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

•Lipid extraction by-product from algae was applied to produce biocrude oil.•Liquefaction of algal lipid extraction residue was performed and compared with lignocellulose.•Maximum biocrude oil yield of 78.5 wt% was obtained from liquefaction of algal lipid extraction residue at 225 °C.•The algal lipid extraction residue-derived biocrude oil was employed to produce gases via catalytic SCWG.•The maximum total gas yield was obtained with K2CO3. 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.