Science Questions

Can ethanol be purified by reverse osmosis?

Sun, 13th Mar 2011

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Question

Dave Glossop asked:

Hi guys great show.

 

Question for you all regarding reverse osmosis water purifiers.

 

I am making my own home brew spirits with dextrose and yeast, then it got me wondering if I could get rid of the water by putting it through the RO plant.

 

Before I boil off the fusels, ethanol and methanol.

 

So when using a RO water plant, if you where to use a 10% alcohol solution would you get any alcohol (ethanol&methanol) through the membrane when processed.

 

Look forward to your answer.

 

Dave Glossop

Answer

Dave -   I don't want to comment on the legality of this so let’s stick to the science!

What is reverse osmosis in the first place?  This is used quite often for purifying water, to get salt out of it.  Essentially, you have a membrane which will let water through but not salt for example.  So, if you apply pressure to one side of saltwater, the water is forced through the membrane, the salt can't get through, so you end up with salty water on one side, and freshwater on the other side.

So essentially, what he’s attempting to do is get a membrane which will let water through but not alcohol, apply pressure to it, and then that pumps all the water out, leaving the alcohol and all the other stuff in there.  I imagine it would end up tasting very, very strongly because very few of the taste molecules are going to get through so it’s going to end up with a very, very flavoursome brew. 

I also think it depends on the membrane.  I've looked up that some membranes are better at this than others.  You’d have to pick one which is particularly good at noticing a difference between the alcohol and the water, and if you get one which works, if you pick the right membrane, there's no reason why it wouldn’t work.

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Dave Glossop asked the Naked Scientists: Hi guys, great show.   Question for you all regarding reverse osmosis water purifiers.   I am making my own home brew spirits with dextrose and yeast, then it got me wondering if I could get rid of the water by putting it through the RO plant.   Before I boil off the fusels, ethanol and methanol.   So when using a RO water plant, if you where to use a 10% alcohol solution would you get any alcohol (ethanol&methanol) through the membrane when processed.   Look forward to your answer.   Dave Glossop What do you think? Dave Glossop , Fri, 11th Mar 2011

Dave - just a word to the wise, I think it is still illegal to distil spirit in the UK even for personal consumption.  I don't know if the law refers only to distillation or is wider and encompasses any form of concentration of alcoholic content (over and above the legal practice of brewing beer and making wine). 

Chances of HMRC caring are pretty slight - but you never know.  But the chances are that if you had an accident any insurance co.s would run a mile screaming that illegal practices render coverage null.  imatfaal, Fri, 11th Mar 2011

Freezing is quite a good way to separate the water from the alcohol. syhprum, Thu, 24th Mar 2011



I knew a "scientist" in the UK who made his own liqueurs that way. He claimed it was not distillation. Geezer, Thu, 24th Mar 2011

He might claim that, but the Customs and Excise people don't agree. Bored chemist, Thu, 24th Mar 2011

That's what I told him  Geezer, Thu, 24th Mar 2011

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