syntheticvibes
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Pulling ethanol from a mess of compounds?
Okay so I'm reviewing what looks to be a really inefficient procedure as-is. At a point in the procedure, the chemist will be left with a mixture of
ethanol, sodium acetate, —edited to remove mention of acetic acid present—, sodium hydroxide, and water. Here, the procedure suggests performing a
liquid-liquid extraction using four portions of xylene, potentially coaxing the ethanol —edited to remove mention of acetic acid present— to the
xylene to be dried with saturated brine and later separated by fractional distillation. My concern is that there would be so much ethanol still left
in the water/NaOH layer. What kind of yield might be expected from this extraction, and is there a better way to separate them?
[Edited on 7-8-2021 by syntheticvibes]
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SWIM
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NaOH and acetic acid in the same solution?
Sounds like you've got sodium acetate in there and whatever is the excess reagent from the acetic acid and NaOH.
Just distill it with an efficient fractionating column.
A Hempel full of some decent packing material (insulated or even better vacuum jacketed).
If you're working with 24/40 or 29/42 size glassware I'd want somewhere between 300 and 500 mm of packed column and a variable reflux distillation
head.
If you don't have a variable reflux head try to arrange for some of the vapor to re-condense and run back down the column (like 1/2 or a bit more).
This can be arranged any number of ways: a Claisen with a cold finger in one of the branches, or a short liebig condenser with water that isn't too
cold, or even wrapping a few turns of rubber hose around the top of the column and running cool water through it.
Getting at least some of the distillate to re-condense and run back down the column really helps with separation efficiency.
I dunno if a few hundred mm if Vigreaux columns would do the trick or not. Depends on how good a separation you're after.
Hempels are a LOT better though.
A 6 valve Snyder would probably do a good job as well.
Edit: this is for the ethanol. I wouldn't hold out much hope for the acetic acid unless you fix it with alkalai and evaporate the water and then free
it with some acid (non-volatile)
Separating acetic acid and water is usually not worth the trouble unless you can use the above route.
Unless the mixture you're talking about has a VERY high acetic acid content.
I have seen patents where acetic acid/water mixtures where it's 80% or more acetic acid are vaporized and condensed into hydrocarbon solvents to
separate the water quickly. However I have never tried this personally.
[Edited on 8-7-2021 by SWIM]
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syntheticvibes
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Ah I totally missed the fact that the acetic acid would have been neutralized. I was too worried overthinking other things. The sodium hydroxide is
added in excess so I really don’t see acetic acid being around later to be an issue. My home labware is all I have access to so I’ve just got the
Vigreux column. I’ll try wrapping the hosing around the top of it to see if that works, and I’ll also attach a Claisen for som extra height.
Thanks for your insight. I am fine with having some wet ethanol, as I have 3Å sieves to dry with.
For clarity, it’s probably best to just try to do the distillation step instead of transferring any of the ethanol to xylene?
"I placed the sand as the boundary for the sea,
a perpetual barrier that it cannot pass;
though the waves toss, they cannot prevail;
though they roar, they cannot pass over it."
- Jeremiah 5:22b
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syntheticvibes
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Would a similar procedure of separation of ethanol from denatured alcohol tainted with methanol and water? I’ve got some laying around that I’m
not gonna use for an alcohol burner anymore
"I placed the sand as the boundary for the sea,
a perpetual barrier that it cannot pass;
though the waves toss, they cannot prevail;
though they roar, they cannot pass over it."
- Jeremiah 5:22b
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unionised
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If you live somewhere really cold, you might be able to freeze some water out of it.
Otherwise I'd just distill it.
Roughly how much alcohol is present?
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SWIM
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Vigreaux columns are pretty popular, and I may have an undeservedly bad opinion of them since I'm do a lot of stuff that involves high powered
distillations.
They'll probably do okay.
Getting methanol and ethanol separated is tough though. That really does call for some high separation power.
Usually a little methanol won't be a problem if you're just using the alcohol as a solvent, but if you need pure ethanol you're a lot better off
buying it in most cases.
I've got a couple of VERY powerful stills (40 theoretical plates), but I wouldn't dare try to use them to un-denature denatured ethanol.
At least not for drinking purposes. It just isn't worth the risk.
When I need ethanol that's not denatured I usually just distill cheap vodka. the result probably has traces of some organic contaminants, but works
okay for things like making ether and diethyl sulfate etc.
And you could drink it too if you were so inclined.
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syntheticvibes
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That’s a good point about the vodka. Since I’m not yet of drinking age (I’m very close and visually pass as being old enough), I didn’t even
think of that. I’ll see if I can get an adult in my life to grab some (strictly for research, of course).
I think the ethanol content is 45-55%. The procedure I’m looking at is actually an experimental procedure that I wrote in the middle of the night
(hence it’s almost like reading someone else’s work lol) and I’m relying on turning the ethanol and methanol first to their acetate states, and
distilling and collecting only the portions relating to the ethoxy-containing compounds and azeotropes, namely ethanol-water AZ, ethyl acetate-water
AZ, ethyl acetate, and ethanol (boiling pints between 70.4° and 78.4°), while first collecting the methoxy-contaminated groups (boil off <60°)
and leaving any non-azeotropic water and contaminants behind.
"I placed the sand as the boundary for the sea,
a perpetual barrier that it cannot pass;
though the waves toss, they cannot prevail;
though they roar, they cannot pass over it."
- Jeremiah 5:22b
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macckone
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That sounds like decomposition of ethyl acetate.
Sodium acetate is very soluble in ethanol.
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syntheticvibes
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Yes, which then after the compounds decompose to ethanol and ethanol-soluble salts, I would perform a distillation to recover ethanol.
"I placed the sand as the boundary for the sea,
a perpetual barrier that it cannot pass;
though the waves toss, they cannot prevail;
though they roar, they cannot pass over it."
- Jeremiah 5:22b
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