Madsen Pirie

I’ve written about osmosis before, and I think it likely that it will be the future way of desalinating seawater.  Eco-maniacs give doom-laden predictions of future “water wars” and urge us to move to lifestyles that use less water, but in all likelihood the desalination of seawater will become cheaper and more efficient.  The main problem is energy.  It takes 1.5kwh per tonne of fresh water, but two new approaches hold out the promise of a huge reduction in that.  Both derive from new forms of carbon.

Chinese scientists have shown that graphyne, which is like graphene but with double and triple bonds in certain places, could be made with holes large enough to admit molecules of water, but too small for sodium and chloride ions.  A computer simulation shows that “None of these ions can permeate through α-graphyne, β-graphyne and graphyne-3.”  The Chinese have already synthesized one form of graphyne, so the race is on to find ways of manufacturing the required forms of it on an industrial scale.

Meanwhile conventional graphene looks to play a role as well.  A team at Lockheed Martin has punched holes in sheets of graphene to turn them into a molecular sieve to remove sodium and chloride ions.  They call it Perforene, duly patented and trademarked.  Both of these new uses of carbon membranes promise to make desalination easier, less energy-consuming, and cheaper.  They’re a much better outcome than any “water wars.”

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