The most popular amateur route to acetic acid is distillation from a mixture of concentrated sulfuric acid and an anhydrous acetate salt. I set myself
to thinking about an easier - and perhaps more efficient way to concentrated acetic acid.
Distillation of a dilute acetic acid solution (such as vinegar), even through a long fractionating column, is impractical. At first, after several
distillations, some concentration may occur, but efficiency of separation will decrease as the concentration of acetic acid in the stillpot increases,
despite the fact that acetic acid and water do not form an azeotrope. (Found on Wikipedia...why does this occur)?
Wikipedia also mentions that an entrainer can be used to break the azeotrope. The ideal entrainer is one that forms a relatively low boiling and
water-rich azeotrope [with water].
Based on Wikipedia's azeotrope data list, here are some selections:
Ethyl Nitrate: Azeotrope BP: 74.4C / Water Content of Azeotrope: 22%
Methyl Ethyl Ketone: 73.5C / 11%
N-propanol: 87.7C / 28.3% (No need to worry about esterification in the presence of acetic acid, as there is no strong acid catalyst present).
Of the above solvents, methyl ethyl ketone may be the most practical option for the amateur chemist, as it seems to be readily available in many
countries. The MEK could be dripped into the flask containing the acetic acid solution, which would be connected to a long fractionating column and a
condenser. The waste solvent would then be recycled and dried. Left in the flask would be a more concentrated solution of acetic acid.
[Edited on 6-8-2014 by Awesomeness]Oscilllator - 5-8-2014 at 19:11
I don't get it, why wouldn't you use an azeotrope of acetic acid instead? That way instead of having to boil off 97% of the solution you only have to
boil off 3%. As an example, wikipedia lists an azeotrope of acetic acid/n-heptane that boils at 92.3°, and is 70% acetic acid. Admittedly 92.3° is a
bit too close to the boiling point of water for comfort but that was just an example, I'm sure there are others.Bert - 5-8-2014 at 19:44
I don't get it, why wouldn't you use an azeotrope of acetic acid instead? That way instead of having to boil off 97% of the solution you only have to
boil off 3%. As an example, wikipedia lists an azeotrope of acetic acid/n-heptane that boils at 92.3°, and is 70% acetic acid. Admittedly 92.3° is a
bit too close to the boiling point of water for comfort but that was just an example, I'm sure there are others.
If you isolate acetic acid as an azeotrope how do you then isolate the acetic acid? Please don't say by distillation.
[Edited on 7-8-2014 by Magpie]
[Edited on 7-8-2014 by Magpie]Oscilllator - 6-8-2014 at 17:04
I gotta admit you have a point there magpie, I can't really think of any method that doesn't involve reacting the acetic acid. Perhaps extracting with
a polar solvent?
Come to think of it though, it often wouldn't matter that much if your acetic acid was full of alkane, since alkanes are almost completely unreactive
and as such probably wouldn't interfere with your reaction. chemrox - 8-8-2014 at 09:17
I have a 5 gal can of "acetic acid" Not "anhydrous acetic acid" so to make a gallon of glacial acetic I should ??subsecret - 8-8-2014 at 21:16
You could distill it with concentrated sulfuric acid, to remove the water. Just find a flask that holds 5 gallons Magpie - 9-8-2014 at 08:07
Ethyl nitrate is not cool. Since we all know, that most amateur chemists heat everything with open flame/Bunsen, and since EtONO2 is highly flammable,
it could easily cause a nice fire. Another thing is, that alkyl nitrates easily hydrolize in acidic media, like acetic acid in water, so it will give
nitric acid dissolved in acetic acid/water and ethanol in less than a minute.
The ethyl-acetate will also hydrolize in acetic acid to give ethanol and acetic acid, so this is also not the best method, for azeotropic water
removal.
The propanol and the MEK could work.kt5000 - 19-8-2014 at 20:56
Since we all know, that most amateur chemists heat everything with open flame/Bunsen, and since EtONO2 is highly flammable, it could easily cause a
nice fire.
I heat everything using a 1kW electric hotplate.. I figured that was the norm, as it seems way safer.Praxichys - 20-8-2014 at 05:06
It's extremely flammable, it'll give you a pounding headache at the slightest whiff, and it can be made to detonate. Probably not ideal for this
application. subsecret - 20-8-2014 at 11:34
My mistake. I'd not looked into the other properties of these compounds. Jimmymajesty - 17-5-2015 at 12:25
Ethyl acetate can be used but it is really difficult to remove all the water with it from a 20% household stuff, it is soluble in water so apart from
possible hydrolysis you drain you entrainer when you drain the water from your trap.
You have to distill all the acetic acid down to dryness to get rid of the orgnaic sludge present in the household stuff.
Then you use toluene as an entrainer, it will remove all the water quite easily with 3 litre 20% AcOOH it took me 24hr, ofc this depends on the setup.
At the end of the azeotropic H2O removal you remove a lot of acetic acid and toluene with very little water since it is not a clean cut separation as
you can imagine and at the end your remaining acetic acid will contain a lot of toluene no matter what you do.
I think this whole azeotropic H2O removal thing is very difficult even for someone with andvanced glassware and it takes several days even to isolate
some 100ml acid.
I also hate the NaOH H2SO4 method, it is wasteful and tedious. Just set up a ketene generator and leave it going for the night. Or go with ethyl
acetate if you have access to it, I also make it with ketene but maybe you live in a better country.macckone - 17-5-2015 at 19:15
It is possible to distill the water out of acetic acid. But it is not cost effective. I use it for cleaning some distillation apparatus. With a 10
to one reflux and a four foot column packed with rings you get almost no vinegar in the output at least at low concentrations. At higher
concentrations. I haven't tried it at high concentrations.byko3y - 17-5-2015 at 19:19
I was sure I've posted the link to a full description of the procedure, but for some reason I cannot see it and neither my post was deleted :/
So here it is http://www.qvf.com/qvf-process-systems/recovery-units/acetic...
Jimmymajesty, "set up a ketene generator" sounds like "go kill yourself" to me.
