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Author: Subject: Acetic acid/ sodium hydroxide
Magpie
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[*] posted on 4-10-2006 at 15:58


I have finished reducing 1 gallon (3875mL) of "triple distilled white vinegar," which is 5% acetic acid, to a much more concentrated form: 87%. It is not yet glacial (99+%) acetic acid but it's definitely getting there.

I made this in 3 batches. The 1st was sort of a hodge-podge of CaAc + NaAc. The NaAc was taken back from a diluted HAc. So this batch (30mL) wasn't too efficient.

The 2nd batch was made from NaAc taken to dryness at about 140C. This yielded about 50 mL.

The 3rd batch was the same as the 2nd only I fused (melted) the NaAc first, then let it solidify, then reground it to a powder. This last step, I think, was a waste of time as it didn't change anything. This also yielded about 50 mL. I combined all distillates for a total 130 mL for a yield of (0.87)(130)/[(3875)(0.05)]x100% = 58%. It would have been better if I hadn't messed around with the 1st batch.

Each batch was done with about 80g of anhydrous NaAc and 60mL of concentrated sulfuric acid (Rooto) in a 500 mL RBF assembled to a simple distillation setup.

In all cases I placed the RBF with powdered NaAc in an ice-bath while adding pre-chilled (w/ice-water) acid. There is a lot of heat generated during this step. Also there is a lot of smoke generated. I don't know what this smoke is. Once this subsides I heated the mix with a bunsen burner as required to get a steady generation of HAc collected as a distillate.

I also noted what others have: generation of a lot of carbon black. Also there are smoky odors like that of a wood fire. Perhaps this is some of the "empyreum" spoken of by the early chemists?

This preparation was a lot of work. It has to be a labor of love as you can buy glacial acetic for reasonable prices. At least I can say that this method beats my previous preparation with calcium acetate and HCl which yielded 65% acid.

[Edited on 6-10-2006 by Magpie]




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[*] posted on 6-10-2006 at 14:23


Not satisfied with 87% acetic acid I continued my quest for homemade glacial acetic acid. I tried to freeze it to glacial plus eutectic solution by taking it down to -26C. It froze alright but the eutectic solution was occluded in the acid and therefore was not separable.

So I went back to trying fractional distillation. I packed my little 8" (20cm) column with broken glass pieces from a smashed food jar. I collected three clear distillate cuts: the 1st was 20mL at 101-104C, the 2nd was 45mL at 104-110C, and the 3rd was 50mL at 110-116C. I left a few mL of brown solution in the pot. So, it is tough to get glacial acid. If I would have had a longer column and glass raschig rings (or other optimized packing) I might have done better.

It amazes me that by concentrating something I put on my salad I can make this really wicked (and useful) reagent. :D

[Edited on 7-10-2006 by Magpie]




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[*] posted on 6-10-2006 at 21:00


Freezing must be done at a controlled rate. For some materials a very slow decrease in the temperature will result in the excess componant freezing out in a fairly compact layer, but not always.

The alternative is to freeze to a slush, and vacuum filter or centrifuge to separate the frozen from the eutectic.

Even after freezing distillation is a good idea, as it cleans the acetic acid up. Even if you distilled it at the start, from adding acid to acetate, if there was more than a few percent of water then other organics will come over in the distillate.
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[*] posted on 7-10-2006 at 19:32


@not_important: Thanks for the information on freezing. I was wondering if there was something I was missing.

Yes, the distillation was good just to clean up the acetic acid. There was a fair amount of carbonaceous junk left in the pot. No wonder the commercial white vinegar is "triple distilled."

I made another attempt to enrich the 2nd cut by fractional distillation but was only mildly successful. My final product is 65 mL at 92.5% acetic acid, which I plan to use for an esterification. I've run out of ideas on how to get it any richer.




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[*] posted on 8-10-2006 at 00:42


Could try dehydration with neutral salts, silica gel, molecular sieves, and so on. Also, I believe that fused (anhydrous) sodium acetate will grab onto the water in the acid. But 90+ percent is fine for most esterfications.

When you distill a mixed solution of the lower alphatic carboxylic acids, a mixture comes over. It will be enriched in some of the acids, but by no means pure ly one acid. But for food use, a small amount of those acids besides acetic, and the other organics, just make a slightly richer taste. It's only we fussy chemists how are bother by it.

If you make sodium or calcium acetate as a step in the process, extracting the dry salt with on orgaic solvent might remove some of the larger organics. As an example, boiling down sodium acetate from vinegar and sodium hydroxide/carbonate/bicarbonate will usually give an off-white to tan product. Stirring thiis with "100%" isopropyl alcohol removes much of the coloured material.
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[*] posted on 21-5-2007 at 10:28


I see most of the effort has been done through distillation. Has anyone tried using god ol' home-plausible process of freezing the vinegar and then collect some of this liquid as it thaws?
I've done it and a weekend with an irritated respiratory tract proved me that this easy process gives off concentrated acetic acid. The only problem is, how can I accurately measure the concentration given based on the rate at which acetic acid thaws compared to that of water?
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[*] posted on 28-8-2007 at 21:37


Summary of above thread

(1)The mysterious azeotrope of the acetic acid/water system is as elusive as the blue-arsed fly; it does not exist. The system is zeotropic.
(2)You can increase the % acetic acid in a solution by distilling and get 55% or better with effort (several distillations)
(3) "Pure" or glacial: good luck. Try freezing a well concentrated solution?

For reference, graphs of vapor (partial) pressure vs. temp are attached to help (all data plotted from CRC 1995-1996 ed.)



Lower trace, acetic acid, middle water, top sum of the two. 101 Kpa ~ 1atm. =760 mm Hg. The top trace is not highly meaningful since the presence of the one solvent in the other reduces the vapor pressure of that component.

The fact that the system is zeotropic tells us that the slope of the boiling temperature of a mixture plotted against composition (0-100% acid) has no maximum nor minimum but must have a positive slope throughout. Raoult’s Law never holds except for low dilution factors but assuming a straight line tells you very roughly where a given composition boils.



This graph shows the ratios of the partial pressures. Remember that these graphs refer to the vapor in contact with the pure liquid only. But they may help.

Regards,

DerAlte

[Edited on 28-8-2007 by DerAlte]

[Edited on 29-8-2007 by DerAlte]
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[*] posted on 29-8-2007 at 10:39


This
http://en.wikipedia.org/wiki/Blue_bottle_fly
is a whole lot more common than any acetic acid/ water azeotrope.
I think you missed out the use of involatile salts- like calcium or sodium acetate and sulphuric acid as a method too. It's a whole lot easier to remove water from sodium acetate than from acetic acid.
Otherwise a useful summary of a remarkably long thread.
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[*] posted on 29-8-2007 at 11:21


@ unionised - LOL! Yup, missed that bit. Better not make an already long thread longer! Regards, Der Alte
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[*] posted on 22-8-2008 at 19:25


Why don't you guys just use phosphoric acid? It is readily available in 85% concentrations. As well it is food grade. I mixed it with some dried NaAc and then did a simple distillation....it VERY pungent. I plan to take this acid and distill with H2SO4 to get pure GAA.
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[*] posted on 5-7-2009 at 15:03


Vacuum crystallization:
US3677023

Note the water remaining when vacuum is not used.
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[*] posted on 5-7-2009 at 15:38


Quote: Originally posted by S.C. Wack  
Vacuum crystallization:
US3677023

Note the water remaining when vacuum is not used.


Gee,simply vacuum stripping the product really.I wouldn't have thought such common technique patentable.I suppose the confined temperature range got it over the line.




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[*] posted on 5-7-2009 at 17:02


I recently tried the procedure in this patent, starting with about 90% acetic acid and had no luck with it.

I'd be very excited to hear that someone else succeeded!:D




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[*] posted on 18-3-2010 at 02:19
freeze crystallisation of acetic acid


Ok, i have used the FSE and couldn't find much so here goes...
The freezing point of vinegar is -2°c at a conc of ~5% acetic acid, and I have seen a photo thread on another website of a person using freeze crystallisation to concentrate acetic acid from wine vinegar (www.alchemywebsite.com) and I wonder if it would it be possible to use this technique to concentrate acetic acid from white vinegar (about 5% conc), or if anyone has done it already? Thanks;)
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[*] posted on 18-3-2010 at 08:25


http://www.sciencemadness.org/talk/viewthread.php?tid=2194&a...



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18-3-2010 at 08:57
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[*] posted on 26-10-2013 at 16:22


This attachment is from 1918 and the serial book Vinegar Bulletin, by Paul Hassack. It's the interesting part of THE CONCENTRATION OF SPIRIT VINEGAR, and OTHER CONCENTRATION METHODS OF FERMENTED VINEGAR pp. 210-211.

Or
http://books.google.com/books?id=axQwAAAAYAAJ&pg=PA210

Attachment: Vinegar_Bulletin.pdf (110kB)
This file has been downloaded 553 times

[Edited on 27-10-2013 by S.C. Wack]




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