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 k2e= 109.8 exp (– 9500/RT) cm3 mole–1 sec–1. The rate constant of the reaction i-C3H7˙→C2H4+ CH3˙(2d) is found to be k2d= 1012±0.2 exp(–34500±500/RT) sec–1 in agreement with the value of Heller and Gordon.8 The value of k2e being known, the rate parameters for the process i-C4H10→i-C3H7˙+ CH3˙(1) can be evaluated. From the experimental data, k1= 1017.8±0.9 exp (– 82,500±3,200/RT) sec–1 In combination with thermochemical data this value yields k–1= 1013.3 exp (600/RT) cm3 mole–1˙ sec–1, which at 800°K yields k–1= 1013.5 cm3 mole–1 sec–1, as would be expected for a cross-combination from the value for methyl-methyl recombination (1013.3 cm3 mole–1 sec–1).