Hydrothermal liquefaction of municipal sludge in sub- and super- critical water

Abstract

Hydrothermal liquefaction of municipal sludge was conducted to investigate the effects of sub- and supercritical water and of the fluid dynamic regime on the quality of the products. Preliminary experimental runs were performed at two different temperatures (350°C and 400°C) changing reaction time in order to work at fixed kinetic severity of the process. An improvement of the C content in the solid residues and of the ratio H/C of the biocrude was obtained when a stirred reactor was used both in sub- and supercritical water. A hydrocarbon fraction was separated from biocrude whose maximum yield of 25% w/w was achieved in supercritical conditions. Results showed that the cumulative energy recovery of the products was significantly higher than 100% suggesting that hydrothermal liquefaction of municipal sludge could be fed by renewable source of thermal energy. Experimental trials of HTL of municipal sludge (MS) in stirred reactors were then performed at the lower investigated reaction temperature of 325°C to study the effect of CoMo/Al2 O3, NiMo/Al2 O3 and activated carbon felt as heterogeneous catalysts.