High-boiling fractions of petroleum are complex because of the great structural diversity of the hydrocarbons and because of the large proportion of heteroatomic compounds. This increased complexity makes impractical the traditional isolate-and-identify approach to composition studies. First, defining the total composition in terms of individual compounds, even if possible, would be hopelessly unwieldy. Second, separated fractions will be complex because of the increasing difficulty of making discrete separations. These factors suggest that a system is needed for classifying the large variety of compositional parameters and that an increased proportion of the analytical information must come from an understanding of the separation itself. A classification system is suggested, which starts with families such as hydrocarbons, thiophenes, and pyrroles and subdivides each family successively according to aromatic rings, cycloalkane rings, alkyl carbons, and individual compounds. An increased proportion of the analytical information can come from the separation itself by taking full advantage of modern separation science. Several separation procedures are examined, in terms of the classification system and modern separation science, with respect to their ability to provide useful separations. A preliminary separation scheme developed by American Petroleum Research Project 60 is discussed.
Proc. 8th World Petroleum Cong., Moscow, U.S.S.S., V. 6, June 1971, PP. 223-230