Effect of pyrolysis temperature on the pyrolytic degradation mechanism of β-aryl ether linkages

This study focused on providing a chemical understanding of the effect of pyrolysis temperature on the pyrolytic depolymerization of lignin polymers in biomass. The lignin network consists of various linkages with phenyl propane units and can be destroyed by the cleavage of various linkages, such as β-O-4, α-O-4, β-β, and β-5. Among of the linkage, the most abundant linkages are β-O-4, which account for more than 40% of the total linkages in softwood lignin and up to 60% in hardwood lignin. For investigating the cleavage of β-aryl ether linkages leading to depolymerization of the lignin polymer, β-O-4 lignin dimer models, guaiacylglycerol-β-guaiacyl ether, guaiacylglycerol-β-coniferyl ether, and p-hydroxyphenylglycerol-β-coumaryl ether were subjected to analytical pyrolysis at various temperatures. Abundant pyrolysis products were identified, and the effect of temperature on the product composition was analyzed. Several cleavage pathways of β-aryl ether linkages have been proposed on the basis of the compositions and structures of the pyrolysis products. The manner of β-aryl ether cleavage is highly susceptible to the pyrolysis temperature, with most secondary products being produced in high yield upon high-temperature pyrolysis.