Sciencemadness Discussion Board

Concentrating storebought 15% muriatic acid

AndrewOfWallachia - 21-3-2024 at 07:52

Hi! I have some 15% Muriatic acid, I really need to concentrate it to 30%. Is that possible by just adding a Hygroscopic material like CaCl2 to it and then boiling it to remove just HCl(g) and the bubbling that through more of the 15% HCl Solution? Or does it only work with higher concentrations of Muriatic acid? Or is there a way to boil the 15% with a reflux condenser so that the steam that rises gets condensed back but the HCl(g) can be bubbled through more Muriatic Acid?
Thanks in advance!

[Edited on 21-3-2024 by AndrewOfWallachia]

fx-991ex - 21-3-2024 at 08:06

Make more HCl with NaCl and NaHSO4 and absorb it in the 15% HCl, carefull its highly hygroscopic.

woelen - 21-3-2024 at 08:07

You can concentrate it a little more to appr. 20% by careful boiling. Initially, mainly water boils off. In this way you can get close to 20% without too much loss. Much more will not be possible, because the azeotrope with water is 22% or so. A few percents below that azeotrope, you already lose so much HCl, that it hardly separates anymore.

With your almost 20% HCl, you then could try the trick with anhydrous CaCl2 and boiling off a mix, which is richer in HCl than 20%.

AndrewOfWallachia - 21-3-2024 at 08:43

Quote: Originally posted by woelen  
You can concentrate it a little more to appr. 20% by careful boiling. Initially, mainly water boils off. In this way you can get close to 20% without too much loss. Much more will not be possible, because the azeotrope with water is 22% or so. A few percents below that azeotrope, you already lose so much HCl, that it hardly separates anymore.

With your almost 20% HCl, you then could try the trick with anhydrous CaCl2 and boiling off a mix, which is richer in HCl than 20%.


Whoa, -ANHYDROUS- CaCl2? As in, perfectly anhydrous? Can I realistically dry it that much?

Precipitates - 21-3-2024 at 17:45

Yes! Just heat it to 300°C or so... :D

CaCl2 will loose the last water molecule at 260°C.

https://rushim.ru/books/spravochniki/handbook-of-inorganic-c...

B(a)P - 21-3-2024 at 17:46

Quote: Originally posted by AndrewOfWallachia  


Whoa, -ANHYDROUS- CaCl2? As in, perfectly anhydrous? Can I realistically dry it that much?


You can easily get to the monohydrate by sticking some calcium chloride in the oven on a tray set to high for an hour or so, depending on volume. I would have thought the monohydrate would be fine for this purpose. If you want to go to anhydrous it is relatively easily achieved in an old stainless frying pan on a very high heat.
If you have the correct vessel, some have reported success using a microwave to dry calcium chloride.

woelen - 22-3-2024 at 02:16

Anhydrous CaCl2 can be obtained in hardware stores as drying agent for air drying purposes. You can buy it in bags of 2 kg or so. At least, where I live, this is available at many places OTC. This stuff is good enough for the purpose I mentioned in my previous post. An indeed, if you can't buy anhydrous material, you can make it by heating more or less hydrated material.

chornedsnorkack - 22-3-2024 at 02:54

Pass the constant compositions by alternate freezing and heating?
Freezing phase diagram:
https://picryl.com/media/phase-diagram-hcl-h2o-s-l-e2e2c6?zo...
15 % HCl should freeze out water ice above -40 and be capable of concentrating until 22...23% eutectic that freezes at -75 degrees if it nucleates. But at 22...23%, you´re past the azeotrope which is 20,2%, and can get more concentrated HCl by distilling your mother liquor.

clearly_not_atara - 26-3-2024 at 05:47

IIRC benzoic acid or TsOH monohydrate have pretty low solubility in acidic water, so you could add benzoic anhydride (by the catalytic thermal dehydration) or anhydrous toluenesulfonic acid (Nicodem's Dean-Stark method) and then simply filter. There will probably be a small amount of contamination, which may or may not be acceptable.

Sulaiman - 26-3-2024 at 15:06

Is 30% actually required (eg vs double quantity of 15%)?

Store bought muriatic acid is likely to contain various impurities,
so I think that purification/distillation should be a part of your concentration procedure.

UC235 - 26-3-2024 at 19:27

Heating HCl solution above the 20.2% azeotropic mixture will just drive off HCl gas. To concentrate to 30%, you need to dissolve additional HCl gas in it. How you produce that is up to you. Sulfuric and NaCl is classic. Watch out for heat of dissolution and the very real suckback risk.

chornedsnorkack - 27-3-2024 at 04:45

Quote: Originally posted by UC235  
Heating HCl solution above the 20.2% azeotropic mixture will just drive off HCl gas. To concentrate to 30%, you need to dissolve additional HCl gas in it. How you produce that is up to you. Sulfuric and NaCl is classic.

Heating HCl solution above the 20.2% azeotropic mixture would be one obvious possibility? Heat one vessel of 20+% solution, direct the vapours into the other vessel of the same, which you are cooling.