Optimizing on flash hydrothermal liquefaction environment for improving the quality of bio-crude

Reducing carbon emissions has become the current focus of attention all over the world. Alternative biofuels are an important means to achieve the carbon reduction. Among them, hydrothermal liquefaction (HTL) of algae-based biomass has been widely studied because of its environmental friendliness and mild conditions. In this paper, the effect of different conditions on microalgae bio-crude enhancement was investigated, using innovative experimental methods, including flash heating HTL with two step or by co-solvent. It showed that recovery of carbon, hydrogen and energy could reach 0.53, 0.48 and 0.58 respectively at 250 °C for 30 min with ethanol-water co-solvent as the medium. The highest total content of fatty acids and fatty acid esters were found in the bio-crude with methanol/ethanol-water co-solvent as the medium. The nitrogen content of the bio-crude obtained by the two-step method is lower than that of the one-step method. The content of cholesterol and vitamin E as indicators of bioactive substances performed well with ethanol-water co-solvent as the liquid phase medium, containing 16.1% in bio-crude at 240 °C for 3 min, and also advantageously with air as the gas phase medium.