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Author: Subject: A slightly dangerous but surprisingly effective way to make HCl
mysteriusbhoice
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[*] posted on 11-9-2020 at 23:15
A slightly dangerous but surprisingly effective way to make HCl


This setup uses a membrane chloroalkali cell which produces Cl2 and H2 and then is hooked up to a bubbler and sent to a quartz tube next to a UVC lamp which produces HCl via these reactions.
HOCl + O3 = HCl + O2
H2 + Cl2 = HCl
The bubbler and the cell produces HOCl along with Cl2 also called wet chlorine.
Cl2 + H2O = HCl + HOCl

overall this process doesnt seem to happen explosively due to the existence of HOCl in the system but the gases produces can still ignite violently and detonate so avoid any sources of ignition.
A future cell using mmo will have a PVC enclosure for the UVC lamp with input for gas and output for HCl liquid and vapor.

Video link below
https://youtu.be/SHX7EDW2hLw



HCl gen.jpg - 59kBHCl gen2.jpg - 62kB
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mysteriusbhoice
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[*] posted on 15-9-2020 at 11:19


Fuming HCl produced after 11 hours of runtime.
https://youtu.be/kMKDrHb4W7Q
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metalresearcher
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[*] posted on 15-9-2020 at 11:42


What kind of membrane do you use ? Because a membrane is mandatory to prevent the OH- reacting with the Cl2 gas.
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mysteriusbhoice
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[*] posted on 15-9-2020 at 12:59


Quote: Originally posted by metalresearcher  
What kind of membrane do you use ? Because a membrane is mandatory to prevent the OH- reacting with the Cl2 gas.

PVA + BORAX on synthetic cloth scaffhold

vid guide below
https://www.youtube.com/watch?v=dR7fW5J7njA
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Syn the Sizer
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[*] posted on 15-9-2020 at 13:51


I much prefer the safer OTC method of reacting sodium bisulfAte with NaCl products are sodium sulfate and HCl vapour. Of course this will also work with H2SO4 with much better results. Though I just get muriatic acid from Canadian Tire for $15/4L
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mysteriusbhoice
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[*] posted on 15-9-2020 at 18:45


Heres my homemade HCl 24 hours runtime its already fuming like in the vid shown.

fumefume.jpg.png - 767kB
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[*] posted on 16-9-2020 at 03:59


Nice, well done.
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mysteriusbhoice
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[*] posted on 18-9-2020 at 01:09


after tweaking the cell a bit and messing with membranes and additives and current density to prolong the operating time I got 2 nice bottles of fuming 12 molar HCl.

HCl.jpg.png - 634kB

I got these by running the setup till HCl vapor was comming out of the 2nd hose in large amounts enough to turn the cumene test strip and pH paper a nice red.

[Edited on 18-9-2020 by mysteriusbhoice]
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mysteriusbhoice
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[*] posted on 19-9-2020 at 02:12


Cost of production 82 Cents per liter of 37% HCl!!
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macckone
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[*] posted on 19-9-2020 at 20:29


What temperature did the pva membrane start failing at?
Was it the base material that failed or the pva started dissolving?
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mysteriusbhoice
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[*] posted on 19-9-2020 at 20:50


Quote: Originally posted by macckone  
What temperature did the pva membrane start failing at?
Was it the base material that failed or the pva started dissolving?

the failure conditions are still unknown because upon testing the membrane fails at temp 95 Celsius when slowly heated on a pot of water on the stove.

The membrane however fails in the cell if I let it run for too long but if I drain it after current reaches a certain value of 5 amps then it wont fail and ive done 3 cycles so far and it didnt fail doing that.

The question is whether its current density that caused failiure or concentration gradient and hence now im running at lower voltage which means lower current and if it still fails or fails before the previous value of current then it will be current density.

The PVA itself failed the base material remained if you used synthetic fabric.

The mode of failure seems to be that the PVA is getting disloged and ends up precipitating or floating around in the cathod chamber only!.
My guess is the current flow being too high caused the ions to migrate even the polymer but I cant say for sure.

addition of copper chloride prevents buildup of hypochlorites in anode chamber.


[Edited on 20-9-2020 by mysteriusbhoice]
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Pumukli
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[*] posted on 19-9-2020 at 22:33


Nice to see this process working!

On the other hand, don't bee fooled by the apparent safety of the reaction! H2 and Cl2 does explode on illumination by a strong light source. (Visible light suffice.) Been there, done that. Keep this in mind before making adjustments to your reactor! :-)
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mysteriusbhoice
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[*] posted on 19-9-2020 at 22:36


Quote: Originally posted by Pumukli  
Nice to see this process working!

On the other hand, don't bee fooled by the apparent safety of the reaction! H2 and Cl2 does explode on illumination by a strong light source. (Visible light suffice.) Been there, done that. Keep this in mind before making adjustments to your reactor! :-)

I know that this can happen suddenly and hence theres now a shield ontop and a pool of water below.
I will even add a safety blow plug and hose in the final design for extra safety and it will be tested by detonation of gas inside.

The risk of this is with higher flow rate of input gas and yes the exit gases are still combustible but not explosive like the input gas when tested in soapy water.

[Edited on 20-9-2020 by mysteriusbhoice]
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[*] posted on 19-9-2020 at 23:25


The problem of failure of the PVA seems to be current density because after running it for really long continiously keeping the current below that value at which it failed it got to a higher concentration and didnt fail completely.
The PVA in the cathode chamber seems to fail tho anyway but the anode chamber looks solid even at higher concentration gradient and since the anode chamber membrane is still intact then I now calculated the current density of the membrane of the anode chamber at which it seems to fail and it looks like its around above 58.4ma/cm^2.
my current operating current density is 51.66ma/cm^2
this is the borate membrane have to test the citrate and terephthalate membrane failure current density but the citrate seems to fail at higher current density but its not easily repairable unlike borate so I will switch to that once care is taken to know the exact value at which it fails probably once I get my variable current regulated power supply.
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[*] posted on 20-9-2020 at 02:53


It sounds like there are three potential failure modes.
1) temperature gets too high (95C+)
2) sodium hydroxide concentration gets too high (commercial membranes fail at around 10%)
3) the current density is too high (58ma/cm^2)

A possible mechanism for the third failure mode is the mobilization of borate ions.
This would lead to depletion on the cathode side.
Since borate is responsible for the stability of the PVA film, its depletion would result in the film failing.

At some current density various nafion membranes fail as well.
So this is expected.
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mysteriusbhoice
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[*] posted on 20-9-2020 at 03:16


I have a new membrane that doesnt fail easily its Citrate crosslinked PVA and Terephthalate crosslinked PVA but if they fail these membranes are harder to repair and unlike borate in which addition of borates into electrolyte mitigates 1 of those failures and borate membranes can be repaired in 30 seconds and used right away.
The NaOH definitely plays a role in fking up my membranes.
unless I can somehow think of a way to pump the NaOH out of solution and replace it or just increase the size of the cathode chamber so it can be run on batch mode which is what I was thinking of in the final design.

The final design will be a 4 Liter cell like my chlorate one and the center will be anode and the 2 side compartments will be NaOH and membranes would be PVA Citrate and using a current regulator buck converter set to a stable output at higher voltage I can essentially keep current constant and calculate the run time based on when the cathode compartment gets to around 9.5% NaOH by wt.

[Edited on 20-9-2020 by mysteriusbhoice]
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[*] posted on 20-9-2020 at 11:05


Nice.

Could you, hypothetically, control the NaOH concentration by dripping in fresh solution from above and draining the used solution below?
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papaya
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[*] posted on 20-9-2020 at 12:17


Quote: Originally posted by mysteriusbhoice  
I have a new membrane that doesnt fail easily its Citrate crosslinked PVA and Terephthalate crosslinked PVA but if they fail these membranes are harder to repair and unlike borate in which addition of borates into electrolyte mitigates 1 of those failures and borate membranes can be repaired in 30 seconds and used right away.
The NaOH definitely plays a role in fking up my membranes.
unless I can somehow think of a way to pump the NaOH out of solution and replace it or just increase the size of the cathode chamber so it can be run on batch mode which is what I was thinking of in the final design.

The final design will be a 4 Liter cell like my chlorate one and the center will be anode and the 2 side compartments will be NaOH and membranes would be PVA Citrate and using a current regulator buck converter set to a stable output at higher voltage I can essentially keep current constant and calculate the run time based on when the cathode compartment gets to around 9.5% NaOH by wt.

[Edited on 20-9-2020 by mysteriusbhoice]


I want to ask you, have you ever tried the Na-CMC based membrane composition (which I proposed in other thread weeks ago), if yes - what are results ? interesting to compare, since evidently you got very well versed in such things, good to know your opinion.
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mysteriusbhoice
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[*] posted on 20-9-2020 at 12:34


I havent found that ice pack containing CMC but I think it is sold on amazon so il try that when I can buy some but these times be rough for international online shopping.
I will be trying Terephthalic acid-PVA membranes next which is easy for me to make now!
Just like the citrate it is probably also strong against acids but im hoping it also lasts longer.
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papaya
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[*] posted on 20-9-2020 at 12:39


Where I live it's sold as a wallpaper adhesive (dry form almost like sawdust), used in renovation etc. Very cheap stuff, can always be found in stores where things like paint plaster etc is sold. But anyway, thanks for reply!

[Edited on 20-9-2020 by papaya]
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[*] posted on 20-9-2020 at 16:37


Na-CMC is going to be problematic outside of a solution that is closer to neutral.
Sodium Hydroxide is pretty aggressive towards cellulose.
Acids can degrade it as well.
Since it is modified cellulose it may hold up ok but I would not bet on it.
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mysteriusbhoice
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[*] posted on 20-9-2020 at 19:11


about removing NaOH from the reactor I can probably hook up a reservoir of water and a pump and also some aquarium tubes with a tap at the bottom which can be opened after every few hours to replenish the electrolyte.

or I could also just do that manually but overall id rather not open the cell XD because obvious reasons usually the chlorine released while opening is........ bad
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[*] posted on 20-9-2020 at 21:39


You may want to use something a bit sturdier than aquarium tubing.
I tend to use HDPE ice maker tubing.
It is less flexible than the the clear pvc but it handles vacuum.

You could put a suction tube and an addition tube in through the lid.
Suction off the hydroxide and add water in measured amounts.
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mysteriusbhoice
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[*] posted on 20-9-2020 at 21:48


would aquarium pumps be fine handling the highly caustic NaOH solution though??
my other idea is to simply use the static head of the water by raising the cell and installing a bottom tap with a valve or plug.

btw borate membranes are pretty robust with boric acid additive in anode chamber which the acid form can crosslink PVA and hence stays in the anode chamber dissolved.
I had one membrane run for 2 days with only a minor tear when it failed at the bottom due to mechanical stress when I manually drain the fluid in the cathode side alone every cycle of dumping the contents of NaOH.

[Edited on 21-9-2020 by mysteriusbhoice]

membrane 2 cycles.jpg - 32kB
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[*] posted on 21-9-2020 at 06:20


You would probably be better served with a siphon type arrangement.
You can modify an aquarium pump to act as a vacuum.
The intermediate vessel can then be emptied without impacting the cell.
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