Chemistry and Biochemistry
Bayer School of Natural and Environmental Sciences
Bruce D. Beaver
Robert E. Morris
Additive, Antioxidant, Autoxidation, Deposit, Jet fuel, Stabilization
The thermal oxidative stability of middle distillate fuels is a topic of considerable concern. There are several examples of ambient temperature oxidation of fuel, leading to particulate matter and filtration issues. It is shown that particulate matter values vary globally based on region and fuel type, suggesting the problem is more than mere inorganic matter. The variability of filtration times is not dependent on absolute particulate matter present; it is suggested to be dependent upon the nature or morphology of deposit.
For a more thorough understanding of the chemistry responsible for deposit formation, flask oxidation was employed to test the Soluble Macromolecular Oxidatively Reactive Species (SMORS) mechanism. Spectral data suggest the presence of alcoholic and carbonylic functionality, which is in agreement with how the SMORS mechanism defines deposit formation. It has also been determined that the introduction of compounds conceivably indigenous to jet fuels has a negative impact on deposit formation. In addition, it has been shown the elemental composition of thermally induced deposit entails significant heteroatom content.
According to the SMORS mechanism, one of the primary reasons for deposit formation is the presence of radical initiators. The paraffinic blending of fuels shows promise in oxidatively stabilizing jet fuels. Research suggests blending reduces oxidation by diluting both the radical initiators and soluble deposit precursors. It is possible the use of this method could improve filter life and decrease operational costs.
A better understanding of the chemistry of deposit formation can lead to improved deposit inhibitors. Additives that have shown promise in bomb tubing studies were tested using flask oxidation. Additionally, extracted fuel polars reintroduced into the fuel at 0.3% v/v were tested for antioxidative activity. It was concluded the introduction of ppm levels of polar compounds extracted from fuel back into a fuel is very successful in limiting oxidative product formation.
One strategy for inhibiting deposit formation is the use of compounds that can act as oxygen/hydroperoxide scavengers. A linear free energy Hammett plot was developed for the reaction between molecular oxygen and triarylphosphines. Results indicate a very small positive charge buildup, suggesting a nonsynchronous concerted reaction.
Kabana, C. (2012). Thermal Oxidative Stability of Middle Distillate Fuels: Chemistry of Deposit Formation & Stabilization (Doctoral dissertation, Duquesne University). Retrieved from https://dsc.duq.edu/etd/721