Supercritical water gasification of biocrude oil from low-temperature liquefaction of algal lipid extraction residue

Abstract The lipid extraction followed by transesterification is the conventional approach for producing liquid bio-fuels from algae, during which protein and carbohydrates in algae are treated as a waste. In this study, the remaining solid after lipid extraction from algae was applied as the feedstock to produce biocrude oil by low-temperature liquefaction. Catalytic liquefaction of lipid extraction by-product was performed at 200–250 °C for 60 min, and compared to commonly used feedstocks (i.e., agricultural and forestry residues). The biocrude oil yield from lipid by-product was 65.4–78.5 wt% and higher than that from rubberwood sawdust (48.8–59.9 wt%) or bamboo sawdust (47.9–63.7 wt%). Besides, the biocrude oil from lipid extraction by-product mainly consisted of nitrogenated compounds, hydrocarbons, aromatics, ketones, and alcohols. Following this, this biocrude oil obtained from liquefaction of algal lipid extraction by-product at the optimal conditions was employed as the feedstock to generate combustible gases by catalytical supercritical water gasification (SCWG) at 500 °C for 60 min with a feedstock loading of 10 wt%. The results indicated that the highest gas yield was obtained when using K2CO3 as the catalyst. Overall, this study provides a possible route to improve the economy of algae-based biorefinery by valorizing the lipid extraction residue to generate biocrude oil and subsequently converts into combustible gases via SCWG.