Distilling IPA from 70% rubbing alcohol

[Mr_Reflux]

If you distill rubbing alcohol (70% IPA +30% water) does it separate fully or form an azeotrope like that of ethanol? Swim tested a 500ml batch and it seemed to separate perfectly -  350ml IPA and 150ml water. Vapour temp was 82 Celcius
Thanks

[raffike]

Azeotrope with water contains ~88% of IPA rest is water of course an boils at 80C.

[Barium]

Add regular sodium chloride to the 70% solution and you'll se two layers form. The top layer is pretty pure IPA.

[ChillyBee]

Hello,

there are many grocery stores that carry both a 70% IPA and a 99% IPA (in the US anyways).  Instead of distilling the water out of 70% IPA, it might be easier to just dry the 99% IPA (assuming this is available to you).  Just a thought...

[El_Zorro]

The only IPA that I've ever been able to find comes in either 70% or 91% concentrations.  Oh well, nothings really as easy as getting a shitload of 70% and dumping in the NaCl, then drying the IPA with MgSO₄

[raffike]

Even Merck Index mentions salting out possibility with IPA:
May be recovered from aq solutions by salting out with sodium chloride,sodium sulfate,sodium hydroxide etc.

[Barium]

You don't distill out the water from IPA, you distill IPA from water. But a azeotrope is formed so the IPA will still contain water after distillation. The salting out process binds the water to the salt. Just like when drying with regular drying agents. In this case NaCl is the drying agent.

[catfish]

El_Zorro-
it's been SWIM's experience that MgSO4 is inappropriate for drying alcohols, as it's solubility in them becomes a problem: the more hydrated the salt becomes, the more soluble it is in the alcohol, according to SWIM's CRC handbook.
However, the phases separated nicely and rather visually when salting out with NaCl. Just don't try to filter to remove the salt; the IPA will float and make it impossible. Decant and take your losses then use a sep funnel.
-catfish

[halfkast]

Thats awesome Barium. So you take away the IPAs H2O molecules, so it isn't miscible anymore, you 'salt it out'. =)
y do i feel like daffy duck? lol DAT (Don't Answer that)

raffike, if the MgSO4 dissolves in the OH itself, then the OH won't be as effective anymore purely because its part used up, is that right?

[pericles]

Aprox. 200 ml 70% isopropyl alcohol was added to aprox 200 ml water in a canning jar. (Water added so that the layers would be larger, and more easily distinguisable)

Kosher salt (containing NaCl and small amounts of yellow prussiate of soda (to prevent caking)) was added to the jar until the solution was saturated, and the jar was then covered and shaken.

"Strands" of (presumably) isopropyl alcohol were observed to rise to the top of the solution, but no layers were visible after sitting 20 minutes.

Does the alcohol require more time to precipitate out? Are the resulting layers not easily distinguished visually?

[pericles]

I've figured out where I went wrong, in case anyone else has the same experience.

Although I thought that the salt was fully saturated in the water, vigorous shaking of the bottle showed otherwise. In fact, I ended up adding about three times as much salt as was initially in the bottle.

Now that the salt is actually saturated, two distinct layers have formed, the top being clear and the bottom murky, with a small layer of excess salt on the bottom.

[LaBTop]

You were just in time!
I was getting really geared up to give you a thorough bashing, but now that I saw you found out yourself, let's keep it to this :

Ofcourse you don't have to add another 200 ml water to the already 30% water part of the 70% IPA !
Just saturate the 30% waterpart from storebought IPA.
And warm up the IPA to f.ex. 40-50 C, then saturate with pure NaCl, so you are sure that when cooled down, the waterpart is for sure saturated 100%. You will see then salt precipitating out again, indicating a 100% saturation.

Please don't try to break through the soundbarrier next time again with a bycicle, hehhe. LT/  

[pericles]

Ofcourse you don't have to add another 200 ml water to the already 30% water part of the 70% IPA !

Well, thanks for being gentle, but I think you misunderstood me. I knew I wouldn't have to add water, I just did so because:
1) I wanted each layer to be reasonably large for ease of identification, this being my first time.
2) There's a ridge on the jar that looked like it was about 30% of the way up that I figured might interfere with accurately determining where the top layer started.

I knew it wouldn't affect anything other than the size of the bottom layer, I just mentioned it in the interest of completeness.

Having said that, since I've managed to drag you into the discussion anyway:
After evaporating the resulting (after epsom salt dehydration as well) 99% IPA on a watchglass I'm left with a white residue, which (to quote The Simpsons) "tastes like burning". Presumably this is either the table salt or the epsom salts. I guess I should distill the IPA into another flask before using?

[hCiLdOdUeDn]

IPA obtained from seperating off a saturated salt solution from 70% IPA, contains small amounts of salt. This ~95% IPA contains a small amount of salt, so distill it. If you want anhydrous IPA add a small amount of anhydrous magnesium sulfate, seperate the IPA from the MgSO4, then distill to obtain ~99% IPA.

[catfish]

Hi all-
just a friendly Hive reminder that MgSO4.x is SOLUBLE in alcohol, so stop using it.
NaCl works much better and can be dehydrated just as easily.
If you use salt and own a sep funnel, decant and voila.
I feel like saying UTFSE, but it's been said already in this thread, fer FUX SAKE!
-catfish

[hCiLdOdUeDn]

NaCl does not dehydrate IPA like anhydrous MgSO4 does. Just dry your IPA over anhydrous epsom salt and distill.

-OR-

Go to the store and buy a gallon of 99% IPA for less than 10 dollars.

[halfkast]

Nope its:

1. Bariums NaCl salt out.
2. LaBTops Barium salt out enhancer technique of warming up for full saturation.
3. MgSO4.nothin-2H2O to finish off. In good excess.

I'm not gonna distill it and I'm going to abuse it badly by using MgSO4.