Hydrogen production via catalytic gasification of ethanol

V. MAS, P. GIUNTA, G. BARONETTI, N. AMADEO, M. LABORDE

Porto de Galinhas, Brasil

Congreso; XIV Congreso Brasileño de Catálisis; 2007

The clean and non-contaminating characteristics of H2 as a fuel will depend on the process, the raw material and the source of energy employed for its production. If it is obtained from fossil hydrocarbons, carbon dioxide is released to the atmosphere, regardless of the technology used; instead, if biomass is used instead of hydrocarbons, carbon dioxide is also released, but in this case the plant consumes the carbon dioxide produced during its growth. Ethanol presents several advantages related to natural availability, storage and handling safety. It can be produced renewably from several biomass sources, including energy plants, waste materials from agro industries or forestry residue materials, organic fraction of municipal solid waste, etc. Besides the bioethanol-to-hydrogen system has the significant advantage of being nearly CO2 neutral, since the carbon dioxide produced is consumed for biomass growth, thus offering a nearly closed carbon cycle. In summary, among the various processes and primary fuels that have been proposed in the production of hydrogen for fuel cell applications, steam reforming of ethanol is the most attractive. The ethanol steam reforming (ESR) process using a Ni(II) Al(III) lamellar double hydroxide (LDH) as catalyst precursor is presented. Ni/Al precursor is synthesized by means of homogeneous precipitation by urea. The use of Ni(II)Al(III) lamellar double-hydroxides (LDHs), allows to reach an intimate mixture of cations in a crystalline structure and turns them into excellent precursors to obtain mixed oxides in a wide range of composition. Hence, its thermal decomposition leads to oxide amorphous crystalline phases which after being subjected to a posterior reduction are transformed into dispersed metallic phases in an oxidic matrix. The ESR kinetic using the same catalyst is discussed. Experimental data were obtained employing a laboratory fixed bed reactor. The H2 yield for ethanol steam reforming using the reduced LDH sample reached values of 5 mol of H2 per mol of ethanol in the feed. The other products obtained during steady state conditions operating between 823 and 923 K, were CO, CO2 and CH4. It was verified that, for each reaction temperature, there was a water/ethanol molar ratio at which ethanol conversion had a maximum. It means that a competition between both reactants adsorbed on the same active sites was verified. There was experimental evidence that both, CO and CO2, are produced from ethanol steam reforming. A simulation of a fixed bed reactor for ESR is presented. The one-dimensional heterogeneous model was used in this simulation, and a parametric sensitivity analysis was performed for some of the process variables, with the purpose of finding criteria to minimize the reactor volume. Temperature and reaction rate profiles obtained indicate that the system is heat transfer-controlled. Low values of effectiveness factors suggest that small or shell - type pellets are recommended, provided that the pressure drop is not too high.