Density Functional Theory Calculations of the Energetics and Kinetics of Jet Fuel Autoxidation Reactions

Abstract

Density functional theory calculations of the energetics and kinetics of important reactions for jet fuel oxidation are reported. The B3LYP functional along with 6-31G(d) and larger basis sets are used for calculation of peroxy radical abstraction reactions from hydrocarbons and heteroatomic species, the reaction of sulfides, disulfides, and phosphines with hydroperoxides to produce nonradical products, and the metal catalysis of hydroperoxide decomposition. Reaction enthalpies and activation energies are determined via DFT calculations of the structures and energies of stable species and transition states. The peroxy radical abstraction study shows the high reactivity (E a 's of 6-11 kcal/mol) of the H atoms which are weakly bonded to heteroatoms, including nitrogen, oxygen, and sulfur. These species, at part-per-million levels, are able to compete for peroxy radicals with the bulk fuel hydrocarbon species. Benzylic hydrogens on aromatic hydrocarbons are shown to be significantly more reactive (by 4 to 5 kcal/mol) than paraffinic hydrogens with the result that the aromatic portion of fuel sustains the bulk of the autoxidation process. Sulfides and disulfides are found to react readily with fuel hydroperoxides (E a 's of 26-29 kcal/mol) to produce alcohols and the oxidized sulfur species. Triphenylphosphine reacts with hydroperoxides with a very low activation energy (12.9 kcal/mol). The metal catalysis of hydroperoxide decomposition is calculated to occur through the formation of a complex with subsequent decomposition to form radical species without regeneration of the metal ion. The reaction pathways found and activation energies calculated can be used to improve chemical kinetic models of fuel autoxidation and deposition.

The oxidative stability of synthetic fuels and fuel blends with monoaromatic blending components

“…Ethylbenzene was found to produce hydroperoxides at lower temperatures than dodecane highlighting that benzylic hydrogens on alkyl aromatics are more reactive than paraffinic hydrogens. Zabarnick's work found that in jet fuels the oxidation pathways are mainly due to alkyl aromatic oxidation and that the normal approximate 80% concentration of paraffins in jet fuel can be considered unreactive with respect to peroxy radical reactions [21,25]. Zabarnick's work highlights the importance of understanding oxidation of potential single component aromatic blending components.…”

The Effects of Storage on Turbine Engine Fuels

“…Studies of these mechanisms however focused on the chemistry of the hydrocarbon components of the fuel. They indicated that aromatic and cyclic hydrocarbons were substantially more reactive than the parainic compounds in the fuels [9]. It is known that free radical autoxidation of hydrocarbons occurs readily at temperatures between 30 and 60°C.…”

Tribological Properties of Vegetable Oils Modified by Reaction with Butanethiol

“…A number of workers have applied ab initio and density functional calculations to predict rates and activation energies of oxidation reactions for different species [41][42][43][44][45][46][47].…”

“…Zabarnick and Phelps [47] employed density functional theory (DFT) to calculate reaction enthalpies and activation energies for abstraction of hydrogen by peroxy radical from hydrocarbons in the autoxidation of jet fuel. They also used DFT to calculate the X-H bond strength, where X is carbon or heteroatom.…”