Effect of Premixed Asphaltenes and Demulsifier on Oil-Water Interfacial Properties

During crude oil recovery, asphaltene-stabilized water-in-oil emulsions are formed. Asphaltenes is the component of crude oil, which is insoluble in n-alkane and is considered to be largely responsible for the stability of water-in-crude oil emulsions. To avoid wide range of problems, water has to be removed from these emulsions by using chemical 'demulsifiers'. How demulsifiers act is still poorly understood. As the real crude oil system is extremely complex, system consisting of model oil with 100 ppm asphaltenes concentration is used as this concentration corresponds to nanoaggregation in the bulk fluid as shown in previous work. The surface pressure values appear to be a result of both asphaltenes and demulsifier competing to adsorb at the interface. The fractional interfacial coverage achieved by each appears to depend on their respective bulk concentrations. Thus demulsifier-asphaltene systems exhibit an equilibrium surface pressure, reached at higher demulsifier concentrations possibly due to adsorption balancing desorption in the demulsifier rich regions, the presence of which block the 'almost insoluble' asphaltenes from further coverage of interface. The behavior of the surface pressure on expansion and contraction of droplets using pendant drop to emulate a Langmuir trough supports the notion of concentration-dependent fractional coverage by each species.