Densification pretreatment using ternary phenolic DES enables efficient biomass fractionation and selective lignin...

Acid deep eutectic solvent (DES)-mediated delignification causes much polysaccharide (especially xylan) degradation, compromising biomass upgrading efficiency. To tackle this issue, a ternary DES densification pretreatment (betaine-guaiacol-salicylic acid, BE-GUA-SCA) was developed, enabling efficient lignin removal and high sugar retention, yielding 73.1% delignification with preservation of 98% glucan and 85% xylan under optimal conditions. Guaiacol spontaneously polymerized with Cα in lignin's β-aryl ether during pretreatment, forming a guaiacolated structure that blocked undesirable condensation. The resulting arylated lignin enriched phenolic hydroxyls and retained β-aryl ethers. Moreover, this ternary DES system showed excellent recyclability (94.42% DES recovery and 96.19% DES purity after 5 cycles) and superior functional stability (>70% delignification, over 90% glucan recovery and 80% xylan recovery after 5 cycles), overcoming traditional acidic catalysis limitations and offering a novel strategy for selective lignin functionalization and polyphenol derivative synthesis.