water system with the stoichiometric method

International Journal of Hydrogen Energy 31 (2006) 21 – 28 www.elsevier.com/locate/ijhydene

Thermodynamic analysis of ethanol/water system with the stoichiometric method V. Mas, R. Kipreos, N. Amadeo, M. Laborde∗ Chemical Engineering Department, School of Engineering, University of Buenos Aires, Pabellón de Industrias, Ciudad Universitaria, 1428 Buenos Aires, Argentina Available online 23 May 2005

Abstract An analysis of the chemical equilibrium of ethanol/water system, using the stoichiometric method, has been performed. Intermediate compounds and coke formation are analyzed. Ethanol is completely converted to ethylene and/or acetaldehyde. Taking into account the equilibrium constant values of formation and transformation reactions of ethylene and acetaldehyde, both compounds are intermediates in this system. Due to the relevance of carbon monoxide if hydrogen is used as feed of a PEM-type fuel cell, CO concentration in the equilibrium mixture was studied assuming two different scenarios: (a) CO as primary product and (b) CO2 as primary product. These two scenarios lead to suggest different routes for reaching the equilibrium. Thus, the results obtained in this work might help to interpret the experimental results far away from the equilibrium with the aim of elucidating the reaction mechanism. The knowledge of this mechanism is essential in order to minimize the CO formation. The thermodynamic feasibility of coke formation shown in a temperature vs. water/ethanol molar ratio has also been analyzed. The results indicate that if moderate temperatures are used, a molar ratio higher than 3 is required to avoid coke formation. 䉷 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Hydrogen; Ethanol steam reforming; Chemical equilibrium

1. Introduction A few years ago, the first thermodynamic analysis on the ethanol/water system was carried out using the nonstoichiometric method [1]. Later, other thermodynamic studies of the same system were published [2–8] due to two reasons: (a) the novel application of hydrogen as fuel and (b) the increasing importance of bioethanol as a renewable feedstock in hydrogen production. The non-stoichiometric method was used in [1] since, at that time, the information about the reaction scheme was scarce. Since then, a considerable amount of experimental papers about ethanol steam reforming has been published [9–19], casting light on the ∗ Corresponding author. Tel./fax: 54 11 45763240/1

E-mail address: [email protected] (M. Laborde).

reaction system. It is known, nowadays, that CO concentration in the hydrogen flow is a key variable since Pt electrode of the fuel cell is deactivated if the hydrogen flow has as low as 20 ppm of CO. Then a purification process is necessary in order to reduce CO produced in the reformer. Another significant variable is the molar ratio water/ethanol in the feed to the reformer. This ratio must be as small as possible in order to close the energetic balance of the entire device including the fuel cell. In addition, the deactivation of the catalyst as a consequence of coke formation can be reduced using a high molar ratio water/ethanol in the feed. In summary, the understanding of ethanol steam reforming has increased significantly in the last few years; nevertheless, many questions are still not answered to date. In order to contribute to the comprehension of the ethanol/water system, the analysis of the chemical

0360-3199/$30.00 䉷 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2005.04.004

22

V. Mas et al. / International Journal of Hydrogen Energy 31 (2006) 21 – 28

K2 =

Nomenclature Kj ni nT r xj X

equilibrium constant mole number total mole number water/ethanol molar ratio extent of reaction, [mole] ethanol conversion defined as: (n0C H OH -n0C H OH )/n0C H OH 2

5

2

2

5

nC2 H4 nH2 O . nC2 H5 OH nT

And the stoichiometric balance, taking into account that n0C H OH = 1 is 2

5

nC2 H5 OH = 1 − x1 − x2 , nH2 = x1 ,

5

Subscripts

nH2 O = r + x2 ,

i j

nC2 H4 O = x1 ,

reactant reaction

Superscripts

nC2 H4 = x2 ,

0

nT = r + 1 + x1 + x2 .

initial

equilibrium of this system is carried out using the stoichiometric method. In this work, a homogeneous system is assumed, except when coke formation is analyzed; and it is considered to be an ideal gas mixture at atmospheric pressure. Calculus were performed considering n0C H OH = 1. 2

5

2. About the intermediate compounds Previous experimental papers [9–13,19] pointed out that working at very low contact times, the main products obtained were acetaldehyde and ethylene, according to the following reactions: C2 H5 OH = C2 H4 O + H2 ,

(1)

C2 H5 OH = C2 H4 + H2 O.

(2)

Conversely, these products were not detected while working at moderate and high contact times. Iwasa [9] detected reaction 1 on copper sites, while Mariño [10–12] and Mas [13] observed these products on copper and nickel sites. The dehydration of ethanol (reaction 2) occurs on acidic sites, such as the acidic sites of alumina, which is a typical component of steam reforming catalysts. In Fig. 1, the equilibrium constant of ethanol dehydrogenation, K1 , and ethanol dehydration, K2 , at different temperatures are shown. It can be seen that both reactions are endothermic; K2 is larger than K1 in the whole range of temperatures analyzed, although K1 increases faster than K2 when temperature is increased. The equilibrium of this system (reactions 1 and 2) is solved using K1 =

nC2 H4 OH nH2 , nC2 H5 OH nT

Fig. 2(a) shows ethanol conversion (X) values vs. water/ ethanol molar ratio, at different temperatures. It can be seen that the equilibrium conversion of ethanol is quite high since at temperatures as low as 400 K and r = 0, conversion value is 0.96 and at T > 500 K ethanol conversion is higher than 0.99 at all r values analyzed. It means that, whatever r value is, for T > 500 K ethanol is not practically present in the equilibrium mixture. On the other hand, previous works have shown that in the presence of a catalyst, ethanol is totally converted at temperatures as low as 523 K even in absence of water [10–13]. Figs. 2(b) and (c) show the extent of reactions 1 and 2 vs. temperature at different r values. The extent of reaction 1, x1 , increases with temperature, in the whole range, due to the endothermicity of this reaction. Despite water not being involved in reaction 1, the extent of this reaction is influenced by r. This fact can be explained by the effect of r on the total mole number. The total mole number increases with r and, due to the stoichiometric, the equilibrium is therefore shifted to products. In the case of reaction 2, despite the fact that this reaction is also endothermic, x2 first increases and decreases afterwards with temperature. This behavior is a consequence of the competition between both reactions when the temperature increases. It must be noted that x2 increases with temperature at low temperatures and when x1 value is nearly zero. The effect of water on reaction 2 is explained by the stoichiometry of the reaction. In summary, x2 is always higher than x1 , for all T and r values analyzed in this work, and then ethanol, from a thermodynamic point of view, is preferentially consumed by the dehydration reaction (reaction 2). It must be noted that the free energy of acetaldehyde is lower than the free energy of ethylene in the range of temperature studied. Nevertheless, the stability of water, the other product of reaction 2, explains the preference of ethanol for this reaction. Only for T > 1200 K and for high r values reaction 1 would be favored.

V. Mas et al. / International Journal of Hydrogen Energy 31 (2006) 21 – 28

23

1.E+11

log K

1.E+07

1.E+03 Reaction 1 Reaction 2 Reaction 3 Reaction 4 Reaction 6

1.E-01

1.E-05 400

500

600

700 800 900 Temperature (K)

1000

1100

1200

Fig. 1. Equilibrium constants of reactions (1)–(6) at different temperatures.

0.5

1

r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r 10

0.4

423 K

0.3

473 K 0.96

x1

Conversion

0.98

523 K 0.2

573 K 623 K

0.94

0.1

0.92

0 0

(a)

2 4 6 8 Water to ethanol ratio (mole H2O/mole EtOH)

10

400

500

600

700 800 900 Temperature (K)

900

1000

1100

1200

(b)

1000

1100

1200

1

0.9 r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r 10

x2

0.8

0.7

0.6

0.5 400

(c)

500

600

700

800

Temperature (K)

Fig. 2. (a) Ethanol conversion vs. water/ethanol molar ratio at different temperatures. (b) Extent of reaction (1) vs. temperature at different r values. (c) Extent of reaction (2) vs. temperature at different r values.

24

V. Mas et al. / International Journal of Hydrogen Energy 31 (2006) 21 – 28

3. About the transformation of intermediate compounds

1.E+12

Acetaldehyde, by a decarboxylation reaction, gives methane and carbon monoxide:

1.E+04

(3)

1.E+00 Reaction 7 Reaction 8 Reaction 9 Reaction 10 Reaction 11

1.E-04 1.E-08

This reaction was postulated by Cavallaro [15] using Rh catalysts and by Mariño and Mas [10–13] working with Cu/alumina and Cu/Ni/alumina catalysts. Acetaldehyde, in presence of water can also be reformed: C2 H4 O + H2 O = CH4 + CO2 + H2 .

log K

C2 H4 O = CH4 + CO.

1.E+08

(4)

This reaction is proposed by Comas [19] working with Ni/alumina catalysts and Fatsikostas [20] using Ni/La2 O3 /Al2 O3 catalysts. The other intermediate compound, ethylene, can be reformed with one or two molecules of water, depending on r value [15,19]: C2 H4 + H2 O = CH4 + CO + H2 ,

(5)

C2 H4 + 2H2 O = CH4 + CO2 + 2H2 .

(6)

Equilibrium constant values of reactions (1)–(6) at different temperatures, given in Fig. 1, indicate that acetaldehyde and ethylene are intermediate compounds.

4. Analysis of chemical equilibrium using the stoichiometric method From a thermodynamic point of view, ethylene and acetaldehyde can be considered unstable compounds, then, in order to examine the chemical equilibrium of the system ethanol/water six compounds must be taken into account, the four final compounds: CO, CO2 , H2 and CH4 and the two reactants: C2 H5 OH and H2 O. These six compounds have three atomic species: H, C and O; consequently, a system of three independent reactions is necessary. To decide on which three reactions should be chosen, the following relations between reactions (1) and (6) can be postulated: (1) + (3) or (2) + (5) = C2 H5 OH = CH4 + CO + H2 ,

(7)

(1) + (4) or (2) + (6) = C2 H5 OH + H2 O = CH4 + CO2 + 2H2 .

(8)

Depending on r values, and which the intermediate compound is, two global reactions can be formulated (reactions (7) and (8)) and one of them should be used in the analysis of the chemical equilibrium. Another two reactions must be considered: the water gas shift (WGS) reaction and the steam reforming of methane since the compounds involved

1.E-12 1.E-16 400

600

800

1000

1200

Temperature (K) Fig. 3. Equilibrium constants of reactions (7)–(11) at different temperatures.

in these reactions are present as final products in reactions (7) and (8): CO + H2 O = CO2 + H2 ,

(9)

CH4 + H2 O = CO + 3H2 .

(10)

In Fig. 3 equilibrium constant values of reactions (7)–(10) at different temperatures are summarized. It can be observed that K7 and K8 values are higher than K9 and K10 values in all the ranges of temperatures. On the other hand, as it was shown in Fig. 2(a), ethanol conversion is higher than 0.99 at temperatures as low as 500 K. Then, it can be assumed that reactions (7) and (8) are completely shifted to products under the conditions studied in this work and ethanol moles in the equilibrium can be disregarded. Experimental evidence supports this assumption [19,20]. Thus, the number of compounds in the equilibrium is reduced from six to five and the number of reactions to be considered is reduced from three to two. These two reactions are the WGS and steam reforming of methane (reactions (9) and (10)). Once the reactions have been defined, the initial composition of the mixture must be chosen. This choice is related to reactions (7) and (8). If reaction (7) occurs (low r values), the initial composition is CH4 :CO:H2 = 1:1:1; for moderate r values reaction (8) occurs and the initial composition is: CH4 :CO2 :H2 = 1:1:2. These two scenarios will be considered; the most important difference between them is that in the first scheme CO is a primary product while in the second one the primary product is CO2 . This difference has also been noted in many experimental works where some authors consider CO2 [19,21] and some others CO [16], as primary products. Other situations could also be considered, such as the case of high and very high r ratios; subsequently, CH4 could be completely consumed by steam reforming, with one or two moles of water obtaining CO and/or CO2 . Nevertheless, it should be taken into account that the energetic balance of the entire system (including the fuel cell) strongly depends

V. Mas et al. / International Journal of Hydrogen Energy 31 (2006) 21 – 28

on the amount of water used in the steam reforming (r value in this work) and surplus water should be limited. Scheme A (CO as primary product): Initial molar composition: CH4 :CO:H2 = 1:1:1. The reactions are:

CH4 + H2 O = CO + 3H2 ,

1.6 1.4 1.2

(9) (10)

1

x9

CO + H2 O = CO2 + H2 ,

0.8

and the stoichiometric balance is

0.6

nCO = 1 − x9 + x10 ,

0.4

nH2 O = r − x9 − x10 ,

0.2

nCO2 = x9 , nH2 = 1 + x9 + 3x10 ,

r8

r9

r 10 600

800

1000

1200

1.2 1 0.8 0.6

x10

0.4

r1

r2

r3

r4

r5

r6

r7

r8

r9

r 10

0.2 0 -0.2 -0.4 -0.6 400

500

600

(b)

700

800

900

1000

1100

1200

Temperature (K)

Fig. 4. (a) Extent of reaction 9 vs. temperature at different r values. (b) Extent of reaction 10 vs. temperature at different r values.

0.6

nH2 O = r − 1 − x9 − x10 ,

0.2 0

x9

nCO2 = 1 + x9 ,

-0.2 -0.4 -0.6 -0.8

The behavior of reaction (10) is equal to that of scheme A, since nCH4 and nH2 O have the same initial values (Fig. 4(b)); WGS reaction behaves quite differently. In this case, the extent of the reaction can be negative, depending on temperature and r values (see Fig. 5), since, initially, nCO =0 and nCO2 = 1. The extent of reaction, as well as in scheme

r4

r7

Temperature (K)

0.4

nT = r + 3 + 2x10 .

r3

r6

400

nCO = 1 − x9 + x10 ,

nCH4 = 1 − x10 ,

r2

r5

(a)

nT = r + 3 + 2x10 .

nH2 = 2 + x9 + 3x10 ,

r1

0

nCH4 = 1 − x10 ,

In Fig. 4(a) and (b), the extent of reactions (9) and (10) vs. temperature and at different r values are presented, respectively. It can be observed that methane steam reforming is thermodynamically possible at T > 700 K for r = 10 and at T > 850 K for r = 1. At T < 700 K the reverse reaction (methanation) is thermodynamically feasible (see Fig. 2(b)). Although the WGS reaction is exothermic, the extent of reaction vs. temperatures presents a maximum. This behavior is owed to the influence of reaction (10), which suddenly increases with temperature. WGS reaction is predominant over methane steam reforming for T > 800 K and r > 5 in agreement with Fishtik [5] who stated that WGS reaction contribution is poor at low temperatures and low r values. In all the ranges analyzed the extent of WGS reaction is always positive (see Fig. 2(a)). Scheme B (CO2 as primary product): Initial molar composition: CH4 :CO2 :H2 = 1:1:2. The reactions considered are the same as in scheme A (reactions (9) and (10)) though in this case the stoichiometric balance is

25

r1

r2

r3

r4

r5

r6

r7

r8

r9

r 10 700

800

-1 400

500

600

900

1000

1100

1200

Temperature (K)

Fig. 5. Effect of temperature and feed ratio on the extent of reaction 9.

V. Mas et al. / International Journal of Hydrogen Energy 31 (2006) 21 – 28

A, is affected by methane steam reforming. At 1 < r < 3 and at all temperatures, x9 < 0, that is, inverse WGS can occur. At r = 4, x9 < 0 except within a small range of T between 800 and 900 K. At r > 5, x9 is positive for a range of temperatures that increases with r. At high T values and at almost all r considered, x9 < 0. From the results obtained with both schemes, the following recommendation can be formulated: if CO is a primary product, the catalyst used in the steam reforming of ethanol should be active for WGS reaction in order to minimize CO formation. On the contrary, if CO2 is a primary product and ethanol steam reforming is carried out in conditions favoring inverse WGS reaction, the catalyst should be inactive for WGS reaction (see Fig. 6). Product distribution: In the equilibrium, product distribution is independent of the scheme used. Mole numbers of H2 , CO and CH4 at equilibrium vs. temperature and at different r values are shown in Figs 7(a) to (c), respectively.

1200 1100 1000

Temperature (K)

26

800 reverse wgs

700 600 500 400 0

2

4

6

8

10

Water to ethanol ratio (mole H2O/mole EtOH)

Fig. 6. Direct and inverse WGS regions.

2

6

5

r1

1.8

r1

r2

1.6

r2

1.4

r3

r3 4

r4

r6 r7

2

r5

nCO

3

r4

1.2

r5

nH2

direct wgs

900

r8

1

r6

0.8

r7

0.6

r8

r9

r9

0.4

r 10

1

r 10 0.2 0

0 400

(a)

500

600

700

800

900

1000

1100

400

1200

500

600

(b)

Temperature (K)

700

800

900

1000

1100

1200

Temperature (K)

1.6

nCH4

1.4

r1

r2

r3

r4

1.2

r5

r6

1.0

r7

r8

r9

r 10

0.8 0.6 0.4 0.2 0.0 400

(c)

600

800

1000

1200

Temperature (K)

Fig. 7. (a) Moles of hydrogen per mole of ethanol fed in the equilibrium at different r values. (b) Moles of carbon monoxide per mole of ethanol fed in the equilibrium at different r values. (c) Moles of methane per mole of ethanol fed in the equilibrium at different r values.

V. Mas et al. / International Journal of Hydrogen Energy 31 (2006) 21 – 28

2CO = CO2 + C,

(11)

CH4 = 2H2 + C,

(12)

CO + H2 = C + H2 O,

(13)

CO2 + 2 H2 = C + 2 H2 O.

(14)

Reaction (11), known as the Boudouard reaction, has the lowest free energy of formation. Then, this reaction is chosen to perform the analysis. Anyway, whatever reaction is used, the results obtained will be the same [22]. In Fig. 3, K11 values vs. temperature are summarized; the exothermic character of this reaction can be appreciated. If coke formation is considered, the total number of compounds at the equilibrium is six and the number of equations needed for the analysis is, therefore, three. Then, reaction 11 must be added to one of the two schemes studied formerly (A or B). If scheme A is chosen, the equations system is CO + H2 O = CO2 + H2 , CH4 + H2 O = CO + 3H2 , 2CO = CO2 + C.

(9) (10)

(11)

1.0 0.5 0.0

x11

-0.5 -1.0 -1.5 -2.0 -2.5 -3.0 400

r1

r2

r3

r4

500

600

700

800

900

1000

1100

1200

Temperature (K)

Fig. 8. Extent of reaction (11) vs. temperature at different r values.

1200 1100 this work

1000

Temperature (K)

The results obtained are similar to those reported previously by other authors [1,2,19]. High temperatures and r values favor hydrogen production; the tendency of methane is exactly the opposite of that of hydrogen. In order to minimize CO formation, low temperatures and high r are suitable. Coke formation: It is known that acetaldehyde and ethylene are promoters of coke formation [6]. In order to analyze coke formation from a thermodynamic point of view it is assumed that carbon formed is elemental, in the graphitic form, hence, free energy of carbon formation (
Gf ) is 0 and vapor pressure is 0 in the range of temperatures analyzed. Possible reactions of coke formation are

27

No carbon region

900 800 700 600

Carbon region

500

García and Laborde

400 0

1

2

3

4

5

6

7

8

9

10

Water to ethanol ratio (mole H2O/mole EtOH)

Fig. 9. Range of conditions for carbon formation.

And the stoichiometric balance is nCO = 1 − x9 + x10 − 2x11 , nH2 O = r − x9 − x10 , nCO2 = x9 + x11 , nH2 = 1 + x9 + 3x10 , nCH4 = 1 − x10 , nT = r + 3 + 2x10 − x11 , nC = x11 . The extent of reaction (11) vs. temperature at different r values, is presented in Fig. 8. It can be seen that the possibility of coke formation is higher if the r value is lower. For

r = 1 this possibility exists for this entire temperature range. When r = 4 coke formation is possible only for T < 450 K. The operation region where coke can be formed, compared to the region presented in the original work of García and Laborde [1], is shown in Fig. 9. It must be noted that in [1] this region was estimated considering a homogeneous system. An objection to this procedure was made by Vasudeva [2]. It is clearly observed that if r = 1 coke formation is likely to occur at all temperatures considered. In order to work in the region free of coke formation, at r = 2, the temperature must be higher than 900 K and at r = 3, temperatures higher than 500 K are suitable. If the ethanol steam reforming reactor is to work in the region where coke formation is thermodynamically feasible, the use of acid catalysts should be avoided.

28

V. Mas et al. / International Journal of Hydrogen Energy 31 (2006) 21 – 28

5. Conclusions The thermodynamics analysis performed in this work agrees with previous experimental results where acetaldehyde and ethylene behave as intermediate compounds in ethanol steam reforming. Ethanol is completely converted into ethylene and/or acetaldehyde; besides, the dehydration reaction is thermodynamically favored. The two scenarios analyzed lead to suggest different routes for reaching the equilibrium. Thus, the results obtained in this work might help to interpret the experimental results far away from the equilibrium with the aim to elucidate the reaction mechanism. The knowledge of this mechanism is essential in order to minimize the CO formation. The thermodynamic feasibility of coke formation shown in a T vs. water ethanol molar ratio has been also analyzed. The results indicate that if moderate temperatures are used, a molar ratio higher than 3 is required to avoid coke formation. Nevertheless, the energetic balance of the entire device including the fuel cell is disfavored by high r values. Then, the efforts must be addressed at developing an adequate catalyst that inhibits coke formation and CO production working at r values as low as possible.

Acknowledgements Authors would like to acknowledge to the University of Buenos Aires and to the ANPCYT for financial support.

References [1] Garcia EY, Laborde MA. Hydrogen production by the steam reforming of ethanol: thermodynamic analysis. Int J Hydrogen Energy 1991;16(5):307–12. [2] Vasudeva K, Mitra N, Umasankar P, Dhingra SC. Steam reforming of ethanol for hydrogen production: thermodynamic analysis. Int J Hydrogen Energy 1996;21(1):13–8. [3] Guimarães da Jr SW, Franco Jr MR, Soares RR. Analise Termodinámica da Produção de Hidrogênio para Células Combustíveis Via (Etanol+Água+Ar). Proceedings 11◦ Congresso Brasileiro de Catálise e 1◦ Congresso de Catalise no Mercosul, vol. 2. 2001, p. 1067–1071. [4] Cheng Y-L, Chen L-D, Seaba JP. Thermodynamic analysis of fuel processing, SAE Paper No. 1999-01-0538. In: Stobart R, Seaba JP, editors. SAE SP-1425, Fuel Cell for Transportation. SAE, 1999. [5] Fishtik I, Alexander A, Datta R, Geana D. A thermodynamic analysis of hydrogen production by steam reforming of ethanol via response reactions. Int J Hydrogen Energy 2000;25: 31–45.

[6] Maggio G, Freni S, Cavallaro S. Light alcohols/methane fuelled molten carbonate fuel cells: a comparative study. J Power Sources 1998;74:17–23. [7] Ioannides T. Thermodynamic analysis of ethanol processors for fuel cell applications. J Power Sources 2001;92:17–25. [8] Douvartzides SL, Coutelieris FA, Tsiakaras PE. On the systematic optimization of ethanol fed SOFC-based electricity generating systems in terms of energy and exergy. J Power Sources 2003;114:203–12. [9] Iwasa N, Takezawa N. Reforming of ethanol—dehydrogenation to ethyl acetate and steam reforming to acetic acid over copper-based catalysts. Bull Chem Soc Jpn 1991;64: 2619–23. [10] Mariño FJ, Cerrella EG, Duhalde S, Jobbagy M, Laborde M. Hydrogen from steam reforming of ethanol. Characterization and performance of copper-nickel supported catalysts. Int J Hydrogen Energy 1998;23(12):1095–101. [11] Mariño FJ, Boveri M, Baronetti G, Laborde M. Hydrogen production from steam reforming of bioethanol using Cu/Ni/K/-Al2 O3 . Effect of Ni. Int J Hydrogen Energy 2001;26(7):665–8. [12] Mariño FJ, Baronetti G, Jobbagy M, Laborde M. Cu/Ni/K/Al2 O3 supported catalysts for ethanol steam reforming. Formation of hydrotalcite-type compounds as a result of metal-support interaction. Appl Catal A: General 2002;6043: 1–14. [13] Mas V. Ethanol steam reforming. Graduated thesis, School of Engineering, University of Buenos Aires, 2002. [14] Freni S, Mondello N, Cavallaro S, Cacciola G, Parmon VN, Sobyanin VA. Hydrogen production by steam reforming of ethanol: a two step process. React Kinet Catal Lett 2000;71(1):143–52. [15] Cavallaro S. Ethanol steam reforming on Rh/Al2 O3 catalysts. Energy Fuels 2000;14:1195–9. [16] Galvita VV, Semin GL, Belyaev VD, Semikolenov VA, Tsiakaras P, Sobyanin VA. Synthesis gas production by steam reforming of ethanol. Appl Catal A: General 2001;220: 123–7. [17] Fierro V, Klouz V, Akdim O, Mirodatos C. Oxidative reforming of biomass derived ethanol for hydrogen production in fuel cell applications. Catal Today 2002;2709:1–4. [18] Klouz V, Fierro V, Denton P, Katz H, Lisse JP, Bouvot-Mauduit S, Mirodatos C. Ethanol reforming for hydrogen production in a hybrid electric vehicle: process optimization. J Power Sources 2001;4549:1–9. [19] Comas J, Mariño F, Laborde M, Amadeo N. Bio-ethanol steam reforming on Ni/Al2 O3 catalyst. Chem Eng J 2004;98:61–8. [20] Fatsikostas AN, Verykios XE. Reaction network of steam reforming of ethanol over Ni-based catalysts. J Catal 2004;225:439–52. [21] Auprêtre F, Descorme C, Duprez D. Bio-ethanol catalytic steam reforming over supported metal catalysts. Catal Commun 2002;3:263–7. [22] Kipreos R. Ethanol/water system. Thermodynamics Analysis. Graduated thesis, School of Engineering, University of Buenos Aires, 2003.