The role of back-mixing in the decomposition of methane

This study examines the predictive capability of our recently proposed reaction mechanism (Norinaga and Deutschmann, Ind Eng Chem Res 2007, 46, 3547) for hydrocarbon pyrolysis at varying temperature. The conventional flow reactor experiments were conducted at 8 kPa, over the temperature range 1073-1373 K, using ethylene, acetylene, and propylene as reactants to validate the mechanism. More than 40 compounds were identified and quantitatively analyzed by on-and off-line gas chromatography. The chemical reaction schemes consisting of 227 species and 827 reactions were coupled with a plug-flow reactor model that incorporated the experimentally measured axial temperature profile of the reactor. Comparisons between the computations and the experiments are presented for more than 30 products including hydrogen and hydrocarbons ranging from methane to coronene as a function of temperature. The model can predict the compositions of major products (mole fractions larger than 10 −2 ) in the pyrolysis of three hydrocarbons with satisfactory accuracies over the whole temperature range considered. Mole fraction profiles of minor compounds including polycyclic aromatic hydrocarbons (PAHs) up to three ring systems, such as phenanthrene, anthracene, and phenylnaphthalene, are also fairly modeled. At temperatures lower than 1273 K, larger PAHs were underpredicted and the deviation became larger with decreasing temperature and increasing molecular mass of PAHs, while better agreements were found at temperatures higher than

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“…An axial diffusion [18] is then likely to have a significant effect on the overall flow characteristics in the reactor.…”

Section: Polycyclic Aromatic Hydrocarbonsmentioning

confidence: 99%

Detailed chemical kinetic modeling of pyrolysis of ethylene, acetylene, and propylene at 1073–1373 K with a plug‐flow reactor model

Norinaga

Janardhanan

Deutschmann

2008

Int J of Chemical Kinetics

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“…We consider the industrially important process of producing carbon fiber-reinforced carbon for which in most cases methane is used as precursor. Owing to the tremendous number of species involved in hydrocarbon chemistry at elevated temperatures, modeling the deposition of solid pyrolytic carbon is indeed a challenge and the chemical kinetics of methane decomposition [52] itself is still an active field of research [53]. Because of the significant amount of chemical reactions taking place during the deposition process, it is usually assumed to decrease the reactions number by the so-called simplified (reduced) reaction scheme.…”

Section: Chemical Reactions Schemementioning

confidence: 99%

Diffuse interface method for simulation of the chemical vapor deposition of pyrolytic carbon: Aspects of the mathematical formulation

Dimitrov

Ekhlakov

Langhoff

2008

Commun. Numer. Meth. Engng.

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SUMMARYThe present work is inspired by Anderson et al. (Phys. D Nonlinear Phenom. 2000; 135(1-2):175-194) and Noll (http://www.math.cmu.edu/wn0g/noll) and falls in the conceptual line of the Ginzburg-Landau class of first-order phase-transition models based on the concept of phase-field parameter. Trying to keep the exposition as much general as possible, we develop below a thermodynamically consistent rationalization of the physical process of (anisotropic) deposition of pyrolytic carbon from a gas phase. The derivation line we follow is well established in the field of the modern continuum physics. From the covariance of the first principle of thermodynamics, the second Newton's law and the Liouville's theorem with respect to the one-dimensional Lie groups of transformations, the balance laws for the temperature, linear momentum and density are formulated. This system of partial differential equations is comprehended further by the constitutive laws for the phase field, the stress, and the heat and entropy fluxes obtained in a form consistent with the Clausius-Duhem understanding of the second law. The result referred to as a local, strongly coupled initial boundary value problem of chemical vapor deposition (IBVP-CVD) constitutes the general mathematical description of the CVD process. The weak form of isotropic IBVP-CVD is then derived and discretized by means of the discontinuous Galerkin method. At the end of the paper, we also derive the weak formulations for the local lifting operators that provide the stabilization mechanism for the discontinuous Galerkin discretization scheme.

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“…They include composition reactions in the gas phase yielding intermediate gas phase species as well as several reactions for carbon formation from different gas phase species. The influence of back-mixing on the decomposition of methane has been studied in Andrä et al (2001).…”

Section: Introductionmentioning

confidence: 99%

Modelling chemical vapour infiltration of pyrolytic carbon as moving boundary problem

Langhoff¹,

Schnack²

2008

Chemical Engineering Science

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Chemical vapour infiltration (CVI) of pyrolytic carbon is described as a moving boundary problem to determine the evolution of the pyrolytic carbon layer in space and time. Derived from real geometries, a one-dimensional single pore model is developed yielding a nonlinear coupled system of partial differential equations for the concentrations of the gas phase species and the height of the carbon layer within cylindrical pores. The evolution of the moving boundary of the gas phase domain is governed by a non-differentiable minimisation condition. Additionally, a CVI reactor model to describe the infiltration of several cylindrical pores within a porous substrate is presented on the basis of the single pore model. Both models are new in that they combine the following features: (i) derivation of the equations rigorously taking into account the temporal change of the gas phase, (ii) the explicit construction of the position of the gas--solid interface, (iii) the influence of the local curvature of the carbon layer on its growth velocity, and (iv) modelling of chemical kinetics using a reduced reaction scheme with intermediate gas phase species and several surface reactions. The models are solved numerically using a staggered strongly decoupled scheme with implicit Euler time integration. The results allow the identification of process conditions and geometries for which a complete infiltration of the pores or the whole substrate is achieved. For low pressures, the predictions of the CVI reactor model are in agreement with the available experimental data.

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The role of back-mixing in the decomposition of methane

Cited by 4 publications

References 10 publications

Detailed chemical kinetic modeling of pyrolysis of ethylene, acetylene, and propylene at 1073–1373 K with a plug‐flow reactor model

Detailed chemical kinetic modeling of pyrolysis of ethylene, acetylene, and propylene at 1073–1373 K with a plug‐flow reactor model

Diffuse interface method for simulation of the chemical vapor deposition of pyrolytic carbon: Aspects of the mathematical formulation

Modelling chemical vapour infiltration of pyrolytic carbon as moving boundary problem

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