Demulsification, or emulsion breaking, is especially important in crude oil production and waste water treatment. In crude oil production, water-in-oil emulsions are typically produced. These emulsions can be extremely stable due to the asphaltenes and resins naturally found in many crude oils. The effective separation of crude oil and water is crucial in terms of crude oil quality but also to ensure the high quality of the separated water phase at the lowest possible cost.
From the process point of view, there are two aspects of demulsifications: the rate at which the separation takes place and the amount of water left in the crude oil. Produced oil often has to meet the company and pipeline specifications. Typically, the oil shipped from a wet crude-handling facility may not contain more than 0.2 % BS &W (basic sediment and water) or 4.5 kg of salt per thousand barrels of crude oil. This rather low concentration requirement is to reduce corrosion and the deposition of salts.
Emulsion separation into oil and water involves the destabilization of the emulsifying film around water droplets. There are several methods that can be used to destabilize the emulsion, such as the addition of chemical demulsifiers, increasing the temperature of the emulsion, applying electrical fields that promote coalescence and changing the physical characteristics of the emulsion. The addition of chemical demulsifiers is by far the most commonly used method.
Demulsifiers are surface active agents that are designed to migrate at the oil-water interface and neutralize the effect of emulsifying agents. The selection of the right demulsifier is crucial in the emulsion-breaking process. Because of the large variety of components present in crude oil, it is important to select the demulsifier based on the crude oil type. Interfacial rheology parameters, especially the interfacial dilatation elasticity, are known to correlate with emulsion stability. The effectiveness of the demulsifiers is thus studied by measuring the interfacial rheology of the oil-water interface in the presence of added demulsifiers.