We present a model explaining the mechanism of water-in-oil (W/O) emulsion stabilization in petroleum systems. According to the model, W/O petroleum emulsions are stabilized by at least two types of chemicals: one is a small subfraction of asphaltenes, and the other is a low-molecularweight, surfactant-like material. Their competition for the oil/water interface is based on adsorption kinetics, rather than on differences in adsorption energies. The asphaltenic material adsorbs slowly and irreversibly and forms rigid skins. Surfactant-like species adsorb fast, reaching equilibrium. Both are effective emulsifiers; however, emulsion breaking requires different strategies, depending on the stabilizer.
The need for alkaline conditions in oil sands processing is, in part, to produce natural surfactants from bitumen. Previous studies have shown that the produced surfactants are primarily carboxylic salts of naphthenic acids with the possibility of sulfonic salts as well. The role of these natural surfactants, particularly those in the naphthenate class, is to provide a physicochemical basis for several subprocesses in bitumen extraction. In this study, it was found that the content of indigenous naphthenic acids in bitumen can destabilize, to some extent, the water-in-oil emulsion by lowering the interfacial tension, reducing the rigidity and promoting the coalescence of water droplets.
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