Unlocking complete sugarcane residue valorisation for sequential fractionation of cellulose, hemicellulose and lignin through a one-pot, two-step deep eutectic solvent strategy

Sugarcane tops and leaves (STL) represent an abundant yet underutilised lignocellulosic residue with significant biorefinery potential for the valorisation of its three principal components: cellulose, hemicellulose, and lignin. However, existing fractionation studies often prioritise lignin removal, while hemicellulose recovery is compromised by acid-catalysed degradation and sugar dehydration. Here, we report a one-pot, two-step deep eutectic solvent (DES) fractionation strategy that decouples hemicellulose extraction from lignin solubilisation using a low-cost oxalic acid:choline chloride (1:1 molar ratio) system. In the first step, a hydrated DES (75 wt%) at 80 °C for 60 min selectively recovered hemicellulose, achieving 95.6% combined conversion to xylose and xylobiose while limiting glucose (5.3%), furfural (3.3%), and 5-hydroxymethylfurfural (1.3%) formation. The second step employed neat DES at 120 °C for controlled delignification, achieving 95.4% lignin recovery within 10 min at 87.8% purity, with reduced condensation compared to a single-step lignin extraction approach. The resulting cellulose-rich pulp contained 80.1% cellulose with enhanced crystallinity (CrI = 34.8%). Importantly, DES regeneration via recrystallisation reduced downstream energy demand. This integrated strategy enables sequential and selective recovery of all three biomass fractions within a single solvent system, advancing circular lignocellulosic biorefinery design.