Molecular Origins of Crude Oil Interfacial Activity. Part 4: Oil–Water Interface Elasticity and Crude Oil Asphaltene Films

Abstract

The ability of crude oil asphaltenes to impart elastic properties to an oil–water interface was investigated. Asphaltenes separated from Tulare, Hamaca, Cold Lake, Hoosier, Celtic, and Talco crude oils were used. These asphaltenes spanned a range of chemical compositions and molecular structures. An oscillatory tenisometer was used to measure the elastic modulus at the oil–water interface. The asphaltene molecular structure strongly influences the magnitude of elasticity imparted to the oil–water interface. Asphaltenes with high nitrogen and nickel contents possess the optimum molecular structure to adsorb and aggregate at the oil–water interface and form elastic films. Asphaltene films formed at the oil–water interface were isolated and examined by cross-polarized light microscopy. These films exhibited strong birefringence, indicating ordered packing of asphaltene molecules in the film. Asphaltene films that impart high elasticity to the oil–water interface stabilize water-in-oil emulsions. For asphaltene-stabilized emulsions, the oil–water interface elastic modulus correlates with emulsion stability. We find that the oil–water interface elastic modulus is a better indicator of emulsion stability compared to interfacial tension reduction.