Direct liquefaction of Dunaliella tertiolecta for bio-oil in sub/supercritical ethanol–water

This paper presents bio-oil preparation by direct liquefaction of Dunaliella tertiolecta (D. tertiolecta) with sub/supercritical ethanol–water as the medium in a batch autoclave with high temperature and high pressure. The results indicated that ethanol and water showed synergistic effects on direct liquefaction of D. tertiolecta. The maximum bio-oil yield was 64.68%, with an optimal D. tertiolecta conversion of 98.24% in sub/supercritical ethanol–water. The detailed chemical compositional analysis of the bio-oil was performed using an EA, FT-IR, and GC–MS. The empirical formulas of the bio-oil obtained using the ethanol–water co-solvent (40%, v/v) and sole water as the reaction medium were CH1.52O0.14N0.06 and CH1.43O0.23N0.09, with calorific values of 34.96 and 29.80 MJ kg−1, respectively. XPS and SEM results showed that ethanol–water is a very effective reaction medium in the liquefaction. A plausible reaction mechanism of the main chemical component in D. tertiolecta is proposed based on our results and the literatures.