You'll put your eye out...

I have been reading your Blog with interest as I have been experimenting and producing Perchlorate with my MMO cell for about 18 months now. I have posted some of my results on another forum in the Past. I use a Power supply capable of up to 40 amps that I can vary the output 0 ~ 10volts. I find it easy to tell when the Perch starts the amperage drops and the voltage has to be almost doubled to maintain the same current. I have not been controlling my PH because I was not concerned about the efficiency but I will try and control this in the future. I first ran my cell at 40~50deg and accidentally let it come to the boil and was surprised to find the material survived. Since then I have been running it around 70~75deg and have not found this to have any detrimental effect on my anodes.

For a cell body I have been using 2 x clear 2.5 ltr chlorine Cell bodies that have 2 x 50mm Ports. They both come out the same side with one at the top and the other on the bottom. Both bodies are plumbed together with PVC so that they can circulate from the heat and rising Gas in the reaction chamber. I think the material is an ABS or modified acrylic but I will find out what it is. As far as I know PVC is quite suitable and can be obtained in clear tube.

I thought that most precipitating material would be in the second chamber but this has not been the case so I am looking to change the design. After I have tried a large cell I will try my dual body design again and add cooling to the second chamber this time. I have found it important to keep the electrodes high in the solution so the precipitating crystals do not bury the electrode. I have obtained a tall 30litre container that cyanuric acid ships in and so I thought I may try this next time to see how a large single cell chamber works. I am very interested in any one else’s results in cell design and method of operation.

I am keen to read any results you have had and what steps you took to get rid of any residual chlorate you had. Do you know if all the same chemical methods for removing sodium chlorate will also work with Potassium?

I must also add that my advice is to use MMO material designed for use in swimming Pool chlorinators.

I note you are getting good results with yours and are not sure what MMO you are using.

The reason I suggest this is that the normal MMO used in commercial chlorate production is used with highly saturated solutions while swimming Pools must run in salt solutions as low as 2500~3000ppm (0.025%) salt. This is very low and they have been specifically designed for operating and surviving very low concentrations of salt.

Hi pkhow, thanks for contributing. You've made some excellent observations.

 

The MMO anode I've used for chlorate is the one offered by Northstar, and it seems to perform very well. I know there are different MMO formulations, coating thicknesses, etc. You bring up an excellent point on pool chlorinators... the usual statement is that "they are not designed for chlorate manufacture and are no good", but the reality is that a HIGHER ion concentration is actually EASIER on an electrode. A typical saltwater pool runs NaCl in the range of 3,000 ppm, or 3 grams per liter, which is LOW when compared to a chlorate cell. The amperage may be kept low, but still, it says a lot about those chlorinators that they can run for years, and keep a 25,000 gallon pool disinfected with no problems.

 

I've got about 6 large, unopened boxes full of materials to fabricate the T-Cell. The materials are expensive and I want to do it right. By having separate cells (that are plumbed together) you have some control over heat, and I do very much want to create a system that will hopefully form crystals in a cool cell, and have the electrodes in a hot cell. I think forced circulation will go a long way into making that a reality. Since I have one main pump, I have been debating whether to pump electrolyte INTO the hot (electrode) cell, or OUT OF that cell. The answer came simply, fabricate it in such a way so that the system can be tried in both configurations. A high-flow through the electrode region should hopefully keep crystals from forming on them.

 

On purifying the perchlorate - I haven't tried it yet. My raw perc batch is bagged and waiting. I have both indigo carmine and phenylanthranilic acid for testing purposes. KClO4 crystals are just about the perfect recrystallization candidate. My best guess is that chlorate destruction methods apply equally to both sodium and potassium, so long as the salt is fully dissolved, and the obvious time to destroy the chlorate is during recrystallization of the raw perchlorate. The salts dissociate into ions anyhow, so the target ion (chlorate - ) is swimming about in solution regardless of which alkali metal it belonged to. The sodium might be more convenient as it is so much more soluble than the potassium, but I'd think both will work. My tests along those lines will be in a few days, and I will report on them.

 

It is obviously crucial for any oxidizer bagged and labeled as perchlorate to be truly chlorate-free, and it would be incredibly irresponsible to sell perc that is not clean. I'm not saying you are doing that, at all! Just that I sometimes wonder about bargain perchlorates out there, just how clean are they? It will be nice to be able to use a sensitive test, and one of the first candidates will be 5lb of commercial perchlorate that I bought a while back.

 

Again, thanks for posting, I hope more people do as well.

I wanted to find what potential there was to damage (passivate) my MMO coating in a Perch cell. I knew in a low salinity chlorine cell that I must avoid exceeding the voltage and make sure the salt levels do not go too low and that this now is extremely low at less than 1 ~ 1.5ppm. I can say I tried several different constructions and running methods of my Perchlorate looking for the telltale increase resistance and MMO coating loss. My conclusion so far is that steps should be taken to minimize crystallized material encasing and bridging anode to cathode as this was the only way I found to end the life of the electrode. This will also happen with a chlorine cell when calcium is allowed to build up so much that it bridges the anode and cathodes together. For this I think you are on the right track with keeping the solution moving I am just not sure why you want to run it cool. I think experimenting so you can stop crystal from forming on the anodes is essential. On the voltage of the cell I know that regardless of the concentration 10 volts is as high and you should go and I keep mine under 9 volts. If you are not getting the current you need then the only option is to increase surface area or bring the electrodes closer. You can use more than 1 cell in series in separate containers or float internal electrodes in between the outer anode and cathode. If you do this you must join a floating anode or cathode or uses dual Polarity MMO that can operate as anode on one side and cathode on the other. I am interested to know the size of your anode and what amperage you are running it at?

I hope your Blog encourages others to try MMO anode and suggest they ask the recommended salinity of the material they are purchasing.

I DON'T want to run the cell cool! I specifically want to run a dedicated, small electrode cell pretty hot, then pump that into a cool cell for crystallization. Efficiencies go up with temperature. I'm going to shoot for 60 to 80 C in the vicinity of the electrodes, then pump that into a collection vat, possibly through a heat exchanger.

 

It should be pretty easy to regulate the temp in the electrode cell by increasing or decreasing the pump volume. My peristaltic pump is variable, and can go from a trickle to something like 8 liters per minute.

My thoughts are that a cooling tank needs to be large enough so that it gets plenty of time to cool and easy to remove the material. With a slow flow it will give this plenty of time and also back ino the bottom of the reaction cell slowly enough not to drop the temp. On the other hand you want a lot of movement to stop cyrstal formation on the electrodes. What do you think about a stirrer pump as well?

I think stirring or agitation in any form is a great idea, bordering on essential. I had a bit of a breakthrough when I remembered, from my days of keeping a reef aquarium, that a ridiculously simple bubbler works admirably to circulate and stir.

 

My second cell, the tall acrylic tower, was a perfect example. Powered on, the top 5 inches was an opaque white emulsion of evolved gasses; below that, crystal-clear electrolyte. The walls of the cell near the electrodes was very hot, while below, it barely warmed up. This makes sense as brines are especially responsive to heat gradients. Cool brine sinks quickly. Thus my system was in two layers, a hot and a cold layer.

 

A length of PTFE tube was routed through the lid, all the way to the bottom. A cheap aquarium air pump and a check valve was plumbed, and the PTFE tube became a bubbler. This immediately produced a uniform electrolyte. Importantly, I think it helped keep evolved chlorine gas in suspension, promoting dissolving of the gas, and this in turn keeps pH where it's supposed to be.

 

When I make this cell, I am going to drill and tap, probably 1/4 tapered pipe thread, several ports in the lid that will simply be utility ports. If not used, these are easily capped with PVC plugs. Otherwise, they can be used to route bubbler or pump tubes, and keep things well-stirred.

 

A true stirrer setup would work great, but with a 40 liter or smaller tank, I think a bubbler would do fine and be 1/10th the cost.