Binary Organosolv Strategy for Simultaneous High Yield and Structure Preservation

Abstract

Lignin valorization faces a critical trilemma: achieving high recovery yields, preserving labile β-O-4 linkages, and maintaining the process under mild conditions. This study resolves this challenge through an innovative binary organosolv strategy that synergistically pairs extraction solvents (dioxane, acetone, γ-valerolactone, Cyrene) with stabilizing solvents (1-butanol, ethanol, ethylene glycol (EG), tri-ethylene glycol (TEG), tetrahydrofuran (THF)) at 100◦C. The optimized systems are capable of delivering a 58% lignin yield and 98% β-O-4 preservation in the 9:1 ratio of ethanol/dioxane extraction, while the greener butanol/GVL system achieves a 62% yield with 94% ether bond protection across diverse high-lignin biomass. The Monomer Yield Potential Index reveals remarkable synergy, with values of 16.3% for butanol/GVL and 14.1% for ethanol/dioxane, outperforming single-organosolv extractions. Comprehensive structural analysis (13C NMR, 2D-HSQC, 31P NMR, GPC) and analysis of Hansen solubility parameters (HSP) confirm a native-like lignin architecture with minimal condensation and preserved functionality and reveal the mechanism of pairs extraction solvents. The synergy of the binary organosolv system combines the strength of dipolar solvents, which enhances biomass hydrolysis for lignin release and provides sufficient polar alcoholic solvent stabilization of lignin benzylic cations This optimized ratio substantially improves the yields of high ether lignin in mild temperatures.