Catalytic hydrothermal liquefaction of Chlorella sorokiniana for high quality biocrude production over Mg modified activated red mud catalyst

The growing demand for renewable fuels has positioned microalgae as a promising feedstock due to its high productivity, non-edible nature, and favourable biochemical profile. In this study, Chlorella sorokiniana (CS) biomass comprising 41.34 wt% protein, 33.07 wt% carbohydrate, and 22.00 wt% lipid was selected for catalytic hydrothermal liquefaction (HTL) to produce energy-dense biocrude. A low-cost industrial residue, red mud (RM), was activated (ARM) and doped with Mg (1–5 wt%) to prepare a series of catalysts (1,3,5 Mg/ARM) using a deposition–precipitation method. HTL experiments were conducted in a batch reactor under varying conditions, including reaction temperature of 275–350 °C, reaction time of 15–60 min, and catalyst loadings of 5–15 wt%. Under the optimized condition, 10 wt% of 3-Mg/ARM catalyst at 325 ºC and 45 min exhibited the best performance, achieving 43.31 wt% biocrude yield. Product characterization by CHNS, FTIR, and GC–MS revealed superiority of the catalyst in enhancing the quality of biocrude by reducing N and O content by 36.22 % and 13.30 % respectively, with a significant enhancement in hydrocarbon content (23.15 %). These results indicated effective deoxygenation and denitrogenation, enhancing the fuel quality of the resulting bio-crude. This study demonstrated the potential of Mg-modified RM as a low-cost and efficient catalyst for sustainable algal biofuel production.