Lipid content in microalgae determines the quality of biocrude and Energy Return On Investment of hydrothermal liquefaction

Abstract

While the potential of hydrothermal liquefaction (HTL) of microalgae to produce biocrude regardless of the types of microalgae (biomass-agnostic) has been noted, the quality of biocrude and the Energy Return On Investment (EROI) of HTL of various microalgal species have not been compared in detail. Here we report that the quality of biocrude and the EROI of microalgal HTL are directly dependent on the lipid contents of microalgae. When Nannochloropsis oceanica (30.2% lipid content) and Golenkinia sp. (17.3% lipid content) were compared for the quality of HTL in terms of the total yield, asphaltene/non-asphaltene contents, heteroatom (O, N, and S) concentrations, and the effective hydrogen-to-carbon ratios (H/C-eff) of the biocrudes, N. oceanica with high lipid content produced biocrude that can be more suitable for catalytic upgrading to transportation fuels than the biocrude from Golenkinia sp. with low lipid content. HTL of N. oceanica at low temperature (200 degrees C) in particular produced the biocrude with EROI that was better than that of Golenkinia sp. These results strongly support that the choice of microalgae with high lipid content is still a key factor that must be considered for biocrude production as much as it is regarded important for biodiesel production using microalgal biomass.