Hydrothermal liquefaction of microalgae for biocrude production: Improving the biocrude properties with vacuum distillation

This paper proposes a two-part process for producing biocrude with reduced impurities. The biocrude was produced from hydrothermal liquefaction (HTL) of Spirulina sp. and Tetraselmis sp. in a batch reactor at both 300 and 350 °C, 5 min, and 16% w/w solid feed composition. The resultant biocrudes were vacuum distilled at a maximum temperature of 360 °C. It was shown that biocrude quality could be enhanced without using catalyst by vacuum distillation (VD). The biocrude yield for Spirulina sp. was 36 wt% at 300 °C, 42 wt% at 350 °C, and for Tetraselmis sp. was 34 wt% at 300 °C, and 58 wt% at 350 °C. VD of Spirulina sp. biocrude obtained at 300 and 350 °C led to 62 and 67 wt% distilled biocrudes yield, respectively. VD of Tetraselmis sp. biocrude obtained at 300 °C was 70 wt%, and 73 wt% at 350 °C. The higher heating values (HHV) increased from 32 MJ/kg to 40 MJ/kg. There were substantial reductions in oxygen, metallic content, and boiling point ranges in distilled biocrudes.