Studies of the Role of Heteroatomic Species in Jet Fuel Thermal Stability: Model Fuel Mixtures and Real Fuels

Abstract

Oxygen consumption and deposition measurements of model fuel mixtures and real fuels are used to explore the roles that heteroatomic fuel species and their interactions play during fuel autoxidation. A range of temperatures, oxygen consumption regimes, and flow environments are employed to provide results applicable over a wide range of fuel autoxidative conditions. The quartz crystal microbalance (QCM) provides a low temperature (140 °C) batch reactor environment for long reaction times (minutes to hours) with oxygen consumption and sensitive, in situ deposition measurements. The JFTOT system provides a flowing environment at higher temperatures (260 to 300 °C) and short residence times (seconds) which is modified with both an outlet oxygen sensor and with quantitative deposition measurements via ellipsometry. These techniques are used to study model systems (Exxsol D80 with added heteroatom species) and real jet fuels to determine the role of heteroatomic species in jet fuel autoxidation and deposition. The QCM results demonstrate that nitrogen and sulfur species (e.g., indoles/anilines and sulfides) interact during jet fuel autoxidation to encourage deposit formation. The further addition of phenol species, which occur naturally in most petroleum-derived jet fuels, facilitates even greater deposit production. This behavior is confirmed in the JFTOT via addition of nitrogen and sulfur-containing species to medium and low sulfur jet fuels. These results, along with gas chromatographic (GC) analysis of samples collected during autoxidation in the QCM, show rapid sulfur autoxidation followed by a slower reaction of the nitrogen species to form deposit precursors, implying a stepwise reaction of sulfur oxidation products with nitrogen species to form deposit precursors. These results have important implications for fuel production strategies and mitigation of thermal stability degradation during fuel pipeline transport, storage, and use.

Studies of the Impact of Fuel Deoxygenation on the Formation of Autoxidative Deposits

“…Deposition rates in flow systems usually decrease downstream of where the dissolved oxygen is consumed. Reactions that might contribute to deposit formation downstream of oxygen consumption include molecular reactions such as the reaction of hydroperoxides with sulfides (reaction 14) and/or reaction of fuel polar species/products with each other, such as nitrogen species with sulfur acids …”

“…Reactions that might contribute to deposit formation downstream of oxygen consumption include molecular reactions such as the reaction of hydroperoxides with sulfides (reaction 14) and/or reaction of fuel polar species/products with each other, such as nitrogen species with sulfur acids. 23 A closer look at the experimental deposition measurements for the 25 and 50% oxygen cases shows that these also display significant deposition after complete oxygen consumption. It is speculated that the 100% oxygen case also exhibits this behavior, but oxygen consumption is complete only near the end of the tube so any additional downstream deposition is not measured for the current experimental conditions.…”

Synthesis and Performance of a Series of Polyisobutylene-Substituted Succinic Acid Ester Dispersants for Reducing Thermal Oxidation Deposition of Jet Fuel

“…The appearance of multiple deposit peaks may result from the existence of nonhindered phenols or other heteroatomic species in the fuel. 19,24 It can be seen that dispersant #2 exhibits the best performance: there is only one small peak left at around 1.35 m along the tube and the total carbon deposition is reduced to 2.5 mg, which means dispersant #2 has 84.6% antideposition efficiency under these experimental conditions. Dispersant #1 also exhibits good performance: with 6.3 mg carbon deposit in total, and both peaks at 0.95 and 1.35 m are obviously decreased.…”

Chemical compositional analysis of jet fuels: Contributions of mass spectrometry in the 21st century

“…This affords an excellent opportunity for the development of alternative fuels that can use such instrumentation to determine which potential alternative fuels will have comparable properties to petroleum-derived fuels before expensive scale-up and engine testing. Despite representing only minor components of aviation fuels, the heteroatom-containing compounds (HCCs) influence important fuel properties such as storage and thermal stability (Balster et al, 2006;Bauserman et al, 2008;Beaver et al, 2005;Corporan et al, 2011;Epping et al, 2014;Frankenfeld et al, 1983;Heneghan & Zabarnick, 1994;Loeffler & Li, 1985;Zabarnick et al, 2019). In the context of this review, stability is defined as the resistance of fuels to react and contribute to insoluble products.…”

“…Despite representing only minor components of aviation fuels, the heteroatom‐containing compounds (HCCs) influence important fuel properties such as storage and thermal stability (Balster et al, 2006; Bauserman et al, 2008; Beaver et al, 2005; Corporan et al, 2011; Epping et al, 2014; Frankenfeld et al, 1983; Heneghan & Zabarnick, 1994; Loeffler & Li, 1985; Zabarnick et al, 2019). In the context of this review, stability is defined as the resistance of fuels to react and contribute to insoluble products.…”