Engineering approximations for activation energies in hydrogen transfer reactions

Blowers, Paul; Masel, Richard I.

doi:10.1002/aic.690461015

Cited by 61 publications

(87 citation statements)

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“…By using Equation (10), tunneling coefficients for hydrogen abstraction reactions of the CÀHÀ-C type involving hydrocar- CHEMPHYSCHEM ARTICLES www.chemphyschem.org bons and organosulfur compounds could be reproduced in the temperature range from 300 to 1500 K within a factor of 1.15. The validity of Equation (10) for hydrogen abstraction reactions involving S-centered radicals will be assessed in this work.…”

Section: Tunnelingmentioning

confidence: 99%

Kinetic Modeling of Hydrogen Abstractions Involving Sulfur Radicals

2013

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One of the requisites for the development of detailed reaction networks is the availability of accurate kinetic data. Group additivity based models linking the Arrhenius parameters to structural characteristics of the transition state have proven to be a valuable tool to obtain those data. In this work, group additivity values are presented to allow a broad range of CH and SH hydrogen abstraction reactions by S radicals to be modeled. Rate coefficients in the temperature range from 300 to 1500 K are obtained by using the CBS-QB3 method in the high-pressure limit and are corrected for tunneling and anharmonicity of rotation about the transitional bond. A total of 149 reactions are studied. From these reactions, a total of 52 group additivity values and 35 resonance corrections are derived. The general applicability of the group additivity method is demonstrated for a test set containing 25 reactions. At 300 K, rate coefficients are on average reproduced within a factor of 2.8. The mean absolute deviations on the Arrhenius parameters are 2 kJ mol(-1) for the activation energy and 0.38 for log A in which A is the pre-exponential factor.

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Section: Tunnelingmentioning

confidence: 99%

Kinetic Modeling of Hydrogen Abstractions Involving Sulfur Radicals

2013

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“…Other and more accurate relations have been proposed based on Bond Order and on Valence Bond theory (Donahue et al, 1998;Zavitsas, 1998;Clarke et al, 2000;Blowers and Masel, 2000;Fischer and Radom, 2001;Shaik et al, 2001). The second category is related to Benson's group additivity method for thermodynamic data.…”

Section: Introductionmentioning

confidence: 97%

“…The ever-increasing computational power and the development of better algorithms bring the accurate calculation of kinetic and thermodynamic parameters for industrially relevant gas-phase reactions from first principles within reach. Hydrocarbon free-radical reactivity and thermochemistry have been studied with a variety of computational methods, ranging from semiempirical to density functional theory (DFT) and postHartree-Fock methods (Wong et al, 1994;Barone and Orlandini, 1995;Heuts et al, 1996;Xiao et al, 1997;Wong and Radom, 1998;Blowers and Masel, 2000;Chuang et al, 2000;Stahl et al, 2001;Sumathi et al, 2001aSumathi et al, ,b, 2002. It is found that in order to obtain results with so-called chemical accuracy for standard enthalpies of formation, that is, better than 4 kJ/mol, calculations on radical species and on radical reactions require large basis set post-Hartree-Fock methods (Mayer et al, 1998;Chuang et al, 2000;Saeys et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Ab initio group contribution method for activation energies for radical additions

et al. 2004

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“…Therefore a variety of methods for rate prediction of radical reactions has been developed. These methods range from correlating the activation energy to the reaction enthalpy, such as Evans-Polanyi correlations and its variations, [15][16][17] to more sophisticated methods based on the structure of the transition state. Several of the latter methods are related to Benson group 2 additivity.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore a variety of methods for rate prediction of radical reactions has been developed. These methods range from correlating the activation energy to the reaction enthalpy, such as Evans-Polanyi correlations and its variations, [15][16][17] Sabbe et al ChemPhysChem 11:195-210 (2010) -pre-reviewed version 2 additivity. [18,19] Among these are: 1. the structural group contribution method of Willems and Froment, [20,21] in which correction terms on the Arrhenius parameters of a reference reaction account for structural differences between the latter and the considered reaction; 2. methods that calculate the thermochemistry of the transition state, such as the method described by Sumathi et al, [22][23][24] 3. the Reaction Class Transition State Theory developed by Truong et al [25,26] and 4. the group additive (GA) method for activation energies as described by Saeys et al [27,28] Experimental determination of all the kinetic and thermodynamic parameters required for these methods is not possible due to scarcity of experimental data.…”

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confidence: 99%

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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Engineering approximations for activation energies in hydrogen transfer reactions

Abstract: Pre®ious in®estigators ha®e often used the Polanyi relationship, extensions due to

Cited by 61 publications

References 35 publications

Kinetic Modeling of Hydrogen Abstractions Involving Sulfur Radicals

Kinetic Modeling of Hydrogen Abstractions Involving Sulfur Radicals

Ab initio group contribution method for activation energies for radical additions

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

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