Wall-less reactor studies. Part 4.—Isobutane pyrolysis

Abstract

The pyrolysis of isobutane has been studied in a wall-less reactor between 970 and 1031 K in excess argon at 600 Torr (1 Torr = 133.3 N m^–2). The radical chain mechanism deduced from conventional studies is used to interpret the observed yields of ethane and methane in terms of the rate constants for chain initiation i-C₄H₁₀→ i-C₃H₇+ CH₃(1) and chain propagation by methyl radicals CH₃+ i-C₄H₁₀→ CH₄+ i-C₄H₉(16) or CH₄+ t-C₄H₉. (17) or The values of the latter are in excellent agreement with the results of work in static vessels, but the former are more than ten times smaller than any previous estimate. The implications of this for the thermodynamic values of the isopropyl radical are discussed. Using ΔH_f(i-C₃H₇) to obtain the activation energy, the Arrhenius expression for the homogeneous gas-phase rate constant k₁ deduced from the mean experimental value k₁(1000 K)=(1.8 ± 0.5)× 10^–3 s^–1 is k₁/s^–1= 8.4 × 10¹⁵ exp (–42 985/T).