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I've been trying to design a device to increase the percentage of ethanol and water, or to at least concentrate the water-alcohol mixture without using distillation.

The way I'm trying to do this is by using a dry ice bath (dry ice+propanol). I then insert a stainless steel vessel in the bath with the said water-alcohol mixture (between 30-60% ethanol to begin with). Going by the ethanol-water phase diagram and the temperature of the ice bath (-78C), I should, in theory, be able to concentrate the mixture up to ~80% ethanol.

Where this goes wrong is that instead of cleanly separating into water ice and concentrated water-ethanol mixture, what I get is a kind of ice-alcohol slushy.

Any suggestions on how to get a clean separation and get ice that I can scoop out?

Thanks!

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  • $\begingroup$ If I remember correctly, 3Å molecular sieves haves been used for the separation of ethanol–water mixture for decades. I suspect you might want to work at the ambient temperatures to utilize the full capacity. $\endgroup$ – andselisk Nov 21 '17 at 4:25
  • $\begingroup$ You’re probably not going to get anywhere near a clean separation and definitely not going to get scoopable ice. I guess there will be people who can point out why. I personally don’t like ‘any suggestions’ questions, they do seem overly broad in my point of view. $\endgroup$ – Jan Nov 25 '17 at 13:14
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One suggestion: try cooling the alcohol-water mixture more slowly. Slower crystal growth may produce larger ice crystals that occlude less of the ethanol and are easier to separate by filtration. How to do it? Place the steel beaker in the outer bath before adding dry ice to the outer bath, then add the dry ice incrementally to gradually bring the temperature down to where you first observe ice crystals, then keep the temperature constant for a while as crystals form. Then lower the temperature a degree or two and repeat the cycle. Probably better not to stir the inner mixture. It will probably help to use a thermometer to carefully monitor the temperature of the alcohol mixture.

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