Analysis of pyrolysis products from light hydrocarbons and kinetic modeling for growth of polycyclic aromatic hydrocarbons with detailed chemistry

Alternative chemical reaction pathways leading to polycyclic aromatic hydrocarbons (PAHs) in the pyrolysis of unsaturated light hydrocarbons were investigated to extend the previously proposed chemical kinetic model [K. Norinaga, O. Deutschmann, Ind. Eng. Chem. Res. 46 (2007) 3547-3557]. Although the previous model provided a reasonably good description of the pyrolysis behaviors observed in flow reactor experiments at 1073-1373 K, the concentration profiles for large PAHs were underestimated significantly. In this study, pyrolysates from ethylene, acetylene, and propylene were analyzed in detail using gas chromatography/mass spectroscopy (GC/MS) to find the intermediates that are believed to be crucial for PAH formation. Based on the newly identified products, reaction schemes for aromatic growth via 1,2-diphenylethylene, 1,2-diphenylacetylene, triphenylene, and benz[f]indene were proposed and added to the previous model. The predictive capabilities improved slightly simply because of the minority of the newly found compounds. The addition of reaction schemes for self-combination of indenyl radicals to form benz[a]anthracene and chrysene had a significant effect, and were found to be necessary to account for the formation of large PAHs such as benz[a]anthracene, chrysene, and benz[a]pyrene. Results from reaction flux analysis to identify the likely chemical pathways important for PAH growth, as well as numerical simulations of the influence of acetone contamination on acetylene pyrolysis, are presented.