Reactions of ethyl radicals with oxygen over the temperature range 400–540° C
Abstract
The reactions of C2H5 radicals with O2 have been studied by adding ethane to mixtures of 2,2,3,3-tetramethylbutane + O2 and of H2+ O2. The only initial products from C2H5 radicals are ethylene and ethylene oxide in relative yields of ≈ 100:1. For all mixtures studied, the ratio [C2H4]/[C2H4O] is constant at low extents of reaction but then decreases due to formation of ethylene oxide by reaction (14). The initial value of the product ratio is independent of variations in mixture composition, total pressure and vessel surface. Over the temperature range 400–540°C, values of A1/A2= 13.6 ± 2.1 and E2–E1= 12.5 ± 1.0 kJ mol–1 are obtained, where reaction (2) is the overall reaction for the formation of ethylene oxide. C2H5+ O2→ C2H4+ HO2(1) C2H5+ O2→ C2H4O + OH (2) HO2+ C2H4→ C2H4O + OH (14) By the use of the trace amounts of butane formed at 540°C to calculate the concentration of C2H5 radicals, k1= 7.7 × 107 dm3 mol–1 s–1 is obtained; combination of this with independent results at 440°C gives E1= 16.2 kJ mole–1 and A1= 108.93 dm3 mol–1 s–1, which are considered the most reliable parameters available for this reaction.
Based on the formation of ethylene oxide in a peroxy radical isomerisation and decomposition sequence, values of log10(A16/s–1)= 13.29 ± 0.50 and E16= 143.7 ± 10 kJ mol–1 are calculated for the transfer of a primary H atom (1,4p) in reaction (16). This A factor is higher, by a factor of about ten, than the figure suggested by Benson for a (1,5) H atom transfer. C2H5OO → C2H4OOH (16)