Base-catalyzed depolymerization of lignin into phenols: methoxy groups' secondary reactions triggered phenol regulation and repolymerization

Lignin depolymerization for aromatic chemicals and liquid fuels is one of the biggest challenges in the developing biomass-based chemical industry. Highly functionalized phenols from base-catalyzed depolymerization (BCD) reactions are not yet common and, therefore, need further processing if they are to be used in intended applications. In the present study, we discuss in detail the effect of reaction time on the yield and distribution of products during the BCD process. We aimed to reveal important phenol formation about a chain reaction mechanism triggered by secondary depolymerization of methoxy groups during a BCD reaction, thereby obtaining high-yield or highly selective phenol products. The experimental results confirm that guaiacol undergoes hydrolysis of the methoxy group and can form catechol and syringol could demethoxylate to form guaiacol and then catechol. The chemical equilibria between the depolymerization and repolymerization reaction of phenol products appeared at 160-min reaction time under 300 degrees C during BCD. In particular, when the reaction time was increased to 160 min, the yield of total phenols reached 20.23%. The present study did not use critical metals, just reaction times to control the secondary depolymerization of methoxy groups, which decreases operating costs and improves the yield and selectivity of phenol compounds. This has great significance regarding the suppression of lignin repolymerization.

Automated summary

This study investigates the effect of reaction time on the yield and distribution of products during base-catalyzed depolymerization (BCD) process for lignin depolymerization. The results reveal a chain reaction mechanism triggered by secondary depolymerization of methoxy groups, leading to high-yield or highly selective phenol products. By controlling the reaction time, the study suggests a cost-effective and efficient method for lignin depolymerization.