Determination of the arrhenius parameters for the initiation reaction C3H6+ O2→ CH2CHCH2+ HO2

Abstract

Results obtained from studies of the oxidation of propene between 400 and 520 °C have been used to obtain the first Arrhenius parameters for the important chain initiation reaction RH + O₂→ R + HO₂, where RH is a hydrocarbon.

A full product analysis in the early stages of reaction has been made for a number of mixtures at 400, 440, 480 and 520 °C. It has been shown that hexa-1,5-diene is a major initial product and that its formation in reaction (8) represents the major termination process. By use of measurements of the initial rate of formation of hexa-1,5-diene [(R_{H D E})₀], so that secondary initiation is negligible, then in the absence of radical branching the simple relationship k₇[C₃H₆][O₂]=(R_{H D E})₀ holds. Values of k₇ at a constant temperature obtained from the relationship vary by less than a factor of two over a wide range of mixture composition, and the average values at each temperature give A₇= 10^9.2 dm³ mol^–1 s^–1 and E₇= 162 kJ mol^–1. CH₃CHCH₂+ O₂→ [graphic omitted] + HO₂(7), [graphic omitted] → CH₂CHCH₂CH₂CHCH₂(8)

When allowance is made for minor termination processes and for the radical-branching reaction (17), the values of A₇ and E₇ change only slightly, confirming the essential validity of the interpretation and of the simple relationship above. Final values of A₇= 10^{9.29 ± 0.41} dm³ mol^–1 s^–1 and E₇= 163.5 ± 6 kJ mol^–1 are obtained for reaction (7). The interpretation also gives reliable Arrhenius parameters of A₁₇= 10^{8.21 ± 0.60} dm³ mol^–1 s^–1 and E₁₇= 72.5 ± 8.3 kJ mol^–1 for the radical-branching reaction (17). No previous estimates are available for either reaction. CH₂CHCH₂+ O₂→ 2 radicals + products (17)