Has anyone ever tried this before? It would basically work by having a solution of low proof ethanol (say 20 proof) and having a solution outside the membraine having a lower water potential. Water would exit the ethanol solution and enter the other solution, leaving higher proof ethanol.

The biggest problem with this would be getting a membrane porous to water and not ethanol. Are there any easily attainable materials I can use as a membrane for this?

If it would work like that, do you not think it would be a wonderfully cheap, and therefore lucrative, and therefore desirable process for large companies who otherwise separate their alcohol via distillation?

To be entirely honest, I don't know why it wouldn't work, so I could well be entirely incorrect, but for one thing, the porosity I imagine would be a problem. I know visking tubing will work with sucrose solution, but I suppose there is a size difference between sucrose and ethanol.

I also imagine you'd have to have a solution with a stupidly low water potential, to gain any serious increase in the percentage concentration of the alcohol. This would therefore cause water molecules to therefore move back into the ethanol solution from the solution with the lower water potential. Of course, with any two solutions & a SPM, an equilibrium would obviously form, water would not merely magically travel.

Also, methinks this could have been answered easily enough in the bullshit thread.

EDIT : I'm more of an idiot than I thought; the equilibria of water potential could easily be solved by copying fish and their cunning gills;

Behold, shit ms paint diagram.

http://i32.tinypic.com/erfw51.gif

So if I'm right, (I'm probably not) your problem is still the semi permeable membrane, and I still find it highly unlikely it would work at all, mainly for my first reason.

Just because it's not frequently done isn't a reason it can't work. I understand the idea of equalibrium. I did some math last night and IIRC a fully saturated nacl soloution outside the ethanol would create something like 25%-30% alcohol. The biggest problem I see is getting a membrane that only water would be able to go through.

Next time try and post something useful and not 'if it worked more people would be doing it'.

Just because it's not frequently done isn't a reason it can't work. I understand the idea of equalibrium. I did some math last night and IIRC a fully saturated nacl soloution outside the ethanol would create something like 25%-30% alcohol. The biggest problem I see is getting a membrane that only water would be able to go through.

Next time try and post something useful and not 'if it worked more people would be doing it'.

a) I would be interested to see your maths please. Not in a bitchy way, not in an aggressive, proof or gtfo way, just out of curiosity way.

b) see edited post, for the most bloody simple way of making it a bit better than a claimed 5 - 10% increase...

c) I wasn't trying to patronise you, I was merely stating the obvious, and I can think of a few posters who, if they'd got to you first, might have been slightly less constructive in their arguments. Genii appear to sometimes overlook the obvious too.

d) In my original post, I suggested a type of semi permeable membrane that I know to work in one case that is easily available, it would obviously be up to you to experiment yourself.

e) A saturated NaCl solution getting you a 5 - 10% increase in conc isn't that much, and if its saturated, you are obviously unable to do much to improve it...

f) This still strikes me as a bullshit thread question, but I don't make the rules, or enforce the rules, so go wild :)

I really doubt this would work because of the fact that they're pretty similar in size...sucrose works because its a huge molecule comparatively. But if you're able to find a selective enough membrane, then I think you've got a decent chance it could work.

The percentage increase would be 15%-20%. That would be more than doubling the ethanol concentration. Another substance with a higher molarity could be used instead of salt, that's not set in stone.

And I believe ethanol can pass through visking tubing.

I will post my math when I go on my computer tonight.

EDIT: Heres the math: A liter of 10% ethanol will have 87.6 grams of ethanol. Ethanol has a molar mass of 46 g/mol so 87.6 / 46 = 1.9 mol. One liter of water can hold 360 grams of nacl. Nacl has a molar mass of 58.4 g/mol so 360 / 58.4 = 6.16 mol. If I have 2 liters of this solution it will have a molarity of 12.32. These solutions will reach an equilibrium at 7.1 mol. This will bring the ethanol solution to about 3.7 times its molarity, or 37% ethanol

Behold, shit ms paint diagram.

The FMGEB is win. It is now an official acronym to confuse the newbies.

I can think of a few posters who, if they'd got to you first, might have been slightly less constructive in their arguments.

Oh yeah, that reminds me... OP... have you considered that anhydrous magnesium sulfate has a very low water content?

For that matter, have you considered that the size difference between water and ethanol really ain't shit, and you'll probably have to go with hydrophobicity exclusions? Or that the crystal matrix of magnesium sulfate is permeable to water (in smaller quantities), yet is usually viewed as somewhat lipophobic?

Have you figured out that the solution on the other side of the membrane need not be of any specific phase state?

Just... spoonfeeding some things to think about...

Well water has a size of 3 angstroms vs. ethanol's 4.5 so I don't think the size difference is enough to make this work.

Since I got this thread reopened, I guess I should at least try to contribute to it. Is distillation used because once you get it set up it is actually pretty efficient and cost-effective, compared to drying agents?

The biggest problem I see is getting a membrane that only water would be able to go through.

A friend of mine bought one of these for cheap on ebay around 1 year ago, i will contact him and ask him the brand name:)

Since I got this thread reopened, I guess I should at least try to contribute to it. Is distillation used because once you get it set up it is actually pretty efficient and cost-effective, compared to drying agents?

I can't tell you because i do both! Distill and then drying agents although, i have to tell you that for the home chemist molecular sieves are THE FUCKING SHIT! Seriously i <3 them!