Recycling of deep eutectic solvent for sustainable and efficient pretreatment of corncob

A deep eutectic solvent (DES), consisting of choline chloride and oxalic acid (ChCl-OX), was used to pretreat corncob. Three different recycling procedures were evaluated in terms of the composition analysis, efficiency of enzymatic hydrolysis, inhibitors formation, XRD and FTIR analysis. The results demonstrated that there were two key factors affecting the pretreatment efficiency for reusing DES, the addition of oxalic acid and the removal of lignin from the recycled ChCl-OX. After ten recycles, the pretreatment efficiencies of the recycled DES, using recycling process with supplemented oxalic acid and removal of lignin from the recovered DES, did not obviously decrease the glucan digestibility and glucose recovery (66.23% and 64.43%, respectively) compared to the original DES pretreatment (72.83% and 68.83%, respectively). The contents of fermentation inhibitors were not obviously increased in the enzymatic hydrolysates, and the cost and pollution were further reduced after the reuse of solvents and recovery of lignin. This study suggests that this recycling method maybe a green, low-cost procedure of biomass pretreatment.