Mixed Interfaces of Asphaltenes and Model Demulsifiers, Part II: Study of Desorption Mechanisms at Liquid/Liquid Interfaces

This article is the continuation of a preceding paper (Part I) in which the adsorption and desorption of asphaltenes from the oil/water interface by pure solvent and model demulsifiers was studied. In this second part, the composition of mixed interfaces of asphaltenes and two demulsifiers (Brij-93 and Pluronic PE8100) was studied. Desorption of asphaltenes by demulsifiers, and vice versa, was determined. First, the composition of a mixed interface (asphaltenes and demulsifiers) through the use of the Langmuir equation of state (EoS) was determined. Second, an experimental setup that mimics, to some extent, the chemical demulsification of water-in-crude oil emulsions during the production stages was used. Desorption of already-adsorbed asphaltenes at the liquid/liquid interface by the action of two demulsifiers was assessed. It was found that desorption is always initiated by interactions between demulsifiers and asphaltenes. It is followed by the plausible formation of complex-like structures to finally end in the replacement, by displacement from the interface, of asphaltenes by demulsifiers. Third, the assessment of Brij-93 and PE8100 desorption from the oil/water interface by the action of asphaltenes was also carried out. It was found that asphaltenes can desorb PE8100 at low surface coverage.