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 Δ E 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 Δ E 0 θ≠ =374.46 kJ / mol . When reaching 1473 K, Δ G θ ≠ of the rate-determining step of reaction path producing 1-hexene ( Δ G θ≠ =284.19 kJ / mol ) is still smaller than Δ G θ ≠ of the rate-determining step of reaction path producing 1,3-butadiene ( Δ G θ≠ =313.10 kJ / mol ). The above results are basically in accord with mass spectroscopy analysis and GPC experiments.