High temperature pyrolysis of methane in shock waves. Rates for dissociative recombination reactions of methyl radicals and for propyne formation reaction

Abstract

The pyrolysis of 2% CHI and 5% CHI diluted with Ar was studied using both a single-pulse and time-resolved spectroscopic methods over the temperature range 1400-2200 K and pressure range 2.3-3.7 atm. The rate constant expressions for dissociative recombination reactions of methyl radicals, CH, + CH3 + C2H, + H and CH, + CH3 + C2H4 + Ha, and for C,H4 formation reaction were investigated. The simulation results required considerably lower value than that reported for CH3 + CH, -+ C2H4 + H2. Propyne formation was interpreted well by reaction C2H, + CH, -+ p-C,H, + H with k = 6.2 x 10'' exp(-17 kcal/RT) cm3 mol-' s-'.

Recombination of Methyl Radicals. 1. New Data between 1175 and 1750 K in the Falloff Region

“…Baulch 36,38,39 give nearly identical results with a bimolecular k(T) ∼ 6.5 × 10 -9 exp{-15430/T(K)} cm 3 s -1 . The latest work by Hidaka et al 40 gives a much lower value of 1.7 × 10 -10 exp{-16103/T(K)} cm 3 s -1 . Gordon et al 41 have calculated the transition state and obtain a barrier of 136 kJ/mol or ∆E/k ≈ 16 400 K. They conclude, "the concerted elimination of molecular hydrogen to form ethylene appears to be a very unlikely process".…”

On the dependence of the lifetime of an atomic cluster on the intensity of its heat exchange with the environment

“…As the heat transfer intensity between the cluster and environment increases, lifetime dependence (2), is transformed into Eq. (1). The key objective of this work is to study the character of the (2) to (1) transformation, as the heat transfer time τ th decreases to a finite value, and to determine the relation between the preexponential factorsξ and ξ of the decay of the thermalized and heatinsulated clusters.…”

“…where k −is the Boltzmann constant, E a − is the decay activation (isomerization) energy, T − is the temperature of the environment in contact with the cluster, and the preexponential factor ξ has the dimension of time and is the inverse of the frequency factor of the corresponding process. In some approaches, this preexponential factor is considered constant (see, e.g., [1]), but in the general case it depends not only on the atomic cluster structure and the characteristic heat transfer time τ th between the cluster and environment, but also on the temperature, i.e., ξ = ξ(τ th , T ) (see, e.g., [2,3]).…”

“…The decay process was considered for the C 20 fullerene and CH 4 molecule. The C 20 fullerene is the lightest of the existing fullerenes; for this reason, methane is added to the series of the clusters under study in order to follow the effect of the cluster mass on the character of the transition from law (2) to law (1).…”

Methane pyrolysis: Literature survey and comparisons of available data for use in numerical simulations

“…Bedarev et al based their work on the Kassel mechanism from the 1930s (4 reactions and 5 species) [42] and on another one (21 reactions, 13 species) developed by Hidaka et al [59]. The kinetic parameters were modified by Bedarev et al The comparison with the experimental data showed that the second mechanism was more suited to modelling the chemistry within the shock wave.…”