Sub-supercritical liquefaction of municipal wet sewage sludge to produce bio-oil: Effect of different organic-water mixed solvents

The effect of different mixed solvents (methanol-water (MeOH-H2O), n-hexane-water (HEX-H2O)) on liquefaction of municipal wet sewage sludge (WSS) was investigated in this study. The highest bio-oil yield of 46.5 wt % was achieved in MeOH-H2O, of which ester content was 38.1% and methyl ester comprised 37.4%. The lowest solid residue yield of 10.3 wt% was achieved in HEX-H2O. The highest fatty acid compounds content was 54.9% of bio-oil obtained in HEX-H2O, of which were in saturated state. The highest calorific value and the lowest oxygen content of bio-oil were achieved in HEX-H2O: 36.45 +/- 0.38 MJ/kg and 7.65 0.26 wt%, respectively. The thermal stability of solid residue was enhanced in HEX-H2O. The formation of esters was promoted in MeOH-H2O, whereas aliphatic compounds could be efficiently extracted in HEX-H2O.