Hydrothermal liquefaction of Chlorella pyrenoidosa in sub- and supercritical ethanol with heterogeneous catalysts

Hydrothermal liquefaction (HTL) of low lipid content microalgae Chlorella pyrenoidosa with heterogeneous catalysts was processed under sub- and supercritical conditions of ethanol (200–300 °C, 2.8–9.0 MPa, 30 min). The HTL products were separated into bio-crude, gas, solid residue and volatile components, and then characterized. The highest mass and energy recovery ratios of bio-crude on the dry basis of alga were 71.3% and 101.8% respectively, obtained at 240 °C, while the highest higher heating value of bio-crude was 36.19 MJ/kg, obtained at 300 °C. Temperature was found to be the most dominant parameter. H2 as a processing gas at an initial pressure of 1.03 MPa slightly improved the bio-crude yield and quality. Raney-Ni and HZSM-5 type zeolite catalysts had no significant effect on the presented HTL process. The results indicated that HTL with ethanol as the solvent was able to produce 50–70 wt.% of bio-crude directly from C. pyrenoidosa.