Sciencemadness Discussion Board

HCL gas from muriatic acid

Gui316 - 20-8-2011 at 04:20

I've found muriatic acid on the super market. Quite impure and low concentration. And we also got some alkalizers on it. I wanna get rid of these but I have no idea of what the impurities are made of. Then I had the idea of removing the HCL gas from the acid and then dissolve it into water. But how can I do that? Any ideas? Would it work?

blogfast25 - 20-8-2011 at 05:16

Starting from low grade hydrochloric acid (modern name for 'muriatic acid') will make it difficult to recover much of the HCl contained in it. Howver, distilling will eventaully concentrate the HCl solution to constant boiling azeotropic hydrochloric acid (about 20 w%), which can then be distilled off, leaving at least the solid contaminants behind.

But strong HCl (up to 37 %) is available from many hardware stores, usually sold as a toilet cleaners because the acid removes lime scale and any ingrained you-know-what very quickly without attacking the ceramic.

Endimion17 - 20-8-2011 at 06:36

I've always wondered how is it possible to sell concentrated hydrochloric acid in stores for everyone to buy.
Not just it's very corrosive for the skin, but it's also more difficult to produce, and while you're using it excess HCl escapes, doing nothing it was intended to.

In my country and pretty much in all of the countries in the region you can buy only 19% (and it has been like that for many decades), which is almost an azeotrope. It doesn't fume unless it's warmed in the winter season, and it attacks and cleans very efficiently without producing so much noxious HCl aerosol.
When you drip 37% HCl on limescale, much of the active ingredient just fumes away, suffocating the one doing the cleaning and creating a cloud in the room. Isn't that an overkill?

[Edited on 20-8-2011 by Endimion17]

not_important - 20-8-2011 at 07:02

The higher concentration is cheaper to ship per unit HCl delivered; it usually gets diluted by the end user. One must remember the relative distances stuff gets shipped in Europe vs N America; kids in some regions of NA will drive long distances to attend a sports event with the same evening round trip being enough to take one across many European countries.

I'll think you'll find that not much of the total HCL escapes from the concentrated solutions in normal use, it doesn't take much HCl to cause rusting or to choke you up.

Endimion17 - 20-8-2011 at 07:33

In general, if it's economically feasible, it's out there. But 37% isn't out there, and somehow I think it's like that in most of Europe.
Then sulphuric acid would be sold at 96%, and the end user would be expected to dillute it. But that's not the case. It's sold as weaker "battery acid". The same goes for nitric and phosphoric acid. They're all dilluted. They're dilluted at the factory, and there are lots of factories which produce hydrochloric acid in the 300 km radius.

Of course, you can buy bigger tanks (50 L, 100 L or more) of concentrated acids with technical purity, but you need some papers, and the buyer would probably always have to be a legal entity.
As for individuals going to shops/malls to buy something, 9 and 19% HCl are the limit.

If you need small quantities of reagent grade acids, you can get concentrated acids without any problems, but the conditions are the same as for big tanks I've described above.

I simply don't understand how is it possible to sell such a hazardous liquid to just anyone. 37% HCl is some scary shit indeed.

blogfast25 - 20-8-2011 at 09:53

Quote: Originally posted by Endimion17  
In general, if it's economically feasible, it's out there. But 37% isn't out there, and somehow I think it's like that in most of Europe.
Then sulphuric acid would be sold at 96%, and the end user would be expected to dillute it.


I can buy cheap (and good) HCl 36 %, 25 L (although I buy 5 L) from a Scottish chemical distributor. Ditto 96 % H2SO4... And 70 % HNO3... No problemo.

And conc. HCl really is the best for a large number of applications, such as dissolution of metals, reactive oxides etc. Use reflux if you don't want to smell it. In industry the use of concentrated solutions is preferred: much 'easier' to manipulate smaller volumes of liquid than larger ones. Space (hence volume) comes at a premium...

[Edited on 20-8-2011 by blogfast25]

Endimion17 - 20-8-2011 at 13:03

^^That was not even my point. I can buy it in my country, too. But not in a regular store.
I was talking about concentrated HCl in hardware stores and generally - stores, where you can come and just buy it. I find it unbelieveable and somewhat irresponsible. To me, it's like buying concentrated nitric acid in a grocery store.
I expect there should be a history of HCl related accidents at home in such countries.

AJKOER - 20-8-2011 at 15:18

Here is a crazy way to make pure HCl from the impure Muriatic acid without distillation. Place a small container with Bleach (composed of NaClO and NaCl and a little NaOH) and Muriactic acid that has a small hole into a large baloon or bag containing ice from distilled water and dilute H2O2. Seal the large baloon/bag container to keep in the generated Chlorine and oxygen. Reactions:

NaClO + HCl -> NaCl + HClO [1]
HClO + HCl <--> Cl2 + H2O [2]
HClO + H2O2 --> HCl + H2O + O2 [3]

So per reactions [1] and [2], the small container generates Cl2. The Cl2 is absorbed into the ice forming HCl and HClO at the bottom of the larger baloon/bag. Shaking may aid in the absorption of the Chlorine. The H2O2 generates O2 after converting any HClO into HCl per [3] and will not be absorbed. Wait several hours before opening/breaking the baloon/bag in a large container (preferably sealed) outdoors to address any splash issues.

Do this reaction outside as Cl2 may escape due to a container rupture.

Now, advantages of this procedure, no distillation equipment required and 1/3 of the Chlorine in the produced HCl comes from the bleach.
Disadvantages, must calculate the volume of Cl2 and O2 produced to avoid a gas generation that could rupture its container. One would also be working with gases under pressure which is inherently dangerous, so safety gear is a must.

One could also have a design where the Muriatic acid very slowly drips and reacts with the NaClO. This would give time for the Cl2 generated to be absorded making for a safer experiment.

[Edited on 20-8-2011 by AJKOER]

Gui316 - 21-8-2011 at 02:48

That sounds quite complicated. But I'll try it. Freezing the hydrogen peroxide will be a problem...Just more one thing: If I generate chlorine gas from muriatic acid and TCCA in a vacuum flask, and then bubble the chlorine gas into water, would I get HCL?

bbartlog - 21-8-2011 at 04:26

No, as AJKOER describes, H2O + Cl2 -> HCl + HOCl, and that's an equilibrium reaction (can just as easily go the other way). That's why he suggests adding H2O2 to decompose the HOCl as it is formed. Seems like a cockamamie way of getting HCl but by all means go for it...

not_important - 21-8-2011 at 06:34

Alternatively:

1) scrounge a used photovoltaic array

2) make a small electrolytic cell that will be powered by the PV array, using aqueous NaCl as the electrolyte

3) Feed the Cl2 from that into an absorption cell containing water, and placed where sunlight will strike it Give it an exit port with a bubbler to give one-way gas flow. The reactions here will be

Cl2 + H2O <=> HCl + HOCl

2 HOCl => 2 HCl + O2

for an overall reaction 2 Cl2 + 2 H2O => 4 HCl + O2

with the O2 being vented out the exit port.

The reaction is very slow in the dark, but then the PV won't be putting out any power to make Cl2 during dark periods either. Change out the electrolysis electrolyte ever so often to replenish the NaCl supply and avoid the NaOH concentration from getting too high.

Salt, water, and sunlight in; HCl(aq) out. Just takes patience to let the rig do its task.

blogfast25 - 21-8-2011 at 07:40

@not_important:

Sounds more like an interesting engineering problem to me...;)
Quote: Originally posted by Endimion17  

I expect there should be a history of HCl related accidents at home in such countries.


In this country I know of only one case (there must be others, of course) and that involved malicious intent. Someone poured 96 % H2SO4 down a toilet w/o telling the targeted person. Unaware of the cause of initial irritation, severe burns on the victim resulted after a while.

Conc. HCl stinks a lot but is pretty safe to use with some decent precautions. It’s replacement with other, milder products has more to do with stench than safety, IMHO.



[Edited on 21-8-2011 by blogfast25]

Gui316 - 21-8-2011 at 07:44

Uhmm...That sounds even more complicated than the ballon idea.
But what I've suggested was making chlorine gas using trichloroisocyanuric acid and HCl, then bubbling the chlorine gas into water, using a similar apparatus as shown on this video:

http://www.youtube.com/watch?v=Yr4GgzVlmmw

(go to 1:20)

Instead of ammonia nitrate and sodium hydroxide, I would use TCCA and HCl.

Endimion17 - 21-8-2011 at 07:47

Quote: Originally posted by Gui316  
That sounds quite complicated. But I'll try it. Freezing the hydrogen peroxide will be a problem...Just more one thing: If I generate chlorine gas from muriatic acid and TCCA in a vacuum flask, and then bubble the chlorine gas into water, would I get HCL?


I would advise you to learn some basic inorganic chemistry before even attempting to mess with chlorine.
Disproportionation of chlorine in water to chloride and hypochlorite ions is one of the fundamental reactions of chlorine chemistry, and people who don't know that should never do anything with chlorine.

Chlorine is a serious acute poison which can act with a delay (pulmonary edema). It's just one step away from the notorious elemental fluorine.
Quote: Originally posted by not_important  
Alternatively:

1) scrounge a used photovoltaic array

2) make a small electrolytic cell that will be powered by the PV array, using aqueous NaCl as the electrolyte

3) Feed the Cl2 from that into an absorption cell containing water, and placed where sunlight will strike it Give it an exit port with a bubbler to give one-way gas flow. The reactions here will be

Cl2 + H2O <=> HCl + HOCl

2 HOCl => 2 HCl + O2

for an overall reaction 2 Cl2 + 2 H2O => 4 HCl + O2

with the O2 being vented out the exit port.

The reaction is very slow in the dark, but then the PV won't be putting out any power to make Cl2 during dark periods either. Change out the electrolysis electrolyte ever so often to replenish the NaCl supply and avoid the NaOH concentration from getting too high.

Salt, water, and sunlight in; HCl(aq) out. Just takes patience to let the rig do its task.


That is extremely inefficient reaction.

I mean, come on. Powering a chloralkali cell with a PV cell?
Chloralkali factories are one of the largest users of electricity and are often placed close to hydroelectric power plants. They require huge amounts of electricity (kiloampere connections). I have no idea why is everyone around here so hooked to PV. It's for powering buoys and remote sheds, not for electrolysis of brine.
And the cost? If he wanted to make half liter of HCl in a matter of few days, the cell would have to be at least one square meter big. And that's expensive.
It's economically inefficient to produce HCl in such manner at industrial scale, let alone on a small scale. For the money spent on this setup he could buy a lifetime stock of the acid.

Setup you depicted here is so slow that HCl would vent out a lot quicker than the chlorine would be produced.

Gui316 - 21-8-2011 at 07:57

I know about chlorine. I had problems with it. 2 times. I don't want that to happen to my worst enemy. Feels like death. But I'm aware know, I got a mask, and from now, I'll aways be careful when messin with chlorine. Just relax and enjoy. It is absolutely not necessary to get angry. Peace.

Endimion17 - 21-8-2011 at 08:04

Quote: Originally posted by Gui316  
I know about chlorine. I had problems with it. 2 times. I don't want that to happen to my worst enemy. Feels like death. But I'm aware know, I got a mask, and from now, I'll aways be careful when messin with chlorine. Just relax and enjoy. It is absolutely not necessary to get angry. Peace.


I was not angry. I was upset. It truly feels like death, doesn't it? And it's scary because it's painful.

Just do the "homework" before you attempt any reaction involving chlorine. It's very reactive.
It would be the best if you did it outside, just watch for the sunlight, as chlorine turns to beast then illuminated by the Sun. It can make organic gases detonate.

Otherwise, do it indoors with strategically placed fans which create an air current or lower pressure in the room, so that everything gaseous moves away from you and exits the room. :)

Gui316 - 21-8-2011 at 08:18

Okay, I'll do it and I'll be careful. I was just wondering if bubbling Cl2 on water would give me a good yield... Thank you for your advises. But now is my time to help you. Go outside. Take a deep breath. Drink a beer or maybe a juice if you don't enjoy alcohol. Breath again. Then thank me xD



[Edited on 21-8-2011 by Gui316]