Making potassium hydroxide

[gatewood]

I've been using potash as a cheap, very abundant basic chemical. I've also been aware that, if you burn it, you'll decompose the carbonates and get the even more basic potassium oxide.

I just wanna know: if I hydrate the potassium oxide (I know it can be dangerous), will I end up with potassium hydroxide?

[SergUpstart]

7 minutes ago, gatewood said:

I just wanna know: if I hydrate the potassium oxide (I know it can be dangerous), will I end up with potassium hydroxide?

Yes you get it

K2O + H2O = 2KOH

[chenbeier]

But you need very high temperature to transfor to K2CO3 => K2O+ CO2

This KOH will be not clean from carbonate.

Better is to use electrolysis with a diaphragma.

The same way NaOH is produced.

Edited June 8, 2021 by chenbeier

[John Cuthber]

9 minutes ago, gatewood said:

I've also been aware that, if you burn it, you'll decompose the carbonates and get the even more basic potassium oxide.

Not to any meaningful extent.

The decomposition temperature is very high and there's a lot of CO2 in a fire which drives the reaction in the "wrong" direction."

 

10 minutes ago, gatewood said:

if I hydrate the potassium oxide (I know it can be dangerous), will I end up with potassium hydroxide?

The question does not arise.

You can make potassium hydroxide from the carbonate by reaction with slaked lime

[gatewood]

48 minutes ago, John Cuthber said:

Not to any meaningful extent.

The decomposition temperature is very high and there's a lot of CO2 in a fire which drives the reaction in the "wrong" direction."

 

The question does not arise.

You can make potassium hydroxide from the carbonate by reaction with slaked lime

 

54 minutes ago, chenbeier said:

But you need very high temperature to transfor to K2CO3 => K2O+ CO2

This KOH will be not clean from carbonate.

Better is to use electrolysis with a diaphragma.

The same way NaOH is produced.

I mentioned the burning process, because Ive been able to make potassium oxide using charcoal and coke furnaces (they can totally melt iron) which is more or less, the way portland cement is made, but you guys are definitely right.

I was thinking of improving the method, by simply separating the chamber that holds the potash, so it heats up by convection but does not let CO and CO2 in (with a small opening to vent off the decomposed CO2).

[chenbeier]

Do you know  the Soda potash digestion. This is used in analytical chemistry. The carbonate of sodium and pottasium are very stable. The decomposition will take place beyond boiling point.  With other words with burning its not possible to obtain Potassium Oxide.

https://en.m.wikipedia.org/wiki/Potassium_carbonate

 

Edited June 8, 2021 by chenbeier

[gatewood]

To my knowledge, that is totally false, it does go beyond the melting point, but not the boiling point because it doesn't even have a boiling point to begin with, it decomposes first:

https://www.google.com/search?client=-b-d&q=potassium+carbonate+decomposition+point

And sodium and calcium carbonates actually decompose bit more easily.

[chenbeier]

Ok, right. But still difficult to get clean K2O.

All methode to produced K2O dont use Carbonate.

Check here below the point production

https://en.m.wikipedia.org/wiki/Potassium_oxide

 

 

 

[John Cuthber]

It is utterly impractical to consider getting K2O  by heating the carbonate. It will not work.
If you want KOH there are ways that do work.
 

The same chemistry they discuss here
https://pubs.acs.org/doi/pdf/10.1021/ie51398a020
is probably the easiest way.

[gatewood]

On 6/9/2021 at 5:10 AM, John Cuthber said:

It is utterly impractical to consider getting K2O  by heating the carbonate. It will not work.
If you want KOH there are ways that do work.
 

The same chemistry they discuss here
https://pubs.acs.org/doi/pdf/10.1021/ie51398a020
is probably the easiest way.

That paper is very interesting (though the term "lime", I think should be replaced with "quicklime"). Most appreciated input kind sir.

Just wanted to say that, the thing I have about using a thermal process, is that it would be rather easy to set up a kiln with charcoal basically anywhere, with no need for reactants or electricity, and the process would be rather straightforward.

Edited June 12, 2021 by gatewood

[John Cuthber]

8 hours ago, gatewood said:

Just wanted to say that, the thing I have about using a thermal process, is that it would be rather easy to set up a kiln with charcoal basically anywhere, with no need for reactants or electricity, and the process would be rather straightforward.

Yes, it would be cheap, simple, low tech and accessible.

But it would not work.
The potassium oxide vapourises at temperatures high enough for potassium carbonate to decompose.

On the other hand, you can use a simple charcoal fire furnace to make quicklime.

And then you can add water to make the calcium hydroxide needed for causticisation.

The by-product is calcium carbonate and you can reuse that by putting it in the furnace again.

Much as I would like to claim credit for this rather clever system, it isn't my invention. The process was used for centuries.

 

8 hours ago, gatewood said:

(though the term "lime", I think should be replaced with "quicklime").

No

Arguably, it should be replaced with "Slaked lime".

Quicklime is calcium oxide and the material used to make caustic in solution is slaked lime..
 

[gatewood]

Fair enough.

I have another question: what happens to a metal carbonate when it is hydrated? Does it split into its metal cation and carbonic acid? (like how sodium chloride splits into its respective ions?).

Edited June 13, 2021 by gatewood

[chenbeier]

Yes it does depending on the soloubility product.

Na2CO3 => 2 Na+ + CO3 2- max. 217 g/l

CaCO3 => Ca2+ + CO3 2- max. 14 mg/l

 

[gatewood]

Thanks for the response.

That's interesting, since carbonic acid is, more or less, an aqueous solution of CO2, wouldn't it be possible to volatilize it, by aerating the water? Or by degassing it?

[chenbeier]

Only  as carbon dioxide in water, like Soda drinks decompose if they stand long time around.

But in combination with a metal cathion, its not possible.

[gatewood]

Where the difference lies exactly?

[chenbeier]

The difference is  on one side you have CO2 dissolved in water. This can be removed easily on the other side you have alkali cathions additionally. Its the same you dissolve CO2 in NaOH for example. This cannot remove.

[exchemist]

10 hours ago, gatewood said:

Where the difference lies exactly?

No H⁺ cations. CO₂ reversibly forms H₂CO₃ (carbonic acid) in water, so if you can convert CO₃²⁻ to H₂CO₃, you will evolve CO₂ from the solution.

That's what happens when you add acid to a carbonate solution: it fizzes. It's why acid rain erodes limestone.

But without a source of H⁺, you can't form  H₂CO₃.  

[chenbeier]

 

 

That is not the goal. The goal was to remove CO2  from the carbonate solution by Ventilation. It is  clear if we add acid to  it. But then we exchange carbonate to another anion from that acid. I think he is still looking to "Filter" the carbonate.

On 6/14/2021 at 1:06 AM, gatewood said:

Thanks for the response.

That's interesting, since carbonic acid is, more or less, an aqueous solution of CO2, wouldn't it be possible to volatilize it, by aerating the water? Or by degassing it?