Molecular characterization of sulfur-containing compounds in the wide fractions of Saudi Arabia atmospheric residue by supercritical fluid extraction fractionation

Saudi Arabia atmospheric residue (SZAR) was subjected to supercritical fluid extraction fractionation (SFEF) and separated into four extractable fractions and an un-extractable end-cut.The SFEF subfractions were subjected to the simulated distillation analysis, gel permeation chromatography (GPC) for their molecular weight distributions, and open column liquid chromatography for their saturates, aromatics, resins, and asphaltenes (SARA) compositions, by high-temperature gas chromatography (GC).The density, carbon residue value, viscosity, and sulfur and nitrogen content along with the extraction pressure were determined.Sulfur compounds in wide fractions were converted to methylsulfonium salts, which were characterized by positive-ion electrospray ionization (ESI) and Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS).The results indicated that the mass range and maximum peak intensity of the SFEF subfraction are increased as the SFEF subfraction becomes heavier.The molecules in various SFEF subfractions are separated by their polarity and molecular weight.The highest level in the various fractions is referred to S₁ class species and meanwhile, benzothiophene turns to be the dominant heteroatom compounds.Compared with the lighter fractions, heavier fractions have higher contents of S₁ and S₂ class species, wider range, higher molecular weight, and more aromatic cores.