Synergistic fractionation of sugarcane bagasse using a [BMIM]Cl–levulinic acid system for enhanced enzymatic saccharification and multi-pathway valorization

Lignocellulosic biomass recalcitrance limits its efficient conversion into value-added products, highlighting the need for effective and sustainable pretreatment strategies. In this work, a green fractionation system based on 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and levulinic acid (LA) was developed for sugarcane bagasse, enabling coordinated utilization of its three main components. Under selected pretreatment conditions, efficient delignification was achieved with a lignin removal of 85.27%. Structural characterizations revealed significant disruption of the biomass matrix and the formation of a cellulose-enriched surface (O/C increased from 0.38 to 0.88; C2 component reached 63.67%), which markedly improved enzyme accessibility, resulting in a glucose yield of 94.7%. The hemicellulose-derived fraction was further converted into furfural with a maximum yield of 94.64% at 60 min. Meanwhile, 2D-HSQC and 31 P NMR analyses confirmed extensive β–O–4 bond cleavage and enrichment of phenolic hydroxyl groups in the regenerated lignin, contributing to its superior antioxidant activity compared with BHT (DPPH scavenging up to 96.7%). DFT calculations further demonstrated that synergistic hydrogen-bonding interactions between [BMIM]Cl–LA and lignin play a key role in promoting lignin depolymerization. Overall, this study provides an efficient and sustainable strategy for the full-component valorization of sugarcane bagasse into fermentable sugars, furfural, and functional lignin.