Sciencemadness Discussion Board - Glacial Acetic Acid via Distillation

Glacial Acetic Acid via Distillation

Deo - 9-10-2025 at 20:56

Generally one does not concentrate acetic acid by distillation from dilute solutions like vinegar, because apparently its quite hard to seperate. However, I'm wondering if this is still the case more concentrated solution. I have some that is about 70%, and I feel like at this concentration, distillation may become a viable method. Has anyone tried distilling more concentrated acetic acid and had any success?

Dr.Bob - 10-10-2025 at 05:41

It might work OK at 70%, but just google "distillation of acetic acid" and there are several articles telling how to do it.

davidfetter - 10-10-2025 at 06:08

It can be and has been done. It's more hassle than you might first expect, but it's well in reach of a pretty basic setup. https://www.sciencemadness.org/smwiki/index.php/Acetic_acid

Fery - 10-10-2025 at 06:20

Personally I wouldn't distill that mixture but if I had to do (world total collapse, severe lockdown, restart from ash after world war) then I would use powerful distillation column (1 meter long Hempel column packed with Raschig rings) and variable ratio distillation head. The difference of boiling points is only 18 C. When such apparatus not available but you achieve something like 95-98% by repeated simple distillations (long lasting, poor yields due to residues in distillation flask) you may try to freeze it to increase its concentration further (note - freezing out method won't work with 70% acetic acid).

Deo - 10-10-2025 at 07:45

18 C difference seems pretty significant no? That's about the difference between 2-propanol and water is it not? I'd assume a Vigreux is probably good enough. Non azeotropic mixture too at that. I've had pretty good success concentrating 2-propanol via distillation when I first got started as a practice. Is there something I'm forgetting to consider that would make a difference here? Obviously aiming for high 90s is unreasonable and I don't plan on getting there by distillation alone, likely get to around 90% then concentrate to 98-99 by other methods.

bnull - 10-10-2025 at 12:08

See https://www.sciencemadness.org/talk/viewthread.php?tid=12898. 3 pages long, lots of ideas and literature.

macckone - 10-10-2025 at 17:55

Acetic acid is volatile with steam. You literally need hundreds of theoretical plates to get good separation. You can go from 70 to 100% but it isn't easy. Dry ethanol can remove water from acetic acid then then treat with potassium permanganate to oxidize remaining ethanol before a second to last distillation. Finally treat with acetic anhydride and a final distillation to get 'bone dry' glacial acetic acid.

Deo - 10-10-2025 at 21:18

Quote: Originally posted by macckone

Acetic acid is volatile with steam. You literally need hundreds of theoretical plates to get good separation. You can go from 70 to 100% but it isn't easy. Dry ethanol can remove water from acetic acid then then treat with potassium permanganate to oxidize remaining ethanol before a second to last distillation. Finally treat with acetic anhydride and a final distillation to get 'bone dry' glacial acetic acid.

What do you mean when you say that "acetic acid is volatile with steam"? Is that not the case for almost every water based mixture to some extent? Almost all these mixtures produce a mixture of vapors. Could you explain what exactly makes acetic acid so much more difficult to separate via distillation as compared a similar mixture, say, isopropanol? Is it H - bonding?

Like I said, I don't plan on going straight to perfect separation via fractional distillation, just to increase the concentration high enough to justify other drying methods like dehydrating agents.

jackchem2001 - 11-10-2025 at 05:24

I assume 'volatile with steam' is shorthand for that about each ideal stage of separation, there is little enrichment of the vapour phase in the most volatile component (water), so you need many stages and high reflux ratio for good separation. Difference in b.p. can sometimes be a rough indicator for ease of separation but a proper model of VLE is really needed

Deo - 11-10-2025 at 10:38

Hmm, I see what you mean. The mol frac of acetic acid in vapor is quite close to the mol frac of acetic acid in the mixture at any given point. The difference for say iPrOH is a lot more dramatic than that of acetic acid. In that case, I don't suppose fractional distillation would be a particularly viable method. Guess I'll have to do something else.

[Edited on 11-10-2025 by Deo]

Sir_Gawain - 11-10-2025 at 12:21

I’ve found that drying acetic acid in general is quite difficult, even at high concentrations. Repeated distillation over sulfuric acid did nothing, the only way I actually got it anhydrous was distilling over acetic anhydride.

bnull - 11-10-2025 at 13:54

I've been thinking. Would anhydrous sodium acetate work to dry acetic acid? I don't know the solubility of sodium acetate in acetic acid but I suppose that it decreases as the temperature is lowered. It could be like this: anhydrous sodium acetate is added to concentrated acetic acid, left alone in a capped bottle for a few hours, then put in the fridge to chill and precipitate hydrated sodium acetate.

macckone - 11-10-2025 at 14:56

Freeze separation is more viable than distillation. It is also a pain. How many gallons are you trying to treat? With the upcoming winter months, freeze separation will be provided by free cold courtesy of mother nature. Provided you live far enough north.

Deo - 11-10-2025 at 15:26

Quote: Originally posted by macckone

Freeze separation is more viable than distillation. It is also a pain. How many gallons are you trying to treat? With the upcoming winter months, freeze separation will be provided by free cold courtesy of mother nature. Provided you live far enough north.

Heh heh, I live in California ....

I'm not in need for large volumes of GAA, just maybe like 200 mL for organic synthesis. Its a shame to hear that I the 2.5L of 70% I bought as vinegar essence won't be very useful at all for making GAA. What should I do with it now then?

Edit: Could you tell me around what temp I should set my freeze at for optimal separation using fractional freezing? It's not a technique I'm very familiar with so I don't really know how to approach it.

[Edited on 12-10-2025 by Deo]

MrDoctor - 12-10-2025 at 00:42

whats wrong with just drying azeotropically using toluene? or using anhydrous sodium sulfate, or magnesium sulfate, or freshly regenerated cobalt indicator-free silica gel?

Deo - 12-10-2025 at 06:12

1. I don’t got no toluene cuz I live in cali. If I do get it I ain’t gonna use it to dry some acid.
2. Way too inefficient to use drying agents for something that still has 30% water content. May also still be soluble in soln so there’s that can of worms.
3. Silica gel is not selective enough. Molecular sieves are not to be used with acid either.

MrDoctor - 12-10-2025 at 14:29

you got gasoline and paint thinners dont you? hexane, heptane and toluene all will work, basically you can broadly use the 70-110C fraction of gasoline, or the same from a can of thinners. actually, you can directly just use naptha as-is. its not very efficient but it will work and get it bone dry at the cost of producing like maybe 10% start vol of very dilute acetic acid

As for using dessicants to get it to freezing range, anhydrous (0) X + solvated (6) X combine to form insoluble X hydrate (3). you can test it easy enough in a test tube or something.

Deo - 12-10-2025 at 14:48

Quote: Originally posted by MrDoctor

you got gasoline and paint thinners dont you? hexane, heptane and toluene all will work, basically you can broadly use the 70-110C fraction of gasoline, or the same from a can of thinners. actually, you can directly just use naptha as-is. its not very efficient but it will work and get it bone dry at the cost of producing like maybe 10% start vol of very dilute acetic acid

As for using dessicants to get it to freezing range, anhydrous (0) X + solvated (6) X combine to form insoluble X hydrate (3). you can test it easy enough in a test tube or something.

So I just add some volume of distilled gasoline and then basically run a makeshift Dean-Stark? Could you tell me what the procedure is for that if you've done it before?

Its also very hard to get solvents in general here. The only things shops sell seem to be "distilled mineral spirits" which is apparently like 12-ish carbon alkanes, so probably not particularly useful. (little to no raoults law deviation due to less imfs with water, higher BP not paritcularly useful either.)

Gasoline surely has plently of these useful solvents but I have no way of telling whether or not the mixture coming over is AA-Solvent or Water-Solvent, and if I don't know what the composition is it'll be quite difficult to post-process the acetic acid for purity after azeotropic distillation.

[Edited on 12-10-2025 by Deo]

MrDoctor - 12-10-2025 at 17:54

paint thinners specifically are easy because they tend to be, napthas/pet ethers, acetone, ethanol, toluene, and occasionally a little ethylbenzene or xylene but that has a substantially different bp from toluene. Nurdrage and other youtubers did videos on how to fractionally seperate them. the main basic composition is ethanol/acetone + toluene, these seperate just by adding water. any hexane will distill out effortlessly, and take residual ethanol with it.

as for gasoline, google the aproximate composition of your local gas and find the octane rating that has the most toluene if paint thinners are illegal. if you collect a fraction that starts close-ish to toluene and ends at toluene, then as long as the contaminants dont form acetic acid azeotropes or solvate it highly, it should be fine. I made an error earlier though, i was thinking of ethanol. pet-ethers like hexane azeotrope with ethanol and can dry it at lower temps than toluene. acetic acid itself does azeotrope with heptane but its less than the toluene-water azeotrope. you can make pure-enough toluene through 2-3 fractional distillations of gasoline, or 1-2 of common paint thinner formulations. by adding ethanol, you form a really low boiling ethanol-hexane-water mixture, same with heptane i think, and while that can effectively remove water, i dont think it is immiscible enough for a dean stark. At very least i was unable to run an ethanol drying cycle with napthas.
https://en.wikipedia.org/wiki/Azeotrope_tables
check this if you have any access to other stuff on the water azeotrope list that arent on the acetic acid list, or, at least their azeotropes like toluene with both, are so different water will come over at a distinctly lower temp and the solvent would be compatible in a dean stark.

As long as overlapping fractional contaminants from gasoline dont function as, steam filler, i.e the volatility of the contaminant has a competing boiling point with the azeotrope, then youll have a good enough toluene fraction to get the job done. and again too, 3 fractional distillations is probably all it will take either way. Once to get broad range that you know will include the entire toluene fraction. the second is then a much more careful fractionation to remove the lighter fraction while pulling as little toluene as possible. at the end of it, also distilling toluene over increasingly slowly so it doesnt pull the heavier fraction with it. then the final one is just omitting the front and end of it and using those for the next batch since its easy to get pure toluene as long as you are ok with just discarding/recycling the first and last 20% or so.

Again theres a bunch of videos on this. gasoline is messy and tricky, but cheap, and produces a bunch of useful solvents too. but the toluene is on average maybe 25% of your gasoline.
paint thinners however, in my experience are 40-60%

Lastly, i havent tried distilling gasoline, i have distilled napthas though. you will want a nice column and pack it full of raschig rings for the maximum seperation.
Ive distilled paint thinners though since its cheaper than buying the pure forms individually. its really simple if you only collect the fractions while the temperature is steady, toluene is perhaps the easiest to isolate of all its components. it works out pretty consistently like you see in videos on the process. you just get the list of ingredients, double check for azeotropes, then make a list of the components, and also, azeotropes which you treat like they are unique chemicals, and then, you just have a list of steady-state temps to expect throughout the distillation. at first water might cause issues but what happens is usually the hexane-water-ethanol azeotrope which boils super low, co-distills with the acetone and/or hexane, and once the water is gone, everything goes nice and smoothely.

Deo - 12-10-2025 at 19:54

Thanks for all that information. I envy the your availability of paint thinners. Acetone and heavier alkanes are the only things I can reasonably get here in California. Naptha, toluene, xylene, etc aren't sold due to environmental protection laws, so it seems gasoline will be my only real option. I'm getting a Dean-Stark from China soon so that might be useful.

Basically I just hope and pray that the distilled gasoline im using doesnt form some stupid miscible mixture with acetic acid and is particularly volatile.

Fery - 12-10-2025 at 20:31

you can use ethyl acetate as entrainer for water+acetic acid mixture

macckone - 13-10-2025 at 17:46

If it is only 2.5L, convert it to the sodium salt and then reconstitute it with pyrophosphoric acid or sulfuric acid. When you said large quantity, I was thinking a couple of drums. It's probably not worth the cost, because a gallon off of Amazon is only $50.

Deo - 13-10-2025 at 22:55

Although fractional distillation won't be very useful for good separation, could it at least be decent for pushing from 70% -> 80% without significant time or loss using a Vigreux?

MrDoctor - 14-10-2025 at 16:26

Quote: Originally posted by Fery

you can use ethyl acetate as entrainer for water+acetic acid mixture

How well does that work, like, does it seperate well enough for use in a dean stark trap? and also, how strong is the azeotrope? how dry can you get it this way? benzene and toluene are known to function as well as most primary dessicants, ethyl acetate is such a clean, non toxic chemical, which has a lower boiling azeotrope than toluene, i wonder why i dont see it used more often?

jackchem2001 - 14-10-2025 at 18:56

Quote: Originally posted by Deo

Although fractional distillation won't be very useful for good separation, could it at least be decent for pushing from 70% -> 80% without significant time or loss using a Vigreux?

Nobody can really say without doing the experiment. You could pack it with glass beads (better have an unclamped stopper on the boiling flask for pressure release) and blow some air across the outside to try improve separation

[Edited on 15-10-2025 by jackchem2001]

Fery - 14-10-2025 at 20:53

Quote: Originally posted by MrDoctor

Quote: Originally posted by Fery

you can use ethyl acetate as entrainer for water+acetic acid mixture

https://demonstrations.wolfram.com/SeparationOfAceticAcidFro...

Deo - 14-10-2025 at 21:57

Very interesting...
I cannot buy ethyl acetate for cheap - although neither can I buy toluene but at least I can get a decent amount through some elbow grease and distillation of gasoline - Ethyl acetate would require me to do an esterification with... glacial acetic acid ... so that is quite circular.

Although it seems to me that methyl acetate would work too would it not? I can get that from acetone free nail polish removers from CVS and whatnot so perhaps I will try with that instead...

MrDoctor - 14-10-2025 at 23:25

Quote: Originally posted by Fery

Quote: Originally posted by MrDoctor

Quote: Originally posted by Fery

you can use ethyl acetate as entrainer for water+acetic acid mixture

https://demonstrations.wolfram.com/SeparationOfAceticAcidFro...

awsome, im looking at this data and finding it problematic that the output is a constant volume though, so i still cant figure out if a dean stark trap would be effective or not. the ethyl acetate had been pretty much eliminated around 95%. Its also strange that the amount of ethyl acetate present drops below the water content, yet water continues to leave at around the same rate rather than the distillate staying the same as solution. I can kind of guess whats happening, if this is a parametric fit equation to actual data, but in practice one would not keep the rate of boiling so hard 1/6th of the acetic acid ends up being removed (unless you had to because water and ethyl acetate needs to flush out of the column), and also, i think, though im not super sure, that if ethyl acetate levels remained high, being replenished thanks to the overflow of the dean stark trap, the profile of the distillation would be very different, rather than what occured here which probably used the absolute minimum amount of ethyl acetate capable of removing the volume of water present even though at the end a large amount of acetic acid has to distill over to flush the last 10% of the azeotropic mixture out because theres no more ethyl acetate.

So i cant really imagine what the rate of water removal is like once there is virtually none. i would be hopeful that it more or less just leaves at a fairly constant rate, so that you would have the entrainer refluxing fully at its boiling point with no acetic acid distilling over, and instead the reaction is considered complete once acetic acid starts distilling over, and the last traces of the entrainer are leaving the system.

Also Deo, methyl acetate would probably work, i dont really see any reason why it wouldnt, although i have a feeling it will be somewhat reliant on a packed reflux column that holds quite a bit of liquid soaked into it, at any given time.

lastly, you probably can get ethyl acetate for cheap. anywhere that gives a damn about environmental impacts of chemicals enough to haphazardly ban things that barely have an impact anyway, will have a major hard-on for ethyl acetate since its such a universally good substitute for so many solvents, including acetone which is fundamentally a petrochemical in origin.
look around some online stores that sell beauty products, they sell all sorts of whack stuff. nail brush cleaner or "saver" is usually acetone, ethyl acetate or some nitroalkane, usually nitromethane. regular nail polish remover formulas tend to just be acetone or ethyl acetate, "acetone free" is usually ethyl acetate, and infrequently i think MEK, but then "ketone free" is pretty much guaranteed to be ethyl acetate.
i bet at your local major hardware store there will be a dozen scattered products also labeled as brush cleaner, or some purpose-specific cleaning solvent for roof painting, fiberglassing, grouting, etc, which is always pure acetone, IPA or EtAC.

but acetone-free nail polish remover or really just any product whatsoever that has "acetone-free" in its name, is probably EtAc.
And end of the day its not restricted so just buy some off amazon

[Edited on 15-10-2025 by MrDoctor]

Deo - 14-10-2025 at 23:29

Quote: Originally posted by MrDoctor

Quote: Originally posted by Fery

Quote: Originally posted by MrDoctor

Quote: Originally posted by Fery

you can use ethyl acetate as entrainer for water+acetic acid mixture

https://demonstrations.wolfram.com/SeparationOfAceticAcidFro...

Apparently according to wikipedia ethyl acetate is immiscible with water? the upper organic layer would be about 90 ish percent EA and the lower water layer is only about 8.7 % EA. So in a sense its just like toluene, but better at its job. Also I've come to realize that as a result, methyl acetate wouldn't work because it IS miscible with water.

MrDoctor - 14-10-2025 at 23:49

with a dean stark? yeah it might not work. maybe. the solubility in water is 25% at rt and unspecified-higher when higher. So you would need to determine how much methyl acetate it takes to remove X amount of water.
in the dean stark trap it might not have enough density difference due to solubility to seperate and recycle, but once outside the system, mixing it with a brine of sodium chloride or something will cause seperation, but frankly you should just make sure you have enough to get the job done in one go.

Deo - 15-10-2025 at 00:05

At the azeotrope temperature (56C) the % solutbility of MeOAc is about 70%. (According to LLE-calc)
At the azeotrope temperature (70C) the % solubility of EtOAC is about 59.4%.

So they are still immiscible to some extent, just that MeOAc will be much less efficient for removal via a Dean Stark, unless perhaps we cool the trap? Seems kinda stupid.

I think in the simulation, it was assuming constant addition of EtOAc as it was depleted as it was deisgned for industrial processes, not a Dean-Stark situation, so miscibility would not matter at all. However, with how cheap MeOAc is for me compared to EtOAc (I can get like 10oz crude in Walmart Nail Polish Remover for $1.98), I might as well use it in the one pot method.

One thing I'm confused about is that the acetates seem to be extremely enriched in the vapor phase (91.9-95%), how does the water get removed so quickly when we have basically less than 10% of the vapor being water? One would have to add an immense volume of acetate.

Toluene is seeming a lot more appealing again with these caveats...

[Edited on 15-10-2025 by Deo]

[Edited on 15-10-2025 by Deo]

MrDoctor - 15-10-2025 at 05:48

i might try this tomorrow with toluene after i clean up my work station, but starting from 90%
if it takes much longer than ethyl acetate is calculated to, then ill try it again with ethyl acetate as well.