Synergistic phenolic acid-ethylene glycol pretreatment for enhanced saccharification and ethanol fermentation of reed through suppressed lignin repolymerization.

Efficient and inhibitor-free fractionation of lignocellulosic biomass remains a central challenge for advancing sustainable biorefineries, largely due to the intrinsic recalcitrance of lignin and its strong tendency to undergo acid-catalyzed repolymerization. Here, we report a synergistic salicylic acid-ethylene glycol/water (SA-EG/H₂O) pretreatment system that enables clean, structure-preserving deconstruction of reed lignocellulose. The ternary medium operates through a cooperative dual mechanism: salicylic acid promotes selective cleavage of β-O-4 linkages and lignin-carbohydrate complexes (LCCs), while ethylene glycol stabilizes reactive lignin fragments via α-hydroxyalkylation, thereby effectively suppressing repolymerization and conserving native lignin motifs. This integrated strategy achieves 81.21% delignification, markedly enhances fiber porosity and surface accessibility, and substantially mitigates non-productive enzyme adsorption, resulting in a high cellulose hydrolysis efficiency of 94.75%. Subsequent semi-simultaneous saccharification and fermentation (S-SSF) yields 66.97% ethanol without producing detectable fermentation inhibitors. Multiscale characterization corroborates the selective disruption of key lignin linkages, the preservation of cellulose crystallinity, and the stabilization of lignin intermediates responsible for inhibiting condensation. This green and scalable pretreatment framework provides mechanistic insights into suppressing lignin repolymerization and establishes a broadly applicable platform for high-value fractionation and biofuel production from reed and other herbaceous feedstocks.