Pyrolysis mechanism of carbon matrix precursor cyclohexane(III)—pyrolysis process of intermediate 1-hexene

The pyrolysis mechanism of important intermediate 1-hexene of carbon matrix precursor cyclohexane was studied theoretically. Possible reaction paths were designed based on the potential surface scan and electron structure of the initial C–C bond breaking reactions. Thermodynamic and kinetic parameters of the possible reaction paths were computed by UB3LYP/6-31+G* at different temperature ranges. The results show that 1-hexene pyrolyzes at 873 K. When below 1273 K, the major reaction paths are those that produce C₃H₄, and above 1273 K, the major reaction paths are those that produce C₃H₃ from the viewpoint of thermodynamics. From the viewpoint of kinetics, the major product is C₃H₃, it results from the pyrolysis reaction of 1-hexene cracking bond C₃–C₄ and generating C₃H₅ and C₃H₇ with the activation energy ΔE₀^≠θ=296.32 kJ/mol. Kinetic results also show that product C₃H₄ accompany simultaneously, which is the side reaction starting from the pyrolysis of 1-hexene forming C₄H₇ and C₂H₅ with the activation energy of 356.73 kJ/mol. When reaching 1473 K, the rate constant of the rate-determining steps of these two reaction paths do not show much difference, which means both the reaction paths exist in the pyrolysis process at the high temperature. The above results are basically in accordance with mass spectrum analysis and far more specific.