A synergistic microwave-assisted hydrated deep eutectic solvent (DES) pretreatment for efficient fractionation of wheat straw

Abstract

The disadvantages of deep eutectic solvents (DES) under their high viscosity and long reaction time make their application in industrial production challenging. In this study, the synthesized DES was coupled with a microwave hydrated method for efficient lignocellulose (wheat straw) grading. To mitigate the viscosity of the DES system and reduce the consumption of DES reagents, water was introduced into the synergistic pretreatment process. Under optimized reaction condition (120 °C, 20 % w/w water), we achieved a delignification efficiency of 88.9 %, hemicellulose removal of 90.2 %, and cellulose retention of 85.4 %. Results indicated that the appropriate reaction pressure during pretreatment facilitated the efficient fractionation of lignocellulosic components. The primary structural alteration in lignin was the cleavage of β-O-4 linkages, and the recovered lignin exhibited a more uniform molecular weight distribution. Furthermore, water addition was found to protect the lignin H-type units from structural degradation. The recovered DES, when recycled for two cycles, retained its efficiency, achieving 77.77 % hemicellulose removal and 74.59 % lignin removal. Therefore, the developed synergistic pretreatment method enables rapid and effective fractionation of lignocellulosic biomass under mild conditions, besides, the reuse of DES maintains a high pretreatment performance while significantly reducing the consumption of chemical reagents.