Biocrude oil and hydrochar production and characterization obtained from hydrothermal liquefaction of microalgae in methanol-water system

Abstract

Hydrothermal liquefaction of microalgae under milder reaction conditions was studied for the production and characterization of high quality biocrude oil and hydrochar confirming its feasibility as sustainable biofuel source. The present study investigates the effects of solvents, temperature and time on the yield of biocrude oil. The comparatively higher yield of biocrude oil (47 wt%) obtained in methanol-water mass ratio of 0.75:0.25 also contained higher amount of ester components resulting in higher biocrude oil quality. Methanol-water co-solvent favored higher biocrude oil yield with lower nitrogen and oxygen contents as compared to pure water. Response surface methodology was applied to study the effects of temperature (222–322 °C), and reaction time (10–60min) at constant pressure of 11.5 MPa for methanol-water and biomass-solvent ratios of 0.75:0.25 and 1:5, respectively. The optimum yield of biocrude oil (57.8 wt%) and highest energy recovery (85.3%) was obtained with 75 wt% of methanol in water at 272 °C and reaction time of 35 min. Subcritical condition (temperature of 222 °C, pressure of 11.5 MPa) resulted in the highest hydrochar yield (19.5 wt%). Hydrochars were also characterized by CHNS, BET, FT-IR and TGA techniques to ascertain their prospective elemental composition, textural properties, functional groups as well as thermal stability.