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bbartlog
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After doing ethanol and water distillation I was so pleased with my 300mm Hempel column that I decided to take a stab at separating acetic acid and
water by mere distillation. I did the following:
Added 248g of anhydrous sodium acetate to a 2l RBF
Added 331g of 31%HCl (aqueous) to this, and stirred briefly
Heated this at reflux for 45 minutes
Began distillation. Over a period of a few hours, 149g of distillate passed over. The head temperature never went over 100C, and the ratio of liquid
dripping back into the flask to that coming over was about 3:1. At this point I was dismayed by the very strong vinegar smell of the distillate, and
decided to examine the result.
Titration of the distillate with 1M Na2CO3 indicated that it was about 24% acetic acid  . After weighing other constituents I concluded that the acid remaining in the RBF was likely no more than 56% on net (considering the
entire flask contents), although settling seemed to result in separation of a salt+NaCl layer so that the acetic acid on top was more concentrated. I
poured off this top layer, which amounted to 107g, and set it aside for later drying and/or evaluation.
Sooo... why are acetic acid and water *so* hard to separate by distillation? They do not form an azeotrope (apparently), and while the separation in
boiling points is not huge (118C vs 100C) I've achieved fairly clean separations of various other fluids with similar differences in boiling point,
like the aforementioned ethanol and water. I thought about this a bit after looking at the way the liquid composition boiling point curve and the
vapor composition dew point curve separate and come together for an azeotrope.
Is there such a thing as a 'near azeotrope', where a pair of such curves drawn for the range of mixtures had neither intermediate maximum nor minimum,
but the curves still deviate from a straight line to the point where the boiling temperature remains *close* to the minimum over an extended range of
mixture compositions? For example, when boiling 50/50 water:acetic acid, could the boiling point be much closer to 100C than to the linear
interpolation of 109C?
Or is it more likely that I had problems because the water/NaCl phase in my RBF formed a separate phase, which being a saturated brine had a boiling
point above that of plain water? I'm skeptical of this explanation just because most of the separation occurs in the column, after the solutes are no
longer relevant.
All in all somewhat disappointing (even if what I poured off is fairly concentrated acetic acid I'll still only end up with about 50% of theoretical
yield), and it's not like a few tweaks to the column will make much difference (I figure it's the equivalent of about six plates when used properly,
which would suggest 20+ plates equivalent to achieve decent separation of acetic acid and water...  )
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Magpie
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The liquid-vapor equilibrium curves for the water/acetic acid system are close together. Ie, the relative volatility is close to 1. So while there is
no azeotrope per se, the number of "theoretical plates" required for separation by fractional distillation may indeed be high.
My graphical estimate indicated 16 theoretical plates are required when starting with 4 mole% acid. Starting at 20 mole% acid or higher in the pot
should be a great help.
There's a lot of information and experience here:
http://www.sciencemadness.org/talk/viewthread.php?tid=2194&a...
[Edited on 18-3-2010 by Magpie]
[Edited on 18-3-2010 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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starman
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Quote: Originally posted by Panache  | | (cut)... The acetate does not decompose below 150, so use an oil bath for the distillation if you're having trouble regulating temperature and never
let it go past 150. |
I've run this a few time now.Each time using 1-2 mole acetate and approx 2 times excess H2SO4 in a 1 litre flask.I find it difficult to drive off all
the acid at this temperature restriction,with the pot still smelling very strongly of acetic acid and yeilds of only 60%.
My last attempt where i allowed the pot temperature way up did in fact lead to some type of decomposition as I was getting a fraction at about
150C.Seemed waxlike and mostly deposited in the condenser.Any idea at what this could be?(acetate and acid both reagent grade).
Any hope of improving yeilds and recovery?My initial thoughts are to use a smaller flask for the pot but I worry at the initial vigourous reaction.Or
perhaps apply (aspirator) vacuum when the distillation stalls.
Comments and suggestions appreciated.
Chemistry- The journey from the end of physics to the beginning of life.(starman)
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rrkss
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I've always heated my acetate + H2SO4 flask until distillation stops somewhat ignoring the temperature. Should not decompose until well into the 400
degrees Celsius range since anhydrous acetate melts in the 300 range. I do find that my product is very contaminated with Sulfur Dioxide and requires
further treatment with anhydrous copper sulfate to dehydrate and remove the sulfur dioxide.
I've given up this route to glacial acetic acid because it is too much hassle since I found a biodiesel supplier supplying ACS grade Glacial Acetic
Acid for dirt cheap.
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Panache
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| Quote: Originally posted by starman | | Quote: Originally posted by Panache | | (cut)... The acetate does not decompose below 150, so use an oil bath for the distillation if you're having trouble regulating temperature and never
let it go past 150. |
I've run this a few time now.Each time using 1-2 mole acetate and approx 2 times excess H2SO4 in a 1 litre flask.I find it difficult to drive off all
the acid at this temperature restriction,with the pot still smelling very strongly of acetic acid and yeilds of only 60%.
My last attempt where i allowed the pot temperature way up did in fact lead to some type of decomposition as I was getting a fraction at about
150C.Seemed waxlike and mostly deposited in the condenser.Any idea at what this could be?(acetate and acid both reagent grade).
Any hope of improving yeilds and recovery?My initial thoughts are to use a smaller flask for the pot but I worry at the initial vigourous reaction.Or
perhaps apply (aspirator) vacuum when the distillation stalls.
Comments and suggestions appreciated. |
its slow tedious and shit but that's tthe best way i've found to ensure purity, definietly use a vacuum and have your oil bath on 150. Believe me it
will still only come over sedately. Using a 5l flask it takes 8hrs to get ~1L glacial. After about 4hrs, cycling the vacuum on and off really helps.
I have been trialling a new method using citric acid(anhydrous) and sodium acetate, the two are combined, well ground in a blender then packed into a
cromatography column. The column leads into a collection vessel that is protected with a cacl2 tube. On top of the tightly packed column i inflate a
large double ballon with dry argon. I leave it in the corner and forget it, occasionally reinflating the ballon. Thus far it isn't working great but i
need to have a proper look at it, there's approximately 1/3 of the expected glacial through in around 10days however it must be tested. If it doesn;t
get better i will try hot argon as a carrier gas, this should work well. In theory some water in this system should help things along without getting
into the final product as long as everything is kept below 40C as the trihydrate of citric acid forms and is an excellent dessicant.
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starman
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Interesting Panache.You must keep us updated on that one.I've been looking at anodic oxidation of ethanol.Apparently its been pretty sucessful with
platinum or gold and I'm wondering if PbO2 coated lead has the required overvoltage to get the job done.
Chemistry- The journey from the end of physics to the beginning of life.(starman)
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Jimmymajesty
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Has anyone here tried to separate butyl acetate + acetic acid mix by distillation with a column?
I failed many times... it cannot be that hard
Here is what I did:
Bought a paint stripper OTC with the following composition on the label: butyl acetate ~60w% butanol ~20w% acetone ~20w%
I shook the paint stipper with water, after the extraction the water had an alcoholic smell, but no acetone. I also fractionated the mixture, but only
one component could be detected. with a B.P. of 124°C... so the stripper is mainly made of butyl acetate.. I presume..
In the next step, i took two litres of "acetic acid escencia" which is sold in my country in supermarkets, and it is 20w% acetic acid + some organic
crap, and I azeotroped the water off by means of the stripper + a dean stark.
Then I poured the water free butyl acetate (?) and acetic acid mix into a RBFL for fractionation, and started to separate them.. but no matter what I
did... I adjusted the reflux, the temp of the reboiler, even replaced the packing in the column, I got the same result every time... a liquid with a
strong smell of acetic, but it is not totally miscible with water, IIRC 50v/v% is lighter than water and floating on top like hexane, and has a stong
smell of.. nail paint..
I am a bit puzzled any help would be appreciated!
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Sedit
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Has anyone any experiance with the acid hydrolysis of Vinyl acetate? Its used in alot of wood glues as the polymer and as a better source I believe would be spackles which is composes around 68% of
the spackle the remaining being light organics and water mostly. Drying the spackle produces the polymer I belive so removing water would be no
problem.
Just curious if anyone has tryed even dilute AcOH from PVA. I believe it has been mentioned but never heard of anyone attempting it.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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The WiZard is In
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| Quote: Originally posted by JohnWW | | It is possible that some additional concentration may be obtainable by distillation with benzene or something, |
----
Tis - it is claimed - done this way on an industrial scale, Azeotropic
distillation.
By da Thorpe sez you can get from 4% vinegar to 40 by freezing,
without loosing flavour.
[Edited on 4-6-2010 by The WiZard is In]
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Ephoton
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thats real handy for pickeling my chillies wiz thanx
and octopus 
[Edited on 6-6-2010 by Ephoton]
e3500 console login: root
bash-2.05#
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Sedit
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But we have discussed these means Over and over again in the past many many times.....
What about Vinylacetate hydrolysis? If the price is right on the PVA or Vinyl acetate product this could prove rather cheep and not really bulky
either.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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mr.crow
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you can also produce acetic anhydride from vinyl acetate. No one has gone into detail on this forum but I have a reference in the reference section.
Double, double toil and trouble; Fire burn, and caldron bubble
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Sedit
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can you PM me a link please? ill look on the SE but if you know where its at then that might be quicker.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Jimmymajesty
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Sedit you have you managed to make acetic acid by ageing the alcholod with dilute nitric acid?
I managed to decompose the denaturating agent by keeping the diluted alcohol + HNO3 mixture at 60°C for a day, but again, nothing acetic.
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Sedit
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Never tryed dilute HNO3 only insitu from KNO3 and H2SO4. The start is violent but nothing unmanageable with a bucket of ice water as the first little
bit of EtOH was added. Don't know how safely it could be scaled due to the large amount of heat and NOx generated in this synthesis. Perhaps outside
in a snowbank you could bucket chemistry it but thats still to be seen.
However it is indeed large amount of AcOH but I have yet to work it up out of fear. After seeing reports of Nitric acid and AcOH exploading with heat
im kind of reluctant to distill it for obvious reasons so its been sitting there bottled up buried up to its neck in sand because I dont know what the
hell to do with it right now and I fear it could go off. I doubt it would spontanously but im not a big fan of "what ifs".
I also do not think what I made is glacial either since it has shown no signs of being so. I got side tracked right after performing the synthesis in
reworking the entie layout of my lab to something that resembles a lab almost so its largely been put on hold.
You will find more then likely BTW that if you heat your mixture until NOx is produced it will start to bubble like soda pop and sustain a reaction
from that point on. As magpie and the papers provided have shown there is an activation temperature needed before this reaction starts else you need
NO2 present already to lower this activation temperature down to almost nothing. What concentration are you speaking of here anyway?
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Panache
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Does anyone have solubility vs temp curves for the systems Acetic Acid/Citric Acid/Sodium Citrate/Sodium Acetate or any combination therefore?
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chucknorris
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I put some 1500ml of vinegar in flask and 500ml of chloroform and then about 50 grams of table salt(to save the 8 grams of chloroform that would be
dissolved into every liter of water otherwise) and mixed the contents for 5 minutes and let it sit for a while, then filtered the contents into
separator and separated the lower layer and distilled off the chloroform, and about 60ml of acetic stenchy stuff remained. I expect it to be somewhat
concentrated acetic acid, still need to test the freezing temp. The salted water that remains, has trace smell of vinegar, so the chloroform does pull
it off.
Anyways, does anybody happen to know the solubility of acetic acid into chloroform? I have found out that it can dissolve up to 40-50% of its volume
of acetic acid, so counting from this, 500ml chloroform could be used to reform about 6-7 liters of vinegar. Ok, I could test this out by myself since
I have some pure reagent grade GAA and chloroform but just if someone has the data already?
Does the acetic acid break down when distilled? The commercial vinegar contains all kind of soluble shit and gunk which would be easy to get rid of by
distillation.
[Edited on 23-7-2012 by chucknorris]
[Edited on 23-7-2012 by chucknorris]
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ManyInterests
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I am bumping this thread as a bit of notes on my own first glacial acetic acid synth.
I used 258 grams of sodium acetate (anhydrous) and 390ml of sulfuric acid (at least 95%). I added cold acid to the sodium acetate in the flask
gradually and left everything to cool before heating it on the mantle. It originally took a while for anything to come over, as this was my first
attempt at glacial acetic acid and my setup currently has no temperature control, I was afraid that I was distilling sulfuric acid over as it took a
while for anything to come over. I did get a yield of 150ml (out of an expected 210ml) and I stopped.
I realized I was a touch too hasty as the flask stank of acetic acid when I removed the distillation joints. At any rate for a first attempt it was
very good. I had a specific gravity of 1.0564. So not 99% for sure, but certainly close.
I added it all to around 30 grams of anhydrous MgSO4 in a flask and I will distill that over shortly.
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ManyInterests
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I did a 2nd distillation and there was no discernable drop in SG. I am still at the exact same thing that happened before. I guess I should have
better luck next time, but for now it is good enough.
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Fery
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You can also try to approximate its purity by its freezing / melting point. It tends to produce supersaturated solution in fridge at +4 C, but on
shaking it suddenly starts to crystallize then. Leaving it in fridge for long enough time, the small temperature oscillations cause the crystals to
regrow in the bottom (higher density) and the liquid to move upwards (lower density) so you can remove more liquid (diluted acid) as less liquid stays
trapped inside solid phase. Solid phase has higher density and thus lower volume so no glass flask cracking unlike when freezing water where solid
phase has lower density and expands in volume.
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chornedsnorkack
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| Quote: Originally posted by Fery | | You can also try to approximate its purity by its freezing / melting point. It tends to produce supersaturated solution in fridge at +4 C, but on
shaking it suddenly starts to crystallize then. Leaving it in fridge for long enough time, the small temperature oscillations cause the crystals to
regrow in the bottom (higher density) and the liquid to move upwards (lower density) so you can remove more liquid (diluted acid) as less liquid stays
trapped inside solid phase. Solid phase has higher density and thus lower volume so no glass flask cracking unlike when freezing water where solid
phase has lower density and expands in volume. |
Now the question is crystal size/cleanliness.
Acetic acid and water make a simple eutectic at -27 C and 60% acetic acid by weight. This means that while concentrated acetic acid is hard to resolve
by distillation (it is not actually an azeotrope, but it is a near-azeotrope, so the vapour composition is nearly the same as liquid), it should give
a neat solid in terms of crystals - solid acetic acid.
Now the question is, does the glacial acetic acid separate as neat big crystals easily cleaned of mother liquor, or fine slush hard to separate?
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Tsjerk
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When 98-99% acetic acid freezes it forms a mesh from which more dilute acid melts when it is allowed to heat up a bit. When you for example freeze at
4 degrees, and slowly thaw at 10, while keeping the bottle upside down, you will get block of porous acetic acid very close to 100%.
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Fery
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I let glass bottles with commercial 98% acetic acid in a fridge for few months. The temperature oscillations around +4 C made the liquid formerly
trapped among crystals to slowly raise upwards (hundreds of partial melting and freezing steps) so finally there was a block of solid mass and a
little of liquid on top (that could be still something like 90% acid, it can be found in tables which concentration freezes/melts at +4 C).
If you do not have so much time, the method posted by Tsjerk is faster.
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Tsjerk
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I have to add my acetic acid was also frozen over many freeze/thaw cycles; in my shed over winter. Probably between 0 and 10 for months.
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ManyInterests
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I never tried to freeze it. But I am not sure if my freezer on max settings can make something go as cold as -27C.
Maybe I did end up making glacial acetic acid and not aware of it. One thing I wonder is that even if it is at 95%, can I still use it to make acetic
anhydride using the calcium chloride/sodium acetate + sulfuric acid route (I post a link to it on the acetic anhydride sticky).
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