Arrhenius parameters for the reaction HO2+ C2H6→ C2H5+ H2O2 over the temperature range 400–500 °C

Abstract

Studies have been made of the addition of C₂H₆ to mixtures of tetramethylbutane (TMB)+ O₂ over the temperature range 400–520 °C in both boric acid-coated and KCl-coated Pyrex vessels. From measurements of the relative yields of i-C₄H₈ and C₂H₄, formed from TMB and C₂H₆, respectively, values of k₁₀/k^½₇ have been determined: HO₂+ C₂H₆→ H₂O₂+ C₂H₅(10), HO₂+ HO₂→ H₂O₂+ O₂. (7) By use of low total pressures (ca. 15 Torr), the contribution of OH attack to the overall formation of C₂H₄ has been reduced to a very low level. At temperatures above 470 °C, the values of k₁₀/k^½₇ in KCl-coated vessels were noticeably above those obtained from the boric acid-coated vessels, and this has been attributed to possible gas-phase regeneration of radicals when H₂O₂ is removed at the KCl surface. Values of E₁₀–½E₇= 82.7 ± 1.5 kJ mol^–1 and A₁₀/A^½₇= 10^{5.49 ± 0.11}(dm³ mol^–1 s^–1)^½ were obtained.

Low-temperature values of k₇ have been partially re-interpreted and combined with Tröe's single temperature value at 1100 K to obtain values of k₇ for use under the conditions of the present study. In this way, Arrhenius parameters of E₁₀= 85.6 ± 2.5 kJ mol^–1 and A₁₀= 10^{10.23 ± 0.16} dm³ mol^–1 s^–1 were obtained. No other data are available for this reaction, but the parameters are in good agreement with A= 10^10.38 dm³ mol^–1 s^–1 and E= 84.5 ± 8 kJ mol^–1 for the reaction of HO₂ radicals with TMB, both alkanes containing only primary C—H bonds.