Multi-stage extraction process to produce enhanced biocrude from solid waste liquefaction

This study explores the effects of hydrothermal liquefaction temperature and multi-stage extraction method on product quality, yield, and underlying reaction mechanisms using organic solid waste feedstock. Hydrothermal liquefaction experiments are conducted at five temperatures ranging from 250 to 350 °C, and product compositions are characterised using thermogravimetric analysis, gas chromatography-mass spectrometry, and elemental analysis. The results demonstrate that the highest biocrude yield of 30–32 % is achieved within the 300–350 °C range, while multi-stage extraction produced biocrude with a higher heating value of 40–43.7 MJ/kg. The multi-stage extraction method enhances the quality of biocrude by separating most of the nitrogen and oxygen heterocyclic compounds and producing biocrude containing 67–70 % lighter fraction. The Hydrothermal liquefaction temperature of 350 °C promotes decarboxylation and deoxygenation reactions, resulting in lower amounts of carboxylic acids in biocrude, which are suitable for fuel applications. The energy feasibility of the extraction is evaluated by a high energy recovery of 70.4 % with a low energy consumption ratio of 0.26, demonstrating the process's net energy gain and sustainability. • Multi-stage extraction removed N & O heterocyclic compounds from biocrude. • A maximum biocrude yield of around 35 % was observed. • Organic acids contributed to the major chemical composition of biocrude. • Highest energy value of 43.7 MJ/kg with 70 % energy recovery was observed.