Citric acid-sorbitol deep eutectic solvent for efficient deconstruction of lignocellulosic biomass and subsequent ethanol fermentation

Abstract

Native lignocellulosic biomass is notoriously recalcitrant because of its highly ordered cellulose crystallites and the encapsulating lignin–hemicellulose matrix, which greatly limits enzymatic hydrolysis and subsequent bioconversion. To overcome this barrier, we set out to design a fully biomass‑derived, recyclable pretreatment solvent capable of selectively disrupting cellulose crystallinity under mild conditions. Here, we report a family of deep eutectic solvents (DES) constituted from polycarboxylic acids (Citric and Tartaric acids) and polyols (Ethylene glycol, Glycerol, Sorbitol) and evaluate their pretreatment efficacy for corn stover. Multiscale characterization by NMR, FT‑IR, XRD, and rheology elucidated the hydrogen‑bond network architectures, viscosity profiles, and their mechanistic roles in the structural transformation of stover cellulose. Among the tested systems, the Citric acid–Sorbitol (CA–Sor) DES featured an optimised hydrogen‑bond network and moderate viscosity (72.2 mPa·s), reducing cellulose crystallinity from 62.3 % to 34.8 % and boosting reducing sugar conversion rate to 89.10 % within 72 h. The resulting hydrolysate could be directly fermented to ethanol without detoxification, achieving an 84 % glucose‑to‑ethanol conversion efficiency. This study therefore furnishes a novel, efficient, and recyclable green pretreatment strategy for the high‑value biorefining of agricultural residues and highlights its attractive potential for industrial deployment.