Desorption Mechanism of Asphaltenes in the Presence of Electrolyte and the Extended Derjaguin–Landau–Verwey–Overbeek Theory

Abstract

Desorption of asphaltenes from silica-coated quartz crystals upon exposure to a series of saline solutions was studied through the measurements of quartz crystal microbalance with dissipation (QCM-D), atomic force microscopy (AFM), and contact angle. Interestingly, it was found that the mass loading and thickness of asphaltene film decreased during the injection of sodium chloride solution at the concentrations ranging from 1 to 10 mM, with the surface tending to be hydrophilic, whereas the mass loading and film thickness increased gradually when the concentration increased from 10 to 1000 mM, with the surface inclined to be hydrophobic. It was also found that the electrostatic force had a great effect on this process due to the interactions between the charged interfaces of oil/water and water/solid. Besides, some additional interactions may arise under small distance at the presence of the electrolyte solution, and therefore, a direct force-measuring technique was introduced, in which the functionalized AFM tips felt a solid surface to model the interactions among three phases of oil, water, and solid. Based on the computed results of disjoining pressure isotherms, the theory of Derjaguin-Landau-Verwey-Overbeek (DLVO) was extended, taking into account of the participation of hydration forces which played an important role at short range. These structural forces mostly originated from the overlap of the hydrated layers under a variety of salinity concentrations, resulting in the balance of resultant interactions.