Chemistry and Biochemistry
Bayer School of Natural and Environmental Sciences
Bruce D. Beaver
David W. Seybert
Fraser F. Fleming
electron transfer initiated oxygenation, jet fuel, oxygen scavenger, phosphadioxirane, phosphine oxidation
It is believed that when air saturated jet fuels are subjected to high temperatures, two major fuel decomposition processes occur; thermal oxidation (autoxidation) and pyrolysis. Thermal oxidative degradation occurs when the fuel reacts with the dissolved oxygen present in the fuel and usually starts at temperatures above 120 °C. The deposition process usually occurs from 200-300 °C with deposits stopping after the consumption of the oxygen at about 300 °C. With increasing temperatures (~ 450 °C) the fuel begins to decompose thermally and form pyrolytic deposits.
It is believed that the autoxidation of jet fuel involves a peroxyl radical chain mechanism. Therefore, an oxygen scavenging additive (Sc) might be designed to react with oxygen to form an innocuous product (ScO). Electron rich molecules that have low oxidation potentials, such as phosphines, should be amenable to oxygen scavenging functions.
Phosphine oxygenation at high temperatures indicates there are two concurrent reactions: a non-radical reaction and a radical chain reaction. The radical chain reaction can be inhibited by a phenolic antioxidant. The oxidation products are phosphine oxide and phosphinate with phosphine oxide being the major product. The distribution of these two products is effected by the phosphine concentration. All these experimental results support the existence of a five coordinate phosphadioxirane being the intermediate for the phosphine oxygenation.
Phosphine oxygenation at high temperatures has been proposed to occur via an electron transfer initiated oxygenation (ETIO). The reaction has a relatively low activation energy (~ 21 kcal/mol), which suggests a partial electron transfer is involved in the initiation step for the ETIO reaction. The activation parameters for different reaction systems are consistent with this revised ETIO mechanism.
Gao, L. (2005). On the Oxidative Degradation and Stabilization of Future Jet Fuels (Doctoral dissertation, Duquesne University). Retrieved from https://dsc.duq.edu/etd/567