A comparison of the pyrolysis behavior of selected β-O-4 type lignin model compounds

The cleavage of intermolecular linkages in lignin is a crucial yet complicated factor to properly deconvolute during the pyrolysis of lignin; thus, four typical beta-O-4 lignin dimer compounds with different substituents on C-alpha and Cp position (including C-alpha=O, C-alpha OH and C-beta-CH2-OH groups) were synthesized. The results showed that a C-beta-CH2OH group greatly inhibited the generation of volatile products, and promoted the generation of char. When the C-alpha=O group existed alone, the volatility of model compounds reached a maximum of similar to 94 mass-%. At low temperatures (< 300 degrees C), the cleavage of intermolecular linkages dominated, followed by secondary pyrolysis of primary products to various gases (e.g., CO2, CH4, CO). Guaiacol and 2-methoxy-benzaldehyde, two typical products, displayed yields that reflected the degree of cleavage of the C-beta-O and C-alpha-C-beta bonds. It was confirmed that oxidation of the C-alpha-OH group to C-alpha=O facilitated cleavage of the C-alpha-C-beta bond and favored formation of 2-methoxy-benzaldehyde. In addition, new dimers that were intermediates during the pyrolysis process were formed via intermolecular elimination reactions that further affected products distribution and selectivity.