Characterization of Saturated Hydrocarbons in Vacuum Petroleum Residua: Redox Derivatization Followed by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Heavy petroleum fractions, which have distinct chemical and physical properties, are becoming important refinery feedstocks. In comparison to aromatic and heteroatom-containing compounds, the saturate compounds in heavy petroleum fractions have rarely been analyzed using recent advanced mass spectrometry methods. In this work, the compositions of saturate fractions derived from six vacuum residua (VR) of different geological origins were determined and compared. Saturate fractions were subjected to ruthenium-ion-catalyzed oxidation (RICO) derivatization and characterized with negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed that the VR-derived saturates consisted of n-paraffins, isoparaffins, and naphthenes with 1–10 rings. The maximum double bond equivalent (DBE) values of species in various VR-derived saturates were similar. The maximum carbon number of VR-derived saturates was up to 100. The maximum carbon numbers of naphthenes in VR-derived saturates were generally greater than that of paraffins. The relative abundances and ranges of carbon numbers of the various species in VR-derived saturates differed depending upon their geological origin and the distillation temperature of samples. Compounds with 0–6 naphthenic rings were highly abundant in the VR-derived saturates. On the basis of the results of this study, the RICO/ESI FT-ICR MS method shows promise as a potential semi-quantitative analysis for saturates in heavy petroleum fractions.