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.

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