What is the function of a demulsifier in oil processing?

• A. Demulsifiers increase interfacial tension
• B. Demulsifiers reduce interfacial tension and promote coalescence of water droplets
• C. Demulsifiers remove solid particulates
• D. Demulsifiers cool the oil

Answer: (B)

Demulsifiers break stable water-in-oil emulsions by acting at the oil–water interface. They adsorb at the interface and lower the interfacial tension, which weakens the protective film surrounding water droplets. With that film softened, droplets collide and merge (coalesce) to form larger droplets that settle out more easily, separating water from the oil. Some demulsifiers also modify the interfacial film or droplet charges to encourage this coalescence. This role is different from removing solids or cooling the oil, which are accomplished by other methods.