Anthraquinone-assisted alkaline deep eutectic solvent for lignin selective separation and carbohydrates protection

To enhance the efficiency of alkaline deep eutectic solvent (ADES) pretreatment on lignocellulose, anthraquinone (AQ) was introduced as a redox-active additive to incorporate AQ into a ChCl/MEA-based ADES using eucalyptus wood as the feedstock. The synergistic mechanism of the AQ-ADES system was systematically elucidated by evaluating chemical composition changes, enzymatic hydrolysis performance, and lignin deconstruction behavior. By leveraging the unique AQ/AHQ redox cycle, AQ facilitates lignin cleavage via reduction to anthrahydroquinone (AHQ), which is then re-oxidized to AQ. This redox-active role remarkably intensifies delignification while simultaneously protecting carbohydrates. Under the optimal conditions (ChCl: MEA molar ratio of 1:6, 1% AQ, 160 °C, 2 h), the system achieved a high lignin removal of 79.25%, with cellulose and hemicellulose retentions reaching 93.72% and 78.74%, respectively, demonstrating exceptional fractionation selectivity. The resulting solid residue exhibited remarkable enzymatic digestibility with a glucose yield of 93.15%. Density functional theory (DFT) and molecular dynamics (MD) simulations revealed that the ADES disrupts native hydrogen-bonding networks to promote component deconstruction. Simultaneously, the redox-active AQ acts as a dual-function agent, facilitating lignin dissolution while protecting carbohydrates. Overall, this study provides an innovative and green pretreatment strategy for the efficient selective fractionation and total valorization of lignocellulosic biomass.