Ionic liquid‐mediated selective extraction of lignin from wood leading to enhanced enzymatic cellulose hydrolysis

TLDR

Lignocellulose is a promising sustainable biomass, yet its inherent recalcitrance limits microbial and enzymatic conversion, necessitating energy‑intensive pretreatments that can degrade key components. The study aims to use the ionic liquid 1‑ethyl‑3‑methylimidazolium acetate to selectively extract lignin from wood flour. The IL pretreatment dissolves lignin while preserving cellulose, and the IL can be reused to produce a concentrated, chemically unmodified lignin stream. After removing 40 % of lignin, cellulose crystallinity dropped below 45, allowing over 90 % hydrolysis by Trichoderma viride cellulase, demonstrating the effectiveness of the IL pretreatment.

Abstract

Lignocellulose represents a key sustainable source of biomass for transformation into biofuels and bio-based products. Unfortunately, lignocellulosic biomass is highly recalcitrant to biotransformation, both microbial and enzymatic, which limits its use and prevents economically viable conversion into value-added products. As a result, effective pretreatment strategies are necessary, which invariably involves high energy processing or results in the degradation of key components of lignocellulose. In this work, the ionic liquid, 1-ethyl-3-methylimidazolium acetate ([Emim][CH3COO]), was used as a pretreatment solvent to extract lignin from wood flour. The cellulose in the pretreated wood flour becomes far less crystalline without undergoing solubilization. When 40% of the lignin was removed, the cellulose crystallinity index dropped below 45, resulting in > 90% of the cellulose in wood flour to be hydrolyzed by Trichoderma viride cellulase. [Emim] [CH3COO] was easily reused, thereby resulting in a highly concentrated solution of chemically unmodified lignin, which may serve as a valuable source of a polyaromatic material as a value-added product.