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View Full Version : Graphene membrane permeable to water vapor?



Siguy
2012-Jul-15, 05:51 AM
From Wikipedia (http://en.wikipedia.org/wiki/Graphene)

Graphene oxide membranes have been shown to be impermeable to all gases including helium, while simultaneously allowing water vapor to pass through the membrane as though no barrier were there.[124] This phenomenon has been used for further distilling vodka sitting in a room-temperature laboratory to higher alcohol concentrations without the application of heat or vacuum normally used in traditional distillation methods.[148] Further development and commercialization of such membranes could revolutionize the economics of biofuel production and the alcoholic beverage industry.

How exactly does this work? Isn't a water molecule much larger than a helium atom? Or are there some other forces that causes gases, but not water vapor, to be repelled?

If it does have this property, I imagine the potential uses are nearly limitless.

Antice
2012-Jul-15, 06:36 AM
From Wikipedia (http://en.wikipedia.org/wiki/Graphene)


How exactly does this work? Isn't a water molecule much larger than a helium atom? Or are there some other forces that causes gases, but not water vapor, to be repelled?

If it does have this property, I imagine the potential uses are nearly limitless.

I'm not entirely certain, but IF it behaves sort of like graphite then it has a propensity for adsorbing liquids onto it's surface.
It does not let gases trough. but it will adsorb anything in a liquid state and allow it to flow trough any holes in the sheet. for a membrane like this to work you need multiple sheets layered together where the gaps in the sheets are staggered so that they do not line up.

The path a molecule follows is one where it condenses onto the surface of one side of the membrane, it will tend to flow to the dryer areas of the sheet, and will thus flow towards any holes that lead to the other side of it. once it enters a hole it will meet the next sheet, and keep flowing towards dryer areas. thus it will end up flowing across the sheets and trough the staggered pinholes. once it reaches the far side of the surface one has to make certain that the molecules are allowed to evaporate away and be removed. otherwise the filter would just saturate and stop working.
It will not let any gas trough however, because molecules in a gaseous state have too much energy in them to be easily adsorbed.

HenrikOlsen
2012-Jul-16, 08:44 AM
Isn't water vapor a gas?

Anyway, a more serious answer is that it's likely because water molecules are rather polar while most of what they're probably talking about when using the word "gases" are non-polar..

That tends to have a strong influence on how molecules interact.

NEOWatcher
2012-Jul-16, 03:16 PM
Isn't water valor a gas?
The quote is in a section regarding room temperature distallation.
My guess is that the vapor is hitting the membrane and condensing.

neilzero
2012-Jul-27, 04:52 AM
If that is the case, it should not only lower the humidity, but warm the graphine permiting pn peltier juctions to generate electricity. That is too good to be true, so likely something was lost in the translation. Neil