Deep eutectic solvents-assisted alkali lignin modification for pyrolytic monophenols production

The efficient valorization of alkali lignin (AL) remains a significant challenge due to the multiple impurities and complex structure of AL. Lignin modification through deep eutectic solvent (DES) and subsequent fast pyrolysis offers a promising alternative for AL valorization. Thus, this study comprehensively investigated the potential of DES-pretreated ALs (DESALs) for producing pyrolytic monophenols, with particular focus on the modification process of AL during DES pretreatment, the interaction of lignin-DES, and the techno-economic feasibility of the integrated technology. Notably, under optimal experimental conditions, the ChCl/ethylene glycol (CCEG) system demonstrated the greatest potential to enhance the yields of 4-vinyl syringol (4VS) and 4-propenyl syringol (4PS) to 12.09 wt%, achieving a selectivity of 40.60 %, without using a catalyst. Moreover, multiscale simulations were performed to illustrate the enhancement effect of DESs on the production of pyrolytic monophenols. The CCEG system exhibited the lowest |HOMO-LUMO| energy gap (161.80 kcal/mol) and the highest interaction energy (-56.56 kcal/mol). The chloride ions played an integral role in forming robust hydrogen bonds between CC and EG. Further investigation indicated that the adduct and acetal structures were synthesized, and their formation pathways were subsequently modeled. Finally, the CCEG system exhibited a negligible environmental impact and high economic feasibility.