Two-faced membrane channel provides a simple, efficient way to separate oil and water

A team of chemists and engineers in China has developed a new, efficient way to separate oil and water mixtures. In their paper published in the journal Science, the group describes how they developed their new technique, how it works and the many possible uses for it.

Xing Yang and Mohammad Hossein Jandaghian from the Department of Chemical Engineering, KU Leuven, in Belgium, have published a Perspective piece in the same journal issue outlining the work done by the team in China.

Oil and water mixtures, such as those used to make salad dressing, will naturally separate after leaving a bottle still for a period of time. Unfortunately, other oil and water mixtures, such as those that result from manufacturing processes, take much longer to separate or do not separate at all.

Thus, recycling involves a variety of techniques ranging from the use of centrifuges, skimming and chemical reactions. In this new effort, the team in China has developed a technique that is both simple and efficient.

The new approach involves the use of two semipermeable membranes, one hydrophilic, the other hydrophobic, with a channel between them whose size can vary from 4 to 125 millimeters. An oil and water mixture is pumped into the chamber under a small amount of pressure. The hydrophilic membrane allows water to pass through, while the hydrophobic membrane allows oil to pass through.

As the oil and water mixture are pumped through the chamber, small oil droplets collide and form bigger droplets, which eventually pass through the hydrophobic membrane and into an external tank. Meanwhile, water escapes through the hydrophilic membrane into a separate tank. The liquid is kept moving by continuously pumping small oil drops into the channel.

The researchers explain that because the two membranes are so close together, a feedback process develops, making the separation more efficient. During testing, the technique was able to recover approximately 97% of the oil in a mixture and 75% of the water.

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