Hydrothermal liquefaction of marine microalgae biomass using co-solvents

Hydrothermal liquefaction (HTL) of microalgae biomass is a promising conversion technology in which wet biomass is treated under high temperature (280–350 °C) and pressure (5–21 MPa), and the associated water in the wet biomass forms the reaction medium. A significant fraction of the microalgae can be converted into biocrude, which separates from the aqueous layer by gravity and/or chemical/mechanical methods. Since the HTL process uses the whole biomass, increasing lipid content during microalgae cultivation is not essential. With an overall goal to utilize highly productive algal strains as feedstocks for liquid hydrocarbon fuel precursors, we investigated the HTL conversion of a marine microalgae (Tetraselmis sp.) in the presence of co-solvents. HTL was performed using a 1.2 L Parr reactor at 275–350 °C for 30 min in the presence or absence of a co-solvent (ethylene glycol and isopropyl alcohol). Results showed that the conversion of Tetraselmis sp. was promoted by higher reaction temperature. The biocrude yield increased from 26.3 ± 1.6% to 31.0 ± 2.1% as the temperature increased from 275 °C to 350 °C. Addition of 10% isopropyl alcohol as co-solvent promoted a 14.5 ± 4.9% increase in biocrude yield and also increased production of gaseous products. In contrast, the use of ethylene glycol as co-solvent did not have a significant effect on biocrude yield.