First yield of KClO3 from my cell

Hello everybody,

I don't know if there is something like a "show your projects" section on this forum but I like to share my first results on a test run I did with my chlorate cell. I don't have exact numbers yet since this was just a test to see if the materials of the cell would hold up. Especially since I 3d printed the lid myself and I couln't find any information about the chlorine resistivity of PETG. I just know that it's resistant to a lot of things so I gave it a go.

My cell is build with a MMO anode and a Ti cathode witch are glued into a lid I printed with my 3D printer. Besides the anodes there are also 2 glass tubes in the lid. One is closed off and can be used to insert a thermometer while the other is open and used to vent of the gasses. The cell holds about a liter electrolyte witch consists of a saturated solution of NaCl with a pinch of K2Cr2O7. The cell was run for 4 days straight while the temperature changed between 60°C to 80°C, due to the changes in ambient temperature. I unfortunately cannot do not know the current it ran at because I don't have a way to measure this (yet). One of the projects I am currently working on is a device that measures voltage, current and temperature and logs these values to a SD card over time. I will be using this in the future to measure the cell and calculate the efficiency.

The product you see in the attachment is KClO3 witch is precipitated from the solution by a double displacement reaction between KCl and NaClO3. The slight yellowish color is due to the K2Cr2O7 witch is still present. I would like to do a crystallization to gain some purity. All the filtrate will be saved for a future run, a bit of potassium in the cell couldn't hurt but I hope that the solubility won't get to low. Any tips or ideas on this?

Besides, i don't really have a goal for the KClO3.
I used to do some pyro back in the day but KClO3 is something I never used and never going to use in pyro due to safety reasons.

Quote: Originally posted by fusso

Why not just electrolyse KCl at the beginning to save yourself from the double displacement step?

Quote: Originally posted by markx

Well done! The dichromate additive can be omitted for simplicity sake. It is poisonous, carcinogenic and a strong sensitizer with permanent effects. The mist from electrolysis can carry it out from the cell, so it tends to spread and contaminate the surroundings. There are safer alternatives available for the prevention of cathodic reduction: At page 288 in the abovementioned text one can find the comparative table with different reduction prevention additives for chlorate production. [Edited on 25-4-2019 by markx]

The text is from "Enzyklopädie der technischen Chemie": Encyclopedia of applied chemistry. Unfortunately I have no english version of it, but I'm sure the book has been also released in english language. Makes for a great motivation to learn german though

In my old university chemistry building we had a really ancient and large original set of german literature dating back to the 19th century and even farther. The treasures that could be picked from there were limitless. Very detailed descriptions of experimental proceedings and conditions. Quite unique.

Hello everybody,

The ultimate goal would be to build a KClO4 cell. A drawback of KClO4 is the low solubility, therefore I would like to start out with NaCl to create NaClO3 and oxidize that further to NaClO4. At last a double displacement would leave me with KClO4. I don't expect to do this anytime soon though since I don't like messing around with soluble lead salts to make my own electrodes and platinum is a bit above the budget right now. Also, I've read that platinum could be destroyed when the ClO3 contents become to low, so lead oxide would be preferred.

I have given the K2Cr2O7 some thought before use because of its toxicity but I think if everything is contained in the cell with a tube bubbling through a neutralizing solution of some sort it will be manageable. I am using a gas washing bottle with a fritted disk for this, so I am not to keen on using hydroxide since that will attack the disk. And those bottles are not cheap... Right now its just filled with water and a bit of sodium carbonate.

I currently don't own a beaker large enough to do a re-crystallization so I ordered some online but that will take some time to arrive. I also have thought about using something like a glass coffee pot as a beaker although I don't know if it is suitable. Besides I am going on a vacation in a short while so the re-crystallization has to wait.

On another note, the PETG and glue holds up quite nicely. Only some discoloration in the plastic is noticeable but its hasn't weakened for as far as I can tell. I will cut it in half eventually because it needs a small redesign at witch time I'll do a closer inspection. The lid is pressed in the glass container using a FKM ring to seal it, but it is a bit to small so it doens't seal properly. I included a picture to show the general idea.

Yesterday is started to work on the current amplifier to measure the current and voltage. The principle of operation can be found here: http://tinyurl.com/yyx4db2z I have soldered this to a prototyping PCB but something isn't quite right yet so I'll have to fix that. Ones I'm happy with it I'll share some photos and source for the arduino so people can recreate it.

@Woelen, Leuk om een andere nederlander te zien, I have used the information on your site when building this cell. It explained everything very clearly. Besides, you mention K2Cr2O7 is a sensitizer, do you mean that in a health or chemically stability perspective?

Regards,
Bas.

Very nice cell construction! If you are not sure about the sealing efficacy of the gaskets and see no heavily detrimental effects upon productivity without the dichromate, then I would advise to avoid the additive, unless you are conducting the synthesis run outside. In my practice I've not had a situation where the cell would show such low productivity that additional "boosters" are unavoidable or dearly needed. Even with nonoptimal electrode sizes and conditions. Woelen mentioned that his cell was of nonagreeable efficacy without the dichromate.....perhaps your set of conditions is similar and the additives are well justified in that case. It sure does help with raising the current efficiency of the synthesis and it is the industry standard, but it is nasty stuff with cumulative effects on health. Causes the immune system to act upon it with inflammatory response, as if it was a foreign disease and to remember that case for future. After that has happened, a very low trace concentration entering your system can provoke an inflammatory reponse, hence "sensitizer". It is not really an "inhale once and drop dead situation" of course, but just saying. Some people are more prone to develop this kind of hypersensitivity and some can work with dichromates for decades, not showing any considerable effects. So it is a rather vague hazard
Soluble platinum salts (platinum group metal salts in general) are way worse at creating this kind of effect in the human body. As far as I know hexachloroplatinic acid is the most potent sensitizer that is known and the effects are irreversible once they emerge. I always work with utter care to avoid this stuff from making contact with my skin or being dispersed into air when I make anodes. It is really scary stuff compared to dichromates and it fills me with horror to see the techniques that are used by some precious metal refiners who handle coupious amounts of these solutions. Boiling them down for concentration purposes and conducting reactions that release gases which disperse the solution droplets into air.

But enough moaning about the hazards.....don't wan't to appear like a "total mincer" !

As far as perchlorate synthesis is concerned you can basically take two working routes: Pt based electrosynthesis or the thermal decomposition of chlorates. Lead dioxide anodes in the amateur setting do not really appear as viable option. The deposition can be conducted rather easily, but achieving a coating that is durable in perchlorate cell conditions is rare as I've learned from the experience of others and my own experiments. The coating can seem quite durable in milder conditions e.g. electrolysis of sulfuric acid for ozone generation, which in itself is already rather agressive as far as anodic conditions go, but the perchlorate cell is a step further (or at least sideways) and seems to make short work of the lead dioxide coatings. The most I've stretched out of my humble attempts are a few days worth of operation before the anode layers are dispersed into solution.

If Pt is out of the question because of cost then the thermal decomposition route remains as the option. Actually it is a pretty quick, cheap and efficient way to process bulk quantities with acceptable yields. The precondition is that your chlorate has to be void of certain metallic contaminants that act as catalysts upon the decomposition and steer the process towards evolution of oxygen and chloride, preventing any perchlorate from forming. Manganese and iron can be noted as such detrimental contaminants, but many other metal salts have this property to a smaller or larger degree.
Once your chlorate cell is operating at expected productivity, the thermal decomposition is a really attractive option for the next stage of conversion. To be honest, even a moderate sized cell can pile up the chlorate stock at a far greater pace than one can utilize in any reasonable way.

Quote: Originally posted by yobbo II

Methylene blue is very sensitive towards perchlorate. Very small concentrations of perk turn the stuff purple.

Put together some cells to have a look at the current distribution on a cathode together with the cathodic reduction 'thing' (wanted products being converted back to starting products which we do not want) .

I have read that dichromate effectively raised the current density by forming a film on the cathode which reduces/eliminates the cathodic reduction and at the same time not giving a higher voltage accross the cell [more power usage, a bad thing] Perhaps this is too simplistic of an explanation.
It is stated elsewhere that the film stops hypochlorite from touching the cathode and allowing other stuff to pass through thus reduction of the hypochlorite cannot take place.




I started with a small MMO anode that was about 14 cm squared on each side.

The cathode (Ti) is large (too large) and is approx. 49cm^2 on each side.
The first cell with the large cathode contained about 1.75 litres and was placed on a hot plate
to warm it up as the current running was unable to get the temperature very high.
The cell was let run for about 14 hours to allow hypochlorite to build up before any measurements were taken.
Current going to/from the cathode was measure using four 0.015 Ohm resistors. One resistor measured the total current with
the other three resistors measuring the way the current split between cathode front, outside back and middle back.
With the temperture at 29C and total cathode current at 5.33 Amps the front cathode current was 4.06 Amps, middle back was
0.37 Amps and the outside back was 0.87 Amps. When temperture was 58C the currents were 3.83, 0.42 and 1.03 Amps. The
higher the temperature the more conductive the solution is, which gives more current on the back side of the cathode.
The larger graphite anode (of similar dimensions to the cathode) give the following at 60C with anode current at 5.33 Amps. 3.54 Amps on front, 0.57 middle back
and 1.2 Amps on back outside of cathode.
As expected there is much lower current density on the back side of the cathode.

Gas measurements were taken using an 500ml volumetric flask filled to its mark with water and inverted in a bowl of water.
The same cathode/anode current (5.33 Amps) was used for all measurements for the first cell.
It took 18.2 minutes to fill (500ml gas) with all parts of cathode running current at 72C.
With only the front of the cathode connected, (same anode current) the time taken to fill 500ml was 15.66 minutes (more gas produced).

Four grams of Na2Cr2O7:2H2O (Sodium Dichromate) was added to the cell. The temperature of the cell fell about 7C from 72 to 65C
(without adjusting the hot plate setting of course) as time went by.
Running current to both sides of the cathode, the time taken to fill 500ml with gas was 12.66 minutes.
Running current to the front of the cathode only, the time to fill 500ml was the same (12.66).
A few hours later the time to fill 500ml was 12 minutes. More gas is being produced when the Na Dichromate is added.

Another cell was set up, this time with a much smaller cahtode (Ti) with the back side of the cathode permanently covered with a plastic
covering so only current went to the side facing the MMO anode. The anode was the same as the first cell and the current was set at
three different values. Working surface area of the cathode was approx. 7cm^2. The hot plate was not used to heat the cell.
Nothing can be read into the different temperature reading as not enough time was given to the cell to stabalize at a given temperature
as currents were varied.

Green cell.
The time taken to produce 500ml of gas at 5.33 Amps was 13.13 minutes. (5.35V accross cell, about 35C)
The time taken to produce 500ml of gas at 2.66 Amps was 25.70 minutes. (4.16V accross cell, about 25C)
The time taken to produce 500ml of gas at 1.33 Amps was 48.00 minutes. (3.90V accross cell, about 18C)

Four grams of Na Dichromate was added to the cell.

The time taken to produce 500ml of gas at 5.33 Amps was 12.0 minutes. (5.26V accross cell, about 30C) [3 hours later it was 12.75 minutes]
The time taken to produce 500ml of gas at 2.66 Amps was 25.65 minutes. (4.57V accross cell, about 21C)
The time taken to produce 500ml of gas at 1.33 Amps was 51.66 minutes. (3.6V accross cell, about 20C)

The is still a time difference between Dichromate and no Dichromate, green and non-green! in favour of the Dichromate but
it is not so large with the smaller cathode with the much higher current density.
(The green cell is actually doing better for the low current run).

The voltage accross the cell will be higher
when a high current density is run on the cathode.

There is quite alot of gas coming from the anode, Oxygen I presume. Dichromate also supresses O generation but it is difficult to
tell the difference between the two situations by looking at the gas coming off the anode. The reduction of O generation
(assuming it is happening) will reduce the 'gas-measured-score' that is being attributed to the addition of Dichromate.

I have read somewhere that it takes a few hours for the anti-reduction film to build up properly on the cathode but is seemed
sudden enough with these cells.

The pH of this cell when measured at 7.7 when gas measurements were ended.


@ Woelen You came up with a figure of 200mA (and above) per square cm as a threashold for cathodic reduction not being a problem. Just wondering where or how you came up with that figure?

I hope to make two similar K cells, put them in series. One with a small cathode, other with normal cathode + dichromate and see if there is much of a difference in KClO3 output. I have always thought the the dichromate give something like a 3 to 6 % current efficiency boost to commercial cells. But I am only guessing. There are other reasons for adding it to cells. It's a buffer, it also protects steel cathodes and other steel components (everything nowadays is probably Ti and teflon) and it also lowers oxygen generation at the anode.


Stay green!!!
Yob











[Edited on 19-5-2020 by yobbo II]

Quote: Originally posted by Alkoholvergiftung

What i read you can have an efficience of 87% with CaCl2. The CaOH forms an Diaphragma on the Cathode and there is an less reduction from the hydrogen. I have tried i too but when you dont use an magnetic stirrer it dosent work or it doesnt work for me. There where only two layern on the top i had an PH of 6 and on the Ground an PH of 12.

Quote: Originally posted by Alkoholvergiftung

Mysteriusbhoice, is your cell an open design, withour an lid? If there is no mixing like in my case the most chlorine get lost.When i work in my Standard cell with NaCl and KCl and an Elektrode distance of 5mm i can work without lid and there is no chlorine smell.

My cell is a closed lid with gasket and temps are around 60-65 celsius and capacity is 4L and theres a bubbler leading to the outside.
I dont add KCl since right now im testing out GSLD electrodes to convert the product from that cell into perchlorate.
The thing with KCl is that the insolubility of KClO3 will cause the current to drop over time.
As for my cell even after the end of the run the smell of chlorine was so noxious!! even after full run time chlorine smell was so prevalent I had to open it outside.... I couldnt even open the cell without getting a strong wiff of Chlorine and hence the bubbler being present.
I really think CaCl2 is amazing but dont use it with potassium salts because the insoluble Ca(OH)2 will force you to recrystalize that stuff.
When I use that nezo brand salt which is 71%KCl and 29% NaCl by wt my CE is usually only 50% region.
When i used that fine raw sea salt which has CaCl2 my CE goes crazy without chromates or shit.
I also read a paper that soluble permanganates increase CE also.
The toxicity of permanganate is very low compared to dichromate because it easily reduces to MnO2.
https://sci-hub.tw/https://www.sciencedirect.com/science/art...
My cell is really old and constructed approx 2 years ago

[Edited on 21-5-2020 by mysteriusbhoice]

[Edited on 21-5-2020 by mysteriusbhoice]