In order to optimize processes such as fuel combustion and hydrocarbon pyrolysis, accurate kinetic models are required. The accuracy of such models is heavily dependent on the accuracy of the used kinetic and thermodynamic data. Ideally, high-level ab initio calculations are performed for each encountered species and reaction. This so-called “on-the-fly” approach is, for the time being, computationally too expensive. Alternative methods are using databases of previously calculated ab initio data and group additivity, with the current state of the art being a combination of both. Ab-initio-derived ΔGAV° values have already been determined for hydrogen abstractions, radical additions and homolytic substitution reactions in various hydrocarbons. This work focusses on another crucial reaction family to combustion and pyrolysis; the intra-molecular hydrogen abstractions or hydrogen shifts. 448 hydrogen shift reaction rates have been calculated at the CBS-QB3 level of theory covering the 1-2 shifts to 1-7 shifts. By systematically introducing different substituents to the reactive atoms, ΔGAV° values have been estimated for 270 groups. The reported model is applicable to a variety of reactions in the 300-1800K temperature range. To improve the accuracy of the group additive model, temperature- and energy dependent correlations for the tunneling coefficients have also been determined. Testing of the model on a set of reactions calculated at the CBS-QB3 level of theory shows a high accuracy with a mean absolute deviation between 1.18 and 1.71.

Ab-initio derived group additivity model for intra-molecular hydrogen abstraction reactions

256th National Meeting (2018)

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