Growth of polycyclic aromatic hydrocarbons (PAHs) by methyl radicals: Pyrene formation from phenanthrene

Georganta, Evgenia; Rahman, Ramees K.; Raj, Abhijeet; Sinha, Sourab

doi:10.1016/j.combustflame.2017.07.011

Cited by 39 publications

(23 citation statements)

References 48 publications

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“…The species considered in the simplified combustion atmosphere include phenanthrene, C 2 H 2 , O 2 , H 2 , H, and N 2 . The mole fractions of phenanthrene, C 2 H 2 , O 2 , and H 2 are fixed at 0.0001, 0.04, 0.15, 0.1, in accordance with the experimental results [30][31][32] . Temperature and mole fraction of H (mole fraction of N 2 = 1 -others) are abstracted at different heights above burner surface (HABs) in the premixed stagnation flame at C 2 H 4 /O 2 /Ar = 16.15/23.44/60.41 with a inlet gas velocity of 20 cm/s, using the ABF mechanism [7] .…”

Section: Simulation For Pyrene Formationsupporting

confidence: 61%

The growth of PAHs and soot in the post-flame region

Liu

Roberts

2019

Proceedings of the Combustion Institute

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The PAHs-C 2 H 2 pathway (PAHs + C 2 H 2 → intermediate → product + H 2 ) has been shown, in theory, to be the important contributor to the growth of polycyclic aromatic hydrocarbons (PAHs) and soot in the post-flame region where H atoms are rare. Calculations of the potential energy surface (PES) using the DFT B3LYP 6-311 + G(d,p) method, and the reaction rate coefficients using the RRKM theory, reveal that armchair and bridge surface sites share similar kinetic characteristics, and are more likely to be the targets of C 2 H 2 molecules in flames compared to zig-zag and 5-membered ring surface sites. Results show that the energy barrier of a 2-H elimination reaction (14-23.8 kcal/mol) is much lower than that of a 1-H elimination (typically 30-40 kcal/mol) for some molecules. The formation of pyrene from phenanthrene via HACA (PAHs + H → PAHs radical ( + C 2 H 2 ) → intermediate → product + H) and PAHs-C 2 H 2 pathways is investigated using a closed homogeneous zero-dimensional reactor with combustion parameters abstracted from the premixed stagnation C 2 H 4 /O 2 /Ar sooting flame. Results show that the HACA pathway is the dominant pathway for the formation of PAHs and soot surface growth in the main-flame region where H atoms are abundant, but that the PAHs-C 2 H 2 pathway is the preferred pathway in the post-flame region. Our study also suggests that the soot nucleation involving a chemical coalescence of moderate-sized PAHs into a crosslinked three-dimensional structure via the addition reactions of PAHs and PAH radicals in the main-flame region should be considered for inclusion in any soot modeling.

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Section: Simulation For Pyrene Formationsupporting

confidence: 61%

The growth of PAHs and soot in the post-flame region

Liu

Roberts

2019

Proceedings of the Combustion Institute

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“…where κ is the transmission coefficient of the tunneling effect, which is calculated using the Wigner method. [14] σ is the reaction path symmetry number, σ = σ rot,R /σ rot,TST , where σ rot,R and σ rot,TST are the rotational symmetry numbers of the reactant and transition state, respectively. k B , h, and R are Boltzmann's constant, Planck's constant, and universal gas constant, respectively.…”

Section: Computational Detailsmentioning

confidence: 99%

“…The temperature‐dependent rate constants k ( T ) are computed at temperatures of 298.15, 1000, 1500, 2000, and 2500 K using the conventional transition state theory (TST), that is,

k ((), T) = italicκσ \frac{k_{B} T}{h} \exp ((), - \frac{Δ G_{f}^{\begin{array}{l} + \\ + \end{array}}}{RT})

where κ is the transmission coefficient of the tunneling effect, which is calculated using the Wigner method. [ 14 ] σ is the reaction path symmetry number, σ = σ rot,R / σ rot,TST , where σ rot,R and σ rot,TST are the rotational symmetry numbers of the reactant and transition state, respectively. k B , h , and R are Boltzmann's constant, Planck's constant, and universal gas constant, respectively.…”

Section: Computational Detailsmentioning

confidence: 99%

Identification of decomposition reactions for HMDSO organosilicon using quantum chemical calculations

Huang

Chen

Zhou

2020

Int J of Quantum Chemistry

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Hexamethyldisiloxane [HMDSO, (CH 3) 3-SiOSi-(CH 3) 3 ] is an important precursor for SiO 2 formation during flame-based silica material synthesis. As a result, HMDSO reactions in flame have been widely investigated experimentally, and many results have indicated that HMDSO decomposition reactions occur very early in this process. In this paper, quantum chemical calculations are performed to identify the initial decomposition of HMDSO and its subsequent reactions using the density functional theory at the level of B3LYP/6-311+G (d, p). Four reaction pathways-(a) Si O bond dissociation of HMDSO, (b) Si C bond dissociation of HMDSO, (c) dissociation and recombination of Si O and Si C bonds, and (d) elimination of a methane molecule from HMDSO-have been examined and identified. From the results, it is found that the barrier of 84.38 kcal/mol and Si O bond dissociation energy of 21.55 kcal/mol are required for the initial decomposition reaction of HMDSO in the first pathway, but the highest free energy barrier (100.69 kcal/mol) is found in the third reaction pathway. By comparing the free energy barriers and reaction rate constants, it is concluded that the most possible initial decomposition reaction of HMDSO is to eliminate the CH 3 radical by Si C bond dissociation.

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“…While the crucial feature of the HACA mechanism is the kinetic-thermodynamic coupling of H abstraction and carbon addition steps and not the particular nature of the carbon species added, 2,5 in combustion environments under soot-forming conditions, acetylene is believed to be the most essential growth species because of the high abundance in flames owing to its thermal stability. [6][7][8][9][10][11][12] The "classical" acetylene-based HACA mechanism is generally successful in kinetic modeling of the PAH growth in various flames and has been directly confirmed by molecular beam experiments in pyrolytic reactors for the formation of naphthalene from benzene, [13][14][15] phenanthrene from biphenyl, and pyrene from phenanthrene. 16,17 However, according to theoretical calculations 18 and experiments in the pyrolytic reactor, 19 classical HACA does not produce benzenoid tricyclic PAHs phenanthrene and anthracene from bicyclic naphthalene under typical combustion conditions forming instead acenaphthylene with two sixand one five-member ring.…”

mentioning

confidence: 93%

“…Molecules and radicals other than acetylene, including aromatics themselves, [8][9][10]20 methyl, 11,12,[21][22][23] vinyl 24 and resonantly-stabilized propargyl 25,26 and allyl 27,28 radicals, and vinylacetylene, [29][30][31][32][33][34][35][36][37] have been proposed to complement acetylene-based HACA, especially in the production of purely benzenoid PAHs. In particular, Shukla et al 21,38 and Xiong et al 39 proposed a mechanism termed PAC (phenyl addition/dehydrocyclization) in which phenyl radical adds to a bay area (armchair edge) of a PAH molecule thus resulting in its extension by two six-member rings, see, for example, the reaction of phenanthrene with C 6 H 5 producing benzo[e]pyrene.…”

mentioning

confidence: 99%

Formation of phenanthrene via H‐assisted isomerization of 2‐ethynylbiphenyl produced in the reaction of phenyl with phenylacetylene

Tuli

Mebel

2020

Int J of Chemical Kinetics

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Model chemistry G3(MP2,CC)//B3LYP/6-311G(d,p) calculations of the potential energy surface for the reaction of phenyl radical (C 6 H 5) with phenylacetylene (C 8 H 6) have been carried out and combined with Rice-Ramsperger-Kassel-Marcus/Master Equation calculations of temperature-and pressure-dependent rate constants. The results showed that the reaction can serve as a viable source for the formation of phenanthrene via an indirect route involving a primary reaction of phenyl addition to the ortho carbon in the ring of phenylacetylene and H elimination producing 2-ethynylbiphenyl followed by secondary H-assisted isomerization of 2-ethynylbiphenyl to phenanthrene. In the secondary reaction, the H atom adds to the α carbon of the ethynyl side chain, then a six-member ring closure takes place followed by aromatization via an H loss. The channel of H addition to the side chain of 2-ethynylbiphenyl appears to be much faster than H addition to the ortho carbon in the ethynyl-substituted ring leading back to the initial C 6 H 5 + C 8 H 6 reactants. Rate constants for the primary C 6 H 5 + C 8 H 6 ← → 2ethynylbiphenyl (p1) + H and secondary p1 + H ← → phenanthrene (p2) + H reactions have been computed in the temperature range of 500-2500 K at pressures of 30 Torr, 1, 10, and 100 atm and fitted to modified Arrhenius expressions. The suggested kinetic scheme and rate constants are proposed as a prototype for the modeling of the growth of polycyclic aromatic hydrocarbons via the phenyl additiondehydrocyclization (PAC) mechanism involving an addition of a PAH radical to an ethynyl-substituted PAH molecule.

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Growth of polycyclic aromatic hydrocarbons (PAHs) by methyl radicals: Pyrene formation from phenanthrene

Cited by 39 publications

References 48 publications

The growth of PAHs and soot in the post-flame region

The growth of PAHs and soot in the post-flame region

Identification of decomposition reactions for HMDSO organosilicon using quantum chemical calculations

Formation of phenanthrene via H‐assisted isomerization of 2‐ethynylbiphenyl produced in the reaction of phenyl with phenylacetylene

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