Determination of rate parameters of cyclohexane and 1-hexene decomposition reactions

Abstract

Peukert et al. recently published (Int. J. Chem. Kinet. 2010; 43: 107–119) the results of a series of shock tube measurements on the thermal decomposition of cyclohexane (c-C6H12) and 1-hexene (1-C6H12). The experimental data included 16 and 23 series, respectively, of H-atom profiles measured behind reflected shock waves by applying the ARAS technique (temperature range 1250–1550 K, pressure range 1.48–2.13 bar). Sensitivity analysis carried out at the experimental conditions revealed that the rate coefficients of the following six reactions have a high influence on the simulated H-atom profiles: R1: c-C6H12 = 1-C6H12, R2: 1-C6H12 = C3H5 + C3H7, R4: C3H5 = aC3H4 + H; R5: C3H7 = C2H4 + CH3; R6: C3H7 = C3H6 + H; R8: C3H5 + H = C3H6. The measured data of Peukert et al. were re-analysed together with the measurement results of Fernandes et al. (J. Phys. Chem. A 2005; 109: 1063–1070) for the rate coefficient of reaction R4, the decomposition of allyl radicals. The optimization resulted in the following Arrhenius parameters: R1: A = 2.441 × 1019, E/R = 52,820; R2: A = 3.539 × 1018, E/R = 42,499; R4: A = 8.563 × 1019, n = −3.665, E/R = 13,825 (high pressure limit); R4: A = 7.676 × 1031n = −3.120, E/R = 40,323 (low pressure limit); R5: A = 3.600 × 1012, E/R = 10699; R6: A = 1.248 × 1017, E/R = 28,538; R8: A = 6212 × 1013, E/R = −970. The rate parameters above are in cm3, mol, s, and K units. Data analysis resulted in the covariance matrix of all these parameters. The standard deviations of the rate coefficients were converted to temperature dependent uncertainty parameter f(T). These uncertainty parameters were typically f = 0.1 for reaction R1, f = 0.1–0.3 for reaction R2, below 0.5 for reaction R8 in the temperature range of 1250–1380 K, and above 1 for reactions R4–R6.