Upgrading straw for lignin separation and levulinic acid production using lactic acid DES and HSO₃-based ionic liquids

Deep eutectic solvents (DES) and ionic liquids (ILs) have emerged as viable alternatives for biomass fractionation. In this study, lactic acid-choline chloride deep eutectic solvents (CCLA), synthesized were utilized for the fractionation of lignin and the cellulose enriched solid (CS) derived from straw. Subsequently, the CS was subjected to hydrothermal conversion to yield levulinic acid (LA) using the IL [C₃SO₃HEim]Cl. The optimal lignin separation rate of 89.3 % was attained when the molar ratio of choline chloride to lactic acid was 1:4. The highest LA yield (30.3 wt%) was obtained from the CS after DES pretreatment under the 1:2 M ratio of choline chloride to lactic acid. This study adopted the approach of experiments combined with density functional theory (DFT) to reveal the positive influence for lignin fractionation and the inhibition for cellulose retention of hydrogen bond donors (HBD), as the core component of CCLA, thereby further affecting the valorization conversion of CS to cellulose based furan products by ILs. Furthermore, Lewis acid salt FeCl₃ was confirmed the benefit for the conversion of CS to LA by the synergistic catalysis with [C₃SO₃HEim]Cl. This study proposes a tandem design of green solvent for lignin recovery and CS valorization production of LA.