INHIBITING EFFECT OF CF3I ON THE REACTION BETWEEN CH4 AND O-2 IN A JET-STIRRED REACTOR

This is an experimental and theoretical study of the inhibiting effect of the addition of 1-5% (relative to the amount of methane) of CF3I o n methane oxidation under the following conditions: equimolecular CH4- O-2 mixtures, temperature from 970 to 1150 K, total pressure 1 bar, sp ace times ranging from 1 to 8 s corresponding to methane conversions o f 1-80%. The main observed effects of the addition of this halogenated compound were a large decrease of the conversions of methane and oxyg en, a reduction of the selectivity in ethane formation, and an importa nt increase of the selectivity in ethylene formation. In the experimen tal range studied, the inhibiting effect slightly increased when the a mount of additive decreased. Methane oxidation and the influence of ha logenated compounds on this reaction were modelled using a detailed ki netic reaction mechanism, including the recent values for the rate con stants of reactions of iodinated compounds. The proposed mechanism was able to reproduce the experimental data. Sensitivity analyses led to a determination of the dominant steps that account for the inhibiting effect of CF3I. The inhibiting influence of CF3I on methane oxidation seems to be mainly due to the two following steps: I + CH4 --> HI + CH 3 and I + HO2 --> O-2 + HI. These two steps form a cycle which acts as a termination reaction between HO2 and CH3 radicals to give CH4 and O -2. (C) 1997 by The Combustion Institute.