Synergistic colloid milling-deep eutectic solvent pretreatment for high-solids corn stover: Enhanced polysaccharide conversion and native lignin preservation

Deep eutectic solvents (DESs) have emerged as promising green media for lignocellulosic biomass pretreatment; however, their large-scale application remains constrained by high viscosity, substantial solvent demand, and hemicellulose degradation. In this study, a synergistic chemomechanical pretreatment strategy was developed by integrating colloid milling (CM) with a ternary DES composed of choline chloride, oxalic acid, and ethylene glycol. This approach enabled high-solids-loading pretreatment (solid-to-liquid ratio of 1:5) of corn stover (CS), achieving 78.4% lignin removal while retaining 90.8% of cellulose and 51.1% of xylan. Enzymatic saccharification of the pretreated residue, with a solids loading of 15%, resulted in 112.4 g/L of fermentable sugars, corresponding to total sugar yields (TSY) of 79.1% for glucan and 44.3% for xylan from the raw corn stover. Structural analyses indicated that CM facilitated DES penetration and enhanced biomass accessibility, whereas the ternary DES preserved the native lignin architecture by suppressing β-O-4 bond cleavage and condensation reactions. The regenerated lignin exhibited high purity (93.7%), low molecular weight (Mw=2700 Da), and well-preserved β-O-4 linkages (30.8 per 100 Ar units), confirming its suitability for downstream valorization. This integrated pretreatment method provides a cost-effective and sustainable route for high-efficiency lignocellulose fractionation and lignin valorization under industrially relevant conditions. • Synergistic pretreatment via colloid milling and ternary DES was developed. • Achieved 78.4% delignification with high cellulose and xylan retention. • 79.1% glucan and 44.3% xylan recovery from raw biomass, yielding 112 g/L fermentable sugars. • Recovered lignin of 93.7% purity with abundant β-O-4 linkages for valorization.