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Author: Subject: Troubling Distilling Ethanol/Acetone Mixture
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[*] posted on 11-7-2015 at 08:55
Troubling Distilling Ethanol/Acetone Mixture


There was a thread on this topic from like 2011, but I figured I would start up a new thread anyway.

So I am purifying 70% ethanol from the drugstore. I first did a simple distillation to collect a distillate of about 90% ethanol (determined by measuring density), with the balance being acetone and water. I then dried the mixture with MgSO4 to remove the water, and setup for fractional distillation to remove the acetone.

Since acetone is a denaturant, it was probably only 5% of the solution.

My fractionating column is just a plain-old tube, so I added steel wool to allow sites for fractionation to occur. On my first distillation, I used way too much wool and it basically became a reflux condenser (no distillate came over).
On my second try, I used a lot less wool and did get a distillate, but it came over at 46 Celsius!!
Of course, ethanol boils at 78.4 and acetone boils at 56. An ethanol-water azeotrope (which shouldn't form anyway since it was dried prior to distilling) boils at 78.2, and no azeotrope exists between acetone and water OR between acetone and ethanol (correct me if I'm wrong).

The thermometer was in the right position. About 2-3 degrees can be explained by a drop of liquid condensing on the thermometer, and another 3-4 degrees can be explained by the innacuracy of the thermometer (an EtOH-water azeotrope on my first distillation came over at 82 deg. instead of the expected 78 deg.).
But still, 10 degrees off of the boiling point of acetone (which should be what came over) does seem a little outrageous.

I stopped the distillation short (today I will run it and see if the vapor temp ever rises above 46 celsius).
I have yet to test the 46 degree distillate with dichromate to see if it contains any ethanol.

Has anyone ever had a similar thermometer problem like this? Can the 10 degree error be accredited to the sources I mentioned above, or is there something really wrong with my procedure?

Thanks for any input!




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Boffis
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[*] posted on 11-7-2015 at 09:26


If you don't want to recover the acetone simply add some solid NaOH and reflux until the acetone has polymerised into brown gunk and then fractionate. I would do this before any other treatment.
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[*] posted on 11-7-2015 at 09:34


Quote: Originally posted by Boffis  
If you don't want to recover the acetone simply add some solid NaOH and reflux until the acetone has polymerised into brown gunk and then fractionate. I would do this before any other treatment.


If I fractionate after that, will the ethanol distill over first?




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[*] posted on 11-7-2015 at 10:03


Ethanol can also do some funky stuff with bases, have you ever seen a base bath that is allowed to sit out? Plus you're going to form water as your base plucks protons from your solvents. I think it could work in theory but personally I would not recommend it.

If you had your thermometer positioned correctly as you say and you had a nice steady distillation, the reading on your thermometer should be spot on your head temperature, especially with some sort of packing in place. I would start wondering if there was something unexpected in there.




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[*] posted on 11-7-2015 at 10:19


Quote: Originally posted by BromicAcid  

I would start wondering if there was something unexpected in there.


The only other ingredients were water, denatonium benzoate, and MIBK, but those should have been removed in the first simple distillation. I can't see how the MgSO4 would have any impurites ( I bought it as "99% pure", albeit in the form of Epsom Salts).

So I really don't know. I guess I will try the distillation again today and see what happens.




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[*] posted on 11-7-2015 at 10:38


Quote: Originally posted by BromicAcid  
I would start wondering if there was something unexpected in there.


I am using vaseline as my joint grease--perhaps this may have something to do with it?




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[*] posted on 11-7-2015 at 16:02


@Bromic You can buy industrial quantities (in the UK) of methanolic KOH or NaOH for bio diesel production and it is quite stable.

For refining the ketones out of "bioethanol" and similar fuels Na or KOH work fine and you don't need tonnes of the stuff just 5g or so per litre is quite adequate.

Where a ketone is used as the denaturant it is usually butanone because it has a similar boiling point and is cheap. Methylisobutyl ketone has a much higher boiling point and if this is the denaturant then it is easy to remove with a half decent fractionating column. Also MIBK is much less prone to self condensation in my experience so the caustic treatment might not be much good anyway.
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