Disintegration of wet microalgae biomass with deep-eutectic-solvent-assisted hydrothermal treatment for sustainable lipid extraction

Abstract

Deep eutectic solvent (DES) with abundant hydrogen bond acceptors and donors was employed to promote the disintegration of microalgae biomass with hydrothermal treatment (HTT) for green lipid extraction. The lipid extraction efficiency after HTT at 160 °C increased from 19.03% to 95.75% with DES assistance under optimum conditions (DES was prepared at a molar ratio of 1 : 2, DES concentration was 25%, and treatment time was 20 min). The increased protein solubilization (from 53.97 mg per g DW to 351.10 mg per g DW) and reducing sugar solubilization (from 13.29 mg per g DW to 50.70 mg per g DW) in the hydrothermal aqueous phase indicated that DES simultaneously promoted the depolymerization and solubilization of microalgae biomass for lipid extraction. The increased z-average molecular weight (from 1043 Da to 3203 Da) of solute in the hydrothermal aqueous phase confirmed that DES promoted the solubilization of biomacromolecules. Characterization of solid residues via thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis revealed that DES destroyed the intermolecular interaction of microalgae biomass by reconstructing the hydrogen bond network and thus facilitated the diffusion of lipids. Density functional theory calculations identified that DES decreased the hydrogen bond strength between microalgae biomass components, reduced the polarity difference between water and microalgae biomass, and lowered the depolymerization energy barrier of microalgae biomass.