Effective deep eutectic solvent pretreatment in one-pot lignocellulose biorefinery for ethanol production

Abstract

Deep eutectic solvents (DES) mediated pretreatment is a promising approach to enhance biofuel yield in lignocellulose biorefinery. However, post-pretreatment DES residues act as inhibitors for enzymatic saccharification requiring biomass washing, leading to significant water and energy consumption. This research aims to develop a novel one-pot method (OP) that eliminates the washing step for the environmentally benign production of lignocellulosic bioethanol from Napier grass. The process involves DES pretreatment using Choline Chloride (ChCl):Sorbitol (1:2), ChCl:Urea (1:2), and ChCl:Lactic acid (1:4), followed by enzymatic saccharification and fermentation with Saccharomyces cerevisiae. By optimizing pretreatment conditions using the OFAT method, the highest sugar yields for ChCl:Sorbitol (ChCl:S), ChCl:Urea (ChCl:U), and ChCl:Lactic acid (ChCl:LA) were increased by 1.92-fold, 1.93-fold, and 1.87-fold, respectively, compared to untreated biomass (at 205.6 mg/g). The effect of different concentrations of DES (0–10 % v/v) on cellulase enzyme and kinetic parameters, Km and Vm, were determined to understand the pattern of inhibition. The study revealed that DES at 5 % v/v minimized uncompetitive inhibition during saccharification after 1 h. There was no inhibition of yeast culture, as evidenced by the absence of inhibition zones. Ethanol analysis revealed significantly higher yields in the OP compared to the conventional approach. Particularly, with ChCl:LA, the ethanol yield reached 0.483 g/g-pretreated biomass, marking a noteworthy 2.42-fold increase compared to the separate hydrolysis and fermentation (SHF). Understanding the impact of pretreatment chemical residues on enzymatic saccharification and fermentation offers opportunities to optimize one-pot processes, leading to advancement in time savings, and the overall efficiency of lignocellulosic bioethanol production.