Effect of hemicellulose and its-derived products on the recycling and efficiency of biomass fractionation using lactic acid/choline chloride (DES)

The recyclability of lactic acid/choline chloride deep eutectic solvent (DES) in lignocellulose fractionation remains challenging. This study demonstrates that DES reuse reduces delignification efficiency, with a residual lignin content of 9.64% after three cycles, resulting in incomplete fiber separation. The molecular weight of dissolved lignin increased, and 2D HSQC NMR revealed reduced β-O-4 cleavage. Accumulated dissolved hemicellulose and its degradation products (e.g., acetic acid, furfural) altered DES properties, increasing viscosity and reducing hydrogen bond basicity, which hindered mass transfer, lignin-carbohydrate complex dissociation, and lignin depolymerization. To address these limitations, activated carbon adsorption (boosting delignification degree to 77%, near fresh DES at 80%) and prehydrolysis (achieving 82% after three cycles vs. 90% for fresh DES) are proposed to remove hemicellulose and its byproducts, minimizing their impact on recycled DES. This study demonstrates the recyclability of DES and proposes two strategies that significantly improve it, ensuring sustainable and efficient biomass fractionation.