Near- and supercritical ethanol treatment of biocrude from hydrothermal liquefaction of microalgae

Biocrude produced from algae by hydrothermal liquefaction was treated with near- and supercritical ethanol and ethanol-water mixtures at 210-290 °C for 0.5-4 h. Longer reaction times and higher temperatures better promoted esterification reactions. Dilution of the ethanol with water led to lower yields of treated biocrude and reduced ester content. The viscosity of treated biocrude was an order of magnitude lower than that of the crude bio-oil, and the treated biocrude exhibited the characteristics of a Newtonian fluid. Overall, treatment of biocrude with near- and supercritical ethanol generated a treated bio-oil with lower viscosity, more ester content, and in nearly 100 wt% yield.