Mixed interfaces of asphaltenes and model demulsifiers part I: Adsorption and desorption of single components

This article is the first in a series of two aiming to understand the competitive adsorption and desorption dynamics of asphaltenes and a model demulsifier (Brij (R)-93) at the liquidliquid interface to broaden the knowledge of the stability of crude-oil emulsions. In this article, the properties of single components are studied. First, the Langmuir and Frumkin isotherms were successfully used to describe the interfacial tension data allowing the determination of the equilibrium adsorption parameters of asphaltenes and Brij (R)-93. Second, desorption of single compounds (from pure xylene, the adsorption medium) was followed through the use of a double coaxial capillary system. It was found that asphaltenes are irreversibly adsorbed (2% amount desorbed) at the oil/water interface even at low surface coverage and adsorption times which confirm the strong interactions present. It was also found that desorption is independent of the pure solvent flow condition and the total volume exchanged. Third, results show that the model demulsifier Brij (R)-93 is partly desorbed (20%) from the oil/water interface. This could be attributed to the distribution of ethyl oxide (EO) groups in the polydisperse sample or to the polydispersity of the aggregates adsorbed which have different adsorption energies. This work provides the fundamental framework for the second part of the series in which adsorption and desorption dynamics of a mixed interface composed of asphaltenes and Brij (R)-93 will be studied.