Co-liquefaction of mixed culture microalgal strains under sub-critical water conditions

We report the co-liquefaction performance of unicellular, red alga Cyanidioschyzon merolae and Galdieria sulphuraria under sub-critical water conditions within a stainless-steel batch reactor under different temperatures (150–300 °C), residence time (15–60 min), and Cyanidioschyzon merolae to Galdieria sulphuraria mass loading (0–100%). Individual liquefaction of C. merolae and G. sulphuraria at 300 °C achieved maximum biocrude oil yield of 18.9 and 14.0%, respectively. The yield of biocrude oil increased to 25.5%, suggesting a positive synergistic effect during the co-liquefaction of 80–20 mass loading of C. merolae to G. sulphuraria. The biocrude oils were analyzed by FT-ICR MS which showed that co-liquefaction did not significantly affect the distribution of product compounds compared to individual oils. The co-liquefied biocrude and biochar have a higher-heating-value of 35.28 and 7.96 MJ/kg. Ultimate and proximate analysis were performed on algae biomass, biocrude and biochar.