Effects of aqueous phase circulation and catalysts on hydrothermal liquefaction (HTL) of penicillin residue (PR): Characteristics of the aqueous phase, solid residue and bio oil.

Abstract Hydrothermal liquefaction (HTL) is a promising thermochemical technology for the treatment of hazardous wastes such as penicillin residue (PR). For the treatment of aqueous waste produced by PR in the HTL process, aqueous phase circulation is an attractive solution, both environmentally and economically. The present study shows that aqueous phase circulation can promote the transfer of organic matter from the aqueous phase to bio–oil. The content of organic acids and alcohols in the aqueous phase decreased significantly, and the bio–oil yield and energy recovery efficiency also increased. Under non–catalytic conditions, the bio–oil yield increased from 26.09 wt.% to 33.72 wt.%. The use of Na2CO3 as a catalyst further improved the bio–oil yield. After a single aqueous phase circulation, the bio–oil yield increased to 34.63 wt.%, and the energy recovery efficiency increased to 66.94%. Under catalytic hydrothermal conditions, the content of organic acids in the bio–oil was reduced using aqueous phase circulations, which improved the quality of the bio–oil. At the same time, the Na2CO3 catalyst promoted the hydrolysis of PR to form small molecule organic matter, inhibited the formation of coke, and reduced the content of carbon, hydrogen and oxygen in the solid residue. An increase of cycle times led to excessive accumulation of Na2CO3, which had a negative impact on the yield of bio–oil. Nitrogen–containing compounds in the bio–oil increased to a certain extent, which renders it necessary to consider denitrification treatments in the future. The work provides a useful reference for further research on the preparation of high quality bio–oil by PR hydrothermal liquefaction.