Kinetic Modeling of Hydrogen Abstractions Involving Sulfur Radicals

Modeling the kinetics of hydrogen abstraction reactions in nitrogen-containing compounds via group additivity

New group additivity values are presented to enable the modeling of a broad range of intermolecular hydrogen abstraction reactions involving nitrogen-containing compounds. From a dataset of 316 reaction rate coefficients calculated at the CBS-QB3 level of theory in the high-pressure limit, 76 group additivity values and 14 resonance corrections have been estimated. The influence of substituents on both the attacked hydrogen and attacking radical, being a carbon or nitrogen atom, has been investigated systematically. The new group additivity models can be applied to approximate the Arrhenius parameters of hydrogen abstraction reactions of nitrogen-containing compounds by hydrogen atoms, carbon-centered and nitrogen-centered radicals in the 300-1800 K temperature range. Complementary to the group additivity model, correlations for the tunneling coefficients, which depend on both the temperature and the activation energy of the reaction in the exothermic direction, have been generated. The good performance of the new group additivity schemes has been demonstrated using a test set of reactions. At 1000 K, the rate coefficients for all test set reactions are approximated on average within a factor of 1.45, 1.47 and 1.34, for the hydrogen abstractions with a reactive center of the type H-H-N, N-H-N and C-H-N respectively.

Detailed kinetic model for hexyl sulfide pyrolysis and its desulfurization by supercritical water

The automated reaction mechanism generator is used to model the decomposition of hexyl sulfide with and without supercritical water.

On-the-fly kinetics of hydrogen abstraction from polycyclic aromatic hydrocarbons by methyl/ethyl radicals

This work provides a rigorous procedure, within the framework of the Reaction Class Transition State Theory (RC-TST) and the Structure-Activity Relationship (SAR), for predicting reliable thermal rate constants on-the-fly for hydrogen abstraction reactions by methyl/ethyl radicals from Polycyclic Aromatic Hydrocarbons (PAHs) in a temperature range of 300-3000 K. All necessary RC-TST parameters were derived from ab initio calculations for a representative set of 36 reactions on which different error analyses and comparisons with available literature data were carried out. In addition to the good agreement between the RC-TST rate constants and the literature data, the detailed error analyses show that RC-TST/SAR, utilizing either the Linear Energy Relationship (LER) where only the reaction energy is needed or Barrier Height Grouping (BHG) where no additional data is needed, can predict the thermal rate constants for any reaction in the title reaction class with an average systematic error of less than 50% when compared to the explicit rate calculations. Therefore, the constructed RC-TST procedure can be confidently used to obtain reliable rate constants on the fly in an attempt to effectively construct detailed kinetic mechanisms for PAH-related fuels.

Automatic mechanism generation for pyrolysis of di-tert-butyl sulfide

The automated Reaction Mechanism Generator (RMG), using rate parameters derived from ab initio CCSD(T) calculations, is used to build reaction networks for the thermal decomposition of di-tert-butyl sulfide.

Combining experiment and theory to elucidate the role of supercritical water in sulfide decomposition

Supercritical water is observed to react with alkyl sulfides, forming H₂S, CO, and alkanes. Quantum chemistry calculations show this occurs via a multistep mechanism involving both free radical and pericyclic reactions, with water acting as both a reagent and a catalyst.