Self Distilling Vodka

29 January 2012
Posted by Dave Ansell.

Graphene is probably the material of the moment, it is made up of carbon atoms bonded to one another in a honeycomb pattern forming extremely strong sheets.  These sheets can be stable at just one atom thick, and have very exciting electrical properties, but are also remarkably impermiable to other atoms.

Members of Professor Sir Andre Geim's group at the University of Manchester, where graphene was first identified, were investigating the permiability of a closely related material called graphene oxide.  This is graphene which has been reacted with a strong oxidising agent, making it more soluble and easier to deal with.

They created membranes made up of small pieces of graphene oxide which pile up like bricks to form an interlocked structure, and then tested how gas-proof they were by using the film as a lid for a container full of various gases.

GrapheneThey found that despite being 500 times thinner than a human hair, it completely stopped Hydrogen, Nitrogen and Argon from escaping, to the limits of their measurements.  It even stopped Helium which, being a tiny single atom will escape from party balloons very quickly, and can even diffuse out through a millimetre of glass.

They then tried various liquids, and found similar behaviour for ethanol, hexane, acetone, decane and propanol vapour, but when they tried normal water it behaved as if the membrane wasn't there, escaping at least a hundred thousand times faster than any of the other materials.  They think the water is forming a layer one molecule thick between the layers of graphene, blocking the route for everything else, but if it dries out, this gap shrinks and seals up.

To make use of this behaviour they put some vodka in the container, and left it for a few days.  Normally ethanol evaporates faster than water so vodka gets weaker over time, but with their membrane, which blocked the ethanol, the vodka got stronger and stronger.

This is extremely interesting behaviour, as seperating water from other solvents is a huge part of many chemical processes.  This is normally done by distillation, which takes a large amount of energy, and the process has to be repeated many times.  Ethanol cannot be concentrated to more than 96% without involving poisonous solvents to remove the water, so this material has a huge potential.

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