Asphaltenes heteroatom concentration

A linear relationship is often observed between vanadium removal and sulfur removal, whereas the relationship between nickel and sulfur removal is linear but of smaller slope (Massagutov et al., 1967). For asphaltene-containing stocks, this phenomenon is interpreted on the basis of heteroatom distribution within the asphaltene micelles (Beuther and Schmid, 1963). Sulfur and vanadium are concentrated on the exterior, whereas nickel is concentrated in the interior. Conversion of the asphaltene generally leads to simultaneous removal of sulfur and vanadium, whereas nickel removal is more difficult. 

Resins and asphaltenes are also of interest as a result of the fact that most of the heteroatoms reside in these fractions [7,16], Beaton and Bertolacini [5] report that about equal amounts of V and Ni reside in the resins as in the asphaltenes, while sulphur is concentrated in resins. The chemical associations between the heteroatoms and organic molecules are far from certain, although general descriptions in terms of porphyrin like structures have been advanced [5]. Sulphur appears to be easily accessible and thiophenic sulphur has been identified [8]. Vanadium is more accessible than nickel. 

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