PAH formation in acetylene-benzene pyrolysis

The contributions of different reaction pathways to the formation of polycy clic aromatic hydrocarbons (PAHs), the actual soot precursors, were investi gated for the shock tube pyrolysis of acetylene, benzene and an acetylene-b enzene (1:1) mixture. This study provides information on the principal reac tion steps leading to the fast formation of high molecular weight PAHs befo re soot inception. It is found that reaction pathways to high molecular wei ght PAHs and soot precursors including only successive growth steps of alip hatic hydrocarbons are in disagreement with the measured induction time of soot formation taken from the literature. The limiting, most time-consuming step in this reaction sequence is shown to be the formation of "outer ring s'', that is, PAHs consisting of four-carbon bay structures. In the model d eveloped in the present study, these difficulties are overcome by introduci ng combinative reaction steps of aryls.