Missing Factors in Alternative Jet Fuel Formulations: Role of Cycloalkanes, Model for Viscosity Prediction, and Quantitation of n-Alkanes, iso-Alkanes, Cycloalkanes, and Alkenes via GCxGC/(+)EI-TOF-MS

The next generation of sustainable (alternative) aviation fuels (SAFs) must abide for simplified chemical compositions that will provide higher gravimetric and volumetric energies with a minimum aromatic content. The use of ethanol in the U.S represents a marvelous technical and economic opportunity to synthesize jet fuel range compounds, especially cycloalkanes, via an alcohol-to-jet (ATJ) process using alkenes (olefins) intermediates by employing existing infrastructure. Cycloalkanes stand out as promising compounds with the potential to achieve higher gravimetric and volumetric energy contents while still meeting fuel drop-in requirements, including the ability to swell O-rings. In this project, the influence of blending target cycloalkanes into Jet A on the energy content, density, and viscosity of Jet A was systematically explored (Chapter 3). Different alkyl-chain lengths, position of substituents, heavy atom connectivities (isomeric structures), molecular geometries, and number of rings provided key technical information to facilitate the control of the physical properties of jet fuels based on addition of cycloalkanes. Complementary, the kinematic viscosity of conventional jet fuels and alternative blending components at -20 °C was successfully predicted based on their chemical composition via GC×GC/FID by using a partial least squares (PLS) model and a Yeo-Johnson transformation offering lower prediction errors than other methods available in the literature (Chapter 4). Finally, a quantitation method for alkanes, branched alkanes, cycloalkanes, and alkenes was proposed by using GC×GC/(+)EI-TOF-MS data only (Chapter 5). This method uses experimental correction factors for the chromatographic peak area for each group of compounds based on their hydrocarbon group, number of carbon atoms, and degree of branching as factors influencing their different ionization efficiencies. This information broadens the understanding of missing factors in the ATJ process by providing insights regarding the role of cycloalkanes in alternative jet fuel formulations, improving the prediction capabilities to estimate the kinematic viscosity of jet fuels and alternative fuel blending components at low temperatures, and helping to facilitate the chemical characterization and quantitation of complex mixtures of hydrocarbons, including alkenes (olefins), without using GC×GC/FID or expensive model compounds.