Molecular characterization of sulfur compounds in Venezuela crude oil and its SARA fractions by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Peng Liu,† Quan Shi,*,† Keng H. Chung,‡ Yahe Zhang,† Na Pan,† Suoqi Zhao,† and Chunming Xu*,† 

†State Key Laboratory of Heavy Oil Processing, China University of Petroleum,Beijing 102249, China, and ‡Well ResourcesInc., 3919-149A Street, Edmonton, Alberta, Canada T6R 1J8

*Corresponding Authors: Quan Shi −  Email: sq@cup.edu.cn; Chunming Xu −  Email: sq@cup.edu.cn xcm@cup.edu.cn

Keywords: Aromatic compounds; Hydrocarbons; Organic polymers; Petrochemicals; Sulfur

Abstract:Venezuela crude oil was separated into saturates, aromatics, resins, and asphaltenes (SARA) fractions. The sulfur compounds in the crude oil and its SARA fractions were reacted with iodomethane in the presence of silver tetrafluoroborate and converted to methylsulfonium salts. The methylsulfonium salts were characterized by positive-ion electrospray ionization (ESI) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The S₁, S₂, S₃, O₁S₁, O₁S₂, O₂S₁, and N₁S₁ class species were identified in crude oil derived methylsulfonium salts. The molecular composition and mass distribution of sulfur compounds in the subfractions were distinctly different. Small amounts of S₁ class species (cyclic-ring sulfides) were present in the saturates fraction. Thiophenic sulfur compounds were dominant in the aromatics fraction. Complex multiheteroatoms (N₁S_y, O_xS_y, and N₁O_xS_y class species) were present in the resins and asphaltenes fractions. The relative abundance plots of double-bond equivalence (DBE) versus the carbon number of S₁, S₂, O₁S₁, and O₂S₁ class species showed that as the molecular polarity of the fraction increased, the DBE values of the abundant S_y class species increased. SARA fractionation isolates the highly aromatic sulfur species in the resins and asphaltenes fractions, which are not observed in the parent crude oil sample.