Recovery of saccharides from lipid-extracted microalgae residue via hot compressed water and its kinetic analysis

Lipid-extracted microalgae residue (LEMR), a by-product of the biodiesel production process, is a potential source of value-added compounds in the microalgae biorefinery field. In this research, we examined the effects of hot compressed water (HCW) conditions and microalgae to water ratios on saccharide recovery from a low-lipid strain of Chlorella vulgaris. The highest recovery yield of saccharides was 57.5% at 200℃ for 15 min. Above 200℃, the reduction in saccharide yield was observed due to the generation of gas and solid by-products. At 200℃, adjusting the microalgae to water ratio significantly influenced the saccharide yield. Reducing the microalgae to water ratio from 1:5 to 0.1:5 nearly doubled the yield. Kinetic analysis was conducted to investigate the solubilization and degradation behaviors of saccharides. The reaction orders for saccharides solubilization and degradation were identified as 1.31 and 1.79, respectively. The rate constants at varying temperatures exhibited a good fit with the identified reaction orders. The activation energies for the solubilization and degradation processes were 79.0 kJ/mol and 104.7 kJ/mol, respectively. This investigation provides insights into saccharide dynamics in LEMR under HCW conditions, offering critical information for enhancing the efficiency and sustainability of microalgae biorefineries.