Group Additive Values for the Gas Phase Standard Enthalpy of Formation of Hydrocarbons and Hydrocarbon Radicals

Sabbe, Maarten; Saeys, Mark; Reyniers, Marie-Françoise; Marin, Guy; Speybroeck, Véronique Van; Waroquier, Michel

doi:10.1021/jp050484r

Cited by 130 publications

(234 citation statements)

References 48 publications

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“…This method divides the molecule into groups, each having its own contribution to thermodynamic properties. Typically, one can obtain properties within 0.96 kcal/mol chemical accuracy 36 . A second order estimation method is also used, in which corrections for 1,4 and 1,5 interactions, optical isomers, cyclization, etc.…”

Section: Updates Of Thermochemical Datamentioning

confidence: 99%

Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetics, and Rate Rule Optimizations for 2-Methylhexane

et al. 2016

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Accurate chemical kinetic combustion models of lightly branched alkanes (e.g., 2-methylalkanes) are important to investigate the combustion behavior of real fuels. Improving the fidelity of existing kinetic models is a necessity, as new experiments and advanced theories show inaccuracies in certain portions of the models. This study focuses on updating thermodynamic data and the kinetic reaction mechanism for a gasoline surrogate component, 2-methylhexane, 2 based on recently published thermodynamic group values and rate rules derived from quantum calculations and experiments. Alternative pathways for the isomerization of peroxyalkylhydroperoxide (OOQOOH) radicals are also investigated. The effects of these updates are compared against new high-pressure shock tube and rapid compression machine ignition delay measurements. It is shown that rate constant modifications are required to improve agreement between kinetic modeling simulations and experimental data. We further demonstrate the ability to optimize the kinetic model using both manual and automated techniques for rate parameter tunings to improve agreement with the measured ignition delay time data. Finally, additional low temperature chain branching reaction pathways are shown to improve the model's performance.The present approach to model development provides better performance across extended operating conditions while also strengthening the fundamental basis of the model.

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Section: Updates Of Thermochemical Datamentioning

confidence: 99%

Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetics, and Rate Rule Optimizations for 2-Methylhexane

et al. 2016

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“…The activation energy is underpredicted by 5.7 kJ mol -1 agreeing very well with the cis contribution to the standard enthalpy of formation of 5.9 kJ mol -1 . [72] For all reactions except those with strong steric interactions in the reactants (reactions 2 and 5, see Table 8), the group additive predicted rate coefficients at 300 K are within a factor 3.5 of the ab initio predicted value. As discussed above, most troublesome is reaction 5, for which the deviation of 12 kJ mol -1 on the β scission activation energy causes the rate to be underestimated by a factor of 160 at 300 K. The addition rate coefficient for reaction 5a remains within a factor of 2.…”

Section: Ab Initio Validationmentioning

confidence: 70%

“…It can be shown quantitatively that the deviation on the activation energy for this β scission is caused by the cis interaction. The double cis interaction as present in 2,3-dimethylbutene has a contribution of 18.3 kJ mol -1 to the standard enthalpy of formation, [72] while the steric interaction of the 2 radical gauche interactions (type 1) in the product radical involves a gauche correction of 5.4 kJ mol -1…”

Section: Ab Initio Validationmentioning

confidence: 99%

“…[72] As the transition state for β scission is very late, it can be assumed that the cis interaction is almost entirely developed in the transition state. Therefore, the neglected change in steric effect on the activation energy can be estimated to be about 18.3 -5.4 = 12.9 kJ mol -1 , which corresponds very well with the observed difference of 12.5 kJ mol -1 between group additive and ab initio activation energy.…”

Section: Ab Initio Validationmentioning

confidence: 99%

“…These tertiary contributions, originating from non-nearest neighbor interactions, are already difficult to model for thermodynamics and modeling these interactions for kinetics is expected to be even more troublesome. [72] The neglect of tertiary contributions however does not have significant effects on the accuracy of the rate coefficients for addition. Therefore, for reactions with severe steric effects, it is suggested to calculate the β scission rate coefficient from the addition rate coefficient and the thermodynamic equilibrium coefficient.…”

Section: Ab Initio Validationmentioning

confidence: 99%

See 2 more Smart Citations

Hydrogen Radical Additions to Unsaturated Hydrocarbons and the Reverse β‐Scission Reactions: Modeling of Activation Energies and Pre‐Exponential Factors

et al. 2010

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The group additivity method for Arrhenius parameters is applied to hydrogen addition to alkenes and alkynes and the reverse β-scission reactions, an important reaction family in thermal processes based on radical chemistry. A consistent set of group additive values for 33 groups is derived to calculate the activation energy and preexponential factor for a broad range of H-addition reactions. The group additive values are determined from CBS-QB3 ab initio calculated rate coefficients. A mean factor of deviation between the CBS-QB3 and the experimental rate coefficients for 7 reactions of only 2 in the range 300-1000 K is found. Tunneling coefficients for these reactions were found to be significant below 400 K and a correlation accounting for tunneling is presented. Application of the obtained group additive values to predict the kinetics for a set of 11 additions and β scissions yields rate coefficients within a factor 3.5 from the CBS-QB3 results except for 2 β scissions with severe steric effects. The mean factor of deviation with experimental rate coefficients is 2.0, showing that the group additive method with tunneling corrections can accurately predict the kinetics, at least as accurate as the most commonly used density functional methods. The constructed group additive model can hence be applied to predict the kinetics of hydrogen radical additions to a broad range of unsaturated compounds. IntroductionThe addition of hydrogen radicals to alkenes and its reverse β scission, are important elementary steps in radical processes such as polymerization, pyrolysis, steam cracking, partial oxidation and combustion.[1] Therefore, the reaction family of hydrogen addition/β scission forms an indispensable part of any radical reaction network.A reliable reactor optimization requires an accurate kinetic model based on elementary reactions. For radical chemistry, on which many of the world largest scale chemical processes are based, the reactive nature of the radical intermediates results in huge reaction networks typically involving hundreds of species and thousands of elementary reactions. [2][3][4] Currently, most elementary reaction networks are automatically generated using advanced algorithms for the selection of the relevant reactions. [5][6][7][8][9][10][11] Sensitivity studies on these reaction networks point out that the main part of the uncertainty on the product yields stems from inaccurate knowledge of kinetic data. [12,13] Therefore, accurate kinetic data are essential to obtain reliable process simulations. Moreover, if rate-based network construction algorithms are applied, [14] accurate rate data are even more important as inaccuracies can result in the construction of an incomplete network that is not capable of grasping the underlying chemistry of the process.A quantitative description of radical processes thus requires that rate parameters be known for all of the different reactions comprising the reaction network. However, it is very difficult to measure kinetic parameters for individual radical r...

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Thermochemistry and Hydrogen Transfer Kinetics

2012

Encyclopedia of Radicals in Chemistry, Biology and Materials

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Bond dissociation energies and enthalpies of formation of common organic compounds and of many radicals are presented and discussed. Simple methods for calculating such thermodynamic values are described, which can be used to calculate such quantities when they are not otherwise available. Details focus on carbon radicals and alkoxyl and hydroperoxyl radicals, as well as on nitrogen‐centered radicals and their precursor compounds. Other topics include radical stabilization energies and scales for them, atom transfer kinetics as affected by thermodynamic information, and substituent effects on bond dissociation enthalpies and radical reactivities.

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Group Additive Values for the Gas Phase Standard Enthalpy of Formation of Hydrocarbons and Hydrocarbon Radicals

Cited by 130 publications

References 48 publications

Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetics, and Rate Rule Optimizations for 2-Methylhexane

Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetics, and Rate Rule Optimizations for 2-Methylhexane

Hydrogen Radical Additions to Unsaturated Hydrocarbons and the Reverse β‐Scission Reactions: Modeling of Activation Energies and Pre‐Exponential Factors

Thermochemistry and Hydrogen Transfer Kinetics

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