Effect of free methyl radicals on slow oxidation of propane and ethane

McDonald, Glen E., Schalla, Rose L.

A study of the effect of free methyl radicals on the slow oxidation of both ethane and propane was made by means of a photochemical decomposition reaction in a static system. The introduction of methyl radicals into a mixture of propane and oxygen or ethane and oxygen substantially lowered the initiation temperature of the combustion of the hydrocarbon. Measurements were made of the amount of propane oxidized in the presence of free methyl radicals at temperatures ranging from 0 degrees to 116 degrees C and for two different concentrations of propane. Oxidation of ethane, which was induced by the free methyl radical, was investigated for only one concentration from 0 degrees to 183 degrees C. From a plot of the log percentage of propane oxidized against the reciprocal temperature (degrees K), a zero activation energy was found for the reaction below 40 degrees C. For ethane the activation energy was zero below 120 degrees C. Above these two temperatures increase in the activation energy was observed. A mechanism is proposed to account for the zero activation energy, but no attempt was made to interpret the higher temperature reactions.

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