making potassium (per) chlorate

[Andead]

 

This is a sodium chlorate cell, right?

 

If so, the product is more soluble than the chloride, so you can either add more chloride and keep running it till the concentration of chlorate is enough to force it out of solution, OR you can chill the electrolyte to drop out a portion of the chlorate, recharge the electrolyte with more chloride and run it more.

 

These are two ways to accomplish the same goal: to force the sodium chlorate out of solution.

 

WSM

Currently I am intending on adding enough sodium chloride that the cell becomes over saturated but based on my cell size being 3 litres that means I must have a minimum of 3kg of sodium chlorate in the cell which is a considerably large amount. What ill probably end up doing once i have enough time is take up some of the electrolyte in the and just cool it down.

 

 

 

I currently dont use a resistor in my cell so why would I need one to make perchlorate and why is it necessary for me to bundle all the 5v leads together with all the negative leads?

[Pyrophury]

 

This is a sodium chlorate cell, right?

 

If so, the product is more soluble than the chloride, so you can either add more chloride and keep running it till the concentration of chlorate is enough to force it out of solution, OR you can chill the electrolyte to drop out a portion of the chlorate, recharge the electrolyte with more chloride and run it more.

 

These are two ways to accomplish the same goal: to force the sodium chlorate out of solution.

 

WSM

 

Yes, sodium chlorate cell. I want to increase the concentration of chlorate to around 600g/l and 100g/l chloride before I start my perchlorate run with the LD anode.

 

I don't think it's worth trying to harvest anything yet, but I'm having difficulty dissolving any more sodium chloride into the cell liquor. So I think my only option is to stop the run and boil away about a third of the water, then top up with saturated sodium chloride solution and run the cell for 3-4 more days until the concentration is around 600g/l.

[PTFE]

 

Yes, sodium chlorate cell. I want to increase the concentration of chlorate to around 600g/l and 100g/l chloride before I start my perchlorate run with the LD anode.

 

I don't think it's worth trying to harvest anything yet, but I'm having difficulty dissolving any more sodium chloride into the cell liquor. So I think my only option is to stop the run and boil away about a third of the water, then top up with saturated sodium chloride solution and run the cell for 3-4 more days until the concentration is around 600g/l.

the undissolved nacl should dissolve in some time when you run your cell so it stays hot.

If you still use the magnetic stirrer it should help dissolving the salt.

 

You also could add a liter of full saturated brine since you have plenty of space left inside of your cell.

[Pyrophury]

I think I've been very over optimistic with the run time. I took a sample of the electrolyte but I was only able to boil off 10-15% of water before salt started to precipitate, I've put it in the freezer but I doubt I'll get any chlorate to ppt.

[PTFE]

I think I've been very over optimistic with the run time. I took a sample of the electrolyte but I was only able to boil off 10-15% of water before salt started to precipitate, I've put it in the freezer but I doubt I'll get any chlorate to ppt.

the precipitant could be nacl because of its low solubility compared do the clorate.

Also when boiling, you increase the solubility of the chlorate a lot but the solubility of the chloride does not increase significant. this means if enough nacl is in solution it will precipitate out first.

I would let the cell run for another week and keep adding full saturated brine or fed nacl in the same rate as it is going into solution.

[WSM]

I currently dont use a resistor in my cell so why would I need one to make perchlorate and why is it necessary for me to bundle all the 5v leads together with all the negative leads?

Combine all the positive leads and connect them to a positive Buss, and do the same to the negative leads.

 

Don't short the positive and negative leads/Busses together or bad things will happen!

 

WSM

[Arthur]

Take a sample of the electrolysed liquor (say250ml) and start adding potassium chloride (saturated solution) to the liquor almost dropwise. When there is chlorate it will ppt out as Kchlorate. Add KCl until no more PPT forms then filter the ppt and weigh it. Calculate backwards how much sodium chlorate there was and how much sodium chloride must have been used.

[WSM]

Take a sample of the electrolysed liquor (say250ml) and start adding potassium chloride (saturated solution) to the liquor almost dropwise. When there is chlorate it will ppt out as Kchlorate. Add KCl until no more PPT forms then filter the ppt and weigh it. Calculate backwards how much sodium chlorate there was and how much sodium chloride must have been used.

 

An excellent suggestion.

 

With careful measurement and observations, an accurate quantitative analysis is possible.

 

Real chemistry is awesome.

 

WSM

Edited February 26, 2020 by WSM

[Arthur]

If you have a perc cell then the final liquor will be a mix of NaCl, NaClO₃ and NaClO₄. Which are of increasing solubility in water.

 

The only way to separate them is to add a saturated solution of KCl and watch the precipitates form, first the perchlorate will ppt out, then the chlorate. The skill is to stop adding KCl just before the chlorate starts to ppt out so that the ppt is pure perc that filters out easily particle size is controlled by the temperature of the reactants and the rate of stirring.

 

Should you add too much KCl and ppt out all the perc and some chlorate then the precipitates are formed in two distinct layers, perc first then chlorate. You can see the different shapes of the crystals.

 

It's good to get a good idea of how your cell is working so that you can work out how much KCl to add to produce only pure KPerc. It's better to have a little sodium perchlorate going back into electrolysis than to have potassium chlorate mixed with the perc.

[WSM]

If you have a perc cell then the final liquor will be a mix of NaCl, NaClO₃ and NaClO₄. Which are of increasing solubility in water.

 

The only(?) way to separate them is to add a saturated solution of KCl and watch the precipitates form, first the perchlorate will ppt out, then the chlorate. The skill is to stop adding KCl just before the chlorate starts to ppt out so that the ppt is pure perc that filters out easily particle size is controlled by the temperature of the reactants and the rate of stirring.

 

When I ran my perchlorate cells, I started with sodium chlorate and converted most of it to perchlorate (tested with methylene blue).

 

Next, I destroyed the chlorate residue by treating the electrolyte with sodium metabisulfite solution, slowly and deep under the surface of the liquid (to keep the evolved sulfur dioxide in solution, where it will do its work and not flash off as gas).

 

When the residual chlorate was broken down, I dropped in the KCl solution all at once, which immediately dropped out fine white powdered potassium perchlorate, making the solution look like milk.

 

After vacuum filtering the fresh KClO4, I rinsed it with chilled distilled water to help remove sodium residues. The sodium wasn't entirely removed, but if I soak the perchlorate in cold distilled water for a while before vacuum filtering, I think more sodium contamination will be removed.

 

WSM

Edited February 27, 2020 by WSM

[abc159201]

Currently I am intending on adding enough sodium chloride that the cell becomes over saturated but based on my cell size being 3 litres that means I must have a minimum of 3kg of sodium chlorate in the cell which is a considerably large amount. What ill probably end up doing once i have enough time is take up some of the electrolyte in the and just cool it down.

 

 

 

I currently dont use a resistor in my cell so why would I need one to make perchlorate and why is it necessary for me to bundle all the 5v leads together with all the negative leads?

 

You don't necessarily need to use a resistor. Some ATX PSU needs some load at 5V rail, some at 12V rail. As long as your PSU keeps working, there is no need to add one.

And is it necessary to bundle all the 5v leads? NO, but recommended. 5V rail is generally single-rail, unlike 12V. You can use one lead only if you are 100% sure that the lead can handle the current. But why bother taking the risk?

[Pyrophury]

The current in my cell dropped to just 5A and hardly any of the 100g of NaCl I added had dissolved, so I stopped the run and siphoned out the contents.

 

I'm unable to boil away hardly any water without salt being precipitated. I chilled a 300ml sample down to -1C and I estimate just 1 gram of crystals had settled on the bottom of the beaker.

 

How cold and how long should I chill the liquor before attempting to harvest anything?

[PTFE]

The current in my cell dropped to just 5A and hardly any of the 100g of NaCl I added had dissolved, so I stopped the run and siphoned out the contents.

 

I'm unable to boil away hardly any water without salt being precipitated. I chilled a 300ml sample down to -1C and I estimate just 1 gram of crystals had settled on the bottom of the beaker.

 

How cold and how long should I chill the liquor before attempting to harvest anything?

this is quite odd. If you continue adding nacl or fresh brine, the current should stay up and the cell will run and naclo3 will settle on the bottom.

Maybe you sould boil of ~50% and top up with fresh brine and run again.

[Pyrophury]

Needless to say I wasn't successful at harvesting any NaClO3. I'm wondering if the anode has passivated again, but if so I've no idea what caused it this time.

 

I've switched to my LD anode and I'm now getting 18A at 4.6V.

 

 

I'm not sure if I should leave it at 4.6V until the current drops before increasing the voltage, or just run it at 6V now?

[markx]

The current in my cell dropped to just 5A and hardly any of the 100g of NaCl I added had dissolved, so I stopped the run and siphoned out the contents.

 

I'm unable to boil away hardly any water without salt being precipitated. I chilled a 300ml sample down to -1C and I estimate just 1 gram of crystals had settled on the bottom of the beaker.

 

How cold and how long should I chill the liquor before attempting to harvest anything?

This much of a decline in current is sucpicious for a chlorate cell and could hint towards a new case of anode passivation. In case of Pt based perchlorate electrosynthesis the decline in current towards the end of the run can be much steeper and still not indicate a major problem at the anode. Try the electrode set with a new batch of chloride solution to see if the currents rise to initial levels.

Adding chloride to a running cell is preferably done in the form of saturated brine, as the solids tend not to dissolve into the electrolyte that is already highly concentrated. They remain on the bottom and clump up into a solid cake that does no good and interferes with or hinders agitation completely.

[markx]

Needless to say I wasn't successful at harvesting any NaClO3. I'm wondering if the anode has passivated again, but if so I've no idea what caused it this time.

 

I've switched to my LD anode and I'm now getting 18A at 4.6V.

 

 

 

I'm not sure if I should leave it at 4.6V until the current drops before increasing the voltage, or just run it at 6V now?

Is there a particular reason why you intend to isolate the sodium chlorate from the electrolyte in solid form? If the goal is to perform a further electrochemical conversion to perchlorate, then there really is no "burning" need for it. Considering the amount of work and effort involved in getting the highly soluble and hygroscopic sodium chlorate to percipitate out in solid form has always deterred me from the approach. It can be handled very conveniently in the form of a solution as far as the purpose of perchlorate synthesis is concerned.

 

I would suggest not to rise the voltage across the cell to 6V.....in fact you could further decrease the voltage to a minimum that is required to maintain a reasonable current through the cell (10A is plenty). The higher the voltage across the cell, the higher the anode polarisation and the higher the anode polarisation goes, the more probable damage and passivation become. That is true for all types of anodes, but especially for those that have a Ti (or other valve metal e.g. niobium) substrate like MMO and the LD one that is currently in the cell.

Perchlorate formation does work very nicely at low cell voltages despite most literature references suggesting much higher values in excess of 5,5V. I've so far only worked with Ti substrate Pt anodes for the purpose and from my experience the higher cell voltages only provoke problems there. Perhaps it is different for commercial LD, but as a precautionary measure I would try and keep the voltages as low as possible and give it ample time to see how things progress. Also watch out for any flaking or erosion happening on the anode.....LD is particularily fond of developing internal tensions that destroy the coating and make it peel off the substrate. Especially when perchlorate cell conditions are involved.

[Pyrophury]

Is there a particular reason why you intend to isolate the sodium chlorate from the electrolyte in solid form? If the goal is to perform a further electrochemical conversion to perchlorate, then there really is no "burning" need for it. Considering the amount of work and effort involved in getting the highly soluble and hygroscopic sodium chlorate to percipitate out in solid form has always deterred me from the approach. It can be handled very conveniently in the form of a solution as far as the purpose of perchlorate synthesis is concerned.

 

I just wanted a higher concentration of chlorate before I started the perc run. The current dropped leading me to believe the chloride level had dropped to 100g/L, but no more chloride would dissolve in the cell so my other option was boiling off water to make room for more saturated solution, but this wasn't possible either as the electrolyte was already saturated leaving me at something of an impasse.

 

 

I would suggest not to rise the voltage across the cell to 6V.....in fact you could further decrease the voltage to a minimum that is required to maintain a reasonable current through the cell (10A is plenty). The higher the voltage across the cell, the higher the anode polarisation and the higher the anode polarisation goes, the more probable damage and passivation become. That is true for all types of anodes, but especially for those that have a Ti (or other valve metal e.g. niobium) substrate like MMO and the LD one that is currently in the cell.

Perchlorate formation does work very nicely at low cell voltages despite most literature references suggesting much higher values in excess of 5,5V. I've so far only worked with Ti substrate Pt anodes for the purpose and from my experience the higher cell voltages only provoke problems there. Perhaps it is different for commercial LD, but as a precautionary measure I would try and keep the voltages as low as possible and give it ample time to see how things progress. Also watch out for any flaking or erosion happening on the anode.....LD is particularily fond of developing internal tensions that destroy the coating and make it peel off the substrate. Especially when perchlorate cell conditions are involved.

 

4.6V is as low as I can go. I'll be patient with it, thanks.

[Andead]

 

 

You don't necessarily need to use a resistor. Some ATX PSU needs some load at 5V rail, some at 12V rail. As long as your PSU keeps working, there is no need to add one.

And is it necessary to bundle all the 5v leads? NO, but recommended. 5V rail is generally single-rail, unlike 12V. You can use one lead only if you are 100% sure that the lead can handle the current. But why bother taking the risk?

 

Ah thanks , I will heed your advice and will return back on my findings later today. I am a college student and we have many experiments throughout the week and I managed to obtain a couple of grams of potassium (II) dichromate hehehehehe.

[ashoka3]

I just wanted a higher concentration of chlorate before I started the perc run. The current dropped leading me to believe the chloride level had dropped to 100g/L.

http://rxmarine.com/Natural-Blue-Biodegradable-Cleaner-Degreaser'> Degreaser

[WSM]

Is there a particular reason why you intend to isolate the sodium chlorate from the electrolyte in solid form? If the goal is to perform a further electrochemical conversion to perchlorate, then there really is no "burning" need for it. Considering the amount of work and effort involved in getting the highly soluble and hygroscopic sodium chlorate to percipitate out in solid form has always deterred me from the approach. It can be handled very conveniently in the form of a solution as far as the purpose of perchlorate synthesis is concerned.

I would suggest not to rise the voltage across the cell to 6V.....in fact you could further decrease the voltage to a minimum that is required to maintain a reasonable current through the cell (10A is plenty). The higher the voltage across the cell, the higher the anode polarisation and the higher the anode polarisation goes, the more probable damage and passivation become. That is true for all types of anodes, but especially for those that have a Ti (or other valve metal e.g. niobium) substrate like MMO and the LD one that is currently in the cell.

Perchlorate formation does work very nicely at low cell voltages despite most literature references suggesting much higher values in excess of 5,5V. I've so far only worked with Ti substrate Pt anodes for the purpose and from my experience the higher cell voltages only provoke problems there. Perhaps it is different for commercial LD, but as a precautionary measure I would try and keep the voltages as low as possible and give it ample time to see how things progress. Also watch out for any flaking or erosion happening on the anode.....LD is particularily fond of developing internal tensions that destroy the coating and make it peel off the substrate. Especially when perchlorate cell conditions are involved.

 

One very good reason to start a perchlorate cell with crystalline sodium chlorate is so you know the exact concentration of your starting electrolyte solution (after it's made up), making the calculations for the "end-of-run" much simpler.

 

Since I started my perchlorate experiments using lab grade NaClO₃, I soon realized the benefits of using dry crystalline material for fairly accurate calculations.

As always, your mileage may vary...

 

WSM

Edited March 1, 2020 by WSM

[WSM]

Another point is that crystallization is nature's way of purifying soluble inorganic matter.

It's good to crystallize your sodium chlorate out of solution in the cell. It's even more important to use starting materials as pure as you can afford, to ensure your end product is high enough quality.

WSM

Edited March 1, 2020 by WSM

[WSM]

If your sodium chloride brine has run the calculated amount of time to convert the bulk of it to chlorate, a workable next step is to chill it to roughly 0^oC where part of the chlorate will crystallize out of solution, but the chlorides will stay IN solution!

That's how my sodium chlorate recovery worked, and I have ~10 lbs of pure crystals, plus more in solution in the "depleted" electrolyte. Next, I'll recharge the electrolyte with purified brine and run the cell again. The cycle continues...

WSM

Edited March 1, 2020 by WSM

[Andead]

I have tried to connect my lead dioxide anode with the +5 volt rail (red) after I had grouped all of the red wires together but this resulted in the ATX power supply simply turning off. However, the 3.3 volt (orange) rail still worked after. Could it be that im doing something wrong or is it just that the red rail has some problem ?

Edited February 29, 2020 by Andead

[Arthur]

Read the label! Some old ATX psu's had 25 to 50 amp rating on the 5volt rail modern psu's have all the power available from the 3.5v rail and maybe only 10a from the 5v rail. Either your 5v rail has broken permanently or it may recover from a possible overload.

[markx]

“End of run” type calculations that are based upon guesstimated anodic efficiency and the assumption that anodic efficiency remains constant throughout the synthesis tend to just point towards the order of magnitude for required runtime. A more precise approach can be taken by performing quantitative analysis on the electrolyte samples while the process runs. E.g. by percipitation with KCl of a known small quantity of the electrolyte and weighing the resulting potassium salt yield. If one has bothered to start with a known quantity of chloride and can measure the volume contained in the cell then a rather precise set of data is obtained.

I’ve also noticed that perchlorate conversions (at least Pt based approaches) tend to perform a sort of “selfpurification” stage at the verge of full conversion. The electrolyte becomes rather caustic and percipitates most if not all of the contaminants as anodic sludge. These sink slowly to the bottom of the cell and a crystal clear translucent sodium perchlorate solution remains. After careful titration to around pH 7 using dilute hydrochloric acid a metathesis reaction can be performed to yield KClO4 without further manipulations. The yielding product is washed twice on a vaccuum filter using deionised water and dried. Purity is very satisfactory as far as can be assumed from lack of sensitivity of the mixes based on the yielded product and flame color development. This is my quick and dirty approach to involve minimum effort and manipulations in the process. But by all means one can refine the process and involve many more purification stages and methods for obtaining truly superior product

If the desired end product is not KClO4, but some other perchlorate then I would at least strongly suggest to add a chlorate destruction stage into the process for increased safety considerations. The insolubility of the potassium salt allows to skip it and use the post percipitation washings to do the job.