Adapting the chlor-alkali process for nitrates

[cvsanchez]

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?

 

[Borek]

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]

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?

 

[Borek]

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]

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.

 

[Borek]

To some extent it should work. However, I suppose electricity cost will be higher that just buying KOH.

 

[cvsanchez]

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

 

[The_architect]

To some extent it should work. However, I suppose electricity cost will be higher that just buying KOH.

to address this you could buy cheap chipped solar cells on someplace like evilBay, and I am reading this because I am also considering using the membrane cell system to crack salts other than sodium chloride as well as possibly using it to crack copper sulfate, leaving the sulfate behind to further strip copper off disconnected copper traces on circuit boards, this way the copper being refined doesn't have to be connected to the electrode on the sacrificial tank side, and should make mining hard to process copper that normally just gets tossed in a land fill or sent to a third world country where they burn the whole thing putting all the toxins you can imagine that come off say burning an iPhone.

One thing I seem to be seeing useful also that might cause an issue, is the energy levels of different elements, like say my idea of a copper refining process that gets say some brass in it, if this happens in the middle of the process then I am going to get a layer of zinc on my electrode since zinc will kick the copper out of the solution then be the metal being pushed (or pulled) across the bridge until it is all gone, while sounding cool if I need pure copper this would be a disaster, and other elements are the same way, so you would have to make sure your nitrogen is the higher state element I guess before any other similar elements in the other tank.

on the solar cell idea, you are using DC power here, and that is what they produce, and the cells themselves are pretty cheap (4000kW worth for $650 or $15 for 70w for smaller experiments) its the batteries and inverters that most people are factoring in for household power that drive the cost of going solar that you are able to remove from your process keeping it cheap, For our processes I would guess just having a step down voltage regulator and enough cells in series to get enough voltage for our needs even in dimmer evening conditions should work fine.