Tar Sands, Bitumen, Asphaltenes, and Crude Oils

Vanadium in Tar Sands, Bitumen, Asphaltenes, and Crude Oils 

Extraction of tar sands with benzene or toluene yields a bitumen fraction and a mineral fraction. Further treatment of the bitumen with heptane or n-pentane yields asphaltenes and petrolene, which are the insoluble and soluble fractions, respectively. Depending on the source, these fractions contain varying amounts of vanadium (117,118). 

The presence of this and other materials presents potential problems in industrial processing, and there is great interest in characterization of the chemical nature of the vanadium species present. EPR is most widely used in these studies since the metal is in the oxo-vanadium(IV) state. Optical spectroscopy in the visible region can also be used on extracts since oxo-vanadium(IV) porphyrins, which absorb at around 572 nm and 534 nm 116,119), can readily be detected. However, it has been shown (120-122) that the total amount of vanadium present in crude oils and tar sand bitumen is higher than can be accounted for by the presence of oxo-vanadium(IV) porphyrins. It has therefore been suggested that the vanadyl may be bound to a range of different tetra-dentate ligands in crude oils (120-123). 

The amazing richness of vanadium complexes in crude oil and shale raises the obvious questions of where these vanadium complexes come from and what their biogenic source is. It is generally believed that the vanadium porphyrins result from the incorporation of vanadium in porphyrin structures originating from chlorophyll. (The reader is re- 

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