Lewis acid-diol deep eutectic solvents for structurally retained lignin fractionation and corn stover saccharification.

Abstract

Lewis acid-diol-based deep eutectic solvents (DESs) were constructed for technical lignin dissolution and corn stover (CS) fractionation. The DESs showed high dissolution capacities toward kraft lignin, enzymatic hydrolysis lignin and alkaline lignin with maximum solubilities of 58.4 wt%, 78.8 wt% and 45.5 wt%, respectively. Structure analysis revealed that lignins with abundant β-aryl ether bonds, hydroxyl groups and syringyl type aromatic units were more favorable for dissolution. Among the screened systems, ZnCl2-1,5-pentanediol significantly enhanced corn stover fractionation under mild conditions, achieving 80.7 % delignification, 89.0 % hemicelluloses removal and 97.5 % cellulose retention. The fractionated lignin was obtained in 70.5 % yield and exhibited partial structural retention, including 30.6/100Ar β-O-4 structures, a weight-average molecular weight of 3420 g/mol, and a hydroxyl groups content of 4.46 mmol/g. These features suggest that diol participation at the lignin α-position contributed to lignin stabilization during fractionation. The cellulose-rich residue was also efficiently hydrolyzed, giving a glucose yield of 92.5 % due to effective lignocellulose deconstruction and the hydroxyl-rich lignin remaining in the pretreated residue. These solvent systems provide an effective route for biomass deconstruction and support more sustainable lignocellulosic biorefinery.