Process diagnosis of coalescence separation of oil-in-water emulsions-two case studies

Coalescence separation is a widely applied technology for oil/water emulsion separation. In this paper, we first review the existing coalescence theories regarding droplet capture, attachment and release. Two case studies are considered, dealing with the separation of oil-in-water emulsions using our recently developed coalescing filters. The first case (Case I) is associated with the separation of surfactant-stabilized hexadecane/water emulsions. The second case (Case II) addresses the separation of sulfonated kerosene/water emulsions in a continuous bench operation. In Case I, known wetting and collision theories were applied to understand the complex coalescence process occurring on the surface of the fibers. For this, the detrimental effect of surfactants on coalescence separation was taken into account. It was found that the best oil wetting coalescing material under water was not the most desired for coalescence, contradicting the existing theory. In addition, once the materials were pre-saturated with surfactant-containing emulsions, the oil wetting was enhanced significantly. However, the separation efficiency was maintained at the same level, unless the material adsorbed surfactant, resulting in minor reductions in the wetting angle. In Case II, based on the fiber properties and operation conditions, the droplet capture efficiency and released droplet size were calculated using the existing models. Fiber diameter and medium face velocity were found to affect not only the capture, but also drop release. Based on model predictions, the dominant capture mechanism was identified as interception followed by van der Waals forces. Overall, this work offers insights about the influencing parameters on oil/water emulsion separation for better designing coalescence systems.