Expert: George Maxwell - 12/14/2007

Question
Hi, When we have water and oil we actually have three phases: water,oil and a solution of water and oil. I want to know how do we seprate water and oil in this phase?( it's very important in the distillation of hydrocarbons as you know.)

Answer
Thank you for your question.

The "third phase" you mention isn't a solution (if it was, you'd have to distill the mixture to seperate water and oil).

It's actually an emulsion - tiny droplets of oil suspended in water,or vice-versa.

One of the easiest ways to seperate an emulsion is to leave it to settle, and to strain off the water from the bottom. This works because the emulsion is unstable, and over time it will naturally seperate out in to two phases - oil on top and water underneath.

In the oil industry, large storage tanks often contain a small layer of water at the bottom, which has seperated out from the main oil. Valves are provided for draining this water off. In other words, it's normal in industry to just let the mixture settle out rather than to actively seperate it.

Whilst it might be possible to remove the water from an emulsion (e.g. using chemicals that react with water), this would be far too expensive on a large scale, though this procedure is often used in small-scale lab experiments.

Hope this helps.

Hope this heps.