
0.4
0.3
0
0.1
0.2
0.3
0.4
0.5
H2 Perm eability
(b)
1
0.9
700K
H2/CO Ratio
0.8
800K
0.7
900K
0.6
1000K
0.5
1100K
0.4
1200K
0.3
0
0.1
0.2
0.3
0.4
0.5
H2 Perm eability
Figure 3: Retentate syngas ratios at different H2 permeability for (a) dense membrane; and (b)
porous membrane
The effects of temperature and H2 permeation on the equilibrium retentate
syngas ratios for both membrane reactors are shown in Fig. 3. It is found that
equilibrium syngas ratio is strongly depends on the operating temperature and H2
permeation. From the results, higher syngas ratio (close to unity) is achieved when the
temperature increases. On the contrary, the syngas ratio drops sharply as the
membrane H2 permeability increases, especially at temperature over 900K. This is
due to more H2 is removed from the retentate stream at higher H2 permeation. From
Fig. 3, it is also found that the retentate syngas ratio drops more noteworthy in dense
membrane compared to porous membrane. The higher retentate syngas ratio for
porous membrane is due to its low selectivity nature, which allows other gases
(especially carbon monoxide) being removed continuously from reaction zone
together with H2.
4. Conclusions
The thermodynamic equilibrium analyses demonstrate that both porous and dense
membrane reactors are applicable for high endothermic reversible process such as
CORM. The reactants conversion, products yield and syngas ratio are enhanced with
the increment of H2 permeability in membrane reactors. However, the advantages of
membrane reactors in this process become less significant when the temperature is
higher than 1000K. Besides, dense membrane reactors show better performance than
porous membrane when both type of membranes operate at same H2 permeation rate.
Nevertheless, this does not mean that dense membrane reactor is more applicable than
porous membrane reactor since porous membrane shows better permeability than
dense membrane in general. If the hydrogen selectivity is not the key factor in
designing a membrane reactor, utilization of porous membrane is more applicable for
CORM process based on the findings from this study.
Acknowledgement
One of the authors (T.C.Y.) gratefully acknowledges the financial supports
received in the form of IRPA research grant (Vot 74005 or Project no: 02-02-060016) and National Science Fellowship from the Ministry of Science, Technology and
Environment, Malaysia.
Reference
[1] Ross, A. R. H., van Keulen, A. N. J., Hegarty, M. E. S. and Seshan, K. (1996).
“The Catalytic Conversion of Natural Gas to useful Products.” Catalysis Today. 30.
193-199.
[2] Wilhelm, D. J., Simbeck, D. R., Karp, A. D. and Dickenson, R. L. (2001). “Syngas
Production for Gas-to-Liquids Applications: Technologies, Issues and Outlook.” Fuel
Processing Technology. 71. 139-148.
[3] Krylova, O. V., Mamedov, A. Kh., and Mirzabekova, S. R. (1998). “Interaction of
Carbon Dioxide with Methane on Oxide Catalysts.” Catalysis Today. 42. 211-215.
[4] Wang, S. B. and Lu, G. Q. (1998). “Reforming of Methane with Carbon Dioxide
over Ni/Al2O3 Catalysts: Effect of Nickel Precursor.” Applied Catalysis A: General.
169. 271-280.
[5] Wang, S. B. and Lu, G. Q. (1998). “Role of CeO2 in Ni/CeO2-Al2O3 Catalysts for
Carbon Dioxide Reforming of Methane.” Applied Catalysis B: Environmental. 19.
267-277.
[6] Ito, M., Tagawa, T. and Goto, S. (1999). “Suppression of Carbonaceous
Depositions on Nickel Catalyst for the Carbon Dioxide Reforming of Methane.”
Applied Catalysis A: General. 177. 15-23.
[7] Matsui, N., Anzai, K., Akamatsu, N., Nakagawa, K., Ikenaga, N. and Suzuki, T.
(1999). “Reaction Mechanisms of Carbon Dioxide Reforming of Methane with Ruloaded Lanthanum Oxide Catalyst.” Applied Catalysis A: General. 179. 247-256.
[8] Wang, H. Y. and Ruckenstein, E. (2000). “Carbon Dioxide Reforming of Methane
to Synthesis Gas over Supported Rhodium Catalysts: The Effect of Support.” Applied
Catalysis A: General. 204. 143–152.
[9] Ruckenstein, E. and Wang, H. Y., (2000). “Carbon Dioxide Reforming of
Methane to Synthesis Gas over Supported Cobalt Catalysts.” Applied Catalysis A:
General. 204. 257–263.
[10] Sehested, J., Jacobsen, C. J. H., Rokni, S. and Rostrup-Nielsen, J. R. (2001).
“Activity and Stability of Molybdenum Carbide as a Catalyst for CO2 Reforming of
Methane.” Journal of Catalysis. 201. 206–212.
[11] Seok, S. H., Choi, S. H., Park, E. D., Han, S. H. and Lee, J. S. (2002). “MnPromoted Ni/Al2O3 Catalysts for Stable Carbon Dioxide Reforming of Methane.”
Journal of Catalysis. 209. 6–15.
[12] Wang, B. J., Hsiao, S. Z. and Huang, T. J. (2003). “Study of Carbon Dioxide
Reforming of Methane over Ni/yttria-doped Ceria and Effect of Thermal Treatments
of Support on the Activity Behaviors.” Applied Catalysis A: General. 8521. 1–15.
[13] Edwards, J. H. and Maitra, A. M. (1995), “The Chemistry of Methane Reforming
with Carbon Dioxide and its Current and Potential Applications.” Fuel Processing
Technology 42, 269-289.
[14] Saracco, G., Neomagus, H. W. J. P., Versteeg, G. F. and van Swaaij, W. P. M.
(1999). “High-Temperature Membrane Reactors: Potential and Problems.” Chemical
Engineering Science. 54. 1997-2017.
[15] Wieland, S., Melina, T. and Lamm, A. (2002). “Membrane Reactors for
Hydrogen Production.” Chemical Engineering Science. 57. 1571 – 1576.
[16] Marigliano, G., Barbieri, G. and Drioli, E. (2003). “Equilibrium Conversion for a
Pd-based Membrane Reactor. Dependence on the Temperature and Pressure.”
Chemical Engineering and Processing. 42. 231-/236.
[17] Kikuchi, E. (1995). “Palladium/Ceramic Membranes for Selective Hydrogen
Permeation and Their Application to Membrane Reactor.” Catalysis Today. 25. 333337.
[18] Won, S. M. and Seung, B. P. (2000). “Design Guide of a Membrane for a
Membrane Reactor in Terms of Permeability and Selectivity.” Journal of Membrane
Science. 170. 43–51.
[19] Kikuchi, E. (1995). “Palladium/Ceramic Membranes for Selective Hydrogen
Permeation and Their Application to Membrane Reactor.” Catalysis Today. 25. 333337.
[20] Cooper, C. A. and Lin, Y. S. (2002). “Microstructural and Gas Separation
Properties of CVD Modified Mesoporous γ-alumina Membranes.” Journal of
Membrane Science. 195. 35-50.
[21] Galuszka, J., Pandey, R. N. and Ahmed, S. (1998). “Methane Conversion to
Syngas in a Palladium Membrane Reactor.” Catalysis Today. 46. 83-89.
[22]Múnera, J., Irusta, S., Cornaglia, L., Lombardo, E. (2003). “CO2 Reforming of
Methane as a Source of Hydrogen Using a Membrane Reactor.” Applied Catalysis A:
General. 6477. 1-13.
[23] Prabhu, A. K. and Oyama, S. T. (2000). “Highly Hydrogen Selective Ceramic
Membranes: Application to the Transformation of Greenhouse Gases.” Journal of
Membrane Science. 176. 233-248.
[24] Ferreira-Aparicio, O., Rodríguez-Ramos, I. and Guerrero-Ruiz. A. (2002). “On
the Applicability of Membrane Technology to the Catalysed Dry Reforming of
Methane.” Applied Catalysis A: General. 237. 239–252.
[25] Paturzo, L., Gallucci, F., Basile, A., Vitulli, G. and Pertici, P. (2003). “An Rubased Catalytic Membrane Reactor for Dry Reforming of Methane - its Catalytic
Performance Compared with Tubular Packed Bed Reactors.” Catalysis Today. 82.
57–65.
[26] Onstot, W. J., Minet, R. G. and Tsotsis, T. T. (2001). “Design Aspects of
Membrane Reactors for Dry Reforming of Methane for the Production of Hydrogen.”
Ind. Eng. Chem. Res. 40. 242-251.
[27] Smith, J. M., van Ness, H. C. and Abbott, M. M.. (1996). Introduction to
Chemical Engineering Thermodynamics. Fifth Edition. New York: The McGraw-Hill
Companies: 559-604.
[28] Prabhu, A. K., Radhakrishnan, R. and Oyama, S. T. (1999). “Supported Nickel
Catalysts for Carbon Dioxide Reforming of Methane in Plug Flow and Membrane
Reactors.” Applied Catalysis A: General. 183. 241-252.
[29] Gurvich, L. V., Iorish, V. S., Yungman, V. S. and Dorofeeva, O. V. (1995).
“Thermodynamic Properties as a Function of Temperature”. CRC Handbook of
Chemistry and Physics. 75th Edition. Boca Raton: CRC Press: Chapter 5:61-84.