Mechanistic insights into the role of deep eutectic solvent toward enhanced production of monophenols from bagasse lignin

The production of monophenols from lignin has been considered as an attractive strategy to produce high valueadded biofuel. In the present study, the selective valorization of bagasse lignin to monophenols was implemented through deep eutectic solvent (DES) pretreatment and catalytic fast pyrolysis (CFP). The bagasse lignin was isolated by DES based on Choline chloride/lactic acid (ChCl/LA), and the yield of lignin reached 86.63 % when ChCl/LA molar ratio was 1: 10. The extracted lignin exhibited the favorable structures of high purity, high uniformity, moderated beta-O-4 linkage and less condensed structure. During the following CFP, the lignin was converted into monophenols with a total yield of 14.68 wt% under optimal conditions. The 4-ethyl phenol (9.27 wt%), 4-ethyl guaiacol (1.57 wt%), 4-propyl guaiacol (1.69 wt%), and 2,6-dimethoxyl phenol (0.43 wt%) were the major products, accounting for 72.82 % of the detected products. Moreover, a detailed understanding of the role of DES in enhancing the monophenols production was comprehensively investigated through quantum chemistry (QC) calculations and reactive molecular dynamics (RMD) simulations. The strong hydrogen bonds were formed between the chloride ion of DES and the hydroxyl groups in lignin, allowing the DES to break both the hydrogen bonding interactions and ether linkages in lignin. The RMD simulations demonstrated that the alpha-acylated lignin structure was generated during the pretreatment, thereby inhibiting the condensation reaction to some extent. Such results are paramount for effectively valorizing biomass to produce high-value monophenols using the fast pyrolysis technology.