Evaluation on the efficiency of "lignin-first" dissolution and biomass fractionation in alcohols solvents systems

In this study, wheat straw (WS) was pretreated using sodium hydroxide (NaOH)/sulfuric acid (H₂SO₄)-catalyzed ethanol, ethylene glycol (EG), and glycerol as solvents. The NaOH-EG pretreatment of WS yielded impressive results with 89.97 % delignification and 79.78 % fermentable sugar yields. Density functional theory analyses revealed that the superior performance of EG originated from its dual hydroxyl groups, which enhanced the molecular polarity index of lignin (15.88 kcal mol^-1) than that by ethanol (14.99 kcal mol^-1) and also increased the electrostatic potential (+66.23 kcal mol^-1). These properties destabilize lignin-carbohydrate complexes while preserving β-O-4 linkages. Experimental validation via Fourier transform infrared spectroscopy and X-ray diffraction confirmed the selective capability of EG for lignin solvation. Simultaneous saccharification and fermentation experiments showed a correlation between theoretical polarity trends and improved ethanol yields. NaOH-EG pretreatment promoted lignin biorefining by achieving higher delignification than H₂SO₄-EG while reducing β-O-4 cleavage, thus ensuring biofuel viability and lignin valorization. This study integrated experimental biomass fractionation with quantum chemical simulations, bridging macroscale biomass processing with atomic-scale solvent-lignin interactions. It provides a rational framework for solvent selection in biorefining, offering insights into optimizing biomass conversion processes.