Reduction of xylan and lignin of rapeseed straw through pretreatment with three-component deep eutectic solvent Choline chloride:Oxalic acid:Aluminum trichloride.

This study focused on the effectual pretreatment of waste rapeseed straw (RS), aiming to enhance its enzymolysis efficiency by increasing elimination of xylan and lignin, improving cellulose accessibility, and weakening surface lignin area. A three-component deep eutectic solvent (DES), Choline chloride: Oxalic acid: Aluminum trichloride (ChCl:OA:AlCl), was prepared for treating RS. Under the optimal treatment conditions (110 °C, 60 min, ChCl:OA:AlCl₃ = 3:1:0.06 mol/mol/mol), enzymolysis efficiency significantly elevated from 37.6 % to 95.3 %, cellulose accessibility rose from 350.0 mg/g to 700.0 mg/g, and surface lignin area weakened significantly. Meanwhile, the value-added by-product xylo-oligosaccharides were acquired in pretreatment liquor. FTIR, SEM and XRD revealed that ChCl:OA:AlCl₃ roughened the surface of RS, reduced its crystallinity and enhanced the accessibility of cellulase. Molecular dynamics simulation showcased the destructive effect of ChCl:OA:AlCl₃ on the structures of lignin and hemicellulose, manifesting that ChCl:OA:AlCl₃ could effectually break the β-O-4 bonds in lignin and the β-1,4-glycosidic bonds in hemicellulose. In view of mass and energy balance analysis, this pretreatment process had good energy utilization efficiency and industrial application potential in the co-production of fermentable sugars (glucose and xylose) and xylo-oligosaccharides, rendering a new approach for biomass resource utilization.