GCxGC-Based iso-Alkane Subgrouping for Enhanced Compositional Analysis of Sustainable Aviation Fuels

Abstract

To evaluate sustainable aviation fuels (SAF) and other novel jet fuels, nontargeted comprehensive analysis by two-dimensional gas chromatography (GCxGC) is commonly utilized. The obtained results are necessary for subsequent model-based prescreening applications. The uncertainty of the respective property predictions is dependent on the degree of compositional detail as some properties (e.g., flash point, freezing point) are strongly influenced by structural molecular features. In the absence of sufficient structural reference data, individual identification from reference databases is usually not possible. Consequently, the results obtained from GCxGC are generally categorized by the carbon number and group type. To obtain greater details on the isomeric structure distribution of fuels, the iso-alkane family was further investigated. Therefore, a multilinear regression model for iso-alkane retention indices (RI) was constructed from molecular descriptors. Subsequently, the combined database from measurement and literature was extended by prediction to complete the data for all possible 42,900 branched isomers within the jet range (C7-C17). The isomeric structures were sorted into subgroups by their respective retention behavior, thereby correlating with the present number of molecular branches. The structural subgroup information was then used to create branching indicators to quantify and compare the subgroup distributions of different fuels. It was evident that isomeric distributions were unique to the respective samples. The new detail of composition will aid the characterization and differentiation of different fuels and present further potential for fuel assessment.