pH control for chlorate cells

[Swede]

I thought this important topic deserves a thread of it's own. Without pH control, a chlorate cell's efficiency is probably going to be at 50% or below, as opposed to a correct system maintained at a pH of between 6.7 and 7.0 that can be better than 85%. My best ever is about 93% CE.

 

I mentioned in the other thread (Making perchlorate by any means possible) that I had gone full circle with acid control, from electronic timers and pumps, to more simplistic, and in my mind, reliable systems. Pumps and timers work fine, but in my case, at least, it was a complex and even noisy affair. There was no simple way to adjust the flow, and the pump was not designed to trickle such minute amounts on a continual basis, so I had to set it up for periodic delivery. Also, it was designed to operate under pressure... to inject chemicals into a pressurized system. A typical chlorate cell does not need this. Another advantage of low but continual dosage is that you do not have a localized evolution of chlorine gas, which happens when strong HCl is injected in any quantity in a cell.

 

A gravity-fed drip solves this problem, and is much simpler than a pump and timer. The only real challenge is metering the flow. I bought an expensive PTFE needle valve which works fine, but there is a better way. Surplus IV (intravenous) equipment, dirt cheap, from eBay.

 

I picked up two samples of these devices. Look for keywords like "IV regulator set" or "IV extension set with control-a-flow regulator".

 

http://www.5bears.com/perc/drip/drip01.jpg

 

http://www.5bears.com/perc/drip/drip02.jpg

 

The blue one is a "Baxter Interlink System Extension Set with Control-a-flow Regulator." The all white setup is a "Braun Rate Flow Regulator IV Set." The latter has a drip observation tube section, which is important. More on that later...

[Swede]

The equipment is inexpensive, a couple of $$ each, and is NIW. Obviously, don't buy anything used! They get surplused for being out of date or other trivial reasons.

 

http://www.5bears.com/perc/drip/drip03.jpg

 

The hardware is good quality. The Baxter rig has Luer lock fittings on both ends, while the Bauer has a piercing probe that gets stuck right into a bag. Both units have a dial that goes from OFF to 250 ml/hour, to "wide open" which would drain a source rapidly... possibly useful for a quick, high dose of HCl.

 

http://www.5bears.com/perc/drip/drip04.jpg

 

I rigged them up using a pair of 60ml plastic syringe bodies, filled them with water, and tested the flow.

 

http://www.5bears.com/perc/drip/drip06.jpg

[Swede]

The units were easy to prime, and both had convenient pinch-locks installed on the tubing, so you can shut them off completely if needed. Handy during the installation phase.

 

I set them both to 125 ml per hour, and let rip. The Baxter unit, the blue one with no drip chamber, delivered a bit low... 109 ml/hour. The white Braun unit did 103 ml/hour. I suspect they were low because the head pressure on my setup did not equate to a taller IV bag as seen in a hospital. Obviously, flow will vary with head pressure of the reservoir, but at these rates, not too bad.

 

http://www.5bears.com/perc/drip/drip07.jpg

 

http://www.5bears.com/perc/drip/drip08.jpg

 

IV rigs with drip tubes typically come calibrated in drops per ml. In the case of the Braun, it is 20 drops per ml, and it was accurate. This gives you a very convenient way to visually confirm acid dosage rate. Count drops in a minute, divide by 20, and there's your ml/minute rate. So if anyone goes for something like this, I'd recommend getting one with a calibrated drip tube. I plan on further calibrating these to see how accurate the dials are with a system set up for use with a cell. One last test is using concentrated HCl to verify that the materials are resistant to the acid, but my gut feel is that all will be well. HCl and plastics in general get along fine.

 

In use, one would need to determine the appropriate dosing for a chlorate cell, and this will vary primarily with the current, rather than the volume of the cell. And there is no reason one could not use these for an acidified top-off rig. Prepare a stock solution with the chloride of your choice, add a known amount of acid, and use that both for topping and pH control. Obviously, got to be careful not to overflow a cell.

 

Anyway, I'd still recommend a few runs testing pH on any new cell so one knows how his cell behaves in terms of acid demand. More acid is needed earlier in a run. I think it'd be possible to plot an acid demand vs. ampere-hours for a setup, and then use one of these, manually adjusting the flow as the reaction progresses. The good news is that I've noticed later in a run, with less acid needed, some sort of buffering takes place, and the pH is generally decently stable. Further, while 6.8 is perfect, really anything between 6.4 and 7.4 is going to be massively more efficient than an uncontrolled cell.

 

I'd like this thread to be devoted to any discussions or devices designed for pH control, so please feel free to contribute ideas.

[WSM]

The units were easy to prime, and both had convenient pinch-locks installed on the tubing, so you can shut them off completely if needed. Handy during the installation phase.

 

I set them both to 125 ml per hour, and let rip. The Baxter unit, the blue one with no drip chamber, delivered a bit low... 109 ml/hour. The white Braun unit did 103 ml/hour. I suspect they were low because the head pressure on my setup did not equate to a taller IV bag as seen in a hospital. Obviously, flow will vary with head pressure of the reservoir, but at these rates, not too bad.

 

http://www.5bears.com/perc/drip/drip07.jpg

 

http://www.5bears.com/perc/drip/drip08.jpg

 

IV rigs with drip tubes typically come calibrated in drops per ml. In the case of the Braun, it is 20 drops per ml, and it was accurate. This gives you a very convenient way to visually confirm acid dosage rate. Count drops in a minute, divide by 20, and there's your ml/minute rate. So if anyone goes for something like this, I'd recommend getting one with a calibrated drip tube. I plan on further calibrating these to see how accurate the dials are with a system set up for use with a cell. One last test is using concentrated HCl to verify that the materials are resistant to the acid, but my gut feel is that all will be well. HCl and plastics in general get along fine.

 

In use, one would need to determine the appropriate dosing for a chlorate cell, and this will vary primarily with the current, rather than the volume of the cell. And there is no reason one could not use these for an acidified top-off rig. Prepare a stock solution with the chloride of your choice, add a known amount of acid, and use that both for topping and pH control. Obviously, got to be careful not to overflow a cell.

 

Anyway, I'd still recommend a few runs testing pH on any new cell so one knows how his cell behaves in terms of acid demand. More acid is needed earlier in a run. I think it'd be possible to plot an acid demand vs. ampere-hours for a setup, and then use one of these, manually adjusting the flow as the reaction progresses. The good news is that I've noticed later in a run, with less acid needed, some sort of buffering takes place, and the pH is generally decently stable. Further, while 6.8 is perfect, really anything between 6.4 and 7.4 is going to be massively more efficient than an uncontrolled cell.

 

I'd like this thread to be devoted to any discussions or devices designed for pH control, so please feel free to contribute ideas.

 

Hi Swede,

 

This looks like the simplest pH scheme yet. I can see it'll lend itself well to a bucket cell.

 

I wonder if a large reservoir (say, about 1 gallon) placed about three feet above the cell would provide the needed head pressure for flawless performance of the pH control system?

I need to try it and add it to my continuous experiments.

 

WSM

[Arthur]

When I did process control analysis for a 8000A plating plant there was a lot of good rule of thumb knowledge on the shop floor by which they did the hourly chemical additions. The daily checks were my responsibility.

 

Maybe it will be possible to build a cell, develop a (rough) top up method, and have a manual check every day or two. The IV assembly looks a fine method for the rough process additions. And if you have the sources a cheap method.

 

WSM found some Iwaki pumps (ex photo lab industry) for a similar use.

[mikeee]

You could purchase a PH probe & electronics to interface with a small PLC.

You will need to program a basic logic into the PLC to control the pump/valve flow.

You might be able to find one on Ebay, look for Rosemount, Foxboro, Endress & Hauser etc.

Most of these instruments use a 4-20ma or 0-10vdc output value to measure the PH with.

You would also need the correct PH probe for the chlorate solution you are measuring.

PH Probe electronics sends out 4-20ma or 0-10vdc value.

PLC receives the 4-20ma or 0-10vdc signal.

PLC logic sends signal to pump or valve to increase or decrease flow of solution.

You will need to calibrate the electronics/probe on a regular basis to guarantee accuracy.

Once you get this setup you will increase the life of the electrodes & production rate.

 

Mikeee

[WSM]

You could purchase a PH probe & electronics to interface with a small PLC.

You will need to program a basic logic into the PLC to control the pump/valve flow.

You might be able to find one on Ebay, look for Rosemount, Foxboro, Endress & Hauser etc.

Most of these instruments use a 4-20ma or 0-10vdc output value to measure the PH with.

You would also need the correct PH probe for the chlorate solution you are measuring.

PH Probe electronics sends out 4-20ma or 0-10vdc value.

PLC receives the 4-20ma or 0-10vdc signal.

PLC logic sends signal to pump or valve to increase or decrease flow of solution.

You will need to calibrate the electronics/probe on a regular basis to guarantee accuracy.

Once you get this setup you will increase the life of the electrodes & production rate.

 

Mikeee

 

Hi Mikeee,

 

It's a nice thought but unfortunately, not that simple. The main problem is; the solution we're trying to control poisons the pH probe and kills it. Swede or Tentacles located a pH probe capable of handling the cell environement, BUT it cost about $900!.

 

The simple solution to the problem is to add a measured amount of acid based on the current consumed in the process.

 

If you read Swede's excellent blogs, you'll catch up quickly and see where we're coming from.

 

Welcome to the discussion...

 

WSM

Edited July 20, 2012 by WSM

[Swede]

True, Mikee, I've killed more than one probe with simple dip pH measurements over a single run. A $20 aquarium pH probe, cheap and single junction, literally stopped functioning after only 10 to 20 short dips in extracted cell liquor. My better probes, the yellow Milwaukee jobs, are a bit more stout, but still seem to suffer badly, requiring recalibration, and slowing terribly, after even modest use. It's horrible.

 

The concept is nice in the sense that it'd be easy to create a pH controller that opens a solenoid valve and delivers HCl on demand, but even a high grade probe, a $350 job, would have a short life, a few days, in an active chlorate cell.

 

I think the answer will lie in determining HCl requirements based upon amp-hours, and using derived delivery backed up by occasional manual pH checks.

 

These materials, the IV rigs, withstood concentrated HCl with zero problems over 24 hours, FWIW. More to come... got to get to work, on a Saturday.

[WSM]

These materials, the IV rigs, withstood concentrated HCl with zero problems over 24 hours, FWIW. More to come... got to get to work, on a Saturday.

 

Okay, Swede, I've taken the bait. I've got six IV rigs on the way and will have them within a week. I'm looking forward to trying them and will report back here when I do.

 

Now what am I going to do with all those miniature 12Vdc teflon valves and few fluorocarbon or PVC needle valves I've collected; not to mention the high accuracy parastaltic pumps?!!! And Arthur is right, I still have those Iwaki bellows pumps (chemical delivery type).

 

Since the regulated IV drip system is so simple I feel it'll lend itself very well to the bucket cell system and I'll have to try it out and see. Thanks for the suggestion.

 

WSM

Edited July 23, 2012 by WSM

[WSM]

Okay, Swede, I've taken the bait. I've got six IV rigs on the way and will have them within a week. I'm looking forward to trying them and will report back here when I do.

Now what am I going to do with all those miniature 12Vdc teflon valves and few fluorocarbon or PVC needle valves I've collected; not to mention the high accuracy parastaltic pumps?!!! And Arthur is right, I still have those Iwaki bellows pumps (chemical delivery type).

Since the regulated IV drip system is so simple I feel it'll lend itself very well to the bucket cell system and I'll have to try it out and see. Thanks for the suggestion.

WSM

 

Amazing! I ordered three of the Braun units on Friday and got them this morning! I need to make the time to try them (to determine the feed rate so I can adjust them for proper pH control of my cells).

 

WSM

[Swede]

Hey WSM, if you've already got the high-grade PTFE needle valves, that'd absolutely be the way to go, using some sort of gravity-fed system. I bought these purely to see if the concept was workable, and if so, it'd be a very nice way to pH control a cell for dirt cheap.

 

I'd suggest anyone creating a cell, especially new guys, incorporate one. Even if you don't have a pH meter, the numbers (HCl delivery based upon current) we have calculated from both industry and experiment, are going to boost efficiency by at least 25% or more, possibly much more. And oddly enough, IMO a pH controlled cell runs "sweeter" for some reason, less fuming and noxiousness from various vents.

 

WSM, what I'd suggest you do, given your nice equipment, is scrap the Braun valve, replace it with your nice needle valve, and use the drop-counter chamber for dosage tracking. Calibrate the device by determining drops per ml. I did this by counting about a thousand freaking drops and measuring the fluid output with a graduated cylinder. The Braun drop chambers ended up being 17 drops per ml rather than 20.

 

I'm going to plot a graph for these things, that will be Amperage vs. Drops/minute, using a specific HCl concentration. That way, all a guy needs to do is check his current, reference the graph, and determine "I need X drops per minute" - and of course, vary whatever valve is used up or down to at least get close to the necessary number. An occasional pH check wouldn't hurt, of course.

 

An elegant way to do it would be to have three or four such plots, each corresponding to a quarter of a run, since acid demand diminishes as the run progresses. Plot #1 would be full theoretical acid delivery. Plot #2 would be (say) 80% of plot #1. Etc, plot #4 being perhaps 40% of plot #1.

[Swede]

Oh yes, I meant to add... I have a possible line on Lead Dioxide anodes from China. These puppies look nice.

 

http://www.5bears.com/ld/chinald.jpg

 

Looks are one thing... how they perform is another. The quoted dimension is 1.0mm x 100mm x 100mm, about 4" x 4", a nice size. Two of these in a big sandwich with three Ti cathodes would probably handle upwards of 100A.

 

It'll probably be a few weeks before they arrive.

 

I have to say I'm conflicted. If they turn out to be killer anodes, the "hunt" for a home-brew LD anode might go out the window, and the chase is half the fun.

[WSM]

Oh yes, I meant to add... I have a possible line on Lead Dioxide anodes from China. These puppies look nice.

 

http://www.5bears.com/ld/chinald.jpg

 

Looks are one thing... how they perform is another. The quoted dimension is 1.0mm x 100mm x 100mm, about 4" x 4", a nice size. Two of these in a big sandwich with three Ti cathodes would probably handle upwards of 100A.

 

It'll probably be a few weeks before they arrive.

 

I have to say I'm conflicted. If they turn out to be killer anodes, the "hunt" for a home-brew LD anode might go out the window, and the chase is half the fun.

 

Hi Swede,

 

Don't put the chemicals away just yet. I have two similar sized Chinese LD anodes I got from patsroom and both of them have damage on them, compromising the LD's integrity. One excellent solution to my problem is to repair them in an LD plating bath!

 

I hope the anodes you get are in better shape than the two I got (if so, I'd be happy to buy one from you; let me know).

 

WSM

Edited July 25, 2012 by WSM

[WSM]

Oh yes, I meant to add... I have a possible line on Lead Dioxide anodes from China. These puppies look nice.

http://www.5bears.com/ld/chinald.jpg

Looks are one thing... how they perform is another. The quoted dimension is 1.0mm x 100mm x 100mm, about 4" x 4", a nice size. Two of these in a big sandwich with three Ti cathodes would probably handle upwards of 100A.

It'll probably be a few weeks before they arrive.

I have to say I'm conflicted. If they turn out to be killer anodes, the "hunt" for a home-brew LD anode might go out the window, and the chase is half the fun.

 

It looks like all we need to do is spot-weld a tubular lead on the end of the strap and we're good to go!

 

WSM

Edited July 25, 2012 by WSM

[WSM]

It looks like all we need to do is spot-weld a tubular lead on the end of the strap and we're good to go!

WSM

 

Now here's the big question, is pH control required or even desirable in the Perchlorate cell? It seems somewhere I read it's not.

 

Also, is it true that ozone production during the process is indicative of an overcurrent condition? Sometimes, the more I learn, the more questions I have. Thanks for any light you can shed on these for me.

 

WSM

[Swede]

WSM, I'd be interested in hearing more about your damaged LD Chinese anode. Damaged in the sense that it no longer works, or does it shed excessively? The thing with perchlorate, regardless of the anode, there are going to be losses due to chemical erosion. If one immersed a one kilo Pt bar into a perchlorate cell, it's going to be less than a kilo when you're done. The factories use Pt because it is so much more efficient than just about anything else, yet they still do Pt recovery techniques with the spent liquor.

 

With LD, we don't have to worry about the losses. LD is very cheap compared to Pt, and some losses are inevitable. But if they have a decent longevity, then it'd be an acceptable loss. Any lead in the resultant batch is going to be insoluble and isolatable if desired.

 

I read about the ozone in a scientific paper about lead dioxide. Some of the guys in SM thought I was a bit nuts that I smelled ozone being generated, but it apparently happens, like you mention, if the current density is excessive. It'd be an interesting experiment to dial up the current slowly on a LD anode, and simply do a sniff test for O3, find the current at which it evolves, and probably limit the current for that particular anode to something a bit less. Energy going into O3 production is probably wasted.

 

Interestingly, in my readings on Boron-doped diamond, there is a company making compact ozonator devices that use BDD to generate O3 using an electrolytic. Two implications...

 

- BDD will make perchlorate

- Any anode that is regularly used to generate O3 gas via electrolysis will also probably make ClO4

 

The old hobby "holy grail" used to be a good LD anode. I think now it is any anode, maybe BDD, that will be 100% inert, no losses, and with a longevity at least as good as MMO is with chlorate. Also, one that can go from chloride to perchlorate in one run, without being chloride sensitive, as both LD and Pt are to some degree.

[Swede]

Oh yes, AFAIK, pH control is both unnecessary and possibly harmful. Dann2 is the only guy I know of who attempted pH control experiments with perchlorate, and the results were disastrous, a wrecked anode and some undesirable side products.

 

Remember, the energy needed to go from chlorate to perchlorate is quite a bit less than chloride to chlorate.

 

Conversion Process Formula for CE in %, Y = yield in grams, Ah = ampere-hours

 

Na Chloride to Chlorate 151.08 * Y / Ah

Na Chlorate to Perchlorate 43.78 * Y / Ah

K Chloride to Chlorate 131.22 * Y / Ah

K Chlorate to Perchlorate 38.69 * Y / Ah

Na Chloride to Perchlorate 175.10 * Y / Ah

 

Chlorate to perchlorate requires roughly 1/3 the coulombs than chloride to chlorate.

[WSM]

WSM, I'd be interested in hearing more about your damaged LD Chinese anode. Damaged in the sense that it no longer works, or does it shed excessively? The thing with perchlorate, regardless of the anode, there are going to be losses due to chemical erosion.

 

Hi Swede,

 

The damage is physical damage; chipping off of the LD in transit by mail. I've hesitated dipping the electrode in electrolyte till I can manage some sort of repair. I'm concerned about the LD delaminating off the titanium substrate (which I believe is coated with MMO prior to the LD plating) and losing conductivity.

 

This is why I think plating a bit more beta-form LD would make an ideal repair to my damaged anodes.

 

WSM

Edited July 26, 2012 by WSM

[pyrojig]

Hi Swede,

 

The damage is physical damage; chipping off of the LD in transit by mail. I've hesitated dipping the electrode in electrolyte till I can manage some sort of repair. I'm concerned about the LD delaminating off the titanium substrate (which I believe is coated with MMO prior to the LD plating) and losing conductivity.

 

This is why I think plating a bit more beta-form LD would make an ideal repair to my damaged anodes.

 

WSM

 

This is brilliant !! You guys should put the repair to the test!! I cant wait to see the results. I have always been intrigued to hear how that LD works for the production of perch. If it is a hit < Im in for joining the testing .

[WSM]

Oh yes, AFAIK, pH control is both unnecessary and possibly harmful. Dann2 is the only guy I know of who attempted pH control experiments with perchlorate, and the results were disastrous, a wrecked anode and some undesirable side products.

Remember, the energy needed to go from chlorate to perchlorate is quite a bit less than chloride to chlorate.

Conversion Process Formula for CE in %, Y = yield in grams, Ah = ampere-hours

Na Chloride to Chlorate 151.08 * Y / Ah

Na Chlorate to Perchlorate 43.78 * Y / Ah

K Chloride to Chlorate 131.22 * Y / Ah

K Chlorate to Perchlorate 38.69 * Y / Ah

Na Chloride to Perchlorate 175.10 * Y / Ah

Chlorate to perchlorate requires roughly 1/3 the coulombs than chloride to chlorate.

 

Another point I (we) need to investigate; it appears from my reading (so far) that the ideal environment for turning chlorate to perchlorate is alkaline (pH 10)!!! I wouldn't have guessed that, but who says chlorate and perchlorate have to be the same? There are other differences in the two processes; might as well add this to the list if it proves to be correct. I've got to do some more reading and try a few experiments to get this all figured out (and hopefully better understood).

 

WSM

Edited July 27, 2012 by WSM

[WSM]

This is brilliant !! You guys should put the repair to the test!! I cant wait to see the results. I have always been intrigued to hear how that LD works for the production of perch. If it is a hit < Im in for joining the testing .

 

I'm up for testing this but I lack some of the required equipment and reagents. It might be better if I spot-weld the tubular titanium lead to it first, fill it with lead-free solder then proceed to try the plating repair.

What do you say, Swede? Want to collaborate on this one?

 

WSM

[WSM]

Another point I (we) need to investigate; it appears from my reading (so far) that the ideal environment for turning chlorate to perchlorate is alkaline (pH 10)!!! I wouldn't have guessed that, but who says chlorate and perchlorate have to be the same? There are other differences in the two processes; might as well add this to the list if it proves to be correct. I've got to do some more reading and try a few experiments to get this all figured out (and hopefully better understood).

WSM

 

Upon further reading and study, the author gives an indication that pH is irrelevant in the perchlorate cell (at least with a platinum anode), and suggests that a pH range anywhere from 2 to 11 is workable. Do we accept this or test it for ourselves? Again, the more I read the more questions I have...

 

WSM

[pyrojig]

Upon further reading and study, the author gives an indication that pH is irrelevant in the perchlorate cell (at least with a platinum anode), and suggests that a pH range anywhere from 2 to 11 is workable. Do we accept this or test it for ourselves? Again, the more I read the more questions I have...

 

WSM

 

Ha, dont you love that....

Just because one author claims it doesnt mean it is correct. A test is always good. I'd assume that for the sake of the cell and hardware , you'd want a close to "N" ph . Also , ( another curve ball) was it Kclo3 or NaClo3 as the starting material. ?

[WSM]

Ha, dont you love that....

Just because one author claims it doesnt mean it is correct. A test is always good. I'd assume that for the sake of the cell and hardware , you'd want a close to "N" ph . Also , ( another curve ball) was it Kclo3 or NaClo3 as the starting material. ?

 

Industry typically uses NaClO₃ but I believe it applies to both. Swede mentioned that Dann2 at sm destroyed several anodes trying pH control in the chlorate to perchlorate process. I'm leaning toward trying perchlorate production without pH control, based on that information alone.

 

Of course we're only discussing one facet of the (complex) reaction. I read that proper current levels (not too low or too high) as well as keeping the chlorate levels up are also vital components of maintaining (perchlorate) anode health.

 

So much to learn and I'm still floundering with chlorate production (I'll get there, just watch and see...).

 

WSM

[pyrojig]

 

 

So much to learn and I'm still floundering with chlorate production (I'll get there, just watch and see...).

 

WSM

 

 

 

Amen to that !!! I would love to follow on learning curve as well. It is fun to do this as a team effort, with combined knowledge. I think we can avoid some bumps in the road because of that .