Solid base catalytic hydrothermal liquefaction of macroalgae: Effects of process parameter on product yield and characterization.

The hydrothermal liquefaction (HTL) of Sargassum tenerrimum (ST) macroalgae was carried out for 15 min, over various solid base catalysts (CaO supported on CeO, AlO, and ZrO) at different reaction temperatures (260-300 °C), different catalyst quantities (5-25 wt%) and using different solvent systems. Maximum bio-oil (BO) yields for the non-catalytic HTL with single solvent water, ethanol, and water-ethanol co-solvent were 3.3 wt%, 23.3 wt%, and 32.0 wt%, respectively, at 280 °C. Ethanol as single solvent elicited highest BO yield of 25.2 wt% with CaO/ZrO (10.0 wt%) catalyst. However, the highest BO yield (33.0 wt%) accompanied by higher conversion (70.5%) was obtained with CaO/ZrO (10.0 wt%) under water-ethanol co-solvent. The selectively higher percentage of ester functional compounds (87.8%) was found with CaO/ZrO catalyst under water-ethanol co-solvent. Also, the bio-oil obtained from catalytic liquefaction showed a higher high heating value (HHV) compared to that from the non-catalytic HTL reaction.