Hydrothermal catalytic gasification of fermentation residues from a biogas plant

► Fermentation residue of a biogas plant could be successfully liquefied with a low rate of coke formation. ► Liquefaction resulted in an incomplete removal of biomass-bound sulfur. ► Low catalyst loadings result in incomplete conversion, implicating catalyst deactivation. ► At 400 °C the observed conversion to methane was highest. ► A residence time dependent biomass to catalyst ratio of 0.45 g g−1 h−1 was determined to yield nearly complete conversion.