Effect of operating conditions on hydrothermal liquefaction of kitchen waste with ethanol-water as a co-solvent for bio-oil production

Hydrothermal liquefaction (HTL) can directly convert kitchen waste (KW) to bio-oil without pre-drying. This study investigated the effect of operating temperatures (240–280 °C), solvent (ethanol, water and ethanol-water co-solvent) on bio-oil production during HTL of KW. The bio-oil was characterized, including composition, boiling point and viscosity. By comparison, higher reaction temperature and ethanol concentration in co-solvent could effectively increase the yield and quality of bio-oil, which implies the promotion of liquefaction efficiency. The highest bio-oil yield of 47.59%, conversion ratio of 72.65%, and high heating value (HHV) of 31.93 MJ/kg were obtained at the ethanol concentration of 62.5% in co-solvent and reaction temperature of 260 °C. Compared to the hydrothermal liquefaction of KW in water, the reaction in ethanol-water co-solvent produced higher energy yield. Moreover, the addition of ethanol in co-solvent could increase the concentration of ester compounds and reduce the viscosity of bio-oil.