High-temperature oxidation of methyl radicals in open systems

Abstract

Rates of CH_3 oxidation by O_2 in a continuous flow, low-pressure reactor were determined by molecular beam mass spectrometry between 982 and 1395 K. F = {([CH_3]_0/[CH_3])- 1}, a measure of the extent of reaction, increases with [O_2] above threshold values [O_2]_c , and exhibits a complex dependence on [CH_3]_0; [O_2]_c values decrease with temperature. These findings are quantitatively accounted for by a gas-phase branched-chain mechanism with carrier losses at the reactor walls. Numerical simulations were performed by using two adjustable parameters. Adoption of recent data for k_2 (CH_3 + O_2 → CH_3O + O) led to〈γ〉= 8 x 10^(-4) for the combined probability of radical recombination on silica in this range and to k_2 (CH_3 + O_2 → CH_2O + OH) values that are in agreement with updated estimates and new shock tube results. An exploratory analysis of the nonlinearities dated with this process provides clues for the rational control of selectivity in the oxidative dimerization of methane.

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