Tailoring properties of lignin through deep eutectic solvent for phenols production

Deep eutectic solvent (DES) has emerged as a promising and green solvent which can extract lignins (DESLs) from biomass. The DESLs hold great potential to produce phenolic compounds by fast pyrolysis. This study aimed to pyrolyze DESLs into a high yield of phenolic compounds with a detailed understanding of the promotional effect of DES on lignin pyrolysis. Three representative biomass, namely eucalyptus (E. grandis x urophylla), pine (Larix gmelinii), and sugarcane bagasse (Saccharum sinensis Roxb.), were pretreated with Choline chloride (ChCl)/lactic acid (LA) to produce eucalyptus DESLs (EuLs), pine DESLs (PiLs), and sugarcane bagasse DESLs (BaLs), respectively. The DESLs were extracted with valorizable properties of high yield (86.74 % for EuLs, 83.46 % for PiLs, and 88.05 % for BaLs), purity (86.13-93.73 %), uniformly reduced molecular weight, less condensed structure, moderated ether bond and elevated volatility, leading to higher yields (rose 126 % for EuLs, rose 8 % for BaLs) and selectivities (from 74.86 % to 78.66 % for EuLs, from 86.36 % to 86.66 % for PiLs, from 88.51 % to 89.46 % for BaLs) of phenolic compounds than those of the corresponding controls. The yields of phenolic compounds were closely related (R-2 > 0.5) to the molecular weight and beta-O-4 bond of DESLs. This is the first report to comprehensively elucidate the enhancement mechanisms of DES on lignin pyrolysis. This work highlighted DES pretreatment as a promising approach for promoting the production of phenolic compounds.