Deep eutectic solvent pretreatment for improving lignin properties and subsequent 4-vinylphenol production: an integrated experimental and modeling investigation†

Abstract

It has recently been estimated that around 36 million tons of sugarcane bagasse are available annually in China. The valorization of bagasse lignin holds great potential for producing high-value chemicals upon its degradation. The degradation of bagasse through fast pyrolysis is generally well established but often inefficient for chemical production due to the presence of other components of bagasse and the complex structure of lignin. Thus, in this work, fast pyrolysis technology was employed at 300, 350, 400, 500, and 600 °C to valorize bagasse lignin obtained from a deep eutectic solvent (DES) fractionation process. This process resulted in a high 4-vinylphenol (4VP) yield (14.19 wt%) with a selectivity of 69.44% without catalyst addition under optimal conditions. Moreover, multiscale computational modeling (including quantum chemical calculations and reactive molecular dynamics simulations) was performed to elucidate the complex DES–lignin molecular interactions and the enhancement effect of DES pretreatment on 4VP production. During DES pretreatment, hydrogen-bonding interactions between the chloride ions of DESs and the hydroxyl groups of lignin formed independently of the DES type and were able to compete with lignin–carbohydrate complex (LCC) linkages. Notably, the decarboxylation reaction of the p-coumaric acid (pCA) ester occurred, resulting in the dissociation of pCA along with lignin. Further investigation demonstrated that various DES adducts were formed through etherification and acetylation reactions, and the reaction pathways and quantities were systematically simulated. These results are considered to shed light on the valorization of bagasse.