Catalytic hydrothermal liquefaction of sewage sludge: Effect of metal support heterogeneous catalysts on products distribution

Abstract

Industrial wastes and natural mixed oxide materials were evaluated as inexpensive heterogeneous catalysts supports for catalytic hydrothermal liquefaction (HTL) of biomass. In this study, Palygorskite (ATP) clay, a hydrated magnesium aluminosilicate clay mineral supported metal catalysts (Co, Mo and Co–Mo/ATP) and Al2O3 supported (Co, Mo, Co–Mo/Al2O3) catalysts were examined for the sewage sludge (SS) hydrothermal liquefaction (HTL). The highest biocrude yield of 34.2 wt% was obtained with Co–Mo/ATP bimetal catalyst. Biocrude characterization revealed that significantly different families of molecules were formed in the presence and absence of catalysts, implying that the main role of the catalyst is to promote rates of thermal reactions, leading to biocrude production. The improved catalytic HTL performance with Co–Mo metal catalyst as attributed to the synergistic effects of both metal sites present on catalyst surfaces. The main components of bio-oil were phenols, N-containing compounds and hydrocarbons, and the increased selectivity to hydrocarbons with Co–Mo/ATP was observed. Maximum yield of aromatic hydrocarbon (20% observed in case of HTL with metal supported ATP catalyst. presence of Co–Mo metal catalysts promoted the deoxygenating by reduction of oxygen in the form of carbon dioxide or water. The distribution of biocrude samples indicates that most compounds in biocrude were light-weighted and had low boiling points. There were more light-weight compounds in biocrude by adding catalyst.