Tree structure for intermolecular hydrogen abstraction from hydrocarbons (C/H) and generic rate constant rules for abstraction by vinyl radical



Modeling of complex reaction systems is necessary in the design, analysis, and optimization of many technologically important processes such as pyrolysis, steam cracking, coking, partial oxidation, and combustion. The complexity in kinetic modeling of all these processes is introduced both by the feed, which is a hydrocarbon mixture, and the high reactivity of radical intermediates. Recent advances in automated mechanism generation tools, although capable of establishing the complex reaction network, pose a big challenge of assigning rate parameters for all the reactions or devising appropriate estimation rules for all reaction classes in the network. The kinetics of free radical reactions dictates the chemistry of technologically important thermal processes. Intermolecular hydrogen abstraction by radicals is one of the dominant reaction types and constitutes a major part (often >50%) in any thermal reaction network owing to their profound effect on product distribution. While abstraction reactions by H atoms (and to some extent by methyl radicals) have been studied extensively in the past, the abstraction kinetics by vinyl radical is less explored even though vinyl radicals play an important role in molecular weight growth chemistry and in predicting acetylene concentrations in pyrolysis and fuel-rich hydrocarbon flames. This study presents the hierarchical tree structure for intermolecular hydrogen abstraction by vinyl radicals from {C/H} molecules and provides generic rate rules that account for most of the variation in C[BOND]H bond energy in the family of aliphatic, aromatic, naphthenic, olefinic, and aromatic naphtheno hydrocarbons. Reaction classes developed in this work are still dictated by immediate neighbors within the spirit of group additivity, although some efforts were made to access the effect of non–next neighbors on generic rate parameters. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 327–349, 2012