Process optimisation and scale-up of biocrude oil production through catalytic hydrothermal liquefaction utilising Chlorella minutissima biomass

In response to the growing global demand for sustainable energy, this study investigates the optimisation and scale-up of biocrude oil production from Chlorella minutissima biomass using catalytic hydrothermal liquefaction (HTL). A preliminary evaluation in a 2-L reactor was conducted to determine the efficiency of various solvents in extracting biocrude oil. The results revealed dichloromethane exhibiting the maximum yield and energy recovery of 40.2 wt% and 71.4 %, respectively, compared to acetone, acetonitrile, hexane and diethyl ether. Later, the effect of biomass load, pH, and catalyst concentration on biocrude oil yield was examined and optimised using response surface methodology. The optimum biocrude yield of 47 wt% was observed at process conditions of 39.2 % w/v biomass load, pH 3.6, and 1.4 M catalyst concentration. These conditions were successfully applied during scale-up in a 10-L HTL reactor, maintaining consistent yields. Comprehensive analysis of the biocrude oil using FTIR, thermogravimetric, and GC-MS techniques confirmed the presence of alkyl, carbonyl, and aromatic groups, ∼90 % volatile fractions, as well as fatty acid methyl esters, alkanes, alcohols, and acetates. This study highlights the importance of reaction optimisation, solvent selection, and by-product valorisation for advancing industrial-scale biofuel production and supporting energy sustainability.