Efficient separation of poplar lignin by a new carboxylic acid based eutectic solvent—choline chloride/malonic acid

Separation of lignin by pretreatment is an important step in biomass refining. This study investigated how a novel dicarboxylic acid-based deep eutectic solvent (DES) - choline chloride (ChCl)/malonic acid (MA) - affected the process of separating lignin from poplar. At 140°C for 3.0 h, with a ChCl:MA molar ratio of 1:3.5, the ideal pretreatment conditions are met, and 91.8% lignin was obtained. Even after five DES reuses, the consistent and effective separation efficiency of 77.9% remains unchanged. The hydrolysate contained 92.4% of the recovered lignin, with a purity of 94.6%. Moreover, the regenerated lignin obtained through the new DES pretreatment exhibited a high phenolic hydroxyl content of 1.9 mmol∙g−1 and a low polydispersity index of 1.4. The results showed efficient and selective separation of lignin using the new binary carboxylic acid-based DES pretreatment was achieved. This research offers a novel approach to effectively separate wood fiber biomass and extract valuable lignin.