Oxidation steam reforming

Separation, combustion, pyrolysis, hydrogena-tion, anaerobic fermen-tation, aerobic fermen-tation, biophotolysis, partial oxidation, steam reforming, chemical hy-drolysis, enzyme hydrol-ysis, other chemical conversions, natural processes... 

H2 production from ethanol (as well as methanol) employs these methodologies either as such or after slight modifications, especially in the ATR process, wherein a separate combustion zone is usually not present (Scheme 3). A mixture of ethanol, steam and 02 with an appropriate ethanol steam 02 ratio directly enters on the catalyst bed to produce syngas at higher temperature, around 700 °C.18,22 The authors of this review believe that under the experimental conditions employed, both steam reforming and partial oxidation could occur on the same catalyst surface exchanging heats between them to produce H2 and carbon oxides. The amount of 02 may be different from what is required to achieve the thermally neutral operation. Consequently the reaction has been referred to as an oxidative steam reforming... 

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

Oxidative steam reforming/autothermal reforming of ethanol... 

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

Fig. 12 Thermodynamic equilibrium compositions on dry basis for the oxidative steam reforming of ethanol. All species are in gas phase. Initial concentrations of CO, CH4, CH3CHO are taken as zero in the calculation.

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

Table 8 Selected best performing catalysts for the low-temperature oxidative steam reforming (OSR) of ethanol... 

Table 10 Steam reforming and oxidative steam reforming of acetaldehyde over Ni-Rh/Ce02 catalyst25...

Reaction conditions temperature 350 °C GHSV = 24 379 h H20/CH3CH0 = 4 in steam reforming while in oxidative steam reforming, H2Q/CH3CHO = 4 and Q2/CH3CHO = 0.4. 

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. 

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. 

S. Velu, K. Suzuki, M. Okazaki, M. P. K oor, T. Osaki, andF. Ohashi, Oxidative steam reforming of methanol over CuZnAl(Zr)-oxide catalysts for flie selective production of hydrogen for fuel cells Catalyst characterization and performance evaluation, J. Catal. 194,373 (2000). 

Compared vdth partial oxidation, steam reforming has received more attention due to its relatively higher conversion efficiency [155]. 

Total oxidation Partial oxidation Steam reforming... 

Feasibility Study for Combined Methane Oxidation/Steam Reforming in an Integrated Heat Exchanger... 

Interesting aspects of autothermal reactor operation arise if an endothermic synthesis reaction is coupled with an exothermic reaction in such a way that the combination is weakly exothermic An example has been given by Amoco for the oxidative steam reforming of methane [48] The application to styrene synthesis has so far been limited to simulation studies (see [49] and references therein)... 

Velu S, Suzuki K. Selective production of hydrogen for fuel cells via oxidative steam reforming of methanol over CuZnAl oxide catalysts effect of substitution of zirconium and cerium on the catalytic performance. Top Catal. 2003 22(3-4) 235-44. 

Turco M, et al. Production of hydrogen from oxidative steam reforming of methanol -I. Preparation and characterization of Cu/ZnO/Al2C>3 catalysts from a hydrotalcite-like LDH precursor. J Catal. 2004 228(l) 43-55. 

As discussed above in the reforming of hydrocarbon fuels, H2 can be produced from alcohol fuels by at least three major catalytic processes, namely steam reforming, partial oxidation and ATR or oxidative steam reforming. The chemistry, thermodynamics, and recent developments in catalysis of methanol and ethanol reforming with steam for H2 production will be discussed in this section. 

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