making potassium (per) chlorate

[WSM]

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:)

 

 

Yes, or even a dosing pump like the ones used for swimming pool acid dosing. There are some quality polymers (plastics) and elastomers (rubbers) that are compatible with dilute HCl, which would work well for a pH control scheme. Some research and understanding will go a long way to ensure success of such a setup.

 

Without pH control, the best efficiency we can hope for won't exceed roughly 60%. With pH control, and a proper setup, we can approach and exceed the magic 90% efficiency threshold that most amateurs find so elusive. It's not easy, but certainly worth the effort, especially with larger setups.

 

It's always prudent and wise to place your active cell in some type of compatible tray or tub, as a "containment", to keep the electrolyte captured in the event of a catastrophic rupture of the cell wall or other structural part of the running cell. Arthur has mentioned several times, about the disastrous environmental effects of chlorate salts and solutions to plant life. Sodium chlorate , for example, is a notorious "indiscriminate herbicide", meaning it kills all plant life (and some animal life) it reaches, and I'm not sure how long the effects will last (I think it depends on the physical limits and duration of the exposure).

 

Be wise and keep control of your experiments.

 

WSM

Edited January 20, 2020 by WSM

[abc159201]

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.

 

 

My question : When the gravity system drip the acid into the tubing, the tubing should also have a lot of chlorate/hypochlorite ions. Acid will react with them and produce Cl2/ClO2 and go up to the acid reservoir side unless this system is pressurized. This is what I have observed. Or maybe that happened because I didn't dilute my acid enough? My acid is 32% and I usually dilute them with tap water at 1:1 ratio .So it should be around 15~16%. Is that considered too concentrated?

 

 

 

Without pH control, the best efficiency we can hope for won't exceed roughly 60%. With pH control, and a proper setup, we can approach and exceed the magic 90% efficiency threshold that most amateurs find so elusive. It's not easy, but certainly worth the effort, especially with larger setups.

 

 

That is so true. Before I tried pH control, I only have 50-55% efficiency. Now, I can achieve 85%. Couldn't be more happy than that. It certainly worth the effort.

Edited January 21, 2020 by abc159201

[WSM]

My question : When the gravity system drip the acid into the tubing, the tubing should also have a lot of chlorate/hypochlorite ions. Acid will react with them and produce Cl2/ClO2 and go up to the acid reservoir side unless this system is pressurized. This is what I have observed. Or maybe that happened because I didn't dilute my acid enough? My acid is 32% and I usually dilute them with tap water at 1:1 ratio .So it should be around 15~16%. Is that considered too concentrated?

That is so true. Before I tried pH control, I only have 50-55% efficiency. Now, I can achieve 85%. Couldn't be more happy than that. It certainly worth the effort.

 

 

I was thinking (in my own setup) of diluting the 32% HCl, 4 to 1 to about 8%, since the running KClO₃ cell consumes water, the 75% H₂O will help restore some that was lost to the process, while the 25% acid would adjust the pH close to what we need.

 

WSM

Edited January 21, 2020 by WSM

[markx]

 

 

I was thinking (in my own setup) of diluting the 32% HCl, 4 to 1 to about 8%, since the running KClO₃ cell consumes water, the 75% H₂O will help restore some that was lost to the process, while the 25% acid would adjust the pH close to what we need.

 

WSM

Diluting under 10% is advantageous with regards to dosing accuracy and also the off gassing that intensifies to a great extent with the use of higher HCl concentrations. My adjustment acid was diluted between 6-8% HCl and when fed into the cell through a thin (0,5mm) PTFE tube it produced noticeable off gassing.

Be especially aware of accidentally overdosing a highly concentrated HCl solution (either by human error or equipment malfunction). The cell can enter a "runaway reaction" mode accompanied with eruptive release of copious amounts of chlorine gas and catastrophic "overboiling". Also all of the formed chlorate shall be destroyed by this process within a matter of seconds. If that should happen in an enclosed space then the results can be literally deadly. It happened to me once, but luckily it was in outside conditions and the deadly cloud had enough chance to dissipate. Was scary enough though....

[Arthur]

IF you can get a cell to evaporate enough water then an acidified mix of saturated brine should make up for pH change and chloride consumption. Much testing and calculation will be needed, but this could become a 24/7/365 operation.

 

The Iwaki bellows pumps I've mentioned before will handle many chemicals and pump volumes controlled by counting pump cycles or seconds. With some process timers it should be possible to pump 1ml every minute quite reliably.

 

From Swede's work (blog and posts) it should be possible to determine the amphours needed to convert chloride, the acid needed per amp hour and the completion point total amp hours consumed. From these, a fair set of "best guesses" can be started and corrected until there is a reliable steady state operating set of parameters.

[WSM]

IF you can get a cell to evaporate enough water then an acidified mix of saturated brine should make up for pH change and chloride consumption. Much testing and calculation will be needed, but this could become a 24/7/365 operation.

The Iwaki bellows pumps I've mentioned before will handle many chemicals and pump volumes controlled by counting pump cycles or seconds. With some process timers it should be possible to pump 1ml every minute quite reliably.

From Swede's work (blog and posts) it should be possible to determine the amp-hours needed to convert chloride, the acid needed per amp hour and the completion point total amp hours consumed. From these, a fair set of "best guesses" can be started and corrected until there is a reliable steady state operating set of parameters.

 

 

It's not hard to get a chlorate cell to evaporate water, but perhaps much more is consumed in the process. The electrodes break the water into it's constituent parts (hydrogen and oxygen), with the hydrogen being attracted to the cathode (and bubbled out as diatomic hydrogen [H₂]) and the oxygen drawn to the anode where it combines with the chlorine ions.

 

I first became aware of the Iwaki pumps of various types from Arthur's descriptions and suggestions. As film photography was seriously waning at the time, and the film processing equipment was flooding the surplus market, many of these otherwise expensive pumps became available at very reasonable prices. I picked up several in eBay for pennies on the dollar, where now they're becoming much more scarce.

 

Swede's work holds lots of clues to the processes of amateur oxidizer production, as batch systems as well as continuous setups. Read his blogs ("You'll shoot your eye out") to catch the vision of his growth through the process.

 

WSM

[WSM]

Diluting under 10% is advantageous with regards to dosing accuracy and also the off gassing that intensifies to a great extent with the use of higher HCl concentrations. My adjustment acid was diluted between 6-8% HCl and when fed into the cell through a thin (0,5mm) PTFE tube it produced noticeable off gassing.

Be especially aware of accidentally overdosing a highly concentrated HCl solution (either by human error or equipment malfunction). The cell can enter a "runaway reaction" mode accompanied with eruptive release of copious amounts of chlorine gas and catastrophic "overboiling". Also all of the formed chlorate shall be destroyed by this process within a matter of seconds. If that should happen in an enclosed space then the results can be literally deadly. It happened to me once, but luckily it was in outside conditions and the deadly cloud had enough chance to dissipate. Was scary enough though....

 

 

It's altogether too easy to gas yourself or others if too strong a concentration of, or too much, acid is added to an active (highly alkaline and heated) chlorate cell; especially if merely dropping it onto the surface of the electrolyte. Swede discovered (re-invented) the technique of adding the acid slowly, and well below the surface of the electrolyte, in an effort to keep the chlorine in solution rather than bubbling out.

 

Thanks for sharing your experiences with that, and the cautions you suggested.

 

WSM

[PTFE]

Hey folks!
Since i've moved several times in the last 2 years I wasn't able to investigate further into electrochemistry but always thought about my cell construction.
At the moment im looking for a place to work. Also i've found my lost 4 MMO Plates (90mm*400mm*1,5mm)which i'll use in the PTFE container showed earlier.

In the past I gathered a bunch of different Titanium Bolts and nuts, some rods (Ø80mm, Ø30mm, Ø20mm), two sheets (450mm*400mm*2mm) one sheet (380mm*450mm*4mm) and two 500mm*120mm Plates 13mm Thick.
Those equipment will be cut and brought to a welder to made all the connections inside the cell. The Anodes will be screwable to change them for new ones, or PbO2.

A bigger problem I encountered with a larger cell running at higher temperatures, was saline spray coming out with the hydrogen through the vent.

Several attempts to alleviate the problem failed before I used a condensation collector inline with my vent exhaust.

The most successful setup involves a thinwalled vinyl tube running from the cell's exhaust port, up and over in a vertical arc, down into a clear jar (pliable polymer is best, maybe thin PET plastic) to collect vaporized mist and salt spray as a liquid, allowing the dryer hydrogen to escape through a vent tube in the top of the condenser bottle.

Most of the condensation occurred in the thin walled vinyl tubing, allowing the saline liquid to reflux back into the cell. Whatever liquid that got past the vinyl tube collected in the jar and the hydrogen went safely up and out of the collection jar through a thin PVC vent pipe (on top of the collection jar) with a T-fitting on the top end to prevent rainwater getting in.

I can try to find a photo of this part of the system when I return home (I'm visiting family and don't have access to my files now), and post one to show how it worked.

WSM

First I will see how this cell operates at 5V/300A.
For the Water loss compensation I will try a 400mm Dimrtoth-cooler with a still head (to provide easy-access for a wash out of any salt crust that may form inside,if any.)
Also I had a little 1.5l cell running some weeks ago, first time using some pressure fittings(ABS-plastic), just to see them melting into a gross goupy material after 24h and I had to quit the experiment.
What I was trying was the impact of an magnetic stirrer and it was amazing to see, how well all those tiny bubbles where kept in solution, not rising nearly as fast as without stirrer.
Ph controll will be much more efficient with fast stirring.
Cooling will be done with a 8x6mm PTFE Spiral inside the cell, and if i could find a Pump I will built an heat exchanger with the old PTFE cell body.
For further improvment I had a dream:P
It was about using a little insulated hot 10A "Slave-cell" without PH-control to directly react any Chlorine-loss with the hot NaOH.

I forgot to mention that the 5 liter reaction flask has a large opening (+-150mm) and there's a groove for an O-ring in the flat flange around the opening.

With a compatible O-ring seal, a flat plate of thick polymer will make an excellent lid and closure for the cell.

We'll see...

WSM

an O-ring is nice, but i like to use flat 1mm PTFE Sheet to cut rings out of it.
PTFE is quite soft and will make perfect sealings with some pressure. I think if you use PTFE body and Lid, you don't even need a Sealing.

 

Thanks for the input. I was thinking it may be a problem, so I planned to use pH control to maintain the hot electrolyte between a pH reading of 6.5 and 7.0, if I can.

I'm using borosilicate glass because the plan is to run the cell at about 110 degrees Celsius. I can't think of anything else to use that's affordable, but I'm open to suggestion.

WSM

I never had any problems with the usage of glass of any kind.
And I always use a Boro.Tube, sealed on one side for inserting a Temp.probe.
Affordable would be PTFE. A 15-30mm thick plate would be awesome for this job!

 

https://www.ebay.com/itm/PTFE-Teflon-Plate-Sheet-Block-158mm-dia-x-15mm-thickness/333143576674?hash=item4d90e79062:g:SxMAAOSwBoxak5e-

 

This could be perfect!!

By nasty to machine read "may contain asbestos" in the UK early bakelites were compounded with 30% asbestos fluff for reinforcing fiber and heat transmission resistance. Obviously this stopped here with the awareness of the hazards of asbestos, New bakelite sheet is asbestos free, but old asbestos stock material could contain asbestos and not be nice to machine due to asbestos loaded dust and turnings.

 

Reading asbestos reminds me of a paper which i have in mind, mentioning asbestos in industrial usage for Membranes in Chlor-alkali cells.
A normal unglazed clay pot may also work nice!

 

 

• build a sustainable power source to run my experiments without undue expense

WSM

For all you american people I have some reeeeeaaally nice that i just found on ebay.

 

https://www.ebay.de/itm/Acdc-Elektronik-Modell-JF5N150P-176-Umschaltbar-Netzteil-5V-150A-Gepruft/273720545481?hash=item3fbb0410c9:g:q7QAAOxy~dNRAVK5

 

 

 

 

 

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.

Im using a 3mm PTFE tube for acid injection by gravity.
At the end the tube is punctured with a needle for better distribution and it goes down to the bottom of the cell. I dilute to ~15% and add NaCl to add as little water as neccessary

Edited January 24, 2020 by PTFE

[PTFE]

 

My question : When the gravity system drip the acid into the tubing, the tubing should also have a lot of chlorate/hypochlorite ions. Acid will react with them and produce Cl2/ClO2 and go up to the acid reservoir side unless this system is pressurized. This is what I have observed. Or maybe that happened because I didn't dilute my acid enough? My acid is 32% and I usually dilute them with tap water at 1:1 ratio .So it should be around 15~16%. Is that considered too concentrated?

 

 

 

That is so true. Before I tried pH control, I only have 50-55% efficiency. Now, I can achieve 85%. Couldn't be more happy than that. It certainly worth the effort.

I had this problem before, coming to the cell and in the silicon tube was a bright yellow liquid. When i placed the HCL reservoir higher, that problem did not occour anymore. Also it happened when i used a smaller diameter for venting the gas out of the cell which resulted in a higher pressure inside of the cell.

 

[WSM]

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.

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.

 

 

I've located the photo of my vapor recovery system, used about four years ago when I was running the first sodium chlorate experiment. The key to the success of it was using thin-walled clear vinyl tubing which allowed most of the vapors to condense on the inner walls of the tubing and run down and back into the cell (a reflux system).

 

 

This photo shows how it was set up. I tried hard PVC pipe (for a vent) which failed, allowing liquid electrolyte to drip down onto the lid of the cell, from the vent outlet (a Tee fitting, to keep rain or dirt from entering the vent pipe); exposing my electrical connections to the corrosive drips. Even when I extended the hard PVC pipe vent tube 1.5-2 (about 6 feet) meters high, the same problem occurred.

 

Only when I set up the recovery system shown, did the problem disappear.

 

WSM

Edited February 2, 2020 by WSM

[PTFE]

This is exactly what i did in previous runs except the trap.

When running a cell with 100a and more I used a 2m long Tube with 30mm diameter for venting.

 

I also like to use a bottle with top-up solution to bubble the Gases through.

 

In my next Run a dimroth will be used for efficient reflux and when the Run comes to an end I will replace it with only a Tube to slowly evaporate some of the electrolyte.

Since im planing to combine my old cell body with the New 10l ptfe Tank, the total Volume will be around 14-15l

 

A Run at 80-90*C will take around 7 days to convert 13,5kg of nacl to 24.5kg clO3 assuming 80% efficiency.

This will lead to max. saturation at 80*C

 

Samples will be taken to see if crystals Start to form and then the electrolyte will be passed through a large vacuum filter and cooled for harvesting.

 

Maybe it works out better then i think at the Moment.

When using my old cell body to build an heat exchanger, maybe nice clean crystals will Start to form on the cool paarts

Edited January 27, 2020 by PTFE

[WSM]

This is exactly what i did in previous runs except the trap.

When running a cell with 100a and more I used a 2m long Tube with 30mm diameter for venting.

I also like to use a bottle with top-up solution to bubble the Gases through.

In my next Run a dimroth will be used for efficient reflux and when the Run comes to an end I will replace it with only a Tube to slowly evaporate some of the electrolyte.

Since im planing to combine my old cell body with the New 10l ptfe Tank, the total Volume will be around 14-15l

A Run at 80-90*C will take around 7 days to convert 13,5kg of nacl to 24.5kg clO3 assuming 80% efficiency.

This will lead to max. saturation at 80*C

Samples will be taken to see if crystals Start to form and then the electrolyte will be passed through a large vacuum filter and cooled for harvesting.

Maybe it works out better then i think at the Moment.

When using my old cell body to build an heat exchanger, maybe nice clean crystals will Start to form on the cool paarts

 

 

I look forward to hear and see more about it as you progress. Photos?!

 

WSM

[abc159201]

I had this problem before, coming to the cell and in the silicon tube was a bright yellow liquid. When i placed the HCL reservoir higher, that problem did not occour anymore. Also it happened when i used a smaller diameter for venting the gas out of the cell which resulted in a higher pressure inside of the cell.

 

 

Wow, I'll try this out. Thanks a lot!

[Andead]

This is exactly what i did in previous runs except the trap.

When running a cell with 100a and more I used a 2m long Tube with 30mm diameter for venting.

 

I also like to use a bottle with top-up solution to bubble the Gases through.

 

In my next Run a dimroth will be used for efficient reflux and when the Run comes to an end I will replace it with only a Tube to slowly evaporate some of the electrolyte.

Since im planing to combine my old cell body with the New 10l ptfe Tank, the total Volume will be around 14-15l

 

A Run at 80-90*C will take around 7 days to convert 13,5kg of nacl to 24.5kg clO3 assuming 80% efficiency.

This will lead to max. saturation at 80*C

 

Samples will be taken to see if crystals Start to form and then the electrolyte will be passed through a large vacuum filter and cooled for harvesting.

 

Maybe it works out better then i think at the Moment.

When using my old cell body to build an heat exchanger, maybe nice clean crystals will Start to form on the cool paarts

This is a monster cell here. I am extremely curious how it turns out so keep us updated

[WSM]

I've located the photo of my vapor recovery system, used about four years ago when I was running the first sodium chlorate experiment. The key to the success of it was using thin-walled clear vinyl tubing which allowed most of the vapors to condense on the inner walls of the tubing and run down and back into the cell (a reflux system).

Chlorate Cell Vapor Recovery System.JPG

This photo shows how it was set up. I tried hard PVC pipe (for a vent) which failed, allowing liquid electrolyte to drip down onto the lid of the cell, from the vent outlet (a Tee fitting, to keep rain or dirt from entering the vent pipe); exposing my electrical connections to the corrosive drips. Even when I extended the hard PVC pipe vent tube 1.5-2 (about 6 feet) meters high, the same problem occurred.

Only when I set up the recovery system shown, did the problem disappear.

WSM

 

The vapor recovery system worked in an outdoor cell setup and was effective in my locale (Coastal Western US). It was a passive system. Passive systems are nice, because they require no additional energy input but work on their own.

 

If an active system is needed, jacketing the reflux tube with a larger, hard plastic pipe with cool water flowing through it, would keep the whole setup operating in hot Summer weather. For Winter weather, exposure to ambient air should be enough (unless you are in arctic conditions [ !], then use antifreeze in the jacket water?).

 

I suppose I'm thinking outside the box here. As always, experimentation is needed to adapt your setup for optimal performance, and your needs and location.

 

WSM

[WSM]

Diluting under 10% is advantageous with regards to dosing accuracy and also the off gassing that intensifies to a great extent with the use of higher HCl concentrations. My adjustment acid was diluted between 6-8% HCl and when fed into the cell through a thin (0,5mm) PTFE tube it produced noticeable off gassing.

Be especially aware of accidentally overdosing a highly concentrated HCl solution (either by human error or equipment malfunction). The cell can enter a "runaway reaction" mode accompanied with eruptive release of copious amounts of chlorine gas and catastrophic "overboiling". Also all of the formed chlorate shall be destroyed by this process within a matter of seconds. If that should happen in an enclosed space then the results can be literally deadly. It happened to me once, but luckily it was in outside conditions and the deadly cloud had enough chance to dissipate. Was scary enough though....

 

 

Regarding overdosing the active cell (or even with the power off) with hydrochloric acid, Arthur shared a patent with me that adds to our understanding of how this affects to chlorate in the system. See (Google search) European patent EP0098500A1 for the industrial method described on how to destroy chlorate in processes designed for making hypochlorite or hydroxides/chlorine.

 

Though industry's goals aren't ours, the methods they use explain what happens if we make procedural errors by incorrectly dosing our cells while trying to make oxidizers. As was stated earlier, we can actually undo all our efforts by quickly destroying all our chlorate, if we add the acid wrong, and possibly harm ourselves or others.

 

WSM

Edited February 2, 2020 by WSM

[Pyrophury]

I know it's been a while, but I've been been busy and have only just got around to testing my chlorate cell. Here it is:

 

 

Things started out OK - 1,650g of sodium chloride (water softener tablets) were dissolved in straight tap water (with the help of a lot of stirring). The viton rubber O ring was lubricated with silicon grease, lid went on, vent tube attached and directed outside, electrodes attached and the power was switched on.

 

After about 30 minutes the temp had risen to around 35C and the current was steady at 20A. But over the next 5 hours it just kept getting hotter and hotter, the current kept getting higher and higher... until it reached around 80C and 50A. I didn't want to risk it getting any higher, so I abandoned the run at this point and siphoned out the electrolyte from the RC and shut down the power.

 

At such high temperature and current I was concerned about excessive wear on both the MMO anode and the 60A power supply. I'd like to figure out a way of limiting the current to about 20 amps, perhaps with a 100W .25 Ohm resistor?

 

But before that I'll try altering the setup so that the power supply is mounted on the wall above the cell, which will be cooled in a large tub of water - hopefully that will be sufficient to dissipate the heat generated.

[markx]

Resistors, although simplest in terms of application, are not the best way of limiting such high currents. The switch mode power supplies usually have a pot for regulating output voltage. I trust the one you use has this option too...in fact I'm pretty sure I can see it beside the green "ON" led in the picture. Turn that pot in the direction of minimizing the output voltage all the way down as far as it goes. They usually allow to regulate voltage in the range of 4.0V-5.5V. Then give it a new go with the minimal voltage setting. It helps to keep the current in check once the cell reaches operational temperature.

If that is not sufficent then a PWM module in series with the power supply could be used to reach the same effect: it will pulse the SMPS output voltage on to the module's output capacitors and finally the cell, effectively limiting the mean voltage value, thus also the current. But you have to find or design a PWM module that is able to operate at low voltages near or below 5V. If you are electronically inclined then a small PWM module could be used to drive a suitable MOSFET of IGBT combination that shall handle the main currents.

Also you could move the electrodes in the cell further apart from each other, but I guess that would require alterations to the cell lid. In essence moving the electrodes further apart shall be equal to adding a series resistor into the circuit.

[Pyrophury]

Resistors, although simplest in terms of application, are not the best way of limiting such high currents. The switch mode power supplies usually have a pot for regulating output voltage. I trust the one you use has this option too...in fact I'm pretty sure I can see it beside the green "ON" led in the picture. Turn that pot in the direction of minimizing the output voltage all the way down as far as it goes. They usually allow to regulate voltage in the range of 4.0V-5.5V. Then give it a new go with the minimal voltage setting. It helps to keep the current in check once the cell reaches operational temperature.

If that is not sufficent then a PWM module in series with the power supply could be used to reach the same effect: it will pulse the SMPS output voltage on to the module's output capacitors and finally the cell, effectively limiting the mean voltage value, thus also the current. But you have to find or design a PWM module that is able to operate at low voltages near or below 5V. If you are electronically inclined then a small PWM module could be used to drive a suitable MOSFET of IGBT combination that shall handle the main currents.

Also you could move the electrodes in the cell further apart from each other, but I guess that would require alterations to the cell lid. In essence moving the electrodes further apart shall be equal to adding a series resistor into the circuit.

 

Moving the electrodes further apart is not really an option I even want to consider, it would be a last resort.

 

The voltage pot is already as low as it will go. I like the suggestion regarding the PWM, I'm inexperienced when it comes to electronics though so unless it's something that I can buy off the shelf I've got no hope. Thanks.

[WSM]

I know it's been a while, but I've been been busy and have only just got around to testing my chlorate cell. Here it is:

 

 

Things started out OK - 1,650g of sodium chloride (water softener tablets) were dissolved in straight tap water (with the help of a lot of stirring). The viton rubber O ring was lubricated with silicon grease, lid went on, vent tube attached and directed outside, electrodes attached and the power was switched on.

 

After about 30 minutes the temp had risen to around 35C and the current was steady at 20A. But over the next 5 hours it just kept getting hotter and hotter, the current kept getting higher and higher... until it reached around 80C and 50A. I didn't want to risk it getting any higher, so I abandoned the run at this point and siphoned out the electrolyte from the RC and shut down the power.

 

At such high temperature and current I was concerned about excessive wear on both the MMO anode and the 60A power supply. I'd like to figure out a way of limiting the current to about 20 amps, perhaps with a 100W .25 Ohm resistor?

 

But before that I'll try altering the setup so that the power supply is mounted on the wall above the cell, which will be cooled in a large tub of water - hopefully that will be sufficient to dissipate the heat generated.

 

 

If I were to guess, I'd say the upper half of the cell is hotter than the lower half, judging by the look of it.

 

If the electrodes are placed lower in the cell, it would encourage more circulation because of "hydrogen lift".

 

Another method of running cooler, is to use smaller electrodes.

 

I'm not telling you to remake your electrodes, BUT it would solve the apparent problems.

 

Something to consider...

 

WSM

[WSM]

Resistors, although simplest in terms of application, are not the best way of limiting such high currents. The switch mode power supplies usually have a pot for regulating output voltage. I trust the one you use has this option too...in fact I'm pretty sure I can see it beside the green "ON" led in the picture. Turn that pot in the direction of minimizing the output voltage all the way down as far as it goes. They usually allow to regulate voltage in the range of 4.0V-5.5V. Then give it a new go with the minimal voltage setting. It helps to keep the current in check once the cell reaches operational temperature.

If that is not sufficent then a PWM module in series with the power supply could be used to reach the same effect: it will pulse the SMPS output voltage on to the module's output capacitors and finally the cell, effectively limiting the mean voltage value, thus also the current. But you have to find or design a PWM module that is able to operate at low voltages near or below 5V. If you are electronically inclined then a small PWM module could be used to drive a suitable MOSFET of IGBT combination that shall handle the main currents.

Also you could move the electrodes in the cell further apart from each other, but I guess that would require alterations to the cell lid. In essence moving the electrodes further apart shall be equal to adding a series resistor into the circuit.

 

As I mentioned in the previous post, smaller electrodes would reduce the demand on the power supply, plus things should run cooler.

 

If you try these steps, see if I'm right.

 

WSM

[PTFE]

If I were to guess, I'd say the upper half of the cell is hotter than the lower half, judging by the look of it.

 

If the electrodes are placed lower in the cell, it would encourage more circulation because of "hydrogen lift".

 

Another method of running cooler, is to use smaller electrodes.

 

I'm not telling you to remake your electrodes, BUT it would solve the apparent problems.

 

Something to consider...

 

WSM

same thought here. I would try to apply a stir bar for better heat distribution.

Also a big tub of water or a fan blowing at the cell could help.

[PTFE]

I had the same problems but when the temperature stabilized below 100°C it was okay for me. My MMO survived many hours without a lot of wear.

[Pyrophury]

If I were to guess, I'd say the upper half of the cell is hotter than the lower half, judging by the look of it.

 

If the electrodes are placed lower in the cell, it would encourage more circulation because of "hydrogen lift".

 

Another method of running cooler, is to use smaller electrodes.

 

I'm not telling you to remake your electrodes, BUT it would solve the apparent problems.

 

Something to consider...

 

WSM

 

Yes, the top was noticeably warmer than the bottom. Unfortunately I didn't make the electrode straps long enough to reach the bottom of the cell (trying to economise on Ti tube). When it comes to the lead dioxide electrodes I'll be sure to make them longer.

 

As I mentioned in the previous post, smaller electrodes would reduce the demand on the power supply, plus things should run cooler.

 

If you try these steps, see if I'm right.

 

WSM

 

It'd be a shame to cut them down, but I'm really surprised at the current draw for what I'd considered already quite modest sized electrodes (35 x 150mm).

 

same thought here. I would try to apply a stir bar for better heat distribution.

Also a big tub of water or a fan blowing at the cell could help.

 

Those seems like the simplest solutions. Although I do have a hotplate/stirrer, it's a bit precarious balanced on there.

 

I had the same problems but when the temperature stabilized below 100°C it was okay for me. My MMO survived many hours without a lot of wear.

 

That's re-assuring. Thanks all.

[Arthur]

If that is the lowest that your PSU will set to, then make a set of leads twice that long, very little resistance is needed to reduce the current considerably. I tried 10 resistors in parallel each was 0.47R so the finished block was 0.047 ohms and that was far too much resistance and the current fell away to nearly nothing.

 

Best plan is to make a long set of leads and shorten them if necessary to limit the current to what you want. I used fat speaker wire and just cut it down til it limited nicely near the PSUs limit current.