Experimental and Theoretical Analysis of the Pyrolysis Mechanism of a Dimeric Lignin Model Compound with α-O-4 Linkage

In this study, 4-benzyloxyphenol was introduced as an α-O-4 dimeric lignin model compound to explore the pyrolysis mechanism of α-O-4 linkage in lignin. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), density functional theory (DFT) calculations, and collision theory were employed to illustrate the pyrolysis process experimentally and theoretically. The results suggest that the pyrolysis of 4-benzyloxyphenol starts from the Cα-O bond homolysis because it has the lowest bond dissociation energy (BDE) (164.9 kJ/mol). Among the four main products, as well as the primary products, the formation of bibenzyl and toluene depend on the probability of molecular collisions, while the formation of p-benzoquinone and hydroquinone is influenced by thermodynamic factors. The minor products, which were basically generated from the secondary pyrolysis of the main products and consisted of oxygenated compounds and polycyclic compounds, were only observed at 600 °C. The energy barrier, the enthalpy change, and their combined effects determined the formation of minor products.