The science behind ultra-thin membranes
BP Magazine explores how to make a material that is 10,000 times thinner than a human hair, and looks into its potential uses in saving energy and cutting carbon emissions in industry.
Membranes are widely used in many industries for filtering or separating liquids and gases at the microscopic or even molecular level. BP currently uses membranes to desalinate seawater, both for drinking water supplies and crude oil processing.
What makes up a membrane?
Typically, membranes are made up of several different layers. Firstly, a supporting later will provide structure and strength to the material, while a separating layer determines which particles will pass through depending on their shape and size, like the mesh of a sieve.“No one has actually been able to work out how the separating layer in a membrane is formed, or how to control the shape and size – the morphology – of that separating layer,” says Professor Andrew Livingston, Head of the Department of Chemical Engineering at Imperial College London and who leads the BP International Centre for Advanced Materials (BP-ICAM) separations programme based at Imperial College London.
Livingston and his team, however, think they have cracked it, publishing a number of findings in Science, one of the world’s leading academic journals. “Firstly, we have found a way of making the separating layer of a membrane independently of the supporting layer,” says Livingston. “Secondly, we have found we are able to vary the morphology of the separating layer, to create a film with a crumpled, rather than a smooth surface. And thirdly, by being able to make the separating layer independently, we are able to put this very, very thin film onto a support of our choosing.”
Thin, crumpled and resistant
The ability to make the separating layer independently means it can be made as a very thin film, making it much more permeable. To make this separate layer, two chemical ingredients are mixed together. At the point where the chemicals meet, they react to form a film that is just 8 to 10 nanometres thick. A stack of 10,000 would only be about the width of a human hair.
By changing the shape of the separating layer, a film with a crumpled surface can be created. This increases the surface area of the film and allows more molecules to be filtered at one time.
The third advantage of an independent separating layer is that it means different materials may be used for the supporting layer. Livingston’s team has been using a material called ‘alumina’, which, unlike commercially used membranes, doesn’t become clogged up during use. Alumina is also resistant to dissolving on contact with oil and seawater.
Together, these three discoveries add up to a huge potential improvement in membrane performance. “We are seeing our crumpled nanofilm membranes separating substances 400 times faster than commercially available membranes,” says Livingstone.
There is a long way to go before this nanofilm membrane can be scaled up from laboratory experiments to commercial production; however Livingston remains confident that his membranes can achieve better results, faster than conventional membranes.“The advantage you might have with nanofilm membranes is the ability to produce lower salinity water at the same rate achievable conventionally, but using fewer membranes,” says Livingston. “That means you could install smaller, lower weight desalination plants on your offshore platforms – and anything that reduces the weight you need to support is going to have significant benefits in an offshore environment,” said Livingston.
The future of nanofilm
Looking towards the future, these ultra-thin membranes could replace more energy-intensive methods currently used to separate materials. Livingston said, “A very long-term goal – a dream – would be to see nanofilm membranes used in refining. In an oil refinery, it is generally estimated that as much as 10 out of every 100 barrels of oil may be used up providing the energy for the refining process. This is some way off, but imagine if you could reduce that energy demand right down using membranes?”This article has been adapted for the QEPrize with the permission of BP For more information, or to read the article in full, visit BP Magazine.
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