Influence of process conditions on hydrothermal liquefaction of eucalyptus biomass for biocrude production and investigation of the inorganics distribution

In the present study, eucalyptus biomass was processed to produce biocrude via hydrothermal liquefaction (HTL) process. The effect of process conditions (temperature, alkali catalyst, etc.) was initially investigated. The maximum biocrude yield (35.78%, daf) was achieved under subcritical condition (350 °C-catalyst) and a comparatively lower yield under supercritical conditions. The effect of retention time on the product yield, organic compounds composition, and distribution of inorganic elements was explored. HTL experiments were conducted at different retention times (5, 10, 15, 20, and 25 min) under optimum condition (350 °C-catalyst) to analyze the process efficiency. For the obtained biocrudes, the results show clear trends of changing the content of different functional groups with a change in retention time. Overall, the majority of inorganics and heavy metal contents were found to migrate to the solid phase, which conformed with the ICP results. It was concluded from this study that catalytic subcritical liquefaction at 15 min retention time is a favorable condition for biofuel production and nutrients recovery.