Understanding the Liberation of Asphaltenes on the Muscovite Surface

摘要

Separation of heavy hydrocarbons from mineral surfaces is the key step for unconventional oil production and remediation of oil-contaminated soils. The presence of asphaltene and the coexistence of mineral rocks are considered as the most challenge during the above separation processes. Herein, the liberation of asphaltenes (and/or heavy oil) on the muscovite [KAl2(Si3Al)O-10(OH)(2))] surface has been systematically investigated through instrumental characterization and molecular dynamics (MD) simulation. It is observed that,, quite different from that on the silica surface, asphaltenes can flake off from the muscovite surface as a result of the weaker adhesion force between asphaltenes and the muscovite surface. This liberation pattern was also found to be influenced by the addition of other oil fractions. The micro force measurements by atomic force microscopy show that the adhesion force between asphaltenes and muscovite is weaker than that between asphaltenes and silica in both air and water. Assisted by the MD simulation, it is found that the detachment of asphaltenes is highly dependent upon the mineral types and the presence of the water film on the mineral surfaces. Although the van der Waals force is found to be the main force between asphaltenes and mineral surfaces, the presence of potassium ions (K+) on the muscovite surface could increase the percentage of the electrostatic forces in the total force. Furthermore, the presence of a 0.4 nm water layer (in the air) between asphaltenes and the muscovite surface could reduce their interactions dramatically compared to that in a vacuum state. This finding suggests that the presence of water between the mineral surface and oil is beneficial for the separation of oil from the mineral surface. In addition, the asphaltene molecules are found to contact with the silica surface by face-to-face (aromatic ring) form, while a much more perpendicular orientation of the asphaltene molecules on the muscovite surface.