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Magpie
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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.
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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?
The single most important condition for a successful synthesis is good mixing - Nicodem
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wpenrose
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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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Nicodem
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Thread Moved
18-9-2011 at 02:29 |
blogfast25
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| 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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wpenrose
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| 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.
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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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blogfast25
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| 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.
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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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Magpie
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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]
The single most important condition for a successful synthesis is good mixing - Nicodem
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S.C. Wack
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CoCl2?
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peach
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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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Picric-A
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| 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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DJF90
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Of course you have. I guess the oleum came from your contact process plant LOL...
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Magpie
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| 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]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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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."
The single most important condition for a successful synthesis is good mixing - Nicodem
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Fyndium
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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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chloric1
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| Quote: Originally posted by Fyndium | 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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In the presence of concentrated hydrochloric acid, calcium chloride reaches the dihydrate stage and not more. So 1 mole of calcium chloride anhydrous
can absorb 2 moles of water from muriatic acid. It seems Damp rid is a mix of monohydate dihydrate with some sort of anti-caking agent. I say this
because it’s advertised as 78% calcium chloride while the monohyrate calculates at 86% calcium chloride by weight and the fact I always have to
filter the solution to get a crystal clear solution. Also it forms nice tetrahydrate cystal spears under certain cooler conditions indicating that
contamination from other cations is low. So dissolving Damp-Rid in minimal boiling water, filtering and allowing tetrahydrate or even hexahydrate to
crystallize, then heating crystals to 400 Fahrenheit for 4 hours should make a good product for HCl generation
Fellow molecular manipulator
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clearly_not_atara
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| Quote: Originally posted by Magpie | | 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] |
There is an alternative:
H2SO4 + SO3 + NaCl >> NaHSO4 + ClSO4H
Both of the half-reactions proceed:
H2SO4 + NaCl >> NaHSO4 + HCl
HCl + SO3 >> ClSO4H
The open question is whether ClSO4H is much stronger than H2SO4 (pKa1). My guess would be that the acid strengths are about equal, so the higher
volatility of ClSO4H will win out.
The use of HCl gas may be common because it allows avoiding the distillation of ClSO4H. If you are trying to make e.g. tosyl chloride you would just
gas oleum with HCl and add toluene. But with NaCl you may end up with some byproducts such as tosyl anhydride:
2 NaHSO4 + 2 TsCl >> Ts2O + Na2S2O8 + 2 HCl ??
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zed
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Ummm. Dripping Hydrochloric Acid into Concentrated Sulfuric Acid is a traditional method to produce HCl gas.
In the past, I just dripped concentrated H2SO4 onto NaCl Rock Salt. This method works well, but it does destroy your H2SO4, and there is no easy way
to regenerate it.
The Hydrochloric Acid/H2SO4 method. Merely hydrates the H2SO4. Thus, the original Mother Acid can be recovered by simply boiling off excess water.
In this age of expensive reagents, and relative difficulty in obtaining fresh supplies; the Hydrochloric Acid/H2SO4 method is gaining attractiveness.
Now, I'm in the USA, and I can easily obtain crap-grade Sulfuric Acid Drain Cleaner, at local hardware stores.
Reagent grade H2SO4, is harder to obtain; I have to purchase a large volume, and pay exorbitant shipping fees. Also, such purchases may attract
unwanted LE attention.
For some of you, outside of the USA, H2SO4 might be damned hard to come by.
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AvBaeyer
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HCL gas prep
Hydrogen chloride can be generated by dropping concentrated hydrochloric acid onto calcium chloride. The attached publication illustrates this
process.
AvB
Attachment: Convenient Way To Generate Hydrogen Chloride.pdf (868kB)
This file has been downloaded 105 times
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