Microwave-assisted ternary deep eutectic solvent pretreatment for improved rice straw saccharification under mild pretreatment conditions

Abstract

The development of a green and cost-effective pretreatment method to overcome biomass recalcitrance is a challenging assignment for the efficient valorization of lignocellulosic compounds. In this study, a ternary deep eutectic solvent (DES) consisting of choline chloride (ChCl), p-toluene sulfonic acid (pTSA) and ethylene glycol (EG) was applied in rice straw (RS) pretreatment under microwave (MW) irradiation for the further conversion of the polysaccharide fraction. The effect of the pretreatment temperature, time and pTSA content in the DES on lignin extraction and polysaccharide hydrolysis was assessed by a central composite design (CCD). Under the selected pretreatment conditions (80 ºC, 22.5 min, ChCl:pTSA:EG 1:1:9), 61.6% delignification was achieved, as well as nearly complete conversion of the initial glucan in RS (93.4% glucose yield) and a good xylan conversion rate (48.3% xylose yield), representing a total polysaccharide exploitation of 78.3%. Energetical requirement was remarkably lower compared to conventional conductive heating. Importantly, the ternary DES showed good recyclability pattern after two reuses. Overall, this study demonstrated the potential of MW-assisted ternary DES pretreatment for improved valorization of biomass polysaccharides under mild pretreatment conditions, representing an efficient and energetical-saving alternative pathway within the biorefinery framework.