Effect of deep eutectic solvents-regulated lignin structure on subsequent pyrolysis products selectivity

The chemical structure of lignin has an important effect on the lignin pyrolysis product distributions. Therefore, it is of great significance to regulate the selectivity of pyrolysis products by modifying the lignin structure. Herein, deep eutectic solvents (DESs) including choline chloride/ethylene glycol (CE), zinc chloride/ethylene glycol (ZE) and choline chloride/acetic acid, treatment of softwood kraft lignin (SKL) is demonstrated. Systematic characterization indicate that the DESs are not only highly conducive to increasing the hydrogen to carbon efficient ratio, reducing the molecular weight and β-O-4 linkage, but also contributes to the maximum degradation rate and thermal stability of SKL. Noticeably, CE and ZE treatment are significantly improved the amount of H-phenols and C-phenols derived lignin pyrolysis, respectively. In addition, DESs pretreatment are also beneficial to the increment of monomer aromatic hydrocarbons. More importantly, the CE pretreatment contributes to the improvement of bio-oil yield and decrease of char content from lignin pyrolysis.