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RogueRose
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Distilling vinegar - removing water before AA passes over?
I was reading some threads about concentrating vinegar and some say distillation is best, others freeze distillation (b/c AA melts at 61-62F) and then
there is turning into salt (make sodium acetate) then adding an acid.
My question is, if you choose to distill, would the water pass over first and then be left with AA coming over? If this is the case then one could
boil off the water leaving more concentrated AA - but this doesn't seem to work. If you do distill, then the water and AA would both come over from
what I've seen.
I haven't tried freeze distillation but I've put vinegar in the fridge at about 34F and I would suspect that is about as close to freezing as we'd get
and I didn't notice much more than cloudy vinegar in some and nothing in other vinegars. Not nice crystals or anything.
Sodium acetate seems most effective if you have a source of acid to rehydrate the salt. The only thing about this is that I've gotten very odd color
NaOAc from pinkish, blueish, green/tealish, orange-ish, brownish, redish (all mainly white, but with a hue of the color) - all using the same white
distilled 5% vinegar and the same container/pot for evaporation - and same baking soda for neutralization.
So, how can it be distilled with heat as boiling seems to drive off H2O and AA so both would come over.
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Fulmen
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According to Wikipedia AA has a boiling point of 118°C, no azeotrope with water. So a fractionating column should work, water will distill off first
leaving AA.
We're not banging rocks together here. We know how to put a man back together.
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Sulaiman
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and a lot of other stuff depending upon your vinegar type https://en.wikipedia.org/wiki/Vinegar
so you will want to distill over the AA too.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Diachrynic
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No idea what kind of vinegar you are using, but I used 25% for 2.5€/kg and sodium carbonate 2€/kg and got a snow white product on dehydration to
dryness and well formed crystalls on cooling. (Note: Done in glassware.)
we apologize for the inconvenience
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RogueRose
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Quote: Originally posted by Diachrynic  | | No idea what kind of vinegar you are using, but I used 25% for 2.5€/kg and sodium carbonate 2€/kg and got a snow white product on dehydration to
dryness and well formed crystalls on cooling. (Note: Done in glassware.) |
I used store brand White distilled vinegar. I tried 2 different store brands and got the same thing. I wondered if something was happening when
boiling off the liquid or drying the NaOAc. I used an HDPE bucket to mix the vinegar and NaHCO3 then a 304 SS kitchen pot to boil. Then a ceramic
cake pan to evaporate the last 5% of water.
I'm guessing that the color has something to do with impurites in the vinegar, maybe the source from which it was fermented. The vinegar was
purchased over different periods of time, so maybe over a year, so each batch could have been a different source but bottled the same.
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RogueRose
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| Quote: Originally posted by Fulmen | | According to Wikipedia AA has a boiling point of 118°C, no azeotrope with water. So a fractionating column should work, water will distill off first
leaving AA. |
So if no azeotrope, then why the need for a fractioning column? If the water boils first then there should be no need for distillation and boiling
should drive off water leaving more concentrated AA - but it seems that the AA in low % vinegar (5%) boils with the water. I know the temp doesn't
get above about 214 (which could be thermometer error and it's really 212) so that's 30F below AA BP. This is what I've always wondered about AA as it
seems to act differently when dilute, similar to how water acts with ethanol, but reversed.
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j_sum1
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Fractionating column is to efficiently separate components that have a close boiling point. 18° is close enough to need it.
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Fulmen
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RR: What you're observing is true in all cases.
Simply put a liquid boils when it's vapor pressure exceeds the atmospheric pressure. For water this occurs at 100°C at normal pressure, for AA it's
118°C. A mixture of water and AA will boil somewhere between these two depending on it's composition. When such a liquid boils, both constituents
will boil off, but not at the same rate. Since water has a higher vapor pressure than AA at any given temperature, more water will boil off. So the
vapor will be richer in AA than the liquid, but it won't be pure AA.
We're not banging rocks together here. We know how to put a man back together.
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Σldritch
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Fractionating AA will not work for some reason. Terrible separation if there is any at all even with dehydrating agent (i used Copper Sulfate). As for
freezing out, it seems to take an awfully long time to freeze and you need to get it pretty cold. < than -18 degrees celsius for 60% acid.
As for other methods: i read a paper where they were able to fractionate it with Tributylamine and then there is the good old Sodium Bisulfate way.
And some of my own speculation, urea to react with the water to form Ammonia and Carbon Dioxide, it would require a lot of urea for dilute acid so
probably would only work for >60% acid.
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happyfooddance
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AA usually means acetic anhydride. Glacial acetic acid is GA or GAA.
I make vinegar in 10 gallon batches. When it reaches 8% concentration (checked by titration against NaOH) I put half of it in a freezer (-18°C). The
other half is used to brew another batch. When it freezes (this takes 2-3 days for my batch size), the water has formed nice crystals which have
practically no vinegar. If you let the syrup drain and let the ice melt a little, it tastes like pure water.
So I put this syrup back in the freezer and repeat the process a few times, since I have much less volume at this point it goes faster than the first
freeze, and I do it until no more crystals form. It is around 70% concentration at this point. Acetic acid and water at this concentration doesn't
freeze at -18°C.
I take this brown syrup and vacuum distill. The sludge in the flask is mostly sugar and soy peptone, and probably some bacteria and cellulose.
I have at this point about 70% strength vinegar, which still has dissolved solids, and is re-distilled through a 400mm vigreux column, at atmospheric
pressure. Even with this somewhat tall column and distilling slowly, my distillate contains a couple% acetic acid for quite a while. Even the last bit
that comes over (at 118°) has some water. This product, however, is quite pure, and makes nice, clear acetate salts.
I could say more about this, but mainly I want to emphasize that even with good fractionation it is very difficult to concentrate acetic acid. To go
from 80% to 100% takes ages and a packed column, and you will only have a small amount of GAA. The rest of your vinegar will be more dilute than what
it started out as.
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battoussai114
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I recall liquid-liquid extractions with Ethyl Acetate being an industrial route to get Acetic Acid out of water. I'll see if I still have any papers
on the matter once I have the time.
Batoussai.
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happyfooddance
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Yes, it is just a simple azeotropic distillation. Ethyl acetate forms an azeotrope with water. There are threads on sciencemadness where the topic of
drying acetic acid is discussed ad nauseum. Salting out with IPA apparently works pretty well, as some SM users have discovered.
http://www.sciencemadness.org/talk/viewthread.php?tid=12898
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WangleSpong5000
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Distilling vinegar is a very long and drawn out process that has a practical ceiling regarding purity. A paper I read (I'll try and find it) suggested
the most efficient way was purification by freezing. Diluted acetic acid placed in a very cold environment (-25 C in my freezer) seperates into icy
chunks of dilute acetic acid in a cold solution of more concentrated acetic acid. The azeotropic nature of the two works both ways it seems. This
method was used in industry in very large quantities and the process would be repeated until greater and greater concentrations were obtained.
But fuck that shit my dude. Anhydrous sodium acetate combined with a slight excess of sulphuric acid, reacted then distilled yields near glacial
acetic acid.
Hyperbole be thy name
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AJKOER
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As vinegar is generally 95% water  perhaps an interesting approach to test
(especially suited for a large scale) would be to remove the water without boiling down (a lot of energy) by adding Fe powder and a touch of NaCl to
freshly heated vinegar to remove any oxygen. Seal in a vessel with no air and a pin hole to vent hydrogen.
Outline of reaction:
2 [ H2O = H+ + OH- ]
Fe --> Fe(ll) + 2 e-
2 [ H+ + e- = H2 ]
Net with water:
Fe + 2 H2O --> Fe(OH)2 (s) + H2 (g)
Also, possible Schikorr reaction:
3 Fe(OH)2 → Fe3O4 + H2 + 2 H2O
Bottom line with time (like at least a week but absent prolong boiling), iron and water is largely converted into Fe(OH)2/Fe3O4 and hydrogen. Some or
all of the 5% acetic acid is converted into soluble ferrous acetate.
[Edited on 17-2-2018 by AJKOER]
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Bert
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When the Klean Strip MEK replacer came out (technical ethyl acetate, less than $30.00/gallon!) it killed several birds with one stone- near anhydrous
ethanol, Sodium acetate, glacial acetic acid and maybe someday, acetic anhydride. Plus it's an OK solvent for some uses.
Then Klean Strip decided MEK didn't need to be replaced and quit selling it to Home Depot, Menards, etc. etc.
I got the last cans off the shelf at several stores.
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aga
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Interesting idea.
I like the Time element. Mostly a reaction MUST complete within about a day, or it is considered a non-reaction.
What is oxidising the Iron in this part ?
Dissolved/disassociated Oxygen ?
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DraconicAcid
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| Quote: Originally posted by AJKOER | | As vinegar is generally 95% water perhaps an interesting approach to test
(especially suited for a large scale) would be to remove the water without boiling down (a lot of energy) by adding Fe powder and a touch of NaCl to
freshly heated vinegar to remove any oxygen. Seal in a vessel with no air and a pin hole to vent hydrogen.....Some or all of the 5% acetic acid is
converted into soluble ferrous acetate. |
Why exclude oxygen? The reaction of iron with oxygen and acetic acid to give water and iron(II) acetate is far more thermodynamically favourable.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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AJKOER
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Draconic Acid: Why exclude oxygen, because the oxygen-free reaction path results in water being broken down (at least in part, into hydrogen gas
consuming some of the problematic excess of water).
-----------------------------------------
Aga: Expanded reaction and references:
H2O = H+ + OH- ]
Fe --> Fe(ll) + 2 e-
H+ + e- = •H
•H + •H --> H2
Net: Fe + 2 H2O --> Fe(OH)2 (s) + H2 (g)
Some references:
https://en.wikipedia.org/wiki/Fe(OH)2
https://chemistry.stackexchange.com/questions/5134/why-cant-...
[Edited on 18-2-2018 by AJKOER]
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DraconicAcid
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But if that were to happen, the iron(II) hydroxide would react with the acetic acid to regenerate water and give iron(II) acetate.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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AJKOER
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| Quote: Originally posted by DraconicAcid | | But if that were to happen, the iron(II) hydroxide would react with the acetic acid to regenerate water and give iron(II) acetate.
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Yes, the 5% part (acetic acid, if otherwise not consumed, see below), not the 95% (water).
I would argue that this reaction:
H+ + e- = •H
could remove H+ sourced from the acetic acid as well.
[Edited on 18-2-2018 by AJKOER]
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LearnedAmateur
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You’d be better off going with potassium acetate for the salt displacement, sodium salts are almost always more hygroscopic and anhydrous NaOAc
readily converts to the trihydrate in air.
How about mixing stoichiometric quantities of potassium acetate with potassium bisulphate and distilling off the GAA, with a few drops of conc. H2SO4
for it to run smoothly? KOAc + KHSO4 -> AcOH + K2SO4. Shouldn’t be too difficult to keep things dry if everything is dry to begin with, and if a
little water isn’t a problem then the sodium salts will get the job done, especially if dehydrated just prior to reacting.
[Edited on 18-2-2018 by LearnedAmateur]
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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Diachrynic
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| Quote: Originally posted by LearnedAmateur | | You’d be better off going with potassium acetate for the salt displacement, sodium salts are almost always more hygroscopic and anhydrous NaOAc
readily converts to the trihydrate in air. |
I can confirm that. The sodium acetate (anhydrous) turns always into a puddle if left in the open. (I like that salt, only the smell is annoying.)
we apologize for the inconvenience
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aga
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Strange.
Personally i find the smell of sodium acetate quite pleasant.
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LearnedAmateur
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I figured it would be similar to the sodium formate I’ve made in the past, have to keep it in a plastic bag wrapped in cling film and even then it
still manages to sequester some water, forming damp clumps.. Sodium carboxylates always seem to be a PITA when it comes to keeping dry, don’t really
have any experience with their potassium counterparts though but I would imagine they’d still be difficult to keep dry. Transition metal acetates,
although not as readily available commercially, might be a better option still than alkali/alkaline earth acetates when it comes to a water-free
reaction.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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NeonPulse
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Funny that this thread is recent. I’m going to be making sodium acetate today. I have found that if you start from vinegar it is best to use
cleaning vinegar. It is generally twice the strength of what is available in grocery stores here. Firstly though I froze the bottle to pour off the
much more concentrated acetic acid. This will then be reacted with the appropriate amount of NaOH after determination of the acid strength by
titration. My only concern is the decomposition temp of the C2H3NaO2 since the trihydrate is meant to decompose at a temp of 122c so wouldn’t it
decompose in the solution which is in contact with a very hot hot plate surface?
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