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Author: Subject: DRY HYDROGEN CHLORIDE GAS
Magpie
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[*] posted on 15-9-2011 at 14:45


Quote: Originally posted by watson.fawkes  
You're adding aqueous HCl to an atmosphere that's (almost) entirely HCl, at least after it runs for a while. Even if it's azeotropic when you add it, it will still dissolve more HCl in that environment. It's not mixed perfectly when you add it, so the dissolution will continue until ordinary steady-state conditions are reestablished. The result is to reduce the partial pressure due to HCl, causing an overall pressure drop.


That answer makes a lot of sense - thank you. IIRC I did not notice this effect until I had pushed most all of the air out of this rather large system. The first batch (10gCaCl2) was pretty much used just to push the air out. Yes, the acid is muriatic so should be somewhere around 36wt% I would think.

Dr Bob: I am planning on making HSO3Cl. I understand it is nasty, but could it be any nastier than 65% oleum?




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[*] posted on 17-9-2011 at 13:13


Perhaps I'm not reading enough. I used to make small amounts of HCl by dripping conc HCl into cold sulfuric acid. If I wanted it dryer, I'd bubble it through another flask of sulfuric acid, but it tended to be pretty dry to begin with. The conversion was quantitative, since I could measure a sample absorbed into water with an electrode, or by titration against silver.

[Caution: Don't try to bubble HCl into water. It will suck back up the line into the generator. It needs to be released above the surface of stirring water.]
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[*] posted on 18-9-2011 at 05:17


Quote: Originally posted by wpenrose  


[Caution: Don't try to bubble HCl into water. It will suck back up the line into the generator. It needs to be released above the surface of stirring water.]


I've 'bubbled' HCl (from CaCl2+ H2SO4) through (unstirred) water w/o problems. I use quote marks because really only one steady-state bubble formed at the open end of the line dipping into the water and the HCl simply went straight through the water-gas interphase from the gas into the water. No problems, no suck-back. Problems might occur is flow rate of HCl is very low.




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[*] posted on 18-9-2011 at 07:15


Quote: Originally posted by blogfast25  
Quote: Originally posted by wpenrose  


[Caution: Don't try to bubble HCl into water. It will suck back up the line into the generator. It needs to be released above the surface of stirring water.]


I've 'bubbled' HCl (from CaCl2+ H2SO4) through (unstirred) water w/o problems.


Nevertheless, you don't want to risk suckback into a flask of conc sulfuric. It has happened to me, long ago.
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[*] posted on 18-9-2011 at 13:27


Quote: Originally posted by wpenrose  
Nevertheless, you don't want to risk suckback into a flask of conc sulfuric. It has happened to me, long ago.


You use an empty flask between the generator and the receiving container. See Magpie's set up, higher up (photo). Any suck back ends up in the empty flask... But 'inverted funnel' works well too...




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[*] posted on 27-9-2011 at 13:21


I recently gassed about 100g of oleum, having an assumed strength of ~50%, with HCl produced with the Spanish method cited above, for the purpose of making chlorosulfonic acid, HSO3Cl. Ie, I used a 100g of CaCl2 and slowly dripped muriatic acid on it. My uptake of HCl was measured at only 4.8g when I should have taken up more like 25g. Also gas was escaping regularly from the oleum and there was no apparent heat of reaction.

Today I distilled the product and obtained about 15g of pure SO3 coming off first then about 10mL of crude HSO3Cl coming off in the range 145C-160C. Liquid remaining in the pot was likely con H2SO4.

I'm assuming my poor uptake was due to one or both of the following:

1. My oleum was much weaker than I thought (not too likely).
2. My HCl was wet, although I saw no water condensed in the test conducted in my post above.

I like using this Spanish method for generating HCl as it is very easy to set up and use. And I could certainly add a con H2SO4 absorber before the suckback trap.

Does anyone know of a test that will indicate the dryness of HCl gas short of cooling it to very low temperature?

[Edited on 27-9-2011 by Magpie]




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[*] posted on 27-9-2011 at 14:25


CoCl2?



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[*] posted on 27-9-2011 at 19:31


From 'The drying agent selection guide'

Residual Water mg H2O / Litre Dried Air

Calcium chloride, 20 mesh; 0.14-0.25
Sulphuric acid; 0.003




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[*] posted on 27-9-2011 at 23:20


Quote: Originally posted by Magpie  
I recently gassed about 100g of oleum, having an assumed strength of ~50%, with HCl produced with the Spanish method cited above, for the purpose of making chlorosulfonic acid, HSO3Cl. Ie, I used a 100g of CaCl2 and slowly dripped muriatic acid on it. My uptake of HCl was measured at only 4.8g when I should have taken up more like 25g. Also gas was escaping regularly from the oleum and there was no apparent heat of reaction.

Today I distilled the product and obtained about 15g of pure SO3 coming off first then about 10mL of crude HSO3Cl coming off in the range 145C-160C. Liquid remaining in the pot was likely con H2SO4.

I'm assuming my poor uptake was due to one or both of the following:

1. My oleum was much weaker than I thought (not too likely).
2. My HCl was wet, although I saw no water condensed in the test conducted in my post above.

I like using this Spanish method for generating HCl as it is very easy to set up and use. And I could certainly add a con H2SO4 absorber before the suckback trap.

Does anyone know of a test that will indicate the dryness of HCl gas short of cooling it to very low temperature?

[Edited on 27-9-2011 by Magpie]




I have made chlorosulphuric acid in the past by slowly adding dry sodium chloride to <30% oleum and then distilling. This method is much easier than attempting to dry the HCl gas and can be a one pot reaction.


[Edited on 28-9-2011 by Picric-A]
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[*] posted on 28-9-2011 at 00:11


Of course you have. I guess the oleum came from your contact process plant LOL...
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[*] posted on 28-9-2011 at 07:17


Quote: Originally posted by Picric-A  

I have made chlorosulphuric acid in the past by slowly adding dry sodium chloride to <30% oleum and then distilling. This method is much easier than attempting to dry the HCl gas and can be a one pot reaction.
[Edited on 28-9-2011 by Picric-A]


Are you saying that this occurs:

H2SO4 + SO3 + 2NaCl ---> 2HSO3Cl + Na2SO4 ??

How did the early chemists miss this easy method?

[Edited on 28-9-2011 by Magpie]




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[*] posted on 29-9-2011 at 12:43


Thanks to SC Wack and Peach for HCl drying ideas. I would try the CoCl2 if I had any. IIRC this is used in laboratory grade CaSO4 drying pellets as an indicator to show when the pellets have been exhausted. Blue to red color change I believe.

I set up a con H2SO4 absorber using a fritted glass sparging tube submerged about 2 inches. This produced a stream of very fine bubbles so I'm confident that the HCl was adequately dried.

This gas was then used to produce chlorosulfonic acid. I will describe this in a separate thread: "chlorosulfonic acid."




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[*] posted on 11-10-2020 at 14:51


It appears that if HCl solution is at hand, cheapest method to produce HCl gas is to dehydrate it with anhydrous CaCl2 which costs about 50C a kg. Using an ordinary dropping funnel for HCl and placing the granules of CaCl2 in a flask would be the basic concept here. I'm not sure how much CaCl2 is enough, so I consider enough being as much as reasonable, because it is dirt cheap and technically can be regenerated if wanted.

A drying tube would be used to ensure the dryness of the gas generated.

The temperature for bisulfate chloride reaction is high, wiki cites at 200C. I broke a flask when testing it out a decade ago, actually.
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