Distribution of Vanadium and Nickel in the Case of Two-Step Solvent Fractionation of Asphaltenes of Heavy Oils

Abstract

General features of the distribution of vanadium and nickel in the products of two-step solvent fractionation of asphaltenes have been using the exampley of heavy crude oils from various fields of the Volga–Urals oil-and-gas basin (Russia). At the first step, during the treatment of a solution of asphaltenes in toluene with an excess of n-hexane, vanadium and nickel are predominantly concentrated in the insoluble fraction that is characterized by increased molecular weight, aromaticity, and degree of condensation with a decreased fraction of heteroatomic sulfur- and oxygen-containing structures. At the second step, during the treatment of the solution of asphaltene fractions in toluene with an excess of dimethylformamide, characteristic features of the distribution of vanadium and nickel in the obtained fractions have been revealed for heavy oils from different fields. As a result, differences in the concentration of metal complexes of vanadyl with asphaltenes have been determined for the heavy oils from Carboniferous and Permian productive sediments.