Adapting the chlor-alkali process for nitrates


by cvsanchez
Tags: adapting, chloralkali, copper nitrate, electrolysis, nitrates, potassium nitrate, process, salt bridge
cvsanchez
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Dec5-13, 12:04 PM
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I recently became interested in the chlor-alkali process, specifically the one using a salt bridge, and wondered if I could adapt the setup to synthesize other salts. I have KNO3, but want to remove the nitrate ion and bind it to some other metal, such as copper, and be left with KOH. Of course, this won't work in a regular cell as Cu(OH)2 will just precipitate out. However, I was thinking I could use a salt bridge and set up the cell as follows to produce the Cu(NO3)2:
Cell 1 has the KNO3 solution with a PbO2 anode (+) while cell 2 is a pure water solution with a Cu cathode (-). The cells are connected via a salt bridge (NaCl maybe?) and powered by a 9.6V battery. Would a cell set up like this produce KOH in cell 1 and Cu(NO3)2 in cell 2? If not, why?
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Borek
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Dec5-13, 12:37 PM
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This is messy, I have a feeling you don't understand the chemistry behind the electrolytic processes. What you describe has nothing to do with the chloralkali process, nor with the electrolytical processes in general.
cvsanchez
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Dec5-13, 02:33 PM
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Quote Quote by Borek View Post
This is messy, I have a feeling you don't understand the chemistry behind the electrolytic processes. What you describe has nothing to do with the chloralkali process, nor with the electrolytical processes in general.
I realized that I did actually make a mistake when describing my cell idea, but before that let me make sure that I'm understanding the chlor-alkali process...
As far as the salt bridge method goes, my understanding is that there are carbon electrodes, one in each cell. Cell 1 contains a solution of NaCl while cell 2 contains just water and the two cells are connected by an NaCl salt bridge. The anode (+) is the carbon rod in Cell 1 and the cathode (-) is the carbon rod in cell 2. Once the power is connected, Na+ ions flow through the bridge into cell 2, where water had been being split into H+ and OH- ions. The H+ ions are drawn to the cathode, where they are reduced and released as H2 gas, leaving behind aqueous NaOH. Meanwhile in cell 1 the Cl- ions are drawn to the anode where they are oxidized and (for the most part) released as Cl2 gas. I attached a quick illustration to help explain how I understand it.

As far as the KNO3 cell goes, my mistake was a mix-up with where the electrodes are positioned. It should have been like this: Cell 1 has a copper electrode and KNO3 solution while cell 2 has a carbon electrode (I thought you could use PbO2 but there may be a reason not to) and water. The salt bridge also uses KNO3 instead of NaCl. So the potassium ions should flow across the salt bridge into cell 2 and form KOH(aq) and H2 gas while the nitrate ions should react with the Cu to produce Cu(NO3)2 (aq).

Is my understanding of the chlor-alkali process correct and should the KNO3 cell function as I expect?
Attached Thumbnails
Chloro alkali process salt bridge.png  

Borek
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Dec7-13, 02:10 AM
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Adapting the chlor-alkali process for nitrates


Quote Quote by cvsanchez View Post
Is my understanding of the chlor-alkali process correct
Looks much better now.

and should the KNO3 cell function as I expect?
What is stopping copper from moving to the right cell?
cvsanchez
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Dec7-13, 10:21 AM
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Quote Quote by Borek View Post
What is stopping copper from moving to the right cell?
Good point, I forgot that the copper would be pulled to the right as well since it's aqueous. What if I were to use only carbon electrodes instead of having one copper? I did some research to try to find out what kind of gases would evolve at the anode, and it seems like only oxygen would be given off, leaving behind the nitrate ion. So with carbon electrodes, it looks like the potassium and the nitrate ions are simply separated into each cell. However, I feel like there's some property I'm overlooking that would prevent this from actually happening.
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Dec7-13, 11:01 AM
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To some extent it should work. However, I suppose electricity cost will be higher that just buying KOH.
cvsanchez
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Dec7-13, 11:19 AM
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Quote Quote by Borek View Post
To some extent it should work. However, I suppose electricity cost will be higher that just buying KOH.
It most likely will, though I want to use this cell more to isolate the nitrate ion for synthesis of other nitrates rather than producing KOH. If I wanted to produce KOH then I'd just use KCl and it would run exactly like the standard chlor-alkali process just with potassium. Since the KNO3 is pretty much my only source of nitrate, I've been trying to strip the nitrate to recombine it with another metal such as copper.

So this process should separate nitrate ions from the potassium to some extent (perhaps forming a very dilute nitric acid?), though consumes a great deal of electricity. Since my ultimate goal is really to just strip the nitrate ion, should I instead create a new thread focused on that? It seems like it would be a little too general of a question


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