One-pot lignocellulose fractionation towards efficient whole sugar conversion and aromatic monomer production using a mild alkaline oxidation system†

The targeted extraction of native-like lignin while retaining highly accessible carbohydrate substrates in a one-pot biorefinery is a promising strategy but suffers from technical challenges. In this study, a mild alkaline-oxidation system (tetramethylammonium hydroxide/urea hydrogen peroxide, TMAH/UHP) was tailored to fractionate lignocellulose into protolignin and a carbohydrate-rich substrate for further renewable energy upgrading. During the TMAH/UHP biorefinery, the diverse reaction intensities and solvent concentrations were investigated to achieve a balance between lignin structure integrity and valuable carbohydrate recovery. A detailed study into lignin structure evolution was conducted to understand how the TMAH/UHP system extracted protolignin efficiently and maintained the high-accessibility of carbohydrate solids. The protolignin with a high content of β-O-4 linkages (45.1%–62.8%) was extracted via the dominant cleavage of lignin-carbohydrate ester bonds. Additionally, the high recovery of carbohydrates achieved an excellent whole-sugar conversion capacity (100.0% glucose yield and >50.0% xylose yield), and the protolignin exhibited feasible downstream valorization for the production of aromatic monomers via a catalytic oxidation process. Meanwhile, the spent solvent was enriched with abundant urea components, which could be used as water-soluble fertilizer for crop growth. This one-pot biorefinery method mitigates the challenge in extracting protolignin without compromising carbohydrate value under mild conditions, which is essential for a sustainable and scale-up future of biorefinery.