Relation between Solution and Interfacial Properties of Asphaltene Aggregates

Abstract

Separate studies of the surface and volume properties of asphaltene aggregates have been conducted during the recent years. It has been shown that both of these properties depend on asphaltene origin, nature of solvent, presence of resins, etc. The aim of this work is to determine the linkage between these surface and volume properties. Asphaltenes have been extracted from different crude oils and dissolved in pure solvents. For one asphaltene the nature of the solvent has been varied and the influence of resins probed. Asphaltene’s adsorption properties have been explored by measuring adsorption isotherms onto silica particles. Volume properties, radius of gyration, Rg, and mass, Mw, of the aggregates are deduced from SAXS measurements. Additional characterization including specific gravity measurement has also been conducted. The isotherms measured can be fitted by a surface saturation model of Langmuir type from which two parameters can be extracted: a surface affinity constant K and the plateau adsorbed amount Γpl. For a given asphaltene in different solvents, Γpl is a function of size or mass of aggregates in the bulk. If different asphaltenes are considered, the relation holds if densities of the asphaltenes are taken into account. We show evidence of a relation between structure (mass) of asphaltene aggregates and interfacial properties (maximum amount at surface saturation), which implies a monolayer of aggregates which become denser at the surface.