Asphaltenes correspond to very complex macromolecules characterized by condensed aromatic and naphthenic ring systems and aliphatic side chains. Heteroatoms may also be present. Asphaltenes tend to aggregate and precipitate causing major damage in operations related to the petroleum industry. They are defined by their solubility properties (i.e. insoluble in saturated hydrocarbons but soluble in aromatics).In order to better understand the tendencies of different types of structures to form aggregates from the association of certain molecules, we developed procedures for their fractionation and characterizations using combinations of solvents. They were employed to separate asphaltenes from: vacuum residues, a very heavy crude oil with a high asphaltene content and field deposits from a very unstable oil with a low asphaltene content. Mixtures of n-aliphatic and naphthenic or aromatic solvents in different proportions were used to precipitate asphaltenes dissolved in the selected mixtures of solvents. Constituents of the insoluble fractions were monitored by proton NMR showing significant variations in relative proportions of nuclei that are part of the aromatic and aliphatic systems of each sub-fraction, indicating that mixtures of these types are able to concentrate constituents according to the functional groups that are present. Furthermore, species that would tend to associate with an aggregate may be concentrated in certain sub-fractions according to their tendency to form aggregates rather than their solubility.

Fractionation of asphaltene constituents from petroleum residues

245th National Meeting (2013)

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