Effect of molecular scale behavior of lignin during alcohols pretreatment of wheat straw on carbohydrates conversion

The recalcitrance of lignocellulosic biomass necessitates efficient pretreatments to valorize both carbohydrates and lignin. Despite alcohols being green alternatives for lignin extraction, the molecular mechanisms driving lignin solubilization and its impact on enzyme accessibility remain poorly understood. Here, we comparatively investigated ethanol (monohydric), ethylene glycol (diol), and glycerol (polyol) for wheat straw fractionation, integrating experimental analysis (2D HSQC NMR, enzymatic hydrolysis) with quantum calculations (DFT, molecular dynamics). Ethylene glycol exhibited superior lignin removal (50 %) and holocellulose conversion (72.86 %), attributed to (1) non-covalent interactions (sumδg = 3.668 vs. <2.75 for ethanol/glycerol) enhancing lignin solubility; (2) α-etherification preserving β-O-4 linkages (50.93 per 100Ar vs. 41.32–43.81 in others); and (3) suppressing cellulase non-productive binding (44.5 % free enzyme retention). NaOH-catalyzed ethylene glycol further elevated glucose yield to 85.09 %, outperforming acid systems. This work decouples solvent hydroxyl density from lignin functionality, proposing ethylene glycol as a process-compatible solvent for integrated biorefineries to advance carbon-neutral bio-economies.