ChemInform Abstract: The Mechanism of the Reversible Reaction: 2 C2H2 ⇌ Vinyl Acetylene and the Pyrolysis of Butadiene

Benson, S. W.

doi:10.1002/chin.198927056

Cited by 3 publications

(3 citation statements)

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“…Benson 15 and many others proposed and argued for the formation of a short-lived biradical formed directly from acetylene dimerization as the key initiation step: One of the arguments for a radical playing a key role is that radical scavengers, such as NO, inhibit the formation of large molecular weight products. According to Benson the biradical in turn rearranges to vinyl acetylene (VA) with a rapid H-shift:…”

Section: Introductionmentioning

confidence: 99%

Initiation Reactions in Acetylene Pyrolysis

2017

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In gas-phase combustion systems the interest in acetylene stems largely from its role in molecular weight growth processes. The consensus is that above 1500 K acetylene pyrolysis starts mainly with the homolytic fission of the C-H bond creating an ethynyl radical and an H atom. However, below ∼1500 K this reaction is too slow to initiate the chain reaction. It has been hypothesized that instead of dissociation, self-reaction initiates this process. Nevertheless, rigorous theoretical or direct experimental evidence is lacking, to an extent that even the molecular mechanism is debated in the literature. In this work we use rigorous ab initio transition-state theory master equation methods to calculate pressure- and temperature-dependent rate coefficients for the association of two acetylene molecules and related reactions. We establish the role of vinylidene, the high-energy isomer of acetylene in this process, compare our results with available experimental data, and assess the competition between the first-order and second-order initiation steps. We also show the effect of the rapid isomerization among the participating wells and highlight the need for time-scale analysis when phenomenological rate coefficients are compared to observed time scales in certain experiments.

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Section: Introductionmentioning

confidence: 99%

Initiation Reactions in Acetylene Pyrolysis

2017

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“…According to the mechanism of H-abstraction and C 2 H 2 -addition (HACA), the reaction C 2 H 2 → C 2 H would trigger the nucleation to form MCMs. 59,60 Thus, it is reasonable for the rapid generation of CMs in C 2 H 2 during pyrolysis, which further leads to the highest disorder of the product among all hydrocarbons, as shown in Figure 2. The CC homolysis, C 2 H 6 → 2CH 3 , occurs with a high frequency during the initial pyrolysis of C 2 H 6 (Table S5 of the Supporting Information), while it is seldom in the others.…”

Section: Resultsmentioning

confidence: 99%

Higher Activity Leading to Higher Disorder: A Case of Four Light Hydrocarbons to Variable Morphological Carbonaceous Materials by Pyrolysis

Liu

et al. 2018

J. Phys. Chem. C

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The subtle and efficient manufacture of high-quality carbonaceous materials dominates their extensive applications. Meanwhile, revealing the underlying mechanism in the formation of carbonaceous materials is crucial to improving their manufacture efficiency. In the present work, we focus upon the pyrolysis mechanism for four light hydrocarbons including methane, CH4, ethane, C2H6, ethylene, C2H4, and acetylene, C2H2, to carbonaceous materials, combined with reactive molecular dynamics (RMD) simulations. The carbonaceous materials with various morphologies are observed in our simulations, and the morphologies are strongly dependent on the initial reactants; i.e., a disorderly C cluster, a crossed C multilayer, and an orderly C monolayer are made from C2H2, C2H4, and C2H6 and CH4, respectively, as ascertained partly in experiments. Tracing the RMD trajectories, we confirm that the pyrolysis of all four light hydrocarbons undergoes three stages, including the C chain elongation with generation of new small carbonaceous molecules or radicals, the formation and growth of polycyclic aromatic hydrocarbons, and the stable growth of C clusters. The morphologic difference of the final C clusters is attributed to the reactant activity and C growth styles. That is, the higher activity and the faster growth by the C2 addition facilitate the more disorderly arrangement of C atoms, and vice versa. Typically, the dense C2H2 tends to form disorderly C black, while the thin CH4, to orderly C nanotubes. It shows that selecting the reactants in terms of their activities is a key to preparing orderly carbonaceous materials. These findings are expected to be useful to understand the formation mechanism and design techniques for efficiently manufacturing high-quality carbonaceous materials.

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“…For the present study on the chlorine-catalyzed oxidative pyrolysis of methane, the reaction mechanism was constructed from a moist CO oxidation submechanism (Yetter et al, 1991), a literature review of reactions for the pyrolysis and oxidation of methane (Tsang and Hampson, 1986), a mechanism for methylchloride pyrolysis and oxidation (Roseler et al, 1994;Ho et al, 1992;Weissman and Benson, 1988;Karra and Senkan, 1988), and mechanisms for the pyrolysis of acetylene (Kiefer et al, 1992;Kiefer and Van Drasek, 1990;Benson, 1989;Chanmugathas and Heicklen, 1986;Tanzawa and Gardiner, 1980). Although soot and carbon deposit formation are not explicitly provided for in the mechanism (Frenklach and Wang, 1990;Frenklach et al, 1983Frenklach et al, , 1984, steps are included for formation of allene and 1,3-butadiene and for cyclization leading to benzene (i.e., indicators or precursors of soot formation in methane pyrolysis).…”

Section: Reaction Mechanismmentioning

confidence: 99%

Methane Conversion to Ethylene and Acetylene: Optimal Control with Chlorine, Oxygen, and Heat Flux

Rojnuckarin

Floudas

Rabitz

et al. 1996

Ind. Eng. Chem. Res.

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In this paper, an optimal control strategy is applied to the problem of finding the flux profiles for the conversion of methane to ethylene and acetylene in a plug flow reactor. A chlorinecatalyzed oxidative pyrolysis mechanism is used in the calculations, in which two mechanistic pathways to the C 2 products were examined. One involves CH 3 Cl and/or CH 2 Cl, and the other involves C 2 H 6 and/or C 2 H 5 as reaction intermediates. Optimal control designs were performed with respect to the final mass fractions of ethylene and acetylene in a plug flow reactor using heat, oxygen, and chlorine fluxes as controls. The simulation results show that for the temperatures (1200 K < T < 1900 K) and pressure (P ) 1 atm) considered, C 2 H 4 is formed initially, which is subsequently converted to C 2 H 2 . Because of the abundant supply of H 2 formed during the reaction, it is possible to reform C 2 H 4 from C 2 H 2 by controlled extraction of energy. The heat flux plays the most important role in determining the final concentration of the desired C 2 products by controlling the temperature and the rate of H-atom radical generation, and thus, the interconversion between C 2 H 2 and C 2 H 4 through the C 2 H 3 radical. The solutions obtained, although not proven to be globally optimal, are of very high quality. More than 40% yield of the desired C 2 products, either ethylene or acetylene, can be obtained in all cases.

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ChemInform Abstract: The Mechanism of the Reversible Reaction: 2 C2H2 ⇌ Vinyl Acetylene and the Pyrolysis of Butadiene

Abstract: ChemInform Abstract (to ethylene and acetylene; kinetics, intermediate radicals).

Cited by 3 publications

References 1 publication

Initiation Reactions in Acetylene Pyrolysis

Initiation Reactions in Acetylene Pyrolysis

Higher Activity Leading to Higher Disorder: A Case of Four Light Hydrocarbons to Variable Morphological Carbonaceous Materials by Pyrolysis

Methane Conversion to Ethylene and Acetylene: Optimal Control with Chlorine, Oxygen, and Heat Flux

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