Initiation of isobutane pyrolysis

Abstract

A study of the kinetics of formation of ethylene and propane in the pyrolysis of isobutane over wide ranges of temperature and initial reactant pressure has established the occurrence of the radical isomerization reaction i-C₃H₇˙+ i-C₄H₁₀→n-C₃H₇˙+ i-C₄H₁₀, (2e) the measured rate constant being k_2e= 10^9.8 exp (– 9500/RT) cm³ mole^–1 sec^–1. The rate constant of the reaction i-C₃H₇˙→C₂H₄+ CH₃˙(2d) is found to be k_2d= 10^12±0.2 exp(–34500±500/RT) sec^–1 in agreement with the value of Heller and Gordon.⁸ The value of k_2e being known, the rate parameters for the process i-C₄H₁₀→i-C₃H₇˙+ CH₃˙(1) can be evaluated. From the experimental data, k₁= 10^17.8±0.9 exp (– 82,500±3,200/RT) sec^–1 In combination with thermochemical data this value yields k_–1= 10^13.3 exp (600/RT) cm³ mole^–1˙ sec^–1, which at 800°K yields k_–1= 10^13.5 cm³ mole^–1 sec^–1, as would be expected for a cross-combination from the value for methyl-methyl recombination (10^13.3 cm³ mole^–1 sec^–1).