Single-pulse shock tube studies of hydrocarbon pyrolysis. Part 6.—The pyrolysis of isobutene

Abstract

The thermal decomposition of isobutene has been studied in the single-pulse shock tube over the temperature range 1055–1325 K. The generalized mechanism for alkane pyrolysis proposed by Bradley (Proc. Roy. Soc. A, 1974, 337, 199) is found to apply to the pyrolysis of alkenes provided allowance is made for the possibilities of initiation by C—H rupture and of longer lifetimes for alkenyl radicals. Both processes prove of minor significance for this particular alkene although they make computer simulation more difficult. Optimization by computer of the critical reaction parameters led to the following rate constants: iso–C₄H₈→ C₃H₅+ CH₃(1), k₁= 1.82 × 10¹⁸ exp(– 375 kJ mol^–1/RT)s^–1 CH₃+ C₄H₈→ CH₄+ C₄H₇(3), k₃= 6.8 × 10¹⁰ exp(– 82 kJ mol^–1/RT)dm³ mol^–1 s^–1 CH₃+ C₂H₆→ CH₄+ C₂H₅(23), k₂₃= 3.2 × 10¹⁰ exp(–75 kJ mol^–1/RT) dm³ mol^–1 s^–1 H + C₄H₈→ H₂+ C₄H₇(4), H + C₄H₈→ C₄H₉(6)k₄/k₆= 6.8 exp(20 kJ mol^–1/RT) C₄H₉→ C₃H₆+ CH₃(13), C₄H₉→ C₂H₄+ C₂H₅(14)k₁₃/k₁₄= 1.8 at 1200 k.