Unraveling the secrets of harnessing a surfactant-modified strategy in organosolv pretreatment of lignocellulosic biomass for efficient fermentable sugar production†

Abstract

Alkaline-catalyzed organosolv pretreatment of lignocellulosic biomass affords excellent delignification, yielding a holocellulose-rich substrate for fermentable sugar production. However, complete lignin removal is impractical, and residual lignin also exacerbates negative effects on subsequent enzymatic hydrolysis. Herein, a novel strategy of developing surfactant-assisted organosolv pretreatment (Triton-X 100, AEO 9 and Tween 80) for in situ lignin modification was proposed to overcome this issue. The results indicated that the pretreated substrates showed considerable enzymatic hydrolyzability with a 15.7%–38.3% higher sugar yield compared to the control group without surfactants. Surfactants could graft on both residual and dissolved lignin through etherification, forming α-etherified lignin, though without significantly changing the component distribution and substrate-related properties. Quantum chemical calculations provided theoretical evidence of strong H-bonding and pronounced interaction energy between lignin and surfactants (maximally at −48.4 kcal mol⁻¹). In particular, this surfactant modification decreased the aliphatic –OH and phenolic –OH contents of residual lignin by 16.0%–22.4% and 13.8%–28.8%, respectively. The reduction of –OH groups mitigated non-productive adsorption between lignin and cellulases via H-bonding interaction, which exhibited a significant correlation with the increased enzymatic hydrolyzability (>−0.9). Overall, this study offers valuable insight into the fundamental understanding of the mechanism involved in lignin modification during surfactant-assisted pretreatment and lignin–enzyme interaction during enzymatic hydrolysis. The new findings underscore the potential application of surfactants in organosolv pretreatment to achieve a feasible approach for developing an efficient enzyme-mediated lignocellulosic sugar platform.