Pyrolysis mechanism of carbon matrix precursor cyclohexane(I)

Possible pyrolysis reaction paths of cyclohexane were studied by UMP2 (FULL )/3-21G*, UB3LYP/3-21G*, UB3LYP/6-31G* and RB3LYP/6-31G* calculation. Pyrol ysis mechanism of cyclohexane at high temperature ranges were studied by UB 3LYP/6-31G*, data DeltaE(0)(theta), DeltaE(theta), DeltaH(theta), DeltaG(th eta) and DeltaE(0)(theta not equal), DeltaE(theta not equal), DeltaH(0 not equal), DeltaG(theta not equal) 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 a re 1-hexene, butadiene and butene, (2) as far as the reaction paths produci ng 1-hexene and producing butene are concerned, when the temperature is hig her than 873 K, The reaction producing butene are more feasible thermodynam ically and dynamically, and the activation energy of rate-determining step is DeltaE(0)(theta not equal) = 374.46 kJ/mol. Furthermore, at 1473 K, kine tic calculation suggests that the both reactions have almost equal reaction rates. (3) In the further pyrolysis reaction, reaction path D that produce s butadiene from 2-butene is supported by kinetics, which means 1,3-butadie ne 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 DeltaE(0)(theta not equa l) = 374.46 kJ/mol. When reaching 1473 K, DeltaG(theta not equal) of the ra te- determining step of reaction path producing 1-hexene (DeltaG(theta not equal) = 284.19 kJ/mol) is still smaller than DeltaG(theta not equal) of th e ratedetermining step of reaction path producing 1,3-butadiene (DeltaG(the ta not equal) = 313.10 kJ/mol). The above results are basically in accord w ith mass spectroscopy analysis and GPC experiments. (C) 2001 Elsevier Scien ce B.V. All rights reserved.