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Author: Subject: HCl by PVC-decomposition
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[*] posted on 4-10-2008 at 01:58
HCl by PVC-decomposition


When I was a kid I would, for my experimenting, make the HCl by dry-distillation of PVC-plastique ... until I read somewhere, that dioxine may be formed ...
Fortunately I had done only small amounts ... but it is an effective way to get HCl !
Can it be done safely (??), eg. temperature controlled, steam filtered ... ? Then good HCl would be everywhere ...

When I did it -- it worked ! I'm not too sure, where the hydrogen came from, but the HCl was dissolved into water (one testtube dry-distillation, bubbling into another testtube with water).

The HCl may have had 10 % (estimated from the CO2-generating-power when put onto some materials) and was useful, eg. for FeS + 2 HCl ==> H2S + ... ;
Maybe it was not fully chlorinated PVC;
perhaps the PVC might be mixed eg. with Poly-Ethylene, or Parrafine, before dry-destilling ? That might also make the process cleaner ...

[Edited on 4-10-2008 by chief]

[Edited on 4-10-2008 by chief]
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[*] posted on 4-10-2008 at 05:13


I would expect distillation of PVC to release vinyl chloride among other things, and this is a carcinogenic gas.

A lot of Thai construction workers who are used to cooking rice in large bamboo tubes, have died after trying to cook rice in PVC plumbing pipe.

So I would advise against this, and I think vinyl chloride would be the immediate concern. The "dioxine" is tetrachlorodibenzodioxane and that does not form from pyrolysis of PVC. It is a byproduct of the manufacture of weed killers, specifically 2,4-D and 2,4,5-T which are chlorinated phenoxyacetic acids. The side reaction to form the tetrachlorodibenzo-p-dioxane ought to be obvious to you from the structure.




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[*] posted on 4-10-2008 at 05:52


Phosgene is another very toxic possible product of the decomposition of chlorinated hydrocarbons in the presence of oxygen or steam, probably PVC included. This does react with water to form HCl but if any makes it out you'd better have some sort of scrubber system. Phosgene has very poor warning characteristics and can be deadly at 5ppm for 1 hour. Using an excess of steam should eliminate its formation, but you should probably treat the exhaust gas as if it were highly toxic anyway and run it through a strong alkaline scrubber in a fume hood or outdoors.

Quite frankly there are far better ways to produce HCl.




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[*] posted on 4-10-2008 at 07:08


Amen to that, KW!



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[*] posted on 4-10-2008 at 15:50


Seems I had the most stupid idea around ...
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[*] posted on 5-10-2008 at 00:29


No need to kick yourself, you had the excellent sense to ask before trying it, didn't you?



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[*] posted on 5-10-2008 at 02:35


I did it (!) when I was a teenager and experimenting; no sources of HCl or HNO3 were available ...
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[*] posted on 5-7-2012 at 08:49


I will post in this old thread since I think it is a good method to produce HCl gas. I have used it quite a lot...
It is important, however, to exclude oxygen from the PVC (otherwise You will get dioxanes) and keep the temperature at 300-350 C. With these conditions, HCl can be isolated in very pure form (this is how it is done in PVC recycling plants).. In order to get rid of the oxygen, add some hydrocarbon, such as petrol, which will distill over to the water filled receptacle first and of course fill the still with hydrocarbon gas, driving out the oxygen. The yield are surprisingly good as PVC "contains" about 50% HCl




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[*] posted on 5-7-2012 at 08:59


Quote: Originally posted by Yo-Yo  
I will post in this old thread since I think it is a good method to produce HCl gas. I have used it quite a lot...
It is important, however, to exclude oxygen from the PVC (otherwise You will get dioxanes) and keep the temperature at 300-350 C.


I have tried this recently on very small scale, 35g of PVC. A 100ml gas wash bottle gets detectably warm from the absorption of HCl. I used a throw-away distilling flask (a 30ml Kjeldal), because I didn't expect it would be possible to clean up the residue. Did you find a better vessel than glass? How are you heating it?
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[*] posted on 5-7-2012 at 09:39


I use pyrexflasks heated in a sandbath on a gas burner. I use a piece of lead (MP 327) in a small hole in the sand as temp control. When the lead has melted, stop heating, when the lead solidified, start heating. When you think most of the HCl has been extracted, remove the receptacle and change it to another.Increase the heat for a while, which will get rid of some of the black goo in the still, and coincidently gives you a small amount of probably very nasty hydrocarbons . After the still is cool, try to get as much goo out as possible. Of course the still can not be used for anything else, but it can be reused for the same procedure.



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[*] posted on 5-7-2012 at 09:47


You certainly get HCl from distilling/pyrolysing PVC.
You also get benzene.

(Based on the lab where I work identification of plastics by pyrolysis IR)
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[*] posted on 5-7-2012 at 09:58


You do get benzen, and several hundred diffrent hydrocarbons, but most of them forms after/at higher temperatures than the dechlorination reaction. The nice thing with the method I use is that the small amount formed during dechlorination, will be extracted into the petrol that I used in order to get the oxygen out of the still.



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