Hydrogen production by biomass gasification in supercritical or subcritical water with Raney-Ni and other catalysts

Abstract

Gasification of peanut shell, sawdust and straw in supercritical or subcritical water has been studied in a batch reactor with the presence of a series of Raney-Ni and its mixture with ZnCl2 or Ca(OH)2. The main gas products were hydrogen, methane, carbon dioxide, and a small amount of carbon monoxide. Different types of Raney-Ni, containing different metal components such as Fe, Mo or Cr, have different influences on the gasification yield and hydrogen selectivity. The catalysis effect can be improved obviously by adding ZnCl2 or Ca(OH)2. Increasing the reaction temperature or adding ZnCl2 and Ca(OH)2 could improve the mass of H2 in gas products and reduce the mass of CH4 and CO2 at the same time. The possible mechanism is that ZnCl2 can decompose the biomass particle by accelerating cellulose hydrolyzation in high-temperature water, increasing more specific surface to admit catalysts, while Ca(OH)2 can absorb CO2 to produce CaCO3 deposit, which can drop out from the reactant system, and which will drive the reaction to get more hydrogen. With respect to the biomass conversion to gas product and selectivity of H2 at low temperature, the series of Raney-Ni has shown many advantages over other catalysts; thus, this kind of catalyst has great potential to be utilized in the hydrogen industry for the gasification of biomass.