What is the purpose of a demulsifier in an oil-water separation train?

• A. To reduce interfacial tension and promote droplet breakup, improving separation.
• B. To increase emulsion strength.
• C. To remove dissolved gases.
• D. To affect the color of the oil.

Answer: (A)

Demulsification aims to destabilize the water-in-oil emulsion so droplets can coalesce and separate more easily. A demulsifier works at the oil–water interface to weaken the emulsifying film that keeps small water droplets dispersed in the oil, effectively reducing interfacial tension and allowing droplets to merge into larger ones. With larger droplets, they settle or rise faster, improving the overall separation and reducing water content in the recovered oil. If you tried to strengthen the emulsion, separation would worsen; removing dissolved gases or altering the oil color don’t address the droplet stability at the interface, so they’re not the purpose of a demulsifier.