Oxidation chemistry of propene in the autoignition region: arrhenius parameters for the allyl + O2 reaction pathways and kinetic data for initiation reactions

Abstract

The oxidation of propene has been studied at a total pressure of 60 Torr between 400 and 520 °C, and a detailed product analysis made in the initial stages of reaction over a wide range of mixture composition. Mechanisms for the formation of the products are discussed. The initial rates of formation of hexa -1,5 -diene (HDE) and carbon monoxide are used to obtain A₈= 10^9.66±0.35 dm³ mol^–1 s^–1 and E₈= 78.6 ± 4.5 kJ mol^–1, the former giving [allyl] from the known value of k₁[graphic omitted] + [graphic omitted] → CH₂ CHCH₂CH₂CH CH₂(1)[graphic omitted] + O₂→ CO + products (8)

Arrhenius parameters are also given for alternative pathways of the allyl + O₂ reaction. All involve high energy barriers.

From measurements of the accelerating effect of small amounts of the additives CH₃CHO, HCHO, HDE and propene oxide, rate constants at 480 °C are obtained (for the first three) for the initiation reaction (21).RH + O₂→ R + HO₂(21)

Very few independent data for this type of reaction are available. The accelerating effect of propene oxide is ascribed to an exothermic isomerisation product which is not thermally stabilised at 60 Torr and undergoes homolysis to radical fragments. HDE is shown to have a spectacular accelerating effect on propene oxidation and value of k_21n/k₁₀= 1050 ± 200 at 480 °C is obtained.C₃H₆+ O₂→ [graphic omitted] + HO₂(10) HDE + O₂→ [graphic omitted]CH₂CH CH₂+ HO₂(21h)