Pyrolysis mechanism of α-O-4 linkage lignin dimer: A theoretical study

Lignin is one of main components in biomass. In order to better understanding of the detailed mechanism of lignin pyrolysis and the forming processes of its main products, the pyrolysis processes of α-O-4 linkage lignin dimer model compound 1 were theoretically investigated by employing density functional theory (DFT) methods at B3LYP/6-31G(d,p) level. Three possible pyrolytic reaction pathways were proposed. The activation energies of each reaction step in the pyrolysis processes were calculated and the effect of alkalis metal ions on bond dissociation energies was analyzed. The calculation results indicate that the homolytic cleavage reaction of CαO bond is the major pyrolysis reaction channel, and the homolytic cleavage of OCH3 bond and the homolytic cleavage reaction of CαCβ bond are the competitive reaction channels in pyrolysis processes of the model compound 1. The main pyrolysis products are phenolic compounds such as guaiacol, p-hydroxyphenyl-ethanol, p-hydroxyphenyl-acetaldehyde and 2-hydroxybenzaldehyde.