Co-Evolution of Volatiles and Pyrolytic Residue during Lignin Pyrolysis

To address knowledge gaps in tracking stage-specific volatile evolution during lignin slow pyrolysis, this study developed a modified Py-GCMS method that enables in situ capture and analysis of pyrolysis volatiles at designated temperature stages. Combined with TG-FTIR, CP/MAS NMR, and kinetic analysis, coevolution mechanisms of volatiles and pyrolytic residues were elucidated. Results show that as the pyrolysis temperature of lignin increased within the range of 150-750 °C, reactions including α- and β-ether bond cleavage, side-chain C-C bond cleavage, and repolymerization occurred progressively. The volatilization of lignin may be attributed to the cleavage of its side chains. The side chain of the volatiles also gradually changed from unsaturated groups to methyl groups or was removed. Owing to these reactions, the predominant components in volatiles undergo noticeable variations across distinct pyrolysis stages of lignin. Moreover, activation energy analysis revealed the relative ease of different reaction pathways, with α- and β-ether bond homolysis requiring the lowest energy.