Equipartitioning of Precipitant Solubles between the Solution Phase and Precipitated Asphaltene in the Precipitation of Asphaltene

Abstract

It is shown by sequential reprecipitation that both n-C5 and n-C7 Athabasca asphaltene contain significant amounts of precipitant solubles, comprising resins and low-molecular-weight asphaltene-like substances in about the same percentage amounts relative to the residual precipitated insoluble asphaltene. All of the several hundred resinous molecules detected in the n-C5 solubles, with some minor exceptions, were also detected in the resin fraction of the maltene. From an estimation of the concentrations of several compound classes in the solution and solid asphaltene phases, values were derived for the equipartitioning coefficients. The results implicate aromatic stacking as the dominant mode of association of resins and asphaltene. The aggregate amount of n-C5 solubles associated with the n-C5 insoluble plus the aggregate amount of n-C7 solubles associated with the n-C7 insoluble residual asphaltene obtained in the sixth reprecipitation is more than 50% of the latter, and in the native oil, it is estimated to exceed 70%. This fraction, representing a fifth compound class of crude oil, plays a paramount role in the stabilization of the colloidal solution of asphaltene and should be investigated more extensively.