Reactions of methyl radicals with propene at temperatures between 750 and 1000 K

Abstract

The pyrolysis of propene, initiated by methyl radicals, has been studied in the temperature range 750–1000 K and at a pressure of 0.13 bar in a quasi-wall-free reactor using laser heating by fast vibrational–translational (V–T) energy transfer. This is a convenient method to study homogeneous high-temperature kinetics since the reactor walls remain cold. The radial temperature distribution in the reactor has been investigated by four different methods: a stationary heat balance, optical absorption, pressure rise, and the temperature dependence of the rate of an isomerization reaction. Methyl radicals were produced ia the fast thermal dissociation of di-tert-butyl-peroxide and the products were analysed using GC-MS. The main products of the overall reaction of the model system propene and methyl (C₃H₆ + CH₃) were isopentane (iso-C₅H₁₂) and but-1-ene (1-C₄H₈), whereas allene (C₃H₄), trans-but-2-ene (trans-2-C₄H₈) and cis-but-2-ene (cis-2-C₄H₈) were minor components, all showing a strong dependence on temperature. The product distribution and the temperature dependence were analysed by a kinetic model of 61 species and 166 reactions developed for the high-temperature oxidation of butane and the low-temperature oxidation of n-pentane and isopentane. It was necessary to include a few missing reactions and to adjust some rate constants to make the modeling agree with the experimental investigations. This extended mechanism has to be evaluated further in forthcoming experiments.