Chemical characterization of asphaltenes from various crude oils

The characterization of asphaltenes recovered from different crude oils is reported in the present work. The properties of the crude oils cover a wide range (API gravity: 10–33°, asphaltene content: 1.7–25.1 wt.%). Asphaltenes were precipitated in a high pressure batch reactor using n-heptane as solvent. Metal content by atomic absorption, elemental analysis, UV-fluorescence spectroscopy and molecular weight distribution by size exclusion chromatography were used as characterization techniques. The content of asphaltenic nickel, vanadium and sulfur was calculated for each crude oil. It was found that the concentration of these three species was higher in heavier crude oils. Heavier crudes also showed significantly higher asphaltene contents, which represented important fractions of the vacuum residue produced from these oils. However, the differences in asphaltene molecular weight distributions were narrower and did not show a clear trend as a function of the origin of the sample.

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► Asphaltene structure was probed by UV-F to verify trends in aromatic cluster sizes.
► No correlation between asphaltene structure and molecular weight distribution.
► Asphaltenes from the heaviest crude oil showed larger polyaromatic ring systems.