Boosting Lignin Dissolution and Biomass Fractionation by Innovative Alkaline Deep Eutectic Solvents

Utilization of deep eutectic solvents (DESs) to extract lignin is a highly attractive strategy for biomass upgrading. Although acidic DESs have been extensively investigated, alkaline DESs (ADESs) have rarely been applied in lignin extraction. Herein, several promising ADESs were prepared for lignin dissolution and biomass pretreatment. Lignin solubility showed a good positive correlation with the Kamlet–Taft parameters and the basicities of the prepared ADESs. Notably, the highest solubility of alkali lignin (AL), enzymatically hydrolyzed lignin (EHL), kraft lignin (KL), and dealkaline lignin (DAL) could reach 49.85, 49.46, 53.14, and 53.17 wt % in ADESs at 60 °C, respectively. Importantly, the prepared ADESs could efficiently remove lignin (80.9–97.8%) from corn stover at 120 °C, significantly improving the enzymatic efficiencies of the residues (71.5–85.4%). Besides, lignin with relatively intact structures or lignin fragments with low molecular weight and good dispersion could be successfully generated. These results confirmed the great potential of ADESs for biomass upgrading.