Smooth trick separates oil and water with 99.9 percent purity

A mixture of oil and water can be efficiently separated by pumping it through narrow channels between semipermeable membranes, paving the way for a cheaper and cleaner way to treat industrial waste. Experimental prototypes successfully recovered both oil and water with purity greater than 99.9 percent.

Various methods already exist for dividing such mixtures into their constituent parts, including spinning the mixture in a centrifuge, mechanically removing oil from the surface, and allowing some substances to pass through but These include dividing mixtures using chemicals, electrical charges, or semipermeable membranes that do not allow other substances to pass through. Membranes are the simplest method, but are currently incomplete and leave behind a stubborn mixture of oily water or watery oil.

Now, Hao-Cheng Yang and colleagues at Zhejiang University in China have found a more efficient method to cleanly separate both, using two membranes: a hydrophobic layer that allows oil to pass through, and a hydrophilic layer that allows water to pass through. developed. .

Yang says the idea has been tried before, but with less than impressive results. This is because when oil and water are removed from the mixture, the concentration of the components changes and the efficiency of the membrane decreases.

To overcome this, the research team injected the mixture into a narrow channel between the two layers. In this confined space, oil droplets are more likely to collide and accumulate. This means that oil droplets can be removed more efficiently by the hydrophobic membrane. This increases the proportion of water in the mixture, creating a beneficial feedback loop that continuously removes both clean oil and water.

“When you bring the membranes together (closely), they influence each other and the process continues,” Yang says. “There is feedback between the two processes.”

In their tests, researchers found that as the channel width narrowed from 125 millimeters to 4 millimeters, total oil recovery increased from just 5% to 97%, and water recovery increased from 19% to 75%. I discovered it. The purity of the recovered oil and water is more than 99.9%, and only a small amount of waste remains, Yang said.

The team is in talks with industry, and Yang believes the process is so simple that it could be easily scaled up to a suitable level within a few years.