Mechanistic modeling of lubricant degradation. 1. Structure-reactivity relationships for free-radical oxidation

A library of kinetic correlations is established that is suitable for estimating rate coefficients and activation energies for condensed-phase free-radical oxidation in hydrocarbons with the specific target application of modeling the thermal degradation of lubricating oils. Structure-reactivity relationships for 17 different reaction families relevant to lubricant degradation are reported. Nine structure-reactivity relationships have not been reported elsewhere in the literature. All of the structure-reactivity relationships are determined by using reaction rate coefficients and activation energies available from experiment or calculated via quantum chemistry and transition state theory. The high-level CBS-QB3 method was used in order to calculate activation energies and heats of reaction for several hydrogen transfer reaction subfamilies. It was shown that, because of the variety of radicals and substrates present in propagation reactions in lubricant degradation, unique reaction subfamilies are important for accurately capturing the different reactivity trends observed. The library of structure-reactivity relationships presented here is subsequently used in Part 2 for kinetic modeling studies.