THE INHIBITING EFFECT OF CF3BR ON THE REACTION CH4+O-2 AT 1070-K

The continuing deterioration of the ozone layer underlines the need to find substitutes for halons (bromochlorofluorocarbons). The development of such replacements requires a good understanding of the mechanism of the inhibition of both combustion and oxidation by the compounds used so far. Therefore, this paper is focused on an experimental and theoretical study of the inhibiting effects of CF3Br on methane oxidation in the following conditions: equimolecular CH4-O-2 mixtures, temperature 1070 K, total pressure 1 bar, space times ranging from 1 to 7 s corresponding to methane conversions of 10%-55%. The main observed effects of the addition of this halogenated compound were a large decrease of the conversion of methane and oxygen and an important reduction of the selectivity in ethane formation. Methane oxidation and the influence of halogenated compounds on this reaction were modeled using a detailed kinetic reaction mechanism including the recent kinetic values involved in the oxidation of C-1-C-2 hydrocarbons and in the reactions of brominated and fluorinated compounds. The proposed mechanism was able to reproduce our experimental data. Sensitivity analyses have facilitated a determination of the dominant steps accounting for the inhibiting effect of CF3Br at 1070 K. The inhibiting influence of CF3Br on methane oxidation seems to be mainly due to a cycle, among Br, HBr, and CH3Br, which acts as a termination step between CH3 and H radicals.