Lignocellulose pretreatment by Deep eutectic solvent and water binary system for enhancement of lignin extraction and cellulose saccharification

The high viscosity of deep eutectic solvent (DES) limits its application in industrial production due to reduced mass transfer efficiency within the solvent system. Incorporating water into the solvent system can effectively reduce the viscosity of DES. In this study, DES based on glycerol and choline chloride were prepared, and the physicochemical properties of DES-water mixtures and the impact of various water contents in the solvent system on the pretreatment efficiency of poplar was investigated. At a 35% water content in the solvent system, the solvent's viscosity drops by 95%. The separation results from poplar experiments demonstrated that adding 10%−15% water to the solvent system promoted lignin dissolution and increased its extraction rate. Following pretreatment, the solid product cellulose exhibited a purity level exceeding 80%, with an enzymatic hydrolysis rate exceeding 95%. Structural characterization analysis revealed that the total phenolic hydroxyl content of lignin increased, along with an increase in cellulose crystallinity. Adding water to the solvent system improved both the purity of lignin and the content of active hydroxyl groups. Additionally, there was a more uniform distribution in molecular weight. This study comprehensively discussed the feasibility of using water as an auxiliary solvent for DES-based lignocellulose pretreatment. This approach is expected to facilitate industrialization and enhance preferential lignin extraction during pretreatment.