Application of Saturates, Aromatics, Resins, and Asphaltenes Crude Oil Fractionation for Detailed Chemical Characterization of Heavy Crude Oils by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Equipped with Atmospheric Pressure Photoionization

Abstract

Heavy crude oil samples, fractionated according to the saturates, aromatics, resins, and asphaltenes (SARA) fractionation method, were analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) equipped with atmospheric pressure photoionization (APPI). SARA fractionation separates the crude oil into four main classes based on polarity and solubility. FT-ICR MS analyses of each if these fractions yielded spectra quite different from those of unfractionated crude oil. However, the spectrum acquired from the aromatics fraction was very similar to those of the unfractionated crude oil. The class, carbon number, and double-bond equivalence distributions obtained from each fraction were in agreement with what is expected from each SARA fraction. The data acquired from SARA fractions can be used to generate four peak lists for each crude oil sample. A master peak list, representing crude oil, was created by adding the same amount of a synthetic standard compound to each fraction. The abundance of the other peaks relative to the standard was used to combine the four peak lists into a single list. The number of compounds in the master list was twice that obtained by APPI FT-ICR MS analysis of unfractionated crude oil. Numerous NOx and SOx class compounds, which were not observed in the direct analysis of unfractionated heavy crude oils, were abundant in the resins fraction. Overall, this study shows that combining chromatographic techniques, including fractionation, with high-resolution MS is needed for a more complete understanding of the heavy molecules in petroleum.