Valorization of the red macroalga Gracilaria corticata by hydrothermal liquefaction: Product yield improvement by optimization of process parameters

Abstract Hydrothermal liquefaction (HTL) of the red alga Gracilaria corticata was carried out at 260, 280 and 300 °C for 15 min using H2O as solvent. The bio-oil yield was maximal (5.25 wt%) at 300 °C. Influence of the solvents methanol, ethanol, acetone and ethanol-water on the distribution as well as nature of the resultant HTL products has also been examined. Organic solvents could markedly improve the bio-oil yield to over 16 wt%. Bio-oil and biochar were characterized through FT-IR, GC–MS and 1H NMR studies. Analysis of GC–MS data in conjunction with FT-IR and 1H NMR derived information revealed that the bio-oil mainly consisted of various derivatives of compounds such as aldehydes, ketones, phenols, acids and esters, besides nitrogenous compounds. This research outcome using HTL as a technique for enhancing bio-oil yield, in particular from red macroalgae, would provide a stimulus for further investigations on potential commercial applications of algal bio-oil.