Sciencemadness Discussion Board - Separating Sodium Perchlorate from Buffer Solution

Separating Sodium Perchlorate from Buffer Solution

AlXe - 21-3-2022 at 06:52

Hi.

I have some buffer solution that contains Sodium Perchlorate, Sodium Acetate, Acetic Acid, Water and Ethanol.
I would like to extract the Perchlorates however for the life of me I can't think of an appropriate way since both share similar solubility profiles and using acids and based just seem to leave me with more products that are hard to separate, or add risk to the extraction. How would you go about it?

clearly_not_atara - 21-3-2022 at 08:56

Why not just precipitate KClO4?

macckone - 22-3-2022 at 17:00

Quote: Originally posted by clearly_not_atara

Why not just precipitate KClO4?

The solution contains sodium acetate.
Sodium acetate is less soluble but not enough difference to get a pure product, especially with the acetic acid. Adding potassium salt is not going to help a lot.

my suggestion would be to first neutralize the acetic acid and evaporate off the ethanol. I would use sodium bicarbonate as it is lower solubility.
That will give a solution of sodium acetate and sodium perchlorate.
Then crystalize the two components by slow evaporation.
You can get some separation with water but it isn't going to be a clean product.

Now the somewhat dangerous part.
This is a potentially explosive mix so take appropriate precautions. Do not apply strong heat, keep away from flames or other ignition sources. Evaporating acetone is a hazard, doing it with a dissolved oxidizer is more so.

sodium perchlorate is much more soluble in acetone than sodium acetate.
Dissolve in acetone and crystalize out the sodium acetate by slow evaporation.
This should give a good separation as the ratio is 52g:5g in 100ml of acetone.

AlXe - 23-3-2022 at 10:49

Thanks. That's exactly what I was after. Mainly I was trying to figure out the best solvent for the task that could help separate.

Fulmen - 23-3-2022 at 11:47

Quote: Originally posted by macckone

Sodium acetate is less soluble but not enough difference to get a pure product, especially with the acetic acid. Adding potassium salt is not going to help a lot.

Sorry, but I don't follow. Potassium perchlorate is two orders of magnitude less soluble than anything else in that solution.

[Edited on 23-3-22 by Fulmen]

woelen - 24-3-2022 at 00:30

This is a very easy separation. Don't add anything else, just add a concentrated solution of KCl or KNO3 and your KClO4 will drop out of solution. Let it cool down in a fridge to maximize the yield.
No need to worry about explosions, perchlorate ion is actually surprisingly inert at room temperature.

The precipitated solid then can be filtered and with some filter paper on tissue you can absorb quite a lot of water.
The still humid solid then can be recrystallized once from boiling distilled water. Add the solid to a little amount of water and heat to boiling. If not all of it dissolves, add a little more water and heat again to boiling. Repeat this step until all of it just dissolves. Then allow to cool down slowly. Once it is at room temperature, put it in a fridge and allow to cool further to below 0 C, but do not let the liquid freeze.
Filter again on filter paper (coffee filter works well) and then put the mass on tissue paper (with filter paper between the crystals and the tissue paper), to allow as much of the water to be absorbed in the tissue. The remaining solid then can be dried. This process will give you snow white very pure KClO4.

[Edited on 24-3-22 by woelen]

macckone - 24-3-2022 at 08:32

Quote: Originally posted by Fulmen

Quote: Originally posted by macckone

Sodium acetate is less soluble but not enough difference to get a pure product, especially with the acetic acid. Adding potassium salt is not going to help a lot.

Sorry, but I don't follow. Potassium perchlorate is two orders of magnitude less soluble than anything else in that solution.

[Edited on 23-3-22 by Fulmen]

The current solution is sodium perchlorate which is very soluble.

I was assuming he is wanting sodium perchlorate.
Also potassium perchlorate is more soluble in acetic acid than in water.
So still going to need to neutralize the acetic acid unless the acetic acid is very low then it may not make a difference.

Fulmen - 24-3-2022 at 09:05

Quote: Originally posted by macckone

I was assuming he is wanting sodium perchlorate

And I assumed it would end up as potassium perc somewhere down the line. Guess we both should stop assuming :-)

macckone - 26-3-2022 at 00:00

Quote: Originally posted by Fulmen

Quote: Originally posted by macckone

I was assuming he is wanting sodium perchlorate

And I assumed it would end up as potassium perc somewhere down the line. Guess we both should stop assuming :-)

Yes, should not assume.
I prefer ammonium perchlorate or lithium perchlorate myself.
The lithium perchlorate has a really good curve for recrystallization but is very hygroscopic.
Both ammonium perchlorate and lithium perchlorate have good weight to thrust ratios for rocket engines as compared to potassium perchlorate.

AlXe - 27-3-2022 at 07:34

Quote: Originally posted by woelen

This is a very easy separation. Don't add anything else, just add a concentrated solution of KCl or KNO3 and your KClO4 will drop out of solution. Let it cool down in a fridge to maximize the yield.

Thanks. The solution is of water, acetic acid and ethanol. Dissolved are Na compounds, instead of K. Could I interchange KCl with NaCl? Is this method based on KCl being more soluble and pushing out the KClO4?

Fulmen - 27-3-2022 at 09:05

That and the very low solubility of KClO4 (<1g/100ml@0°C). So no, NaCl won't work.

AlXe - 29-3-2022 at 03:41

Quote: Originally posted by macckone

sodium perchlorate is much more soluble in acetone than sodium acetate.
Dissolve in acetone and crystalize out the sodium acetate by slow evaporation.
This should give a good separation as the ratio is 52g:5g in 100ml of acetone.

Quote: Originally posted by Fulmen

That and the very low solubility of KClO4 (<1g/100ml@0°C). So no, NaCl won't work.

Do you know a good link where information of different substances solubilities in various common solvents can be found? Wiki is only really consistent with water solubility at room temperature.

This would be my preferred method and works best with my knowledge base. My knowledge on the other method is limited but it does seem easier.

My main confusion is in the attachment taken from wiki. KClO4 appears to be the most soluble at 167g/100ml @0C.

Would KNO4 be the best because it has the lowest solubility compared to the electrolyte KClO4, salting it out?

I had a lot of practical chemical and biochem tech roles and good with the setup of components but I have only salted out something once before and my chemistry knowledge is placed around a very rusty first year. I don't remember how to relate the solubility information to this procedure.
Generally I would like to figure this out by experiment, but I don't have much of the buffer.

Any brief further info/link on why NaCl can't be used instead of KCl?

If your happy to could you expand on the second method slightly?

AlXe - 29-3-2022 at 03:46

Quote: Originally posted by macckone

How did you work out that final part?

macckone - 29-3-2022 at 09:16

Quote: Originally posted by AlXe

Quote: Originally posted by macckone

How did you work out that final part?

52g/100ml is the solubility of perchlorate in acetone (literature value)
5g/100ml is the solubility of acetate in acetone (literature value)

That is a 10:1 ratio. Which is very good.
Sodium acetate will crystalize out first due to the lower solubility in acetone.
For this type of crystallization slow evaporation is best.
That and heating a potentially explosive mixture of oxidizer and fuel is not a great idea.

You may need to do two or three passes if you need a very pure product.
During the first pass assume equal parts (which probably isn't true), you will get most of the acetate out, then a mixed product and finally an improved perchlorate that is 90% pure (possibly more or less depending on common ion effects). In this case it is going to be more pure.

The second pass would improve that to as much as 99% purity. Technique is more important in the second pass.

If you have compounds of equal solubility in one solvent and significantly different solubility in a second solvent, doing a crystallization from the differing solvent will give you a relatively pure product of the first product to precipitate. Using the solvent where they are more equal for the second pass will give a precipitate of the second component because the second component is no where near saturation.

Repeat as needed to achieve a high quality product.

Texium - 29-3-2022 at 11:41

Quote: Originally posted by AlXe

I had a lot of practical chemical and biochem tech roles and good with the setup of components but I have only salted out something once before and my chemistry knowledge is placed around a very rusty first year. I don't remember how to relate the solubility information to this procedure.
Generally I would like to figure this out by experiment, but I don't have much of the buffer.

Any brief further info/link on why NaCl can't be used instead of KCl?

If your happy to could you expand on the second method slightly?

It's quite simple: KClO₄ is much less soluble than NaClO₄ or KCl, so when you combine solutions of NaClO₄ and KCl (keeping in mind that these salts are fully dissociated into ions in solution), KClO₄ is what will crystallize out first. NaOAc and KOAc are both highly soluble so the acetate shouldn't cause any issues.

NaClO₄ (aq) + KCl (aq) → NaCl (aq) + KClO₄ ↓

If you were to add NaCl to the solution it wouldn't help anything. The common ion effect can be used to decrease the solubility of a salt, but since NaCl has a lower solubility than NaClO₄, all that you would manage to crystallize out would be NaCl.

AlXe - 24-4-2022 at 07:32

The responses have been really helpful thank you for the time you have taken.

AlXe - 25-4-2022 at 08:16

Quote: Originally posted by macckone

Quote: Originally posted by AlXe

Quote: Originally posted by macckone

I tried both methods.

Salting out with KCl is most definitely preferable. It took 2.5 liters of acetone to dissolve the Acetate and the perchlorate