Oil and water are difficult to separate without leaving behind some impurities
Abaca Press/Alay
Mixtures of oil and water can be efficiently separated by pumping through thin channels between semipermeable membranes, opening the way to cheaper and cleaner ways to deal with industrial waste. Experimental prototypes managed to recover oil and water with purity greater than 99.9 percent.
Several methods already exist to separate such mixtures into their component parts, including spinning in a centrifuge, mechanically skimming oil from the surface, and separating with chemicals, electrical charges, or semipermeable membranes that allow some substances to pass through but not others. Membranes are the simplest method, but are currently imperfect, leaving behind a stubborn mixture of oily water or water oils.
now, Hao-Cheng Yang At China’s Zhejiang University and his colleagues, they have developed a more efficient method that uses two membranes – a hydrophobic layer that allows oil to pass through and a hydrophilic layer that allows water to pass through – to cleanly separate the two.
Yang says this idea has been tried before with less impressive results. This is because as oil or water is removed from the mixture, the concentration of the components changes, making the membranes less effective.
To overcome this, the team pumped the mixture into a thin channel between the two layers. In this confined space, oil droplets are more likely to collide and accumulate, and are therefore more efficiently removed by the hydrophobic membrane. This in turn increases the proportion of water in the mixture, creating a beneficial feedback loop that ensures clean oil and water are continuously removed.
“When we bring the membranes (closely) together, they will affect each other, making the process continue,” says Yang. “There is a feedback loop between the two processes.”
In tests, the researchers found that total oil recovery increases from 5 percent to 97 percent and water recovery increases from 19 percent to 75 percent as the channel width is reduced from 125 millimeters to 4 millimeters. The purity of the recovered oil and water is more than 99.9 percent, leaving only small amounts of residue, Yang says.
The team is talking to the industry and Yang believes that the process is so simple that it can easily be scaled up to the appropriate levels within a few years.
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