Hydrothermal liquefaction of municipal sewage sludge: Effect of red mud catalyst in ethylene and inert ambiences

Abstract In this study, ethylene and nitrogen(inert) reaction environments were applied into the hydrothermal liquefaction (HTL) process of municipal sewage sludge with red mud catalyst to evaluate the effects on biocrude and other byproducts. Red mud in three oxidation states was used: red mud calcined at 575 °C (CRM), reduced at 500 °C (RRM500), and 700 °C (RRM700). The RRM500 lowered the acidity by 14%; whereas, the RRM700 minimized the viscosity by 47% comparing to non-catalytic-inert biocrude samples. The ethylene ambience successfully maximized the biocrude yield by 41.6 wt% without any catalyst. The viscosity of the biocrudes produced under ethylene environment showed lower differences compared to nitrogen environment. The RRM500-ethylene reaction efficiently reduced the nitrogen content in the biocrude by 14%. These results suggested that the ethylene atmosphere has the potential for improved biocrude production during catalytic HTL treatment.