The main goal of this paper is the extension of a general semidetailed kinetic scheme of hydrocarbon oxidation to heavy fuels. Taking previous n-pentane and n-heptane kinetic modeling experience a step further, a lumped approach was systematically applied to n-decane, n-dodecane, and n-hexadecane. These semidetailed submodels for higher n-alkanes are directly derived from the complete set of primary propagation reactions, automatically generated by the MAMOX++ program on the basis of a small set of reference kinetic parameters. This proposed approach and lumped model are supported by a wide range of comparisons with a large variety of experimental measurements relating to stirred and flow reactors, premixed and diffusion flames, and fuel droplet combustion under microgravity conditions. The general agreement obtained in the overall range of conditions further confirms and supports the soundness of the small set of kinetic parameters used as reference values for the different classes of the primary propaga...

Wide-Range Kinetic Modeling Study of the Pyrolysis, Partial Oxidation, and Combustion of Heavy n-Alkanes

A wide-range modeling study of n-heptane oxidation

Low-temperature combustion: Automatic generation of primary oxidation reactions and lumping procedures

Modeling of thermal cracking kinetics—I

n-Heptane is the most important straight chain paraffin in the fossil-fuel industry. In this work, pyrolysis of n-heptane at high temperature is investigated by a series of ReaxFF based reactive molecular dynamic simulations. The pyrolysis correlated intermediate reactions, important product/intermediate distributions, and corresponding kinetics behaviors are systematically analyzed at atomistic level. The results indicate that the entire pyrolysis process is radical-dominated. The unimolecular dissociation is the main pathway of n-heptane decomposition. Initiation of the decomposition is mainly through C-C bond fission. Central C-C bonds would dissociate prior to the terminal ones. Besides, the Rice-Kossiakoff theory is proved for the pyrolysis of n-heptane at the atomistic level. To give a better description of the pyrolysis behavior, some alkane related intermolecular reactions should be considered in the mechanism. The apparent activation energy extracted from the present simulations is 43.02-54.49 kcal/mol in the temperature range 2400-3000 K, which is reasonably consistent with the experimental results.

A Reactive Molecular Dynamics Study of n-Heptane Pyrolysis at High Temperature

The extension of the free-radical chain mechanism to heavy paraffinic hydrocarbons has been studied for practical purposes. A generalization of the mechanism is attempted based on the Markov chain theory and presented in a form suitable to computer analysis. This generalization allows easier prediction of the distributions of initial pyrolytic products. Better agreement with experimental results is achieved by taking into account the equilibrium among all the possible isomers for higher homologues of hydrocarbon free radicals. However, the calculation of products is complicated by inclusion of radical isomerization which has not been ascertained experimentally. A new model is constructed herein by avoiding a direct approach to the problem of isomerization, while preserving its effect on the distribution of products. In this treatment, radical isomerization is replaced by a hypothetical process that accompanies the decrease of primary radicals and the increase of secondary radicals. The initial product distributions predicted by the model show good agreement with the observations for a series of normal paraffins from n-butane to n-hexadecane.

Prediction of initial product distributions from pyrolysis of normal paraffinic hydrocarbons

A simulation model for high-conversion pyrolysis of normal paraffinic hydrocarbons

normal paraffinic hydrocarbons was proposed on the basis of the free-radical chain reaction mechanism. It was then assumed that all ethyl radicals produced in each reaction step converted to ethane via intermolecular H-atom abstraction reaction. The assumption holds well in the relatively low temperature range up to about 500°C and near atmospheric pressure. In practice, however, hydrocarbons are sometimes pyrolyzed at higher temperatures and under lower partial pressures. In such cases, the decomposition of ethyl radicals would occur competitively with the H-atomabstraction reaction8>n). As a result, the amounts of reaction products hydrogen, ethylene, and ethane are considerably affected by the reaction conditions. Nevertheless, no calculations have been published based on both H-atom abstraction and ethyl radical decomposition reactions, except for w-butane pyrolysis shown by Pacey and Purnell10). In this paper, the authors investigated the effect of the ethyl radical decomposition reaction on initial product distribution. By introducing the ethyl radical decomposition reaction into the previously proposed model9\\ the initial product distribution under various reaction conditions can be predicted.

PREDICTION OF INITIAL PRODUCT DISTRIBUTION FROM n-PARAFFIN PYROLYSIS AT HIGHER TEMPERATURES BY CONSIDERING ETHYL RADICAL DECOMPOSITION

=radius of spherical (cylindrical) catalyst =radial co-ordinate = Reynolds number (=Dppu/fj) = Reynolds number (=<pDppul6(l -eout)) =Schmidt number (=v/Z>) = Sherwood number (=kn\\m.DPjD) (Eq. (12)) = average contact time based on superficial flow rate [sec] wOut, and «= superficial velocity in catalyst bed [cm/sec] Kin . = superficial velocity of intraparticle flow [cm/sec] X = conversion of reactant [-] z longitudinal co-ordinate [cm] £ = void fraction \\ [-] ju = viscosity [g/cm « sec] p = density [g/cm3] t = residence time [sec]

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Simulation of pyrolysis of paraffinic hydrocarbon binary mixtures

Three normal and branched alkane mixtures: n-pentane+n-hexane+n-heptane, 2-methylbutane+2-methylpentane+2-methylhexane, and 2-methylbutane+n-pentane+2-methylpentane+n-hexane+2-methylhexane+n-heptane were pyrolyzed at 700°C under atmospheric pressure. The alkane mixtures were diluted by nitrogen so as to give almost the same partial pressure for each component as that in the commercial cracking of naphtha, and the product distributions over a wide range of conversions are presented. A simulation model for the product distribution, which has been proposed for pure alkane in a previous study, was applied to the pyrolysis of alkane mixtures by taking into account the interaction between coexisting components. It was found by comparing with the experimental results that the present simulation model can be applied to simulate the product distributions over a wide range of conversions for normal and branched alkane mixtures.

Mitsuo Murata

Papers

Prediction of initial product distributions from pyrolysis of normal paraffinic hydrocarbons

A simulation model for high-conversion pyrolysis of normal paraffinic hydrocarbons

PREDICTION OF INITIAL PRODUCT DISTRIBUTION FROM n-PARAFFIN PYROLYSIS AT HIGHER TEMPERATURES BY CONSIDERING ETHYL RADICAL DECOMPOSITION

Simulation of pyrolysis of paraffinic hydrocarbon binary mixtures

Simulation of product distributions from pyrolysis of normal and branched alkane mixtures over a wide range of conversions