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Thread: Fractional distilling + reflux results

  1. #1 Fractional distilling + reflux results 
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    I got a project about fractional distilling a solvent solution.
    I have a distilling column with the possibillity to reflux and I wan't to separate a solution of 40% Acetone and 45% Ethanol and 15% unknown compounds.

    Which is the best way to separate the solution to achive the purest result using fractional distillation with reflux?

    Hope there are chemical distillation experts that can give some good advice, I'm not a chemist just so you know, so keep it simple.


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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    A set up of the equipment needed is here:

    https://thehaberboschprocess.files.w..._apparatus.png

    Basically, it is similar to normal distillation with the addition of a fractionating column packed with glass beads to increase the efficiency of separation if the components of your mixture have similar boiling points. Once this is set up start heating your mixture, heat gently and do not let the temperature climb too high too fast. Monitor the temperature and collect the liquid that comes out of the condenser at a temperature below 50 C (this may be some of your unknown components or maybe nothing boils off at this low temperature). Remove the collection flask when the temperature rises above 50C. Place a new collection flask at the end of the condenser and collect the liquid that boils over at a temperature of 50-60 C, this will be mostly acetone (boiling point 56 C), once the temperature climbs above 60 C remove the flask and place a new flask under the condenser, collect the liquid that comes off at 70-80 C, this will be mostly ethanol (boiling point 78 C). If you want to increase the purity of each fraction they can be distilled again.

    Hope this helps.


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  4. #3  
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    I used my setup with reflux, but even with 100% reflux for several hours the purity of the first acetone is only 94%
    Both boiler and column were stable at 78 and 56 degrees C. So why cant I achive higher purity on the Acetone? Or is it impossible to create such a perfect separation?
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    Bullshit Intolerant PhDemon's Avatar
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    I'd need to check for your specific components but there may be an azeotrope formed. https://en.m.wikipedia.org/wiki/Azeotrope if this is the case that is as pure as you're going to get with a distillation.
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  6. #5  
    Bullshit Intolerant PhDemon's Avatar
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    I've had a quick look and can't find any data for either acetone/ethanol binary azeotropes or any ternary azeotropes containing these compounds. So, if you distill your 94% acetone you should be able to get a higher purity. Distillation is not perfect as volatile compounds can evaporate below their boiling point (the reason puddles dry up without having to heat them to 100C!) and it is common to have to distill a few times to get a high purity.
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  7. #6  
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    Okay, now with testing reaching a high purity needs a 100% reflux for a considerable time.
    So my next question is if it's quicker with just destill at at low reflux rate and redestill the solution for the same purity result?
    Reflux vs re-destillation? Any thoughts or experiences?
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    Bullshit Intolerant PhDemon's Avatar
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    Reflux, doesn't do separation, that is where what you boil off recondenses and enters the mixture... You need to do distillation, repeatedly for higher purities...
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