Study on two-step hydrothermal liquefaction of macroalgae for improving bio-oil

In this work, the conversion of Enteromorpha clathrata into bio-oil through hydrothermal liquefaction (HTL) was investigated under different preparation conditions. A two-step reaction method was compared with single-step reaction. At a high temperature, bio-oil produced through the two-step hydrothermal reaction displayed slight changes in yield, but solid residue rate was low. The liquid-to-material ratio of the optimal preparation condition was 40/4 (mL/g). Bio-oil produced in each experiment at this ratio was further analyzed using GC/MS. Furthermore, density functional theory (DFT) quantitative calculation was used in analyzing and proving the possible reaction path of the conversion of furan compounds to aromatic compounds during a direct high-temperature liquefaction process. Results revealed that the two-step method can ensure a high bio-oil yield, while preventing the occurrence of side reactions caused by long-term high-temperature reactions, and improve the bio-oil quality.