High-performance liquid chromatography (HPLC) based techniques are used to investigate the role of polar species in deposit formation during jet fuel autoxidation and to explore the relative contributions of the various species classes which compose the polar fraction. More specifically, HPLC with UV-vis absorption detection was employed to quantify the polar species in jet fuel as a class, and a technique which combines solid-phase extraction (SPE) with HPLC and gas chromatography with mass spectrometric detection (GC-MS) was used to identify the species classes which compose the polar fraction in typical jet fuels. The analytical results were combined with surface deposit data obtained in a quartz crystal microbalance (QCM) system for a series of twenty jet fuels. The results indicate a relationship between the total amount of polar species measured and the amount of surface deposits produced. Results also suggest that phenols, various other oxygenated polar species, indoles, and carbazoles have a significant positive correlation with jet fuel surface deposit formation, while pyridines, anilines, and quinolines do not demonstrate a strong correlation with the tendency of a fuel to form surface deposits.

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Aviation fuel is so complex that it is virtually impossible to separate all of the major components of the mixture, much less the minor components. The minor components are typically separated from the major components using preparative techniques (such as solid phase extraction;SPE) and then re-examined by gas chromatography-mass spectrometry (GC-MS). Without SPE, GC-MS is not capable of a comprehensive determination of the trace polar components in jet fuel due to fuel complexity. In this contribution, jet fuel mixtures are preseparated by normal-phase SPE, followed by a single analysis using multidimensional gas chromatography-time of flight mass spectrometry (MDGC-TOFMS), which is similar to the recently popularized technique of GCÂGC. This two-column sequential analysis followed by TOFMS identifications is able to accurately identify more of the polar components of jet fuel. Automated data analysis routines, based on improved mass spectral library identifications (due to the better chromatographic separations), are able to determine individual components in the polar fractions that are of interest. Spreadsheet-based sorting of the highest quality identifications was also performed and used to quantify important polar fuel classes such as amines, indoles, pyridines, anilines, sulfur compounds, oxygenates, aromatics, and others. The relative amounts of each group were determined and related to similar measurements found in the literature. The ability to identify and quantify polar components in fuel may be useful in developing relationships between fuel composition and properties such as thermal stability.

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Changes in the liquid-phase oxidation of a cycloparaffinic/paraffinic solvent resulting from the introduction of natural and synthetic fuel antioxidants are studied by tracking the depletion of dissolved O 2 in a closed system at 185 °C and 3.2 MPa. A Jet-A fuel of reduced thermal stability is the source of natural fuel antioxidants that are introduced by making dilute (<20%) blends with the solvent. The synthetic hindered-phenol antioxidant BHT is added at concentrations of 3-50 mg/L. The individual and combined effects of natural and synthetic antioxidants on paraffin autoxidation are determined on the basis of increased reaction time required to deplete initial dissolved O 2 by 50%. Synergistic effects of ∼40% are observed for certain antioxidant concentrations. The roles of natural and synthetic antioxidants in the liquid-phase oxidation of jet fuel are discussed.

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Autoxidation of a thermally stable JPTS aviation fuel has been studied at 185 °C in a single-pass heat exchanger by monitoring the disappearance of dissolved O2 as a function of reaction time. All measurements were made in a single liquid phase at elevated pressure. We report empirical changes in autoxidation caused by (1) introducing a hindered phenol antioxidant (BHT), (2) adding a phenylenediamine antioxidant mixture (A0−24), (3) introducing natural fuel inhibitors in the form of a straight-run fuel, (4) adding selected combinations of the above antioxidants, (5) varying initial O2 concentration, (6) diluting (1/1) with a paraffinic solvent, and, finally, (7) introducing dispersants.