Abstract
Asphaltenes are shown to be amphoteric, containing acidic and basic species that can ionize at low and high pH respectively when they come in contact with water. We have used a mass transfer model in order to determine the partition coefficients of asphaltenes between oil and water. We have compared the influence of type of asphaltenes on interfacial tension and on mass transfer between oil and water and analysed the influence of an added surfactant. We have also compared the behavior of asphaltenes dissolved in model solvents with that of diluted heavy crude oils. Although asphaltenes qualitatively reproduce the behavior of crude oil components at the oil-water interface, differences were observed, either in interfacial tensions at low pH, or in partition coefficients at high pH. These differences are due to other molecules present in crude oil, which are either more interfacially active or more soluble in water.
Highlights
Asphaltenes are the highest molecular weight components of crude oils [1]
These emulsions are formed during water injection in petroleum wells or when surfactants are added for oil transport [4, 5]
We found that the oilwater interfacial tension is decreased by the addition of surfactant, especially if it is ionic and contains aromatic groups such as SDBS (Sodium Dodecyl Benzene Sulfonate)
Summary
Asphaltenes are the highest molecular weight components of crude oils [1]. They are the most polar and they form aggregates in the bulk crude oil [2] and adsorb at interfaces between oil and water [3]. The behavior of asphaltenes at oil-water interfaces has been extensively studied in order to better understand the stability of crude oil-water emulsions. These emulsions are formed during water injection in petroleum wells or when surfactants are added for oil transport [4, 5]. They can be very stable when the concentration of asphaltenes is large, posing problems in oil-water separation methods
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