Co-Liquefaction of Mixed Culture Microalgal Strains Under Subcritical Water Conditions

Hydrothermal liquefaction (HTL) is one of the productive thermochemical conversion processes capable of converting wet feedstock into renewable bio-oils. In this study, microalgae Cyanidioschyzon merolae (CM) and Galdieria sulphuraria (GS) were co-liquefied under hydrothermal conditions in a stainless-steel batch reactor. The temperatures and CM/GS mass ratios were varied from 150 to 300°C and 0 to 100% respectively. All the experiments were performed at 20% solid loading and at a reaction time of 30 min. The maximum bio-crude yield was obtained at 300°C and at a mass ratio of 4:1 (CM/GS). A positive synergetic effect is observed for the bio-crude yield, which is dependent on temperature and mass ratio. The biocrude oils were analyzed using Gas Chromatography Mass Spectrometry (GC-MS) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR MS). FT-ICR MS analysis of the biocrude oils indicate that both the co-liquefied and pure individual algal oils are compositionally similar but their relative intensities changed with process parameters. Ultimate and proximate analysis was also performed for the biomass, biocrude oil and biochar.