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Author: Subject: Distilling vinegar - removing water before AA passes over?
RogueRose
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[*] posted on 13-2-2018 at 01:53
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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[*] posted on 13-2-2018 at 02:18


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.



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[*] posted on 13-2-2018 at 02:38


Quote: Originally posted by Fulmen  
... water will distill off first leaving AA.

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.




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[*] posted on 13-2-2018 at 03:05


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.)



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RogueRose
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[*] posted on 13-2-2018 at 03:48


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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[*] posted on 13-2-2018 at 03:52


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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[*] posted on 13-2-2018 at 04:12


Fractionating column is to efficiently separate components that have a close boiling point. 18° is close enough to need it.



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[*] posted on 13-2-2018 at 05:32


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.




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[*] posted on 13-2-2018 at 06:30


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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[*] posted on 13-2-2018 at 07:32


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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[*] posted on 13-2-2018 at 08:08


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.



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[*] posted on 13-2-2018 at 08:46


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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[*] posted on 16-2-2018 at 18:06


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.




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[*] posted on 17-2-2018 at 13:36


As vinegar is generally 95% water :o 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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[*] posted on 17-2-2018 at 14:01


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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[*] posted on 17-2-2018 at 15:06


Interesting idea.

I like the Time element. Mostly a reaction MUST complete within about a day, or it is considered a non-reaction.

Quote: Originally posted by AJKOER  

Fe --> Fe(ll) + 2 e-


What is oxidising the Iron in this part ?

Dissolved/disassociated Oxygen ?




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[*] posted on 17-2-2018 at 15:37


Quote: Originally posted by AJKOER  
As vinegar is generally 95% water :o 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.




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[*] posted on 17-2-2018 at 17:05


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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[*] posted on 17-2-2018 at 17:07


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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[*] posted on 17-2-2018 at 17:17


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.


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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[*] posted on 18-2-2018 at 08:15


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]




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[*] posted on 18-2-2018 at 13:02


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.)




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[*] posted on 18-2-2018 at 13:51


Strange.

Personally i find the smell of sodium acetate quite pleasant.




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[*] posted on 18-2-2018 at 13:53


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.



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[*] posted on 23-2-2018 at 16:50


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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