The pyrolysis of methylcyclopentadiene: Isomerization and formation of aromatics

Ikeda, Eitatsu; Tranter, Robert S.; Kiefer, J. H.; Kern, R. D.; Singh, Hari Ji; Zhang, Q.

doi:10.1016/s0082-0784(00)80573-1

Cited by 44 publications

(53 citation statements)

References 18 publications

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“…Most of the hexadienes that produced the larger [C 6 H 6 ] max also produced large [C 5 H 6 ] max and [C 5 H 8 ] max , which suggests the following benzene formation mechanism for these hexadienes: (1) cyclization of linear C5 decomposition products to fivemembered ring compounds, (2) dehydrogenation of the five-membered ring compounds to cyclopentadienyl (C 5 H 5 ), (3) methyl addition to C 5 H 5 to produce methylcyclopentadienyl (C 5 H 4 CH 3 ), (4) isomerization of C 5 H 4 CH 3 to fulvene (C 6 H 6 ) + H, and (5) isomerization of fulvene to benzene. Benzene formation via steps (3) to (5) has been demonstrated theoretically and in shock tubes [46][47][48]. Furthermore, our measurements in cyclopentene-doped nonpremixed methane flames [49] and measurements and modeling in cyclopentene premixed flames [50,51] show that steps (2) to (5) readily convert cyclopentene to benzene.…”

Section: Benzenesupporting

confidence: 61%

Decomposition and hydrocarbon growth processes for hexadienes in nonpremixed flames

McEnally¹,

Pfefferle²

2008

Combustion and Flame

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Alkadienes are formed during the decomposition of alkanes and play a key role in the formation of aromatics due to their degree of unsaturation. The experiments in this paper examined the decomposition and hydrocarbon growth mechanisms of a wide range of hexadiene isomers in soot-forming nonpremixed flames. Specifically, C3 to C12 hydrocarbon concentrations were measured on the centerlines of atmospheric-pressure methane/air coflowing nonpremixed flames doped with 2000 ppm of 1,3-, 1,4-, 1,5-, and 2,4-hexadiene and 2-methyl-1,3-, 3-methyl-1,3-, 2-methyl-1,4-, 3-methyl-1,4-pentadiene, and 2,3-dimethyl-1,3-butadiene. The hexadiene decomposition rates and hydrocarbon product concentrations showed that the primary decomposition mechanism was unimolecular fission of C-C single bonds, whose fission produced allyl and other resonantly stabilized products. The one isomer that does not contain any of these bonds, 2,4-hexadiene, isomerized by a six-center mechanism to 1,3-hexadiene. These decomposition pathways differ from those that have been observed previously for propadiene and 1,3-butadiene, and these differences affect aromatic hydrocarbon formation. 1,5-Hexadiene and 2,3-dimethyl-1,3-butadiene produced significantly more C 3 H 4 and C 4 H 4 than the other isomers, but less benzene, which suggests that benzene formation pathways other than the conventional C3 + C3 and C4 + C2 pathways were important in most of the hexadiene-doped flames. The most likely additional mechanism is cyclization of highly unsaturated C5 decomposition products, followed by methyl addition to cyclopentadienyl radicals.

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Section: Benzenesupporting

confidence: 61%

Decomposition and hydrocarbon growth processes for hexadienes in nonpremixed flames

McEnally¹,

Pfefferle²

2008

Combustion and Flame

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“…Here the proposed path involves the steps C 3 H 3 + C 2 H 2 → c-C 5 H 5 (1) c-C 5 H 5 + CH 3 → C 6 H 6 + 2H (2) 2c-C 5 H 5 → c-C 8 H 10 + 2H (3) There is certainly convincing evidence for these reactions, taken individually; the issue is rather their efficacy compared to other competing paths. Reaction (1) is the reverse of the path already proposed for CPDL dissociation [6][7][8] and Reaction (2) has also been supported both theoretically and experimentally [4,9,10] as has Reaction (3) [1,4,5]. The success of this scheme for aromatic formation is most sensitive to the rate of Reaction (1), and the extraction of this from its reverse dissociation rate requires a solid equilibrium constant, i.e., a good set of thermodynamic functions for all involved, especially the CPDL.…”

Section: Introductionsupporting

confidence: 55%

“…There are at least two previous estimates of thermodynamic functions for CPDL available, one due to Burcat et al [26], apparently the origin of the thermodynamic tables of ChemKin [29], and the other due to Ikeda et al 10 . These estimates do not directly treat the pseudorotation.…”

Section: /T and Smentioning

confidence: 99%

Thermodynamic functions for the cyclopentadienyl radical: The effect of Jahn–Teller distortion

Kiefer

Tranter

Wang

et al. 2001

Int J of Chemical Kinetics

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We report CASSCF/cc-PVDZ calculations of the potential surface for the title JahnTeller molecule. Energies are calculated along all normal coordinates that can be affected by Jahn-Teller distortion. Both the E 2 in-plane bend and stretch modes are found to be involved, but the bend contribution is very small and its contribution to the entropy is negligible. The in-plane stretch modes strongly dominate, affording a maximum stabilization energy of 4.73 kcal/mol. Harmonic frequencies are calculated for the other modes in the D 5h configuration, and these are scaled in accordance with a comparison of experimental frequencies with similar calculations on cyclopentadiene. Energy levels for nuclear motion in the JahnTeller modes are then determined using the calculated surface, and these are combined with the scaled harmonic frequencies to obtain complete thermodynamic functions for the radical. The results are then fit to both the NASA polynomial form and a compact power series in inverse temperature for modeling applications. Because of changes in degeneracy and symmetry number, the entropy is actually lower than previous estimates. Nonetheless, the effect of the pseudorotation on the entropy is noticeable over the entire span of temperatures. This work is evidently the first to present both energy levels and thermodynamic functions for a Jahn-Teller molecule derived from a complete and consistent theoretical treatment.

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“…By far the most important resonantly stabilized C 5 radical is cyclo-C 5 H 5 (cyclopentadienyl radical), which has been proposed to form naphthalene through a selfrecombination reaction [2,5,6,149,170,173], or to form fulvene through reaction with methyl radicals [170,174,175]. As a consequence, cyclopentadienyl may be an important intermediate in the growth of higher hydrocarbons (PAHs) and soot in rich flames.…”

Section: Hansen Et Al Identified C 4 H 3 and C 4 H 5 Isomers In Fuelmentioning

confidence: 99%

Recent contributions of flame-sampling molecular-beam mass spectrometry to a fundamental understanding of combustion chemistry

Hansen

Cool

Westmoreland

et al. 2009

Progress in Energy and Combustion Science

329

261

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a b s t r a c tFlame-sampling molecular-beam mass spectrometry of premixed, laminar, low-pressure flat flames has been demonstrated to be an efficient tool to study combustion chemistry. In this technique, flame gases are sampled through a small opening in a quartz probe, and after formation of a molecular beam, all flame species are separated using mass spectrometry. The present review focuses on critical aspects of the experimental approach including probe sampling effects, different ionization processes, and mass separation procedures. The capability for isomer-resolved flame species measurements, achievable by employing tunable vacuum-ultraviolet radiation for single-photon ionization, has greatly benefited flame-sampling molecular-beam mass spectrometry. This review also offers an overview of recent combustion chemistry studies of flames fueled by hydrocarbons and oxygenates. The identity of a variety of intermediates in hydrocarbon flames, including resonantly stabilized radicals and closed-shell intermediates, is described, thus establishing a more detailed understanding of the fundamentals of molecular-weight growth processes. Finally, molecular-beam mass-spectrometric studies of reaction paths in flames of alcohols, ethers, and esters, which have been performed to support the development and validation of kinetic models for bio-derived alternative fuels, are reviewed.

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The pyrolysis of methylcyclopentadiene: Isomerization and formation of aromatics

Cited by 44 publications

References 18 publications

Decomposition and hydrocarbon growth processes for hexadienes in nonpremixed flames

Decomposition and hydrocarbon growth processes for hexadienes in nonpremixed flames

Thermodynamic functions for the cyclopentadienyl radical: The effect of Jahn–Teller distortion

Recent contributions of flame-sampling molecular-beam mass spectrometry to a fundamental understanding of combustion chemistry

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