Residuum fraction distributions

The distributions of Ni, V, N, and S in several atmospheric residuum fractions (Reynolds, 1985) are shown in Table VII. As is evident from the table, the distributions of heteroatoms and metals in the fractions vary greatly with the petroleum source. The Kern River resid is considerably different than that from the other petroleums in having a low asphaltene... 

Figure 2-77 shows how the weight distributions of the different molecular types vary during the fractional distillation of a naphthenic crude oil. Saturated aliphatic hydrocarbons (i.e., paraffins and naphthenes) are the predominant constituents in the light gasoline fraction. As the boiling point is raised, the paraffin content decreases, and the NSO content increases continuously. About 75 wt% of tbe residuum is composed of aromatics and NSO compounds. 

Thus, when petroleum is separated into fractions by distillation, the asphaltenes remain in the heaviest fraction, the residuum, while the resins are distributed through the various fractions according to volatility. The color of these distillates almost entirely depends on the presence of resins. The color of the heaviest fraction, residuum, is determined to a great extent by the presence of asphaltenes. 

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