Interfacial Aspects of Water-in-Crude Oil Emulsion Stability

Abstract

In certain crude oils the wax crystal size has a major influence on the stability of water-in-crude oil emulsions. Interfacial viscosity and other data suggest that the crystals form a barrier at the water/oil interface which retards the coalescence of colliding water droplets. In order to associate with the interface in this way the normally hydrophobic wax must acquire some affinity for the water phase, possibly via adsorption of polar asphaltenes and resins from the crude oil. Studies with octacosane (n-C₂₈H₅₈), a model crude oil wax, show that a limited wax/asphaltene/resin interaction does exist. However, the adsorbed layer does not confer hydrophilicity to the surface of either octacosane or a real crude oil wax. Therefore, the effect of wax on emulsion stability does not appear to be through action at the interface. Instead, the wax may act in the bulk oil phase by inhibiting film thinning between approaching droplets or by scavenging demulsifier. It is the asphaltenes and resins which were found to affect stability via interfacial action. They can adsorb in either dissolved or solid form and thereby inhibit water separation.