Novel Deep Eutectic Solvent for Native Lignin Extraction through Heterocycle Induced Interaction

N-Heterocycle was introduced in deep eutectic solvent during biomass fractionation to improve the native-like lignin extraction. The unique hydrogen bonding properties of pyrazole formed strong interactions with lignin that provided high extraction yield and reduced ether cleavage. 50% to 90% of lignin was extracted from wheat straw biomass at different conditions from 90°C to 145°C with different structures, high ether linkage native-like lignin (66% ether linkage per 100 aromatic unit) and depolymerized homogenous lignin. The lower acidity of N-heterocycle DES prevented the condensation of lignin and the formation of chromophores. The study demonstrated a novel approach to extract native lignin at high yield and purity, also established a new strategy for future DES design.