Pyruvic acid-based reactive deep eutectic solvents enable in-situ lignin stabilization for enhanced biomass valorization

Lignin condensation during biomass pretreatment severely limits both cellulose accessibility and lignin valorization, posing a fundamental challenge to lignocellulosic biorefineries. Herein, a pyruvic acid-based reactive deep eutectic solvent (PA-DES) composed of choline chloride and pyruvic acid was developed, in which PA serves as not only the hydrogen bond donor but also a reactive agent potentially contributing to lignin regulation. Kamlet–Taft analysis revealed favorable solvent properties for biomass fractionation, enabling superior delignification (up to 98.66%) compared with conventional lactic acid-based DES (LA-DES). Consequently, near-complete enzymatic hydrolysis was achieved at a low enzyme loading (5 FPU/g glucan) after alkaline washing. Notably, PA-DES produced lignin with structural characteristics consistent with a lower extent of condensation relative to lignin produced with LA-DES under the conditions investigated, despite the acidic pretreatment environment. Structural analyses suggest that PA may have contributed to lignin structural regulation and may have limited condensation while simultaneously introducing carboxyl functionalities during pretreatment, yielding lignin with a carboxyl group content of 0.78 mmol/g. The resulting lignin could be directly utilized as a functional adsorbent without additional post-modification, exhibiting a maximum methylene blue adsorption capacity of 331.64 mg/g. Furthermore, a solvent-property-guided regeneration strategy enabled repeated reuse of recovered PA-DES after component replenishment while maintaining high pretreatment performance. Overall, this work demonstrates that reactive DES design can simultaneously enable biomass fractionation and lignin functionalization, providing an effective strategy for integrated lignocellulosic valorization.