The Dissociation of Diacetyl: A Shock Tube and Theoretical Study

Abstract

The dissociation of diacetyl dilute in krypton has been studied in a shock tube using laser schlieren densitometry at 1200-1800 K and reaction pressures of 55 +/- 2, 120 +/- 3, and 225 +/- 5 Torr. The experimentally determined rate coefficients show falloff and an ab initio/Master Equation/VRC-TST analysis was used to determine pressure-dependent rate coefficient expressions that are in good agreement with the experimental data. From the theoretical calculations k(infinity)(T) = 5.029 x 10(19) (T/298 K)(-3.40) exp(-37665/T) s(-1) for 300 < T < 2000 K. The laser schlieren profiles were simulated using a model for methyl recombination with appropriate additions for diacetyl. From the simulations rate coefficients were determined for CH(3) + CH(3) = C(2)H(6) and CH(3) + C(4)H(6)O(2) = CH(3)CO + CH(2)CO + CH(4) (k(T) = 2.818T(4.00) exp(-5737/T) cm(3) mol(-1) s(-1)). Excellent agreement is found between the simulations and experimental profiles, and Troe type parameters have been calculated for the dissociation of diacetyl and the recombination of methyl radicals.

A shock tube and theoretical study on the pyrolysis of 1,4-dioxane

“…a Sub-mechanism for recombination of methyl radicals taken from references. 48,51 Preliminary master equation calculations were carried out for the ring opening of 1,4-dioxane using the composite PES discussed above. In agreement with the experimental results, the formation of C3a and 2 CH 2 O + CH 2 CH 2 via SP4 is found to be small (o1%), and formation of EGVE and 2EOA are the two major channels.…”

Thermal dissociation of alkyl nitrites and recombination of alkyl radicals

“…Consequently, dissociation of n-propyl and subsequent reactions of methyl are not negligible, particularly for T 2 >~850 K. In this work, abstraction reactions by methyl are not competitive with addition reactions and thus methyl radicals are consumed by reactions 9 and 10 giving butane or ethane, respectively. Reaction 10, CH 3 +CH 3 ,was previously studied by DFST/LS and k 10 is taken from reference [38]. An estimate of k 9,n-propyl was obtained by analogy with CH 3 + C 2 H 5 =C 3 H 8 [23].…”

High‐temperature dissociation of ethyl radicals and ethyl iodide

“…Although the HI elimination channel has little effect on the observed initial density gradient, its inclusion in the reaction mechanism (Table I) used to simulate the complete density-gradient profile is important as it removes a source of H-atoms. k 1a was obtained through an iterative procedure where an initial estimate of dρ/dx at [28,34]. b The branching ratio of C-I bond dissociation and HI molecular elimination is temperature independent and k 1 /(k 1 + k 2 ) = 0.87 [8].…”

“…The model essentially consists of two parts, namely a portion that describes the chemistry associated with ethyl iodide, C2 species and halogenated species, reactions (1), (29)- (49), and a submechanism that describes the reactions related to methyl radicals. This latter part was taken from recent DFST/LS studies on the dissociation of methyl iodide and diacetyl [24,34] over a similar range of temperatures and pressures to the current work. For reactions with pressure dependencies, the rate coefficients were calculated at each reaction pressure.…”