making potassium (per) chlorate

[WSM]

I have finally started running my first perchlorate cell and i cant thank you guys enough !!!

Making chlorate has always been a great challenge for the past year and now i can do it at ease thanks to you guys.

Now i shall be looking to make potassium and ammonium perchlorate

As i have previously stated i cant thank you guys enough for the vast amounts of information and time you have dedicated to this topic.

Andead

 

 

Welcome to the discussion, Andead.

 

Now that you've started posting, share your experiences that brought you to this point and your progress as you move into perchlorate production. You never know what bit of information you share will open an avenue for progress that a fellow experimenter is struggling with.

 

Looking forward to hear more...

 

WSM

[WSM]

Looking forward to the coming year, I'm listing my electrochemical goals in no particular order:

• complete and start a test run of the high temperature sodium chlorate cell
• carry on with my perchlorate production experiments
• continue my purification of raw materials experiment to produce "better than commercial" oxidizers
• set up a purified water station using an RO system, coupled with a de-ionizer, to quickly and cheaply make DI water
• build a sustainable power source to run my experiments without undue expense
• continue writing and adding to the Homegrown Oxidizers series plus add them to the Blogs here

The first and most important step was buying a new computer a few days ago. I was seriously handicapped without one for over half a year, but have acquired a reasonably powerful unit with lots of memory. It's freeing to tap at a keyboard rather than poke at my cellphone to answer questions and make suggestions here. Once I have this new tool fully set up, my desktop publishing efforts can resume at full speed!

 

Happy New Year to all of us.

 

WSM

Edited December 30, 2019 by WSM

[Redox]

Hello.

Edit: the optimal pH is more or less 6.7 (slightly acid) and the bulk reaction occurs at this pH when/where the ratio of hypochlorous to hypochlorite ions is about 2:1, according to the researchers I've studied

That optimal ratio only applies to the uncatalyzed bulk reaction. If you add some chromate (or dichromate) to the solution then you will also have some catalyzed processes going on so the ideal pH might be different. I have a scientific paper that suggests the optimal pH for uncatalyzed reactions is rather 7.2.

The "bulk container" you refer to sounds similar to the "bulk reaction" mentioned in literature, as when the pH is optimal for producing chlorate throughout the cell rather than just at the anode. This is based on the ratio of hypochlorous to hypochlorite ions, and not the volume of the cell container.

Yes, like someone on this forum (Swede?) said - with electrolysis you don't make the chlorate, but rather percursors for chlorate. And these percursors need their own time and conditions to react. The volume of the bulk container (and thus the solution in circulation) will dictate the speed at which the chlorate is formed from hypochlorite i.e. if you have twice as much solution then the chlorate will be formed twice as fast - the goal here is to have only as large container as needed so that all percursors will react in a timely manner and not start to saturate inside the cell. This is why I was wondering, if anyone has done any research into kinetics of hypochlorite decomposition.

Cheers!

EDIT: Updated.
EDIT2: Uploaded the paper, see attachment. Mods, if you think this paper is against the rules please feel free to remove.

C8DT00120K.pdf

Edited December 29, 2019 by Redox

[WSM]

Hello.

That optimal ratio only applies to the uncatalyzed bulk reaction. If you add some chromate (or dichromate) to the solution then you will also have some catalyzed processes going on so the ideal pH might be different. I have a scientific paper that suggests the optimal pH for uncatalyzed reactions is rather 7.2.

Yes, like someone on this forum (Swede?) said - with electrolysis you don't make the chlorate, but rather percursors for chlorate. And these percursors need their own time and conditions to react. The volume of the bulk container (and thus the solution in circulation) will dictate the speed at which the chlorate is formed from hypochlorite i.e. if you have twice as much solution then the chlorate will be formed twice as fast - the goal here is to have only as large container as needed so that all percursors will react in a timely manner and not start to saturate inside the cell. This is why I was wondering, if anyone has done any research into kinetics of hypochlorite decomposition.

Cheers!

EDIT: Updated.

EDIT2: Uploaded the paper, see attachment. Mods, if you think this paper is against the rules please feel free to remove.

 

 

Thanks for the article, Redox.

 

I love being proven wrong, as an opportunity to learn. For me, it isn't that catalysis doesn't work, but my desire to avoid handling known carcinogens (hexavalent chromium in this case) unnecessarily. I've dealt with my share of chromates in the past (as in using dichromates to treat magnesium and in catalyzing perchlorate compositions), but would rather avoid them in the case of chlorate production, accepting the resulting inefficiency as a cost of doing business and enjoying the reduced risks in the process.

 

I have some barium chloride to use for removal of chromium compounds in used electrolyte, but feel the risks (both personal and environmental) out weigh the potential benefits of using them, especially in an amateur setting. Personally, I'd rather not go there. I'm not afraid of them; I'd just rather not bother with them.

 

WSM

[Redox]

Well, damn!

 

The place I work at has just been cleaning old laboratories and they found a crapload of old and unused chemicals. The guys doing the cleaning were not chemists so they just threw everything into large barrels left for disposal. Luckily I happened to have walked by the barrels and saw all these unused chems inside. So I asked my boss whether I could take some of them home and he has allowed me to do so. I managed to salvage large amounts (like 1 kg) of potassium chromate and dichromate as well as nearly half a kilo of solid AgNO₃. There were also multiple indicators and I got about 200g of methylene blue (indicator for perchlorate).

[WSM]

Well, damn!

The place I work at has just been cleaning old laboratories and they found a crapload of old and unused chemicals. The guys doing the cleaning were not chemists so they just threw everything into large barrels left for disposal. Luckily I happened to have walked by the barrels and saw all these unused chems inside. So I asked my boss whether I could take some of them home and he has allowed me to do so. I managed to salvage large amounts (like 1 kg) of potassium chromate and dichromate as well as nearly half a kilo of solid AgNO₃. There were also multiple indicators and I got about 200g of methylene blue (indicator for perchlorate).

 

Score!

 

An excellent find. I'd have done the same thing. Congratulations!!!

 

WSM

[Redox]

Thanks.

 

Hey, if you don't mind, I have some questions since I'm still trying to come up with a decent cell design. You mentioned mist generated by evolved hydrogen in the cell... I am guessing this mist will then stick to the walls and electrodes where the crystals will start to accumulate after evaporation, possibly causing salt creep and electrode corrosion at unprotected places. What solution do you propose to suppress this mist? I know ventilation is one of the possibilities, but it does not completely eliminate the problem. I was thinking of loading the top of the chamber with some kind of plastic foam to act as a demister, but it will probably get clogged up with crystals.

 

See ya.

[Arthur]

There are a range of useful food containers made of polypropylene (PP) that is adequately resistant for a few months. They are intended for storing either breakfast cereal or fruit juice (in the fridge door). Major supermarkets sell them for £2 - £5 I've seen them in volumes about 3 to 6 litres. They have a lid and small pouring spout with cover. They keep the spray inside if you are careful cutting the holes for the electrode hangers.

[WSM]

Thanks.

Hey, if you don't mind, I have some questions since I'm still trying to come up with a decent cell design. You mentioned mist generated by evolved hydrogen in the cell... I am guessing this mist will then stick to the walls and electrodes where the crystals will start to accumulate after evaporation, possibly causing salt creep and electrode corrosion at unprotected places. What solution do you propose to suppress this mist? I know ventilation is one of the possibilities, but it does not completely eliminate the problem. I was thinking of loading the top of the chamber with some kind of plastic foam to act as a demister, but it will probably get clogged up with crystals.

See ya.

 

 

There are a couple of techniques I've used to contain the mist and prevent salt creep.

 

One of the first I learned from a fellow electrochemist, is to allow several inches (100 mm to 150 mm) between the surface of the electrolyte and the lid of the cell. This gives an open space for the bubbles to pop above the electrolyte. It's not perfect, but helps a little.

 

To prevent salt creep at the rim of the cell, I use a silicone tubing seal on the lid (see in my blog postings).

 

When I ran my first sodium chlorate cell experiments a few years ago, it was on a larger scale than previous cells (19-22 liters capacity) and the heat plus volume caused a lot of salt mist to escape via the vent. After several unsuccessful tries, the successful method was to run thin vinyl tubing from the cell lid in an arc; up, over and down into a 4 liter glass jar (sitting on the top of the cell lid), which had a separate vent tube on its own (PVC pipe cap, ~120 mm ID) lid. The way this setup worked with the running cell was to reflux (condense the mist to liquid and run it back down the tubing wall) the hot mist in the thin vinyl tube, back into the cell. What little mist that got past the reflux tube, collected in the bottom of jar, so only dry fumes got out of the vent in the collection jar. This system was also recommended by the same fellow who suggested the large gap above the electrolyte.

 

This last method worked surprisingly well, despite my first doubts.

 

When the thin vinyl tubing (roughly 12 mm ID with 1.5 mm walls) starts to break down, due to the corrosive nature of the mists, replace it with new vinyl tubing (a cheap fix since the clear vinyl tubing costs so little). I used PVDF fittings with this system.

 

WSM

Edited December 30, 2019 by WSM

[WSM]

Thanks.

Hey, if you don't mind, I have some questions since I'm still trying to come up with a decent cell design. You mentioned mist generated by evolved hydrogen in the cell... I am guessing this mist will then stick to the walls and electrodes where the crystals will start to accumulate after evaporation, possibly causing salt creep and electrode corrosion at unprotected places. What solution do you propose to suppress this mist? I know ventilation is one of the possibilities, but it does not completely eliminate the problem. I was thinking of loading the top of the chamber with some kind of plastic foam to act as a demister, but it will probably get clogged up with crystals.

See ya.

 

 

If corrosion of the electrode leads inside the cell is a concern, PVDF shrink tube can be used to cover that part which is exposed to the mist above the electrolyte. It takes a fair amount of heat to properly shrink the tubing onto the leads, so use an actual heat gun to apply it. Avoid using a propane torch which is likely to scorch the tubing unless great care is used in its application.

 

Alternatively, slipping silicone tubing over the leads may offer some protection, but I don't know how long it'll last or how well it can work.

 

Good luck.

 

WSM

 

Edit: I haven't had a problem with electrode corrosion since following Swede's suggestion (in his blogs) to spot-weld, filled titanium tubing to the electrodes and seal them in Kynar (PVDF) compression fittings. Commercially pure (CP) titanium is highly resistant to the electrolyte, especially while the current is running, so there's no need for extra protection.

Edited December 30, 2019 by WSM

[Redox]

Hey, thanks for the suggestions. And a happy new year 2020 to everyone! Arthur: I was going to build my own cell out of 10mm thick CPVC sheets by cutting them to size and attaching them together with PVC cement to form a rectangular container with a lid. As for the outer layer I could probalby apply another 10mm of regular PVC outside to reinforce the chamber or maybe even use fiber + polyester.

 

One of the first I learned from a fellow electrochemist, is to allow several inches (100 mm to 150 mm) between the surface of the electrolyte and the lid of the cell. This gives an open space for the bubbles to pop above the electrolyte. It's not perfect, but helps a little.

This is an interesting idea, I can definitely modify the design to accomodate this change.

 

When I ran my first sodium chlorate cell experiments a few years ago, it was on a larger scale than previous cells (19-22 liters capacity) and the heat plus volume caused a lot of salt mist to escape via the vent.

I have to admit I haven't thought about this. My original idea was to use a demister i.e. a piece of perforated plastic foam (or wool) ontop of the electrodes to reduce the amount of mist generated inside the cell and to use active ventilation like a fan connected to one of the two vents on the lid via a vinyl tube to suck the noxious fumes out of the chamber. I don't know, if this will sufficiently prevent crystals from forming on the walls due to mist and evaporation. I gave it some thought and I decided I will be using a non-saturated solution of KCl i.e. 300 g/L. This is to reduce potential crystalization and salt creep near liquid surface contacts with walls, but at the same time it should not be too low to cause electrode erosion.

[Redox]

Anyway, I was going to use my old graphite/SS electrodes that I used in a previous experiment with HBr/Br₂ since they're the only ones I currently have at hand. These are made from laser-cut SS plates and actual compressed graphite plates that I salvaged from a large block of graphite from an old Cl₂/H₂/HCl furnace. The surface area should be plenty to handle 50 amps so hopefully there will not be too much erosion. They worked for just fine for about a month in the bromide solution. One thing I'm worried about are the threaded SS rods I'm using to connect the individual plates - these will somehow need to be protected from the mist. Previously I used normal threaded steel rods, and they heavily corroded during the experiment.

[WSM]

Anyway, I was going to use my old graphite/SS electrodes that I used in a previous experiment with HBr/Br₂ since they're the only ones I currently have at hand. These are made from laser-cut SS plates and actual compressed graphite plates that I salvaged from a large block of graphite from an old Cl₂/H₂/HCl furnace. The surface area should be plenty to handle 50 amps so hopefully there will not be too much erosion. They worked for just fine for about a month in the bromide solution. One thing I'm worried about are the threaded SS rods I'm using to connect the individual plates - these will somehow need to be protected from the mist. Previously I used normal threaded steel rods, and they heavily corroded during the experiment.

 

 

I suggest controlling the temperature to prevent degradation of the graphite anodes (re: pH using graphite anodes, see post #381 on page 20 of this thread). If the stainless all-thread electrical connections are outside the electrolyte, they may survive longer than if submerged in it.

 

What material is being used for the connecting bolts holding the spacing between the plates? If it's PTFE, it'll be okay. If PVDF, higher pH will cause damage to it over time; pH control will keep that in check and all will be well. Most other polymers will likely show degradation over time in the cell, and a few won't last at all (nylon comes to mind).

 

The electrodes look nice, though. Good craftsmanship. If they were MMO and CP titanium, I'd expect long life and good production, even at high temperatures.

 

WSM

Edited January 2, 2020 by WSM

[Redox]

Hah! So the electrode cell should operate at a low temperature while the reaction needs a high temperature to proceed. Kind of contradicts itself, doesn't it? This is one of those details I wasn't sure about. Should I put the electrode into the bulk vessel and have it act as a heating element or should I place it into a separate cell and use a secondary heater in the bulk vessel to heat and circulate the solution in the vessel. I think I'll go with the option #2.

 

WSM: The spacer rings between electrodes are 3 mm PTFE. As for the threaded rod and the nuts, I have no idea what they are made of. Maybe they are PVC, maybe Nylon66, ABS or some other plastic, I honestly can't tell since it was ages ago when I built the electrode. I remember choosing a chemically resistant plastic for electrolyzing bromide into bromine so it should probably do fine with chlorides. We'll see. If not, I'll replace them with PTFE.

 

Red

[WSM]

Hah! So the electrode cell should operate at a low temperature while the reaction needs a high temperature to proceed (?). Kind of contradicts itself, doesn't it? This is one of those details I wasn't sure about. Should I put the electrode into the bulk vessel and have it act as a heating element or should I place it into a separate cell and use a secondary heater in the bulk vessel to heat and circulate the solution in the vessel. I think I'll go with the option #2.

WSM: The spacer rings between electrodes are 3 mm PTFE. As for the threaded rod and the nuts, I have no idea what they are made of. Maybe they are PVC, maybe Nylon66, ABS or some other plastic, I honestly can't tell since it was ages ago when I built the electrode. I remember choosing a chemically resistant plastic for electrolyzing bromide into bromine so it should probably do fine with chlorides. We'll see. If not, I'll replace them with PTFE.

Red

 

 

The reaction doesn't need a high temperature to proceed, though it depends on what you mean by high temperature. If I remember correctly, graphite should not run at much more than 40^oC, where lower than this is optimal. MMO can run at substantially higher temperatures without noticeable damage or degradation of the coating.

 

Running the electrodes in a "bulk vessel" or a separate reaction chamber is a matter of choice, but the single vessel cell is a simpler setup and the default of most amateur electrochemists. While the cell runs, electrical inefficiencies in the cell manifest as heat. As such, the electrodes operating in the electrolyte, naturally heat the cell. The higher the electrical efficiency in the cell setup, the lower amount of heating observed.

 

WSM

 

Edit: First, the voltage of the running cell should be at least the minimum to keep the reaction going (>1.7 Vdc), and industry typically calls for 3.6 Vdc as a standard. Most amateurs run their cell between 3 and 5 Vdc with no problem.

 

Then, the optimal way to control the internal temperature of a running cell is by controlling the current flow (higher current = higher temperature, and lower current = lower temperature). Current demand in the cell is directly related to the reactive surface area of the anode, matched to the surface area of the cathode, among other factors.

Edited January 3, 2020 by WSM

[Andead]

I am currently encountering a strange problem with a new computer power supply i am trying to use. Once i wire the green wire and black wire together they temporarily begin to work ( the cooling fan begins to operate) then for no apparent reason the cooling fan stops turning indicating a lose of power. Why is this occuring and how can i fix it ?

 

Thanks in advance

 

Andead

Edited January 6, 2020 by Andead

[Arthur]

Assuming that you have proof that it is a good unit. Some PSUs turn off at zero load. Add a small indicator lamp to the +12 or the +5v rails, maybe you need to draw a whole watt or two which is easier with tungsten than LED! https://www.youtube.com/watch?v=z2oSFpKh_Uw

[Andead]

Thanks alot Arthur, ill get around to do it this weekend .

 

Andead

[WSM]

Assuming that you have proof that it is a good unit. Some PSUs turn off at zero load. Add a small indicator lamp to the +12 or the +5v rails, maybe you need to draw a whole watt or two which is easier with tungsten than LED! https://www.youtube.com/watch?v=z2oSFpKh_Uw

 

 

That reminds me of a suggestion someone made, to add a resistor in parallel to the power supply's output. If I remember correctly, a specialty high wattage, low Ohm (ceramic) resistor was suggested. these are available from electronic component supply shops at reasonable cost.

 

See if that doesn't work for you.

 

WSM

Edited January 8, 2020 by WSM

[Andead]

You are helpful as always WSM, thanks alot ! Ill see if my friend has the resistor himself and if he doesnt ill get around to buying it.

 

Andead

[WSM]

You are helpful as always WSM, thanks alot ! Ill see if my friend has the resistor himself and if he doesnt ill get around to buying it.

Andead

 

 

You're welcome, I'm glad it helps. The video that Arthur posted a link to, shows how to attach the resister to keep the power supply switched on.

 

WSM

Edited January 9, 2020 by WSM

[WSM]

I'll be on the road the next few days (we were visiting Family for Christmas and the New Years celebrations, but are heading home now), so my responses will probably be slower than they were lately.

 

I'm looking forward to making real progress in my electrochemical research this year. This should be fun!

 

I'll post my progress here for everyone's edification and learning; plus, as Swede put it, this site is a useful online logbook.

 

WSM

[abc159201]

I'll be on the road the next few days (we were visiting Family for Christmas and the New Years celebrations, but are heading home now), so my responses will probably be slower than they were lately.

 

I'm looking forward to making real progress in my electrochemical research this year. This should be fun!

 

I'll post my progress here for everyone's edification and learning; plus, as Swede put it, this site is a useful online logbook.

 

WSM

 

WSM Would you mind sharing how you control the pH? Swade's way is insert a tube/pipe and drill some hole below the surface of the electrolyte and uses some gravity feed system to drip the acid into the tube. But wouldn't the acid react with chlorate in tube first? Also,I have tried this method before but it failed miserably. Maybe because i ran my cell at relatively high temp(80-90C). Those tube(PVC and silicon) quickly deteriorated , became hard and then broke into several pieces. So i'm still using the most primitive dangerous way --- very strong stirring + use pipette to add acid below the surface (of course with my 3M respirator). By doing so, adding acid barely creates any chlorine/chlorine dioxide and I get pretty good current efficiency(avg@85%). But still want a more elegant way to do this.

Edited January 20, 2020 by abc159201

[markx]

Peristaltic pump operated from a timer unit might make a pretty elegant solution for the acid dosing system. You could use thin ptfe tube submersed into the middle of the cell....it will not deteriorate under the cell conditions. A gravity fed IV drip type of solution should also work relatively reliably. I've tried both options out of scientific curiosity, but in the end decided the pH control was too much of a hassle, extra equipment and numerous extra possibilites for everything to fail. The gains in yield hardly made sense for me (unless one produces on a semi industrial scale) to deal with the added mess of operating the system and worrying about when exactly universe will find a way to mess it up in some unforeseeable and apocalyptic way:)

[WSM]

 

WSM Would you mind sharing how you control the pH? Swade's way is insert a tube/pipe and drill some hole below the surface of the electrolyte and uses some gravity feed system to drip the acid into the tube. But wouldn't the acid react with chlorate in tube first? Also,I have tried this method before but it failed miserably. Maybe because i ran my cell at relatively high temp(80-90C). Those tube(PVC and silicon) quickly deteriorated , became hard and then broke into several pieces. So i'm still using the most primitive dangerous way --- very strong stirring + use pipette to add acid below the surface (of course with my 3M respirator). By doing so, adding acid barely creates any chlorine/chlorine dioxide and I get pretty good current efficiency(avg@85%). But still want a more elegant way to do this.

 

 

I plan to use PTFE tubing or some other compatible material for the acid injections. To make things easier, I've already planned to use dilute HCl and not full-strength acid. I have the ability and equipment for pressured acid injection, but my choice is to use a gravity fed system.

 

To achieve this, I'm placing the acid reservoir on a shelf above the cell, high enough to create sufficient head pressure for the acid to flow without a powered pump. Swede gave me the idea, and I like the simple elegance of it.

 

The best way to inject the acid, is well below the surface of the electrolyte, so chlorine will stay in the solution to do its work; and not escape as free chlorine gas like it does when you dump acid onto the surface of the hot cell mother liquor.

 

I'll see if I can access my old photos of the various parts of the pH control components I built, and post some for a better idea of how this works.

 

WSM

 

Edit: Also, review Swede's blogs ("You'll shoot your eye out.") and see how his thoughts on pH control developed as he progressed. His contributions have helped us all to expand our understanding of the details required to be effective electrochemists.

Edited January 20, 2020 by WSM