Sciencemadness Discussion Board

KOH purification from bbq cleaner

BauArf56 - 17-8-2021 at 11:38

I got 500 ml of liquid barbeque cleaner and it says to have 15-30% potassium hydroxide solution + capryl/caprylyl glucoside and PPG 2 methyl ether. How can i destroy these two? they tend to foam a lot and it's quite annoying.

macckone - 20-8-2021 at 09:25

Both are organics that will be destroyed by heat or oxidation.
Hydrogen peroxide is the obvious oxidant.
Otherwise heat until reasonable dry then move to high heat.
Both of these will increase the carbonate contaminants.
Carbonate contaminants can be removed by treating with calcium hydroxide.

If you can get calcium hydroxide it is likely to be a better source of potassium hydroxide as you can simply add potassium carbonate solution to excess calcium hydroxide and stir. It is a pain to filter but you can use the wash and decant method then boil off the water. potassium hydroxide dries a lot easier than sodium hydroxide in my experience.

An expensive yet clean way of getting potassium carbonate is to heat cream of tartar, potassium bitartrate.
A messier way is from wood ash, but it will have significant sodium contamination.

Sodium carbonate is much less soluble than potassium carbonate 50g/100ml vs 110g/100ml so you should be able to separate them fairly easily.

BauArf56 - 21-8-2021 at 03:11

Thanks! I tried adding some 3% hydrogen peroxide to it but i didn't notice anything. Then i tried to put in solution a small piece of al foil to see if it would foam again, but it reacted barely. Could this be caused by the formation of potassium peroxide?

I already have lots of calcium hydroxide, and i made some sodium hydroxide too, but getting cheaply and easily potassium carbonate seems quite difficult. Decomposing bitartrate gives an horrible smell and the product contains a lot of carbon. How about bubbling co2 directly through the koh solution, filtering carbonate and reacting with calcium hydroxide?

macckone - 21-8-2021 at 22:18

I don't know where you are but potassium carbonate is commonly available in brewing stores if they have home brewing where you are, that would be a good source.

You can also get potassium hydroxide from soap making suppliers, again depends on country.

hissingnoise - 22-8-2021 at 03:17

Quote: Originally posted by macckone  

You can also get potassium hydroxide from soap making suppliers, again depends on country.

I bought KOH recently on ebay ─ turned out the supplier was based just a few miles from me...

It was slightly impure (some slight flocculence on dissolving) but reasonably priced.

unionised - 22-8-2021 at 03:27

If you oxidise the organics you will get CO2.
That will react with the KOH so you will get K2CO3 (or even KHCO3)
You will spend lot of time and effort (and money if you use H2O2) getting an impure carbonate, and it's easy enough to buy that.
What you certainly won't get is pure KOH.

Burning off the organic matter in oven cleaner will not smell much better than burning cream of tartar.

Potassium carbonate is very soluble in water and won't precipitate from a solution of KOH when you add CO2.
Potassium bicarbonate will - but not very well.

In principle, adding an excess of CO2 to the oven cleaner will precipitate some of the potassium as bicarbonate.
You can filter that off, heat it to convert it to carbonate and then causticise that with slaked lime.

I'm not sure it would be easier than buying KOH.