Efficient Separation of Poplar Lignin Using a New Carboxylic Acid‐Based Deep Eutectic Solvents – 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 were 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.