Sciencemadness Discussion Board

Graphene wiki page, what does this mean?

Random - 24-8-2013 at 19:15

http://en.wikipedia.org/wiki/Graphene
Quote:

Ethanol distillation Graphene oxide membranes allow water vapor to pass through, but have been shown to be impermeable to all other liquids and gases including helium .[143] This phenomenon has been used for further distilling of vodka to higher alcohol concentrations, in a room-temperature laboratory, without the application of heat or vacuum normally used in traditional distillation methods.[194] Further development and commercialization of such membranes could revolutionize the economics of biofuel production and the alcoholic beverage industry.



does this mean we could just filter the water off the ethanol leaving 100% ethanol in the graphene filter?

elementcollector1 - 24-8-2013 at 19:36

Looks like you have to distill it with graphene in the boiling flask?

bfesser - 24-8-2013 at 20:50

The Wikipedia article cites this page:
<strong><a href="http://www.dailymail.co.uk/sciencetech/article-2092321/Hi-tech-wonder-material-graphene-unexpected-use--distill-vodka-room-temperature.html" target="_blank">Hi-tech 'wonder material' graphene has an unexpected use - it can distill vodka at room temperature</a></strong> <img src="../scipics/_ext.png" />

A quick search reveals that "the research, reported today in the journal Science," is this paper:

<strong>Unimpeded Permeation of Water Through Helium-Leak–Tight Graphene-Based Membranes</strong>
R.R. Nair, H.A. Wu, P.N. Jayaram, I.V. Grigorieva, A.K. Geim
<em>Science</em>. 27 January 2012. Vol. 335 no. 6067 pp. 442-444.
DOI: <a href="http://dx.doi.org/10.1126/science.1211694" target="_blank">10.1126/science.1211694</a> <img src="../scipics/_ext.png" />

IrC - 24-8-2013 at 23:59

Quote: Originally posted by elementcollector1  
Looks like you have to distill it with graphene in the boiling flask?


At room temperature I doubt the boiling flask is needed, any old jar will do. I would imagine the alcohol is lowest, with a graphene barrier sealing it off from the air above it. H2O preferentially evaporates into the air thus increasing the percentage of alcohol below the barrier. Having no access to bfessers link I cannot read the text of the paper but this seems the most logical conclusion. What confuses me is it passes through a two dimensional tube. How is this possible with a three dimensional water molecule? Does it take three tubes, one for each atom of O or H while the bonding forces are not disturbed between the atoms in the water molecule (not such a leap of imagination if you remember the barrier is a surface with a thickness of only one atom). Is this even possible or is a single tube greater in diameter than the entire H2O molecule. I just hate the papers the average layperson cannot read without a subscription. Maybe someone knows a link to a similar paper anyone can read.


[Edited on 8-25-2013 by IrC]

No, you can't.

Thebrain - 25-8-2013 at 04:42

The water will migrate both directions through a graphene filter. You can concentrate the ethanol, but not purify in a filter. The water on the other side of the filter from the ethanol should be pure. Ant that's the real point.
Graphene filters have the potential to turn sea water into fresh for just a fraction of a penny per cubic meter.

IrC - 25-8-2013 at 11:14

Quote: Originally posted by Thebrain  
The water will migrate both directions through a graphene filter. You can concentrate the ethanol, but not purify in a filter. The water on the other side of the filter from the ethanol should be pure. Ant that's the real point.
Graphene filters have the potential to turn sea water into fresh for just a fraction of a penny per cubic meter.


So you are saying even if the outside air is as dry as the Sahara water will still go back into the alcohol as easily as it is blown away in the wind? I was not describing a graphene filter paper where you pour it on top collecting what is going through it. I was describing a vessel full of Scotch for example with a graphene lid exposed to the atmosphere.

AndersHoveland - 25-8-2013 at 12:11

Probably there will be an osmotic pressure effect. This could potentially hinder all the water from evaporating out if the pressure inside becomes reduced. I am not sure how a tiny air intake vent would effect things, if it could neutralize the pressure difference without letting any significant amount of alcohol escape.

Quote:
H2O permeates through the membranes at least 1010 times faster than He. We attribute these seemingly incompatible observations to a low-friction flow of a monolayer of water through two-dimensional capillaries formed by closely spaced graphene sheets. Diffusion of other molecules is blocked by reversible narrowing of the capillaries in low humidity and/or by their clogging with water.

"Unimpeded Permeation of Water Through Helium-Leak–Tight Graphene-Based Membranes" , R. R. Nair, H. A. Wu, P. N. Jayaram, I. V. Grigorieva, A. K. Geim


[Edited on 25-8-2013 by AndersHoveland]

froot - 26-8-2013 at 03:06

Makes me wonder if graphene could be used as a proton exchange membrane.