Sciencemadness Discussion Board

Seperation of potassium chlorate and perchlorate from perchlorate cell

itsallgoodjames - 26-11-2020 at 13:14

Is there an easy way to do this? I plan to make a potassium perchlorate cell, make perchloric acid, and with that, ammonium perchlorate. From what I understand, both chloric acid and ammonium chlorate are unstable and shock sensitive explosives. I don't really want my ammonium perchlorate or the rocket moters I make with it to randomly explode, so is there a way to get rid of the chlorate, while leaving the perchlorate? I'm doing this on a multi kilogram scale, so I can't seperate them by chromatography or something like that. Otherwise, I'd just do that. Sorry if I'm overlooking something really obvious, though google didn't return anything really relevant.

B(a)P - 26-11-2020 at 15:34

There is a lot of really good information here, including the removal of chlorate.
https://pyrodata.com/PyroGuide/index.php%5Etitle=Preparing_p...

aromaticfanatic - 26-11-2020 at 21:36

Quote: Originally posted by itsallgoodjames  
Is there an easy way to do this? I plan to make a potassium perchlorate cell, make perchloric acid, and with that, ammonium perchlorate. From what I understand, both chloric acid and ammonium chlorate are unstable and shock sensitive explosives. I don't really want my ammonium perchlorate or the rocket moters I make with it to randomly explode, so is there a way to get rid of the chlorate, while leaving the perchlorate? I'm doing this on a multi kilogram scale, so I can't seperate them by chromatography or something like that. Otherwise, I'd just do that. Sorry if I'm overlooking something really obvious, though google didn't return anything really relevant.


I think Dr. Liptakov has a video up on this using acetone. Check his channel out.

B(a)P - 26-11-2020 at 21:45

Quote: Originally posted by aromaticfanatic  


I think Dr. Liptakov has a video up on this using acetone. Check his channel out.


That is for sodium chlorate/perchlorate, the OP was after advice on the potassium salts for which acetone will not really help you.

symboom - 26-11-2020 at 23:00

heat it up potassium chlorate is much more soluble in hot water then filter off the potassium perchlorate.

Potassium chlorate
3.13 g/100 mL (0 °C)
4.46 g/100 mL (10 °C)
8.15 g/100 mL (25 °C)
13.21 g/100 mL (40 °C)
53.51 g/100 mL (100 °C)
183 g/100 g (190 °C)
2930 g/100 g (330 °C)

Potassium perchlorate
0.76 g/100 mL (0 °C)
1.5 g/100 mL (25 °C)
4.76 g/100 mL (40 °C)
21.08 g/100 mL (100 °C)

When heated to 357° C., potassium chlorate undergoes no perceptible decomposition, but the particles cake together, and under the microscope exhibit signs of incipient fusion. At a slightly higher temperature the salt melts, and there is rapid evolution of oxygen between 370° and 380° C., several reactions being initiated.
Potassium perchlorate is formed by autoxidation, the exothermic reaction corresponding with the equation

KClO3 + 3KClO3 = 3KClO4 + KCl + 61.3 Cal.

Scobai has proved the reaction to take place in accordance with this equation by measuring the velocity of formation of potassium perchlorate at 395° C., and has also demonstrated its quadrimolecular nature.
Simultaneously, a unimolecular reaction occurs, potassium chlorate decomposing with formation of potassium chloride, and evolution of oxygen:

2KClO3 = 2KCl + 3O2.
A sufficient rise in temperature initiates the decomposition of the potassium perchlorate, chiefly in accordance with the equation

KClO4 = KCl + 2O2;

and at 445° C. there is complete decomposition in the sense indicated, except for a small proportion of potassium chlorate simultaneously regenerated.

Thermal decomposition to potassium perchlorate
https://www.youtube.com/watch?v=Sl78zQfTFEY
https://www.youtube.com/watch?v=vPCo_jDAOr4


[Edited on 27-11-2020 by symboom]

aromaticfanatic - 26-11-2020 at 23:10

Quote: Originally posted by B(a)P  
Quote: Originally posted by aromaticfanatic  


I think Dr. Liptakov has a video up on this using acetone. Check his channel out.


That is for sodium chlorate/perchlorate, the OP was after advice on the potassium salts for which acetone will not really help you.


Oh the method doesn't work for potassium salts? Didn't know that. Thanks.

Bedlasky - 27-11-2020 at 00:27

How do you plan to make HClO4 from KClO4? Only one procedure which I remember is distlling off azeotropic HClO4 from KClO4 + H2SO4 mixture, but this require quite a high temperature. NaClO4 offers more ways.

woelen - 27-11-2020 at 00:27

You really should make NaClO4, not KClO4.

Getting rid of chlorate is easy. Add some excess HCl to the solution and heat, until boiling. Any chlorate is destroyed (formation of mainly Cl2 with some ClO2 as well). You drive off the gases by boiling and only the perchlorate is left. If you get crystals on adding HCl, ignore that. Just keep them. On boiling they will redissolve again. If not, then just add a little water. The solution must have been completely clear for a few minutes, just to be sure that all chlorate is destroyed. For this reason it also is important to have some excess HCl.

You can continue boiling down. In this way you get a very concentrated solution of NaClO4, together with some NaCl. Let the solution cool down, until it is luke warm. If any crystals are formed at this stage, add a little water and heat until they are dissolved and let cool down again. Try to get the solution as concentrated as possible, without having crystals in it, but try not to be zealous in this. Having a little bit too much water in the mix is no disaster.

Then slowly add concentrated HCl to the solution, while stirring, use an excess amount of 35% HCl or better. NaCl will precipitate, HClO4 remains in solution. Filter off the NaCl and boil down again, up to appr. 140 C. Let cool down. Any crystalline solid should be removed. Now you have a fairly concentrated solution of HClO4 (maybe 50% to 60% by weight). This solution may be yellow, due to impurities in the HCl. For the purpose of making NH4ClO4 this is no big problem. Carefully mix this solution with excess 10% ammonia and allow to evaporate. NH4ClO4 will settle. If your NH4ClO4 is not purely white, you can recrystallize it, but for pyrotechnics, it most likely is OK after the first step.

If you make KClO4, then you are stuck. KClO4 is nearly insoluble in water at room temperature, much less so than NH4ClO4. You will not be able to convert that to the free acid, unless you are willing to distill the anhydrous acid from a mix of concentrated H2SO4 and KClO4, which is INSANE in a home/amateur setting. Distilling HClO4 from H2SO4/KClO4 is NOT similar to distilling HNO3 from H2SO4/KNO3!



[Edited on 27-11-20 by woelen]

Bedlasky - 27-11-2020 at 00:46

Woelen: Should be possible distill off azeotropic HClO4 from KClO4 + H2SO4 mixture, if you add required amount off water in to the mixture? This should be somewhat safer.

[Edited on 27-11-2020 by Bedlasky]

woelen - 27-11-2020 at 01:35

No, not really. It is safer, but the end-product is not very pure. The azeotrope of HClO4 and water has a boiling point well over 200 C, but at that temperature, there also is some decomposition of the acid (formation of O2, Cl2, H2O, HCl and minor amounts of ClO2). So, in practice, distilling the azeotrope is not the way to go, at least not without vacuum distillation.

itsallgoodjames - 27-11-2020 at 05:16

Huh, I guess I really was overlooking a bunch of easily available information. I guess I can make sodium perchlorate rather than potassium perchlorate, if that makes the process easier. To make the perchloric acid, I intend to react it with sulfuric acid and distill off the product. I intend to dilute it a bunch in water, so I don't end up with a concentration any higher than ~30 or 40%. Failing that, I could start with calcium perchlorate, react that with the sulfuric acid, and precipite out the calcium sulfate. I can't imagine it'd be too hard to get a perchlorate cell to make calcium perchlorate, no?

woelen - 27-11-2020 at 07:38

No, you are not willing to distill any perchloric acid from sulfuric acid, even if you decide to dilute the product in water. The main risk is in the boiling flask, not in the receiving flask. You run the risk of a massive explosion if you distill HClO4 from concentrated H2SO4, also if you use NaClO4 as starting material.

The reason I suggest you to make NaClO4 is that the procedure I gave above, can be used with that. With KClO4 this is not possible, due to its low solubility. Using Ca(ClO4)2 as intermediate is not practical. Electrolysing solutions with Ca-salts in them is a pain in the ass, due to low solubility of Ca(OH)2 and insolubility of CaCO3, which forms on absorption of CO2 from air.

itsallgoodjames - 27-11-2020 at 08:42

Ok, thanks. I'll do that.

clearly_not_atara - 27-11-2020 at 12:08

If ammonium bitartrate is available, this will take KClO4 directly to NH4ClO4 by salt metathesis. The solubility of KClO4 is about three times the solubility of KH(O2CCHOH)2, and NH4ClO4 remains in solution.

However, I would recommend instead preparing NaClO4 as per woelen, and only resort to ammonium bitartrate if you already have KClO4.

itsallgoodjames - 27-11-2020 at 13:22

Yeah, I plan to just do what woelen reccomended. HCl seems to be multiple orders of magnitude cheaper than ammonium bitartrate, as the only places that seem to sell it are chemical suppliers, along with the fact that sodium chloride is cheaper than potassium chloride, so I don't really see a compelling reason to do it. Thanks anyways though.

Download - 27-11-2020 at 17:04

If you are using lead dioxide electrodes keep running the cell until there is little chlorate left. You should have some idea as to when that is from the calculations found on exrockets. I'd suggest using sodium rather that potassium in your cell due to solubility issues.

Once done, remove your cell liquid, place it into a suitable HCl resistant and heat resistant container. Add HCl until the pH is below 1 which should destroy any chlorate present. This step makes chlorine and chlorine dioxide fumes so don't breath it. You should then bring the pH back up by heating to remove the HCl or by adding a base.

Once this is done you should test to verify no chlorate is present. In this step you should also test that your test actually works. I used the indigo carmine test described on exrockets and tested it with a 1:100k sodium chlorate solution. It took several minutes at that concentration to work but it did verify the test can detect down to that level. You should perform your own test as your indigo carmine may not be the real deal. I bought cheap food grade stuff, but even the stuff from an analytical supply place might on occasion be dodgy. All it takes is someone mislabelling a container and if they mislabel it you will die.

You can then convert your solution to potassium perchlorate or ammonium perchlorate.

A lot of the methods others have described so far are unnecessarily hazardous. Molten perchlorate/chlorate is scary.

Bedlasky - 27-11-2020 at 18:18

itsallgoodjames: Ammonium bitartrate can be make from tartaric acid and ammonia, which are both cheap and easy to obtain.

Download: I use aniline hydrochloride test for detection of chlorates. Just dissolve your sample in water, add some aniline hydrochloride reagent (you can make it just by mixing aniline with hydrochloric acid) and add 1 ml of concentrated HCl. If chlorate is present, solution turns red. Other oxidizers also reacts with aniline but this red colour can be see just with chlorate. Low pH and presence of hydrochloric acid is crucial, because ClO2 is active oxidizer, not chlorate. With sulfuric acid this test doesn't work.

itsallgoodjames - 27-11-2020 at 18:34

Thanks for the suggestion bedlasky, but I think I'm going to stick to what woelen was saying. I do intend to use the perchloric acid for a few things besides ammonium perchlorate, such as making the perchlorate salts of some metal complexes, so I do need actual perchloric acid, rather than just ammonium perchlorate.

Assuming it works, I'll use indego carmine to test for chlorate, as I don't have (and I don't really want to make) aniline.

I'm using platinum, or failing that, MMO electrodes download. Doesn't really impact anything, but I felt I should mention it.

Thanks everyone for all the help so far.

Download - 27-11-2020 at 18:55

Quote: Originally posted by Bedlasky  
itsallgoodjames: Ammonium bitartrate can be make from tartaric acid and ammonia, which are both cheap and easy to obtain.

Download: I use aniline hydrochloride test for detection of chlorates. Just dissolve your sample in water, add some aniline hydrochloride reagent (you can make it just by mixing aniline with hydrochloric acid) and add 1 ml of concentrated HCl. If chlorate is present, solution turns red. Other oxidizers also reacts with aniline but this red colour can be see just with chlorate. Low pH and presence of hydrochloric acid is crucial, because ClO2 is active oxidizer, not chlorate. With sulfuric acid this test doesn't work.


You need HCl for indigo carmine too. Pretty sure it works o nthe same process only it breaks down indigo carmine making it colourless.
Quote: Originally posted by itsallgoodjames  
Thanks for the suggestion bedlasky, but I think I'm going to stick to what woelen was saying. I do intend to use the perchloric acid for a few things besides ammonium perchlorate, such as making the perchlorate salts of some metal complexes, so I do need actual perchloric acid, rather than just ammonium perchlorate.

Assuming it works, I'll use indego carmine to test for chlorate, as I don't have (and I don't really want to make) aniline.

I'm using platinum, or failing that, MMO electrodes download. Doesn't really impact anything, but I felt I should mention it.

Thanks everyone for all the help so far.


According to exrockets platinum electrodes wear excessively near the tail end of perchlorate synthesis as chlorate levels drop. This requires you to stop early and then when you go to remove chlorate using chemical methods the amounts of Cl and ClO2 produces is very excessive. Pt might be fine for small runs bit if you're doing multi-kilo runs your want PbO2.

feanor.forges on eBay sells PbO2 anodes. They might be ~US$100 a set, but they will last you ages without any special additions to your cell electrolyte.

itsallgoodjames - 29-11-2020 at 07:57

Oh, thanks for the information. I was under the impression that platinum electrodes would stand up well in a perchlorate cell. I'll have to get a set.

Indigo Carmine

MadHatter - 29-11-2020 at 14:46

This is 1 of my older posts(16 years ago) on the
chlorate detection test. 3rd post down.

http://www.sciencemadness.org/talk/viewthread.php?tid=306&am...

The test is extremely sensitive.

As for producing NaClO4 instead of KClO4, I agree
with my fellow madscientists that NaClO4 should be
produced due to its greater solubility.

[Edited on 2020/11/29 by MadHatter]

itsallgoodjames - 29-11-2020 at 15:48

Using Na instead of K makes the process more cost effective as well, as NaCl is significantly cheaper than KCl. I'll get some indego carmine for chlorate testing.