Study on hydrothermal liquefaction of antibiotic residues for bio-oil in ethanol-water system

Abstract

In this study, antibiotic residue was converted into bio-oil by hydrothermal liquefaction (HTL) in subcritical or supercritical ethanol/water system. The bio-oil yield increased firstly as the ethanol/water ratio < 1:1, reaction temperature < 280 °C, residence time < 150 min, and thereafter decreased. However, the bio-oil yield continuously decreased with a plunge at 15% as the solid/liquid ratio increased. The change tendency of O/C, H/C and N/C of bio-oil indicated different reaction mechanism of HTL. The addition of ethanol significantly promoted the esterification reaction, leading to increase of aliphatics content of bio-oil, especially branched long-chain aliphatics. Comprehensively considering the bio-oil yield, production cost, higher heating value (HHV) and chemical composition, the optimal process parameters of HTL were obtained as follows: ethanol/water ratio of 1:1, reaction temperature of 280 °C, residence time of 150 min, and solid/liquid ratio of 15%, under which the bio-oil yield was 33.29 wt%, HHV was 33.47 MJ/kg, and the main compositions of bio-oil were esters (>48%).