Pyrolysis mechanism of carbon matrix precursor cyclohexane(I)

Abstract

Possible pyrolysis reaction paths of cyclohexane were studied by UMP2 (FULL)/3-21G ∗, UB3LYP/3-21G ∗, UB3LYP/6-31G ∗ and RB3LYP/6-31G ∗ calculation. Pyrolysis mechanism of cyclohexane at high temperature ranges were studied by UB3LYP/6-31G ∗, data Δ E 0 θ , Δ E θ , Δ H θ , Δ G θ and Δ E 0 θ≠ , Δ E θ≠ , Δ H θ≠ , Δ G θ≠ of five reaction paths (13 reaction steps) and reaction rates at 298–1473 K were obtained. The calculations show: (1) the pyrolysis temperature of cyclohexane is about 873 K, and the products are 1-hexene, butadiene and butene, (2) as far as the reaction paths producing 1-hexene and producing butene are concerned, when the temperature is higher than 873 K, The reaction producing butene are more feasible thermodynamically and dynamically, and the activation energy of rate-determining step is ΔE 0 θ≠=374.46 kJ/ mol. Furthermore, at 1473 K, kinetic calculation suggests that the both reactions have almost equal reaction rates. (3) In the further pyrolysis reaction, reaction path D that produces butadiene from 2-butene is supported by kinetics, which means 1,3-butadiene is the main product. (4) At 298–1473 K, for the reaction paths producing 1-hexene and producing butadiene, the former is supported by kinetics, and the activation energy of rate-determining step is ΔE 0 θ≠=374.46 kJ/ mol. When reaching 1473 K, Δ G θ≠ of the rate-determining step of reaction path producing 1-hexene ( ΔG θ≠=284.19 kJ/ mol) is still smaller than Δ G θ≠ of the rate-determining step of reaction path producing 1,3-butadiene ( ΔG θ≠=313.10 kJ/ mol). The above results are basically in accord with mass spectroscopy analysis and GPC experiments.