High-Resolution Mass Spectrometry Investigation of Diesel Storage Stability Focused on Nitrogen-Containing Compounds

Diesel fuel is essential intercontinentally, as it plays critical roles for industry, agriculture, military, and healthcare sectors. Hence, the storage stability of diesel is an essential aspect of maintaining daily operations globally. As the nitrogen-containing compounds (NCCs) are known to facilitate storage stability failure of diesel, their chemical characterization is vital. In this work, (+) electrospray ionization coupled to an orbitrap mass spectrometer was employed to qualitatively characterize ionized NCCs derived from stable and unstable diesels, and from sediment obtained from the unstable diesel fuel. Remarkably, up to 40 and 63 individual homologue ion series (ions sharing the same general molecular formula, each representative of at least one chemical class (e.g., pyrroles, quinolines, carbazoles)) were detected in diesel fuel and sediment, respectively. Hence, this work provided more comprehensive qualitative information for diesel fuels and sediments than previously documented. Upon comparison of diesel fuels, important compositional differences were observed, notably greater abundances of NCCs with the general formula of C x H y NO and C x H y NO 2 in the unstable diesel. Upon analysis of sediment, ions of the general formula of C x H y N, C x H y NO, C x H y NO 2, C x H y NO 3, and C x H y N 2 O 2 were detected. Interestingly, NCCs of smaller alkyl carbon number showed greater propensity to contribute to sediment formation. Additional stress studies using ASTM D5304 were completed on copper-doped and nondoped diesel fuels. Upon stressing the nondoped and copper-doped stable diesel fuels, oxidized NCCs clearly increased in abundance, especially for the copper-doped diesels, demonstrating its significance for accelerating oxidative reactions. Additional qualitative data was reported for the NCCs detected in fuels and sediments and by individual ion series (i.e., range and average molecular masses) as well as Kendrick Mass Defect plots. Overall, the reported qualitative information showcased the proficiency of the orbitrap at providing vital information for enhancing our current understanding of diesel storage stability.