Potassium perchlorate production

[YTS]

Whos got a good or simple way of producing it from potassium chlorate i know you have to heat to 400 c or something near that but i would appreciate your methods instead of wasting time & chlorate which i have to produce from naclo3 .ie heating in a pyrex sausepan with a thermometer for a certain amount of time CHEERS

[kingspaz]

ok there are two ways i know of. one is to heat the chlorate to melting point and hold it there for a few hours allowing it to be oxidised further by oxygen in the air. i'm not sure of the temperature because i have never done it. another way is to make a saturated solution of NaClO3 and electrolise it with graphite (use graphite because it won't react with the gasses made and will yield a purer product) electrodes for a week. then evaporate the water and convert to KClO4 in a similar to how way you made your KClO3.

[Mr Cool]

Graphit only works in a chlorate cell. For a perchlorate cell you need platinum (or ruthenium, iridium, osmium, rhodium and the other one which I can't remember could also probably be used. I expect gold would work too), or lead dioxide coated ceramic or graphite. If you have a graphite rod, you can use electrolysis to coat it with PbO2 in a soln. of Pb(NO3)2 with a bit of soap to give it a better surface and make it adhere better to the graphite. That's all I can remember about the process. It won't last long (maybe one reaction or two could be expected), but it's easy to make.

[J]

Correct me if I'm wrong, but don't car batteries use Pb02 coated electrodes? I seem to remember reading that the electrode changed composition as the battery was charged/discharged.

J

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[kingspaz]

yer thats right. a completely CHARGED car battery should have a positive electrode made completely of PbO2. the negative electrode being a lead/antimony alloy.


[This message has been edited by kingspaz (edited August 10, 2001).]

[Mr Cool]

That's right. I'll have a look to see if I can find an old car battery some place.

[Wedge]

Titanium or tantalum works as well

[tmp]

Go with the electrolysis method for KClO4. Graphite is cheap. I use a car battery
charger set at 6 volts and 15 amps. It's slower but be patient. At the lower
voltage your graphite rods won't deteriorate as quickly because the temperature
stays down. I produce all the KClO4 I need this way.
BTW, titanium metal deteriorated within 30 minutes. I'll try manganese dioxide next.
I just need a way to press it into rods.

[Guerilla]

Graphite anodes cannot be used for electrolyzing perchlorates as they start to erode(oxidize) quickly after the chloride concentration drops down to a point where the production of perchlorate starts. Has anyone successfully used magnetite anodes in chlorate/perchlorate cells? I've used 0.5x100mm Pt-wire with success, but I'm not satisfied with the low current (~3A) and thus slow production rate that such a small wire gives..

[tmp]

Guerilla, I forget now where I found this on the web, but read on:


Making chlorate and perchlorate
This file has two parts... the first is predominantly about KClO4, and the second about KClO3. Both were taken from the net, original sources unknown.
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MAKING POTASSIUM PERCHLORATE
This proceedure is a "tried and true" method. Unlike some rec.pyro postings, which are informational, or just plain speculative, this proceedure WORKS. I have used it myself to make my own supply of perchlorate - until I decided to quit because I was making it far too fast to use.

This proceedure works well to make chlorates as well. The proceedure can be modified easily to make only chlorates. When using this proceedure to make perchlorate, it produces significant amounts of chlorate as a by-product. This is because carbon rods are not highly efficient in converting chlorate to perchlorate. Other anodes work better, but this proceedure was designed using easily available common materials and supplies. --- Author


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Carbon Rods
Get some carbon rods from the welding shop. They are made by "arcair", and are 3/8" diameter by 12" long, and cost between 40 to 60 cents(US) each. They are copper plated, and they are used for a welding proceedure known as "gouging".

Cut off the top of a plastic 1 gallon milk jug. This is a good cheap source of containers for using in this proceedure.

Dissolve 1/2 cup of salt in 2 liters of warm water. Put this in a small plastic container. Cut out a piece of coffee can, roughly 4" by 4" with a tab extending up to connect a wire to. The dimensions are not critical. With a 6 volt battery charger, connect the minus (-) connector to the piece of coffee can. Wrap some aluminum foil on the end of the carbon rod, to improve the electrical connection, and connect the plus (+) connector of the charger to it.

Turn on the charger, and let it run for about 20 minutes. The copper will be removed from the rod. If some still remains, run it for a little longer till it is free of copper.

Discard the salt water used to remove the copper.

You can probably use a 12V charger, but the current may get too high, so you may need to reduce how much of the rod is being etched at one time.


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Electrolyte solution
Make a mixture of salt and potassium chloride solutions. Dissolve roughly 2 ounces (60 grams) of salt, and 8 ounces (240 grams) of potassium chloride in 2 liters (just a bit more than 2 quarts) of hot water. There is much room for inaccuracy here, because the exact mixture is not absolutely critical.

At this point, it is good to add between 2 to 10 grams of either potassium chromate or dichromate. While this is not absolutely necessary, it helps improve how much perchlorate is finally produced. The process will work without it, but not quite as well.

NOTE: Potassium chloride can be obtained as several commonly available products, such as: dietary salt substitute, ice melter (look at label for actual contents), and "muriate of potash" from farm and garden supply shops. Hagenow Laboratories carries potassium dichromate.

The reason a mixture of salt and KCl is used, is two fold. First, salt is more easily electrolyzed than KCl, but after it converts to chlorate (and perchlorate), it will tend form the potassium salt instead of the sodium salt. The electrolysis tends to work on the sodium salt, while the final potassium perchlorate forms, and due to it's poor solubility, tends to crystalize out of solution. Secondly, the concentration of KCl is chosen to help prevent chlorate from crystalizing out, while being too high for the perchlorate to remain in solution, which causes it to crystalize out as it is created. These concentrations may be varied, to compensate for different operating temperatures. It was designed to operate at 40C, and will work fine above that temp, but below it, you might get some chlorate crysatlizing out, in which case you might need to reduce the amount of KCl just a little.

I have been using a little salt in my mixture, but someone could exclusively electrolyze KCl, without the addition of salt. The purpose of the salt is to provide a sodium salt which is more easily electrolyzed than the potassium salt. It is NOT necessary, and will probably work well with only KCl. ****** (Chlorate note) ******

BTW, chlorates are produced here as an intermediate chemical product. Chlorates tend to be the predominant component around 1 1/2 to 2 days of operation. Chlorate could be caused to crystalize out during electrolysis if the concentration of KCl in the starting electrolyte solution is increased to nearly saturation (about 21 ounces KCl/ with 2 ounces of salt). Although I have not concentrated on chlorate production, I would expect that you could actually run it for more than 2 days - possibly up to 4 or 5 days, and keep building up a layer of largely chlorate crystals on the bottom. In that case, I would _GUESS_ that you could get around 2 pounds of chlorate after 5 days of operation.

Electrolysis
Using a coffee can for a source of steel, cut it out to form an inverted U shaped trough. Insert it in the mixture of salt and KCl dissolved in water. The (-) connector is connected to the steel. The steel U trough (similar to a rain gutter, except upside down) is setting at an angle to increase the amount of surface area in contact with the liquid. The carbon rod has some aluminum foil wrapped around the end of the rod, and the (+) connector is connected to it. The rod is positioned within the U shaped trough - under it, without touching. The charger is turned on, and he position & depth of the rod is adjusted to get 8 to 12 amps of current.
NOTE: A setup with the electrodes running electricity through an electrolyte is called a "Cell". This setup is commonly refered to as a cell throughout this description.

Let the liquid electrolyze for about 5 days continuously. Add water to make up for water lost during the process, and try to keep it roughly constant.

A couple times a day, you will need to check the current level, and adjust the rod position to keep the current in the 8-12amp range. Mine has been running between 40 - 50C, but commercial proceedures keep the temp just below 40C to reduce carbon rod errosion. The rods will gradually errode away, but if you use a 6V charger, one rod will probably last for the full 5 days.

You can also use higher voltage chargers, but you will probably need to connect several electrolytic cells together to keep the voltage accross ONE cell to be about 6 volts. If you use a 12 V charger, you will need 2 cells ( 12V/(6V per cell) = 2cells). If you connect more than 1 cell in series, you may need to use a voltmeter to check the actual voltage accross each cell - because it will change depending upon the resistance differences between the cells, which can be adjusted by re-positioning the rods.

The purpose for the U shaped trough cathode (-) electrode, is to cause the gas bubbles formed to generate a convection flow up through the trough. This causes the chemical products produced at each electrode to mix and react efficiently. Other electrode geometries will work, some better, and others worse. The key is to cause the two electrodes to be very close to each other, and cause the chemical products to mix well to help form chlorate and perchlorates. The WORST case situation is where the electrodes are on opposite sides of the cell, causing the chlorine gas produced at the anode (+) to tend to bubble and escape out of solution into the air.

Crystalization
The potassium perchlorate crystalizes out as it electrolyzes. When you're done, you have a mixture of black carbon, perchlorate, and some chlorate after you drain off the liquid. I generally get a layer of perchlorate crystals about 1 inch (2.5cm) thick on the bottom, which tends to be about 1 pound.

Cool the liquid in a freezer to help increase the amount of perchlorate that is crystalized out, before draining the electrolyte liquid. When draining the electrolyte, save it if you want to re-electrolyze it to make even more perchlorate again.

Load the crystals into a filter, and use boiling water to dissolve the perchlorate out. As it filters, the perchlorate forms nice flat rhombic shaped (almost square) flakes that float out of solution. You watch it as it cools, and watch for chlorate crystals, which tend to look like clusters of cactus needles. When they start to form (well after the perchlorate has largely crystalized out), you drain the liquid, and add some room temp water which is to be about 2 - 3 times the volume of the crystals you have in the container. Shake them, and let it stand overnight to dissolve any chlorate crystals. Then drain, wash (with ice cold water), and dry the crystals.

NOTE: Coffee filters generally aren't good enough to filter out the black carbon particles. You can load a coffee filter with a good layer of diatomaceous earth, and then use it to filter the liquid. Diatomaceous earth is used to filter swimming pool water, and a 10 pound bag can be obtained for less than US$10.00.

You can purify them again by weighing the dried crystals, and adding enough water to dissolve the whole mass as if it was pure chlorate (i.e. 7g/100ml water)*. Use hot water, and then cool it down to room temp. You might even need to cool get the perchlorate to begin to crystalize (it seems to super saturate commonly). You might be able to get it started by adding a small amount of perchlorate dust as crystal seeds - if you have some to start with.. Then wash your crystals (with ICE COLD water), and dry them. That will help produce a higher purity product of perchlorate. If you want to make a chlorate-free batch of perchlorate, repeat this process again. It will be essentailly free of chlorate if you double crystalize it, and make certain you wash the crystals several times with cold water.

Example: 100 grams of crystals would require 100grams/(7gm/100ml) = 14.3 (100 ml), or 1430 ml of water, or about 48 ounces.

NOTE: When harvesting the crystals, a cotton cloth makes a good filter. I wear rubber gloves, and squeeze the excess liquid from the crystals before & during washing them. Squeezing helps remove additional contaminants which are dissolved in the liquid that wouldn't otherwise be removed by simple gravity filtering. While this method loses very small crystaline particles, the loss tends to be very small in comparison to the amount of crystals harvested.

Perchlorate is very easy to make, but it takes a little work. The hardest ingredient to get is patience.

WARNINGS
This proceedure generates small amounts of chlorine gas, as well as hydrogen gas. It should be conducted outdoors, or in a well ventilated building which is NOT used for living quarters! Hydrogen can accumulate in non-ventilated and sealed rooms to form potentially explosive mixtures with air!! Chlorine generally is more of a irritant, but can be poisonous at high concentrations. There are also other (?) chlorine oxides and/or ozone produced which should also be avoided.

Chlorates and perchlorates are NOT chemicals for playing!! They are serious oxidizing agents which can be used to make VERY DANGEROUS pyrotechnic mixtures - _ESPECIALLY CHLORATES_ !!! Be certain to read up on all litterature describing the use and dangers of these compounds! It is VERY EASY to forget the safety hazards associated with these oxidizers in a time of haste - and lose a limb or your life as a result of your forgetfulness! Be careful to clean up any oxidizer which is spilled on carpets, or solutions which have spilled or splashed on any form of flamable material, including clothes, wood, paper, etc.

CHLORATES ARE ESPECIALLY FRICTION AND SHOCK SENSITIVE! PERCHLORATES CAN ALSO PRESENT THE SAME HAZARDS, BUT NOT AS BADLY AS CHLORATES!

ALSO, AVOID THE DISASTEROUS MIXTURE OF CHLORATE WITH SULFUR. NEVER MIX EITHER OF THESE WITH ANY FORM OF PHOSPHORUS, AS IT CAN IGNITE OR EXPLODE BY THE FRICTION OF SIMPLY MIXING THEM!!!!!

Also, chlorates must be kept from any form of acids, especially sulfuric. Even small traces of acids (from the presence of sulfur, etc) can cause what "appeared" to be a stable mixture, to ignite at some unknown time later!



I can honestly say it works for me. Your call !

[Zeitgeist]

You can also use Sodium or Ammonium Peroxydisulfate (Persulfate) sold in electronics stores for etching PCB's, it will directly oxidise ClO3- to ClO4-, although i haven't tried it personally

[Ollie Snowie]

Wouter talked about this on his page, and he got poor results, from either or both of the following:-
The persulfate in PCB etcher is diluted a lot.
The reaction gives a low yield.

It sounds like electrolysis is the best method, because persulfates are produced by electrolysis in the first place.

Also, don't use ammonium persulfate with a chlorate, because the nasty ammonium chlorate could form.

I tried electrolysing a tiny amount of very conc. salt solution at ~2amps, with Pt electrodes, until the water had boiled off from the heat produced. Some of it got onto my trousers and bleached them very quickly (lots of sodium hypochlorite). I'm sure this could be thermally decomposed to sodium perchlorate and then double decomposed with KCl. Otherwise, it could be electrolysed until the low temperatures of the next ice age/heat death of the universe forces it to stop, and then double decomposed with KCl. (just think about it, you might end being the last person to posess salt crystals before the big crunch) :)

[Guerilla]

tmp, I'm still quite impressed if that electrolysis yields that much perchlorate as the author claims.. It has been said to yield very little or no perchlorate in many places, and recognizing KClO4 merely by a crystal shape isnt quite the best way as it may vary depending on purity and other factors..but then again I have never tried this by myself with graphite anodes.. Have you determined the chlorate content of the final product? One good method was to add a few drops of conc H2SO4 on a pile of impure KClO4 and sugar (1:1 ratio), IIRC it will only ignite if there's more than some 5% of chlorate present.

[Tuatara]

This (http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/leaddiox/jes1958.html) is really interesting. About half way down the page they show the increase in current efficiency from adding some persulfate to the electrolyte - its almost doubled! This is particularly attractive as persulphates are much easier to come by than NaF, and nowhere near as nasty.
This is for lead dioxide anodes, not graphite ones.

Ollie, if persulphates are produced by electrolysis too, would that mean we could simply add a bit of sodium sulphate to the electrolyte and have it converted in situ to the persulphate? Maybe thats a dumb question, as thats probably exactly how the increase in efficiency occurs - sulphate -> persulphate
persulphate + chlorate -> sulphate + perchlorate


On another note, the processes for producing lead dioxide anodes often mention the use of non-ionic surfactants to prevent pinholes in the anode. I've found an OTC source for the surfactant. Yates make a product called 'Sprayfix', its a wetting agent for use with garden sprays to make the spray stick to the plants. It contains "non-ionic sufactant : 50g/l alkylaryl polyglycol ether" according to the label, so I going to give it a whirl with the next anode I make. You should be able to find the same or similar products in your local garden store - look for anything described as a wetting or sticking agent.

[Ollie Snowie]

Yep, I think that is the reason why adding a persulfate or sulfate increases efficiency. I was going to post this, but I thought it would contaminate the perchlorate too much. I suppose it could be used in trace amounts and purified by fractional crystalisation. I think NaF increases efficiency by a different mechanism; it forms a layer around the cathode that stops perchlorate being reduced to chloride at the cathode. In some cells sodium dichromate is required - Check Wouter's page.

Something else to try:- Persulfuric acid is also made with sulfuric acid and hydrogen peroxide, so maybe chlorates could be oxidised with hydrogen peroxide and sulfuric acid as a catalyst.

[tmp]

Guerilla, I did perform the acid test. No flareup occured. I ran my cell until the
electrolysis was almost nil. The problem with the graphite erosion seems to be
directly related to the heat produced. So I kept the rods far apart to keep the
heat down. Also, potassium dichromate does help the reaction along.
The perchlorate crystalizes out pretty fast as it is considerably less soluble
than the chlorate. Wouter claims that perchlorate formation doesn't start
until the percent of chloride, by weight, drops below 10%. This may be the
reason the method works because the solution starts out at just over 14%.
I altered the method and started at 9% which kicks in the reaction faster if
Wouter is correct. My anode and cathode are both graphite rods. The cathode
showed no sign of erosion although the anode did eventually erode.
I'm still going ahead with plans to use manganese dioxide to see how well
it performs. The reason I don't use a metal cathode is because I hate cleaning
out the voluminous iron hydroxide that forms from eroding steel.


These are the solubility ranges I found in CRC 52nd Edition 1971 - 1972

Solubility is grams per 100 ml water:

KCl----------34.7g @ 20 C--------56.7g @ 100 C
KClO3--------7.1g @ 20 C--------57.0g @ 100 C
KClO4--------.75g @ 0 C--------21.8g @ 100 C

[Tuatara]

The required amount of persulphate is between 1g/l and 10g/l. Thats less than 1% contamination by sulphate.

[tmp]

Testing for presence of chlorate in a perchlorate cell.

In addition to flareup tests, I found this on the net
and it works extremely well.

1 gram of indigo carmine is dissolved in a litre of water.
Indigo carmine is expensive(found some on eBay) no
matter where you buy it but 1 gram provides for a lot
of testing.

Boil 1 ml of the indigo carmine solution with 5 ml of some
concentrated HCl(the 31% stuff from the hardware store
works). Add 5 ml of the electrolyte from the perchlorate.
5 ppm of chlorate will cause the indigo to change color.
Even 1 ppm causes a color change.

[T_Pyro]

Regarding tests for Chlorates, Perchlorates, chlorites, and hypochlorites, you should see this (http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/tests.html). Very informative!

Regarding anodes:
The GSLD (Graphite substrate lead dioxide) anodes seem the most promising, but for obtaining a low current density with a high current, a large surface area of the anode is required. Therefore, I was wondering if aluminium tubes could be used as the substrate instead of the graphite. The advantages are numerous- with two surfaces (inner and outer) to a tube, the surface area is practically doubled, and aluminium tubes are quite cheap, too. Has anybody tried something similar? If so, what were the results like?

[tmp]

T_Pyro, my apologies for not giving credit where it is due. The link you
posted is EXACTLY where I got that information. The manganous sulphate/
phosphoric acid test is the most sensitive IIRC but the procedure is a pain in
the ass. The other tests, other than indigo carmine, are not as sensitive or
require the use of sulphuric acid which I do not like to part with. H2SO4 is
too valuable for other uses. The indigo test is cheaper overall and is
sensitive down to 1 ppm chlorate. This is more than sufficient for my
perchlorate production. I paid 24.00 USD for 50 grams of indigo carmine.
Considering that the solution is only 1 gram per litre of water and only 1 ml
of solution is needed for the test it's relatively cheap.

As for using aluminum tubes, the electrolysis might oxidize and therefore
passivate them rather quickly if any of the electrolyte gets through the
PbO2 coating. I've been using graphite rods kept at a distance to slow
down the inevitable erosion, however it's possible my local source of these
cheap rods may dry up due to less and less use by professional arc welders
as gouging rods. I'm still looking for a way to produce a solid rod of PbO2
that won't erode so quickly. I've used Ti, TiO2, MnO2, and PbO2 to produce
rods but the electrolysis still tears them up. I sure as hell don't want to go
the route of platinum because it would cheaper to just buy the KClO4 at
that point !

[T_Pyro]

That's odd, I was under the impression that lead dioxide coated anodes were quite inert. How thick was your lead dioxide coating? Were there any visible holes in the lead dioxide layer? It's also possible that your graphite anodes weren't being rotated at a high enough angular velocity while depoisition of the coating, to prevent pitting.

[tmp]

I honestly don't know how thick the PbO2 was on my rods but the anode
eroded albeit at a slower rate than an uncoated rod. I've found other info on
substrates that may work without the erosion. Another net source has
suggested using plastic surface with plumbers cement and to roll the rods in the
PbO2 obtaining a relatively thick coat. I tried using a porcelain substrate
however the electrolyte crawls up the rod and corrodes the connections.
Looks like plastic will be my next test.

[HarmonyWave]

Regarding the addition of dichromate-addition to raise efficiancy.
Could one instead add another, less dangerous, chemical with the same effect? Perhaps KMnO4?

Thanks.

[tmp]

HarmonyWave, I've never seen info on potassium permanganate being used
for perchlorates. BTW, how did you determine it is less dangerous than
the dichromate ?

[HarmonyWave]

tmp, meant to say 'less dangerous to ones health'. Actually i remember reading about a person who used KMnO4 in his electrolyte, but i cant seem to find the reference in all my mess :/ I could be wront though.

But if no-one from this forum have heard about it, i guess it is false anyway...+

[Zeitgeist]

Dichromate is carcinogenic, as i'm sure we all know.

KMnO4 is also alot easier to come by

[Bugger]

KMnO4 is also a more powerful aqueous oxidant than chromate or dichromate; although not as powerful as plumbate, bismuthate, cerium tetranitrate, hypochlorite, or chlorite, or gaseous Cl2 (and of course F2 and high-valence fluorides).

Perchlorate is also a potentially powerful oxidant, but it is kinetically slow, which enables the existence of ammonium perchlorate and organic perchlorate esters, although they are highly explosive.

Bugger.

[freaky_frank]

To get back on the persulfate idea.
It is indeed possible to oxidize KClO₃ to KClO₄ with potassiumpersulfate, K₂S₂O₈.
Normally this happens when boiling those two chemicals together in solution, but this seems to give bad yields.
Because persulfate contains a peroxidebond there doesn't need to be added a base or an acid according to the redox theory,actually there does need to be added a base but not as a catalyst this base gets reacted up by the reaction and is thus not a catalyst.

S₂O₈ ^2- + 2e^- --> 2SO₄^2-

ClO₃^- - 2e^- --> ClO₄^-
---------------------------------
S₂O₈^2- + ClO₃^- --> 2SO₄^2- + ClO₄^-

left: 3- right: 5-

--> 2OH^- ---> H₂O

--> S₂O₈^2- + ClO₃^- + 2OH^- --> 2SO₄^2- + ClO₄^- + H₂O

--> K₂S₂O₈ + KClO₃ + 2KOH --> 2K₂SO₄ + KClO₄ + H₂O

[Bugger]

Have you any data on the kinetics of the peroxydisulfate-chlorate reaction to produce perchlorate? It may explain the "bad yields". The rate constants for various oxidations by peroxydisulfate, e.g. of iodide, have been quite extensively studied and measured in the past.

Bugger.

[freaky_frank]

Sorry don't have information about that...

[FUTI]

peroxodisulphate have one problem it have oxidation potential that is fine for this
reaction, but when it comes to the kinetics...not good because reaction goes faster the less atom movement it takes to complete it (enthropy almost as big as mine text....focus man:) and when you look that anion you see lot of atoms it can be promoted sometimes with extremly small quantity of silver ion because it actualy oxidise silver to +2 state that then react with reductive substance (back to +1) and so on...( if I remember from mine first year chemistry it has to do with silver-peroxodisulfate complex compound...if ion is already bind before and after reaction not to much bond movement...only electrons...which makes whole process look very much like electrolysis).