Hydrogen-enhanced catalytic hydrothermal gasification of biomass

The impact of hydrogen co-feeding on the catalytic hydrothermal gasification of wet biomass was explored in a continuous test rig using a feed of 10 wt% glycerol in water and a fixed bed of a carbon-supported ruthenium catalyst. The reactor was operated at a nominal temperature of 400 °C and at pressures of 26–28 MPa. Variation of the hydrogen-to-glycerol ratio as well as of the total pressure showed clearly the methanation reaction to be promoted at the expense of carbon dioxide and hydrogen formation. This is explained by a higher hydrogen surface coverage and consecutively higher rates for hydrogenation of surface-bound carbon. An increase in peak temperature of ca. 75 K occurred in the catalytic fixed-bed when co-feeding hydrogen. The measured product gas composition was close to the thermodynamic equilibrium calculated at the outlet temperature of the reactor. A maximum methane concentration of 86 vol% in the raw gas was obtained at 28 MPa with a stoichiometric addition of hydrogen. Full catalytic activity was maintained during and after the hydrogen co-feeding experiments, verified by comparing the performance of a run with a 10 wt% glycerol in water feed after co-feeding hydrogen, for which the product distribution was very close to the experiments before hydrogen co-feeding.