11-13-03 22:08
No 470695
This is a rather worn out topic but I found this interesting tidbit in Ullmans...........A way to obtain pure acid is to add urea or potassium acetate to the acid. Then, glacial acetic acid can be distilled............... I'm trying to find an EASY way to reclaim GAA and if you ever tried to distill the stuff forget it unless you have a column 2 meters long and a week to wait for a liter. With a 300mm SS sponge packed column it took 3 hours to collect about 200ml of the acid and the temp never did get near 118deg and this was after I thought most of the water was removed. I just had to try it so don't laugh.
Anyway I've got to either reclaim the stuff or get rid of it because it's taking up way too much room. I wonder if the fertilizer grade Urea would work. Any ideas or suggestions? I did wear out TFSE on this topic.
(Synaptic Self-Mutilator)
11-14-03 03:21
No 470755
(Rated as: good read)
You can use liquid-liquid extraction, azeotropic distillation and extractive distillation to purify aqueous acetic acid. Simple and fractional distillation do not work at lab scale, fractional distillation requires many stages at industrial scale and is never done as it's not economically feasible to build columns that big (although is technicaly possible).
If you're talking low concentrations of acetic acid, first use liquid-liquid extraction. One you get your more purified acid, it'll still be wet, then you have to go on to azeotropic distillation. A suitable solvent for liquid-liquid extraction is ethyl acetate. If it's a relatively concentrated solution, then use azeotropic distillation. Azeotropic distillation can be a bitch but it is totally possible... you just use toluene to remove the water using a Dean-Stark trap with a fractionating column... recycling until you hit the BP of toluene. Then fractionally distill what remains to separate the toluene and acetic acid.
My only suggestion for a kitchen chemist who doesn't want to go thru that extensive labor and pricey distillation equipment is to add baking soda, form NaOAc, dry that, add sulfuric and distill. You can search for my nick on how to do this... but, I know you're going to be asking yourself--is it worth it for something as easy to obtain as GAA?
Fuck, I don't even think it was worth my time writing this reply.
(Newbee)
11-14-03 08:17
No 470804
Thanks Chromic, I had already read your other posts on the subject. I think the sulfuric and base method just don't make sense. Hell the Acetic CP grade is cheaper than those two chems never minding the electricity and time.
The Urea method i'm trying to figure out what this does. Maybe too good to be tue.
(Hive Bee)
11-22-03 20:33
No 472526
Sodium acetate loses water at 120C (http://www.uiowa.edu/~chemsafe/MSDS/Sodi
(Chief Bee)
11-22-03 21:32
No 472541
Dehydrating sodium acetate trihydrate to the anhydrous form is easy in the microwave, as the salt stops absorbing microwaves as soon as it is dry...
(Horrible Personality)
11-23-03 20:10
No 472686
recommended if you have acetic acid with more than 80percent conc. - thats the usual procedure as described in the ORGANIKUM 21st ed. to yield GAA pure enough for most purposes.
and thats easy.
(A Different Title)
12-01-03 12:02
No 474047
Sodium acetate + H2SO4 to get GAA works, but for some reason I always got black crud in the flask which I could only remove mechanically afterwards.
Check the density / congealing point of your 'GAA' afterwards as well, sometimes water gets into the system somehow (either H2SO4 not as concentrated as you think and/or NaOAc wetter than you think).
Eventually I wised up and just started buying GAA.
They call them fingers, but I never see them fing... oh, there they go.