Reactions of methyl radicals with isobutane at temperatures between 800 and 950 Kelvin

The methyl radical induced pyrolysis of isobutane has been studied in the temperature range of 800-950 K and at pressures of 80 and 130 mbar. We used Co-2-laser induced heating by fast vibrational-translational (V-T) energy transfer from SF6 to the reaction mixture, 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: stationary heat balance, optical absorption, pressure rise, and the temperature dependence of the rate of an isomerization reaction. Methyl radicals were produced in the presence of isobutane via the fast thermal decomposition of di-tert-butyl-peroxide and the products were analyzed using gas chromatography and mass spectroscopy. The main products of the overall reaction were propene (C3H6) and isobutene (i-C4H8), whereas ethene (C2H4), propane (C3H8), neo-pentane (neo-C5H12), and isopentane (i-C5H12) were minor products. The product distribution showed strong temperature dependence, The product yields and their temperature dependence were analyzed by a kinetic model developed for the high temperature oxidation of n-butane and the low temperature oxidation of n-pentane, and isopentane. We included a few missing reactions and slightly adjusted some rate constants to obtain a better agreement between the modeling and the experiments. The extended mechanism consists of 63 species and 171 reactions to be evaluated further in forthcoming experiments. (C) 2001 John Wiley & Sons, Inc.