Hydrogen Formation from Biomass Model Compounds and Real Biomass by Partial Oxidation in High Temperature High Pressure Water

Abstract

Model compounds (glucose and glycerol) and real biomass (sugarcane bagasse and Chlorococcum littorale) were partially oxidized to hydrogen in high temperature high pressure water (120-300 °C at saturated pressure of water). Biomass conversion into gas directly by partial oxidation in a one-pot process was considered by use of a catalyst in a batch type reactor. The total gas yield and hydrogen selectivity from all the reactants were low. To improve the gasification efficiency, a two-step process was proposed: partial oxidation of the organic compound into hydrogen precursor (here formic acid) followed by selective decomposition of the intermediate into hydrogen. To clarify the possibility of the process, model compounds (glycerol and glucose) were used. The effects of operation parameters for each step (temperature, water to organic ratio, oxygen to organic ratio, catalyst) were investigated using a batch reactor. For glycerol oxidation at lower temperature (120-160 °C), kinetic analysis was performed to clarify the reaction mechanism and formic acid formation. For formic acid decomposition into hydrogen, several metal oxides were carried out to accelerate the reaction rate, and ZnO was found to be effective at 300 °C. The yield of hydrogen from the combination of formic acid formation from glucose and hydrogen formation from the oxidized material including formic acid was investigated using a flow apparatus. However, the yield of hydrogen was lower than expected and further improvement of the two-step reaction process is required.