Comparative Study of Anisole and 4-Vinylanisole Pyrolysis: Insight into Char, Tar, and Particle Formation During Lignin Pyrolysis
Journal Article
Overview
abstract
; Lignin pyrolysis generates oxygenated aromatics that can serve as renewable biofuel precursors. Anisole and substituted anisoles are widely used as model compounds to probe processes related to their production and use. We present a comparative study of anisole and 4-vinylanisole thermal decomposition using vacuum-ultraviolet photoionization mass spectrometry in a silicon carbide microreactor from 300 to 1300 K. For both molecular species, the initial decomposition pathway is; ; ; ; O; ; ; ; —; ; ; CH; 3; ; ; bond cleavage. The vinyl substituent lowers the bond dissociation energy, shifting decomposition to lower temperatures for 4-vinylanisole. Anisole pyrolysis produces hydrogen-atom, methyl, propargyl, phenoxy, and cyclopentadienyl radicals, phenol, cyclopentadiene, cyclopentadienyl dimer, methylcyclopentadiene,; ; CO; ; , acetylene, and benzene via methylcyclopentadiene. The products of 4-vinylanisole pyrolysis include hydrogen-atom, methyl, propargyl, fulvenallenyl, vinylphenoxy, vinylcyclopentadienyl, and cyclopentadienyl radicals, vinylphenol, vinylcyclopentadiene, dimethylfulvene, fulvenallene, vinylacetylene,; ; CO; ; , and acetylene, but no benzene. Vinyl substitution thus facilitates resonance-stabilized radical (RSR) formation at temperatures lower than the cracking temperature of anisole. Whereas 4-vinylanisole decomposes at a lower temperature than anisole, both species produce significant RSR products that facilitate aromatic growth and gas-to-condensed-phase hydrocarbon conversion, in contrast to their methyl-substituted analog. These new insights into RSR formation are applicable to lignin pyrolysis and may be useful for limiting char or tar formation during biofuel production and for developing predictive models of emissions from smoldering and propagating flaming wildfires.;
