Determination of the rate constant for HO2+ CH4→ H2O2+ CH3at 443 °C

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Abstract
Studies have been made of the addition of CH4 to mixtures of tetramethylbutane (TMB)+ O2 at 443 °C in KCl-coated Pyrex vessels. From measurements of isobutene and formaldehyde, formed virtually as sole products from TMB and CH4, respectively, a value of k10/k1/2 7= 1.00×10–2(dm3 mol–1 s–1)1/2 has been obtained. HO2+ CH4→ H2O2+ CH3(10), HO2+ HO2→ H2O2+ O2(7). Computer analysis shows that this value is very sensitive to the value of k18/k9 which controls the proportion of CH4 removed by OH attack, and the optimum conditions for studying reaction (10) were carefully selected. Use of A7= 109.48 dm3 mol–1 s–1 and E7= 5.8 kJ mol–1, obtained recently, gives k10=(3.39 ± 0.78)×102 dm3mol–1s–1 at 443 °C. No other experimental determinations of this rate constant have been reported. Based on the reasonable assumption of equal A factors per C—H bond for HO2+ CH4 and HO2+ C2H6, then Arrhenius parameters of A10= 10.05 ± 0.3 dm3mol–1s–1 and E10=103.1 ± 3.5 kJ mol–1 are suggested for the temperature range 350–1000 °C. OH + TMB → H2O + C8H17(9), OH + CH4→ H2O + CH3(18)

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