Demethylation of a methoxy group to inhibit repolymerization during alkaline lignin pyrolysis

• Published in: Fuel (Guildford) Vol. 286; p. 119394
• Main Authors: Ma, Hao, Li, Tengfei, Wu, Shubin, Zhang, Xiaohua
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.02.2021; Elsevier BV
• Subjects: Demethylation; Lignin; Methoxy group; Phenolic compounds; Phenols; Pyrolysis; Repolymerization; Repolymerization; Lignin; Pyrolysis; Demethylation; Methoxy group
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2020.119394

•Methoxy group demethylation can reduce the Ea of the late pyrolysis of lignin.•Methoxy group demethylation can reduce the yeild of lignin pyrolytic char.•Methoxy group can promote char formation via interaction with phenolic hydroxyl.•Iodocyclohexane not only promotes demethylation but also causes ether-bond breakage. The methoxy group in lignin was demethylated using iodocyclohexane; then, lignins with different methoxy group contents and six model compounds were pyrolyzed at 600 °C to investigate the role of methoxy groups during lignin pyrolysis. The results indicated that iodocyclohexane modification not only promotes methoxy demethylation but also causes side chain ether bond breakage. Demethylation of the methoxy group could inhibit the repolymerization reaction and reduce the activation energy during later lignin pyrolysis, and could also promote the homolysis of Ar-Cα. The pyrolysis experiments of the model compounds showed that the methoxy group is not an essential factor for the formation of pyrolytic char; however, it could promote the repolymerization reaction by intramolecular interaction with phenolic hydroxyl.