https://www.newscientist.com/article/2212346-a-super-thin-slice-of-wood-can-be-used-to-turn-saltwater-drinkable/
[links in online article]
A super-thin slice of wood can be used to turn saltwater drinkable
2 August 2019
By Leah Crane
Filtering the salt from seawater can take a lot of energy or specialised
engineering. A thin membrane made of porous wood may be able to fix that.
In membrane distillation, salty water is pumped through a film, usually
made of some sort of polymer with very narrow pores that filter out the
salt and allow only water molecules through. Jason Ren at Princeton
University in New Jersey and his colleagues developed a new kind of
membrane made of natural wood instead of plastic.
“If you think of traditional water filtration, you need very
high-pressure pumping to squeeze the water through, so it uses a lot of
energy,” says Ren. “This is more energy efficient and it doesn’t use
fossil-fuel based materials like many other membranes for water filtration.”
His team’s membrane is made of a thin piece of American basswood, which
undergoes a chemical treatment to strip away extra fibres in the wood
and to make its surface slippery to water molecules. One side of the
membrane is heated so that when water flows over that side it is vapourised.
The water vapour then travels through the pores in the membrane toward
its colder side and leaves the salt behind, condensing as fresh, cool
water. This takes far less energy than simply boiling all of the
saltwater because there’s no need to maintain a high temperature for
more than a thin layer of water at a time, Ren says.
This method filters about 20 kilograms of water per square metre of
membrane per hour, which is not quite as quick as polymer membranes. The
researchers think that may be because they did not have the equipment to
make their membrane as thin: it is 500 micrometres thick, whereas the
polymer membranes are generally closer to 130 micrometres thick.
Making the wood membranes thinner shouldn’t be too hard with the right
equipment, Ren says. “The functional part of the membrane is a
micrometre thick,” he says. “The rest is just a supporting structure to
make it harder to break.”
Journal reference: Science Advances, DOI: 10.1126/sciadv.aaw3203
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