Sodium chlorate cell questions.

[THEONE]

I am planning to drive it wth 3-4 amps max and always keep feeding the solution with Naclo3. Also I may add some caps with couple μF to smooth the current. Thanks for the tips.

 

Edit: I have seen voltages from 5v to 7v for perchlorate cell. Which voltage is the ideal ?

Edited December 13, 2019 by THEONE

[WSM]

I am planning to drive it wth 3-4 amps max and always keep feeding the solution with Naclo3. Also I may add some caps with couple μF to smooth the current. Thanks for the tips.

Edit: I have seen voltages from 5v to 7v for perchlorate cell. Which voltage is the ideal ?

 

When I last ran my perchlorate cell, it ran at roughly 4 Vdc. The current level was between 1 to 1.5 Amps per square centimeter. It was slow but it ran without much trouble.

 

WSM

[THEONE]

I guess the lower the voltage the better for minimum erosion of the electrode, right? So 4v are ok for perchlorates, interesting. Thanks

 

Edit: My platinum electrode is 2x3 inches so it has an area of 6x2,54= 15.24cm^2. Despite that i am planning to run it at 4 amps max because i dont want to damage it due to excessive current.

Edited December 13, 2019 by THEONE

[WSM]

I forgot to mention, the power supply I used was run in constant current mode. The cell held roughly 3-4 liters of electrolyte and worked quite well.

 

WSM

[markx]

I guess the lower the voltage the better for minimum erosion of the electrode, right? So 4v are ok for perchlorates, interesting. Thanks

 

Edit: My platinum electrode is 2x3 inches so it has an area of 6x2,54= 15.24cm^2. Despite that i am planning to run it at 4 amps max because i dont want to damage it due to excessive current.

 

Literature seems to hold contradicting information about the optimal cell voltage regarding perchlorate electrosynthesis with bulk of the references ponting towards voltages in excess of 5V. But my personal experience so far seems to point towards the range between from 4 up to 5V. That applies to platinized titanium substrate anodes....I have not used thick Pt clad or pure bulk Pt anodes. Applying in excess of 5V across the cell shall markedly increase the rate of anode passivation when a Ti substrate is involved, but 4+V seems to work very neatly as far as longevity and yield goes.

 

Also a word of warning regarding constant current mode: the most likely failure mode of the perchlorate cell will be the passivation or otherwise degradation of the anode. It shall manifest itself as an increasing summary resistance of cell system that is connected to the power supply. The supply shall raise the output voltage in response....in order to drive the same amperage through the system. This in turn will accelerate the failure of the anode because of higher polarisation values due to the increased cell voltages. Up to the point of maximum output voltage of the power supply and this can be as high as 40-50V when "garden variety" CC modules or supplies are used.

I managed to boil and melt a small plastic perchlorate cell that I was driving in CC mode. The anode gradually failed and the supply increased the voltage up to the point where the cell boiled, melted and metallic Ti started to dissolve under the immense anodic potential.

In constant voltage mode this kind of a series of unfortunate events is impossible, as the cell current would simply start to decrease in response to a failing anode. Surely the current may increase to some extent if the cell warms up in CV mode, but I've yet to see it raising to dangerous levels. But a generic CC setup without appropriate failsafes is more than able to completely destroy the cell internals if left unsupervised.

[TomasBrod]

Seller of the electrodes on Ebay is Feanor and he is a regular in the other APC discord. References to persulphate additive, that Feanor recommends, can be found on the Chlorates and Perchlorates page and in Patent 2813825. (links should be clickable)

I bought some sodium persulphate from a chemical distributor, and I am planning to use it in a future experiment.

[THEONE]

I am running now the Nacl cell for a couple of days and a really strange thing happened. A lot of ppt came out of electrolyte, i dried a sample of it and tried to burn it with sugar but nothing. The electrolyte looks oily, i guess most of the Naclo3 is there but i have no idea why all that salt ppt out, and the more the cell runs the more ppt out. My only guess is that as long as the cell runs, Naclo3 concentration increases and Nacl ppt out, i am not sure though. Any ideas?

 

Edit: I just boiled off some electrolyte and it looks like it is full of chlorate, from a small volume of electrolyte i got a big amount of salt. Test with sugar it barely burned so maybe there is some Nacl i am not sure. Anyway my conclusion is Nacl is a lot more of a pain compared to Kcl unfortunately. I am seriously thinking to just forget about Nacl due to its difficulties.

Edited December 16, 2019 by THEONE

[markx]

The sodium route is viable if one further proceeds to create perchlorates by electrosynthesis....or for synthesis of other chlorates via metathesis methods. Although it is a major pain to get rid of the sodium impurities to the extent that they do not disturb flame colors.

 

I have not witnessed the formation of percipitate during NaClO3 synthesis so far, but during perchlorate synthesis stage there seems to arise a situation (if highly concentrated stock solutions are used) where either the perchlorate or chlorate tends to temporarily percipitate out in large cristals that redissolve as the synthesis proceeds towards the rise of perchlorate content in the cell liqour.

[THEONE]

Thanks markx for the info. It is obvious that the Naclo3 ppt out is a myth. Nacl ppt out the more the electrolyte become saturated with Naclo3. I am actually thinking to use now that electrolyte for Naclo4 because it is saturated with Naclo3. It looks like oil due to saturation.

[WSM]

Thanks markx for the info. It is obvious that the Naclo3 ppt out is a myth.

The sodium salts (chlorate and perchlorate) are more and more soluble as the oxygen levels increase, so they naturally dilute themselves as the cells run.

 

With so much extra water, the chlorate won't drop out until the concentrations are MUCH higher.

 

The trick I used to harvest sodium chlorate crystals from the saturated electrolyte, was to put the solution in a refrigerator at about 0 degrees C, and wait for one to three days, and the crystals grew. It didn't remove all the chlorate, but the remaining electrolyte is then saturated with brine and run again, and produces more chlorate quicker than the initial run.

 

FYI

 

WSM

[WSM]

When harvesting sodium chlorate, the reason I chose Zero degrees Celsius is the chlorate will crystallize out while leaving the sodium chloride in solution. It's a natural way to separate them.

 

WSM

[THEONE]

WSM have you got any point on where to stop the electrolysis for harvest? I guess a density measurement will be quite acurate

[Arthur]

The important thing to notice is the change of solubility with temperature of the chloride, chlorate and perchlorate salts. The chlorides have almost the same solubility in water at any temperature, the oxidised salts have a much steeper solubility change with temperature. SO as you cool the mixed solution the chloride stays in solution BUT the chlorate/perc will crystalise out if they are concentrated enough.

[WSM]

WSM have you got any point on where to stop the electrolysis for harvest? I guess a density measurement will be quite acurate

 

The density measurement works with a potassium cell because most of the KClO3 drops out as it forms, continually changing the density of the electrolyte.

 

My remembrance is that this won't work the same in a sodium chlorate cell, since everything stays in solution.

 

WSM

Edited December 18, 2019 by WSM

[WSM]

The important thing to notice is the change of solubility with temperature of the chloride, chlorate and perchlorate salts. The chlorides have almost the same solubility in water at any temperature, the oxidised salts have a much steeper solubility change with temperature. SO as you cool the mixed solution the chloride stays in solution BUT the chlorate/perc will crystalise out if they are concentrated enough.

That's right.

 

One method of increasing the concentration is to boil away excess water in the solution. I haven't done this but I'm told it works. I think the temperature will stay low enough while the water boils, but do be careful.

 

WSM

[Arthur]

Swede's work in blog and posts on here gives the number of amphours needed to convert grammes of chloride to chlorate or perchlorate.

 

If you find this calculation and use it to give a 100% completion time for all the chloride to be converted you should -accounting for inefficiencies have a nice safe quantity of electricity to put into the cell to start with a saturated brine and get the most chlorate possible in one pass.

[THEONE]

Well, the strange thing is that my electrolyte seems like a heavy oil at RT but even if i freeze it to -15c, i will not get any ppt out and i am quite sure it is saturated with Naclo3.

 

Also why the density measurement wont work with Naclo3 too ? The more the Naclo3 in solution, the higher the density will be so you could get an idea when you have to stop in order to prevent anode erosion.

Edited December 19, 2019 by THEONE

[WSM]

Also why the density measurement wont work with Naclo3 too ? The more the Naclo3 in solution, the higher the density will be so you could get an idea when you have to stop in order to prevent anode erosion.

If I remember correctly, the density (specific gravity) of sodium chloride and sodium chlorate solutions are so similar to each other that it's difficult to tell the difference between them using a hydrometer.

 

The difference IS measurable with potassium salts due to the fact that potassium chlorate drops out of solution as it reaches saturation.

 

WSM

[THEONE]

Wouldnt saturated naclo3 solution got higher density than nacl saturated solution, as long as naclo3 is much more soluble than nacl ?

[WSM]

Wouldnt saturated naclo3 solution got higher density than nacl saturated solution, as long as naclo3 is much more soluble than nacl ?

 

That's a good point. But if there is mostly chlorate, it should drop out when chilled to no lower than -5 degrees C, leaving the chloride in solution.

 

The filtered and dried crystals will test positive for chlorate by burning vigorously when mixed with a fuel. Sodium chloride obviously won't.

 

If your starting electrolyte is too thick (not totally dissolved) it's hard to gauge when the run is completed. I usually start with a brine concentration of about 350g/liter (roughly 10 times the average for sea water), if memory serves.

 

The sodium chlorate is MUCH more soluble, somewhere between 600g and 800g per liter, I think.

 

If your starting electrolyte is so thick it "looks like oil", it should thin out considerably when the bulk of the chloride is converted to chlorate, I believe; so long as the water isn't boiling off.

 

Run the cell longer, and see if I'm right. Good luck.

 

WSM

[THEONE]

I am afraid to run the cell even more because i may damage the MMO. I am quite sure that the electrolyte is saturated with naclo3

[Arthur]

You need to do the maths of the chemical processes. A saturated NaCl solution completely oxidises to a very under saturated NaClO₃ solution.

[THEONE]

I had an excess of Nacl into my cell sitting at the bottom. I am sure my solution is quite saturated with Naclo3. I am thinking to run the same solution with Pt anode for Naclo4. I just have to calculate how much naclo3 i have in my solution and run the cell accordingly

Edited December 23, 2019 by THEONE

[markx]

Boil a small volume of your chlorate stock dry and weigh how much solid is left behind. Assuming you do not heat it to decomposition, then the residue should be mostly sodium chlorate. Alternatively you could also measure the density of your stock solution. Again assuming that it it mostly sodium chlorate solution you can find the chlorate content by examining the concentration/density relationship of the system. But even if you establish the exact concentration of your stock solution you are still going to fly blind as you do not know the efficiency of your perchlorate cell. The presumed amp hours for full conversion are dependant on cell efficiency, which is unknown at best. Also cell efficiency is subject to change during the synthesis: during the first days you may not generate any perchlorate at all and then the efficiency suddenly skyrockets. Long story short, it is near to impossible to precicely calculate the required amp hours beforehand. And secondly the Pt plated anode can in general be regarded as a consumable item in a nearly complete conversion of chlorate to perchlorate.

[THEONE]

I am planning to run the cell for about 80% conversion assuming 100% efficiency, then separate Naclo3 from Naclo4 with acetone and repeat the same process.