Nickel and Vanadyl Porphyrins in Saudi Arabian Crude Oils

This study reports the isolation and characterization of nickel and vanadyl porphyrins in the residue (535 °C+) and asphaltenes from Arabian Heavy crude oil. The residue was obtained by distillation of crude oil, whereas the asphaltenes were precipitated by n-heptane from the crude oil. Metalloporphyrins were first extracted from the residue and the asphaltenes. The nickel porphyrins were separated from vanadyl porphyrins by means of adsorption chromatography on silica gel and alumina using solvents of increasing polarity. The chromatographic separation process was monitored by ultraviolet-visible spectrophotometry. Both nickel and vanadyl porphyrins were identified and characterized by ultraviolet-visible spectrophotometry and mass spectrometry.