Reforming of ethanol

Garcia, E. Y. Laborde, M. A., Hydrogen production by the steam reforming of ethanol Thermodynamic analysis. International Journal of Hydrogen Energy 1991,16(5), 307-312. 

Vasudeva, K. Mitra, N. Umasankar, P. Dhingra, S. C., Steam reforming of ethanol for hydrogen production. International Journal of Hydrogen Energy 1996,21(1), 13-18. 

Fishtik, I. Alexander, A. Datta, R. Geana, D., A thermodynamic analysis of hydrogen production by steam reforming of ethanol via response reactions. International Journal of Hydrogen Energy 2000,25, 31-45. 

Oxidative Steam Reforming (OSR) / Autothermal Reforming of Ethanol... 

Table 1 Non-noble metal-based catalysts employed in the steam reforming of ethanol (SRE) for hydrogen production... 

Thus, the thermodynamic analysis suggests that the steam reforming of ethanol into H2 and C02 is thermodynamically feasible above 200 °C. A mixture of H2, C02, CO and CH4 will be produced at lower temperatures, below 400 °C. The CH4 formed will be subsequently reformed into syngas at higher temperatures, above 650 °C. 

Fig. 7 Thermodynamic equilibrium compositions on dry basis for the steam reforming of ethanol. All species are in gas phase. Initial concentrations of CO, CH4, CH3CHO are taken as zero in the calculation.

Table 4 Selected best performing catalysts for the middle-, and high-temperature steam reforming of ethanol (SRE) reaction"...

Table 5 Kinetic data of the steam reforming of ethanol over various supported Ni catalysts...

Oxidative steam reforming/autothermal reforming of ethanol... 

Fig. 11 Free energy changes in the oxidative steam reforming/autothermal reforming of ethanol, acetaldehyde and methane.

The catalysts for low-temperature and high-temperature reforming of ethanol under OSR/autothermal conditions are listed in Tables 8 and 9, respectively. In the absence of added 02, each mole of ethanol converted should produce 6 moles of H2 and 2 moles of C02, which corresponds to an exit H2 composition of 75%. Depending upon the 02/EtOH ratio used in the OSRE reaction, the composition of H2 will vary between 50% for 02/EtOH ratio of 1.5 and H20/EtOH ratio of 0, and 75% for 02/EtOH ratio of 0 and H20/EtOH ratio of 3. 

Kinetics. Being a relatively new approach for the production of H2 from ethanol, work on the kinetics of the OSR/autothermal reforming of ethanol has been very limited in the literature. Kinetic studies would be very helpful to understand the rate determining step and activation energies of this complex reaction. 

Table 7 References on oxidative steam reforming (OSR) and autothermal reforming of ethanol for hydrogen production... 

Scheme 6 Proposed reaction pathway for the oxidative steam reforming/ autothermal reforming of ethanol. The dehydration into ethylene intermediate followed by ethylene reforming are not shown. 

Among three different reforming processes discussed above, the steam reforming of ethanol yields more H2 in the reformate, 6 moles per mole of ethanol converted because the process extracts about 3 moles of H2 from water. This makes the process more attractive in terms of power generation via fuel cells. Assuming only 60% efficiency of a fuel cell, an useful electrical work output of about 12 828 kJ could be obtained from 1 liter of ethanol via steam reforming, which is about 3 times higher... 

Fig. 14 Mechanistic model for the carbon scavenging activity of stable Ni/La203 catalyst employed in the steam reforming of ethanol for H2 production.67...

This review analyzed the chemistry involved, thermodynamics, catalysts used, reaction pathways and mechanisms of various reforming techniques reported for the conversion of ethanol into H2-rich gas. The known reforming processes are broadly classified into three categories, namely steam reforming of ethanol (SRE), partial oxidation of ethanol (POE) and oxidative steam reforming (OSR)/autothermal reforming of ethanol. All these reactions are thermodynamically favorable even at lower temperatures, above 200 °C. 

Most of the work on ethanol reforming to date focused mainly on catalyst development, optimization of reaction operations and thermodynamic analyses. However, detailed kinetic studies, which are very useful to understand the activity at the molecular level and to build a suitable catalytic reactor on an industrial scale for the reforming of ethanol need to be pursued. 

Steam Reforming of Ethanol Even though all the samples containing 20 wt.% or above of Ni exhibited similar activity and selectivity (Table 11.6), their stability over a 500 h duration run varied sample 6A, with 40% Ni and a Ce02/Zr02 ratio of 1 was the most stable. The Ce/Zr ratio has a marked effect on the catalytic stability of these materials. 

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