A study on the pyrolysis mechanism of a β-O-4 lignin dimer model compound using DFT combined with Py-GC/MS

Lignin is abundant in natural world, and it can be converted into value-added chemicals by thermo-chemical method. Since the insufficient understanding of the lignin pyrolysis mechanism limits practical application of lignin pyrolysis, it is quite important to deeply understand the mechanism of lignin pyrolysis from the molecular level. In this work, 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-ethanol was chosen as a β-O-4 type dimer model compound of lignin. Combining the density functional theory (DFT) method with Py-GC/MS to analyze the pyrolysis behavior of lignin dimer model compound, 9 reasonable reaction paths were studied by DFT. The results showed that 2-methoxy-4-vinylphenol (P3) and 2-methoxyphenol (P4) are the main products of lignin dimer model compound pyrolysis. The kinetic and thermodynamics analysis indicates the homolytic cleavage of Cβ–O is the initial reaction step for forming P3 and P4. In the subsequent reactions, P3 is mainly formed by hydrogenation and then dehydration. P4 is mainly formed by hydrogenation. Increasing temperature can promote the spontaneous reaction of the main paths. The exploration for the pyrolysis mechanism of lignin dimer is helpful to directionally regulate lignin pyrolysis products in future studies.