Unlocking complete sugarcane residue valorisation for sequential fractionation of cellulose, hemicellulose and lignin...

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.