Deep eutectic solvent-mediated delignification of corn stover for improved fermentable sugar yield and bioethanol production

• Corn stover was pretreated using eighteen different deep eutectic solvents (DESs). • SEM analysis of pretreated biomass showed selective delignification. • DES with highest delignification was selected for saccharification and fermentation. • Fermentation resulted in ethanol production of 18.69 g /L of hydrolysate . • Reusability of DES makes it an economical method for biomass delignification. Deep eutectic solvents (DESs) are cost-effective and environmentally friendly pretreatment agents for delignifying lignocellulosic biomass. This study aimed to identify the most efficient DES system for corn stover delignification, improve fermentable sugar accessibility, and enhance bioethanol yield. Corn stover was pretreated using 18 DES formulations derived from oxalic acid, lactic acid, and urea, each combined with choline chloride. The most effective DES system was evaluated based on lignin removal, cellulose retention, and enzymatic digestibility. Among all formulations, choline chloride–lactic acid (1:8) achieved the highest delignification (82.5 %) while retaining 69.3 % cellulose and 67.0 % hemicellulose. Enzymatic saccharification of the pretreated biomass produced 58.94 g/L of reducing sugars with a saccharification efficiency of 65.15 %. Fermentation using Saccharomyces cerevisiae (hexoses fermenting) and Pachysolen tannophilus (pentose fermenting) yielded 18.69 g/L of ethanol, with a fermentation efficiency of 70.4 % and an ethanol yield percentage (YPS) of 36.0 %. Scaling up the process to 1 kg of corn stover resulted in an ethanol yield of 149.56 g. The reusability of the choline chloride–lactic acid (1:8) system was also evaluated, showing minimal reduction in pretreatment efficiency after the first recycle but a significant decline after the second. These findings highlight the potential of DES-based pretreatment for sustainable bioethanol production. The present study comprehensively assesses the efficiency, scalability, and reusability of DES-based pretreatment for corn stover, demonstrating its potential for sustainable bioethanol production.