Low-temperature and Low-pressure HydroThermal Liquefaction (L-HTL) of biomass using ultrasonic cavitation to achieve a local supercritical state in water

Abstract

HydroThermal Liquefaction (HTL) is a process that involves the reaction of polymer compounds such as cellulose, lignin, synthetic plastics, etc. with near-critical or supercritical water to form low molecular weight liquid compounds, similar to natural oil which is believed to have formed over millions of years. Compared to other biomass recovery methods such as pyrolysis or anaerobic digestion, HTL is highly efficient with an energy efficiency of up to 90%, while the others have an efficiency of only around 30%. However, traditional HTL requires extremely high temperatures (250–450 °C) and pressures (100–350 bar), which are challenging to achieve using large-scale industrial equipment. This study proposes the use of ultrasonic cavitation to induce a supercritical state in water locally, rather than throughout the entire reactor, making it possible to perform HTL reactions using inexpensive and simple devices. The study demonstrates the successful conversion of pure cellulose to low molecular weight liquid compounds using potassium hydroxide as a catalyst.