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Deo
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Glacial Acetic Acid via Distillation
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?
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Dr.Bob
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It might work OK at 70%, but just google "distillation of acetic acid" and there are several articles telling how to do it.
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davidfetter
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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
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Fery
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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).
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Deo
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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.
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bnull
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See https://www.sciencemadness.org/talk/viewthread.php?tid=12898. 3 pages long, lots of ideas and literature.
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macckone
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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.
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Deo
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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.
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jackchem2001
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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
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Deo
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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]
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Sir_Gawain
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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.
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bnull
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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.
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macckone
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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.
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Deo
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| 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]
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MrDoctor
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whats wrong with just drying azeotropically using toluene? or using anhydrous sodium sulfate, or magnesium sulfate, or freshly regenerated cobalt
indicator-free silica gel?
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Deo
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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.
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MrDoctor
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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.
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Deo
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| 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]
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MrDoctor
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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.
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Deo
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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.
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Fery
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you can use ethyl acetate as entrainer for water+acetic acid mixture
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macckone
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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.
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Deo
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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?
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MrDoctor
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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?
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jackchem2001
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| 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]
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