Sciencemadness Discussion Board

Potassium Hydroxide Synthesis

mericad193724 - 11-10-2006 at 11:57

We all have easy access to NaOH crystals as drain opener, but it is much harder if not impossible to come across Potassium Hydroxide crystals OTC. KOH is usually found as a very dilute solution of KOH in drain openers.

Would it be possible to make KOH in the following way:

KCl + NaOH --> NaCl + KOH

Potassium is more reactive then Sodium so it should displace it, right?

After this reaction KOH would need to be extracted and this would be difficult because boiling down a very concentrated KOH solution is not my idea of fun. The KOH could be extracted with the use of Ether, since it is insoluble in it. (2 solvent recrystallization).

Would this work?

thanks

Mericad

woelen - 11-10-2006 at 12:03

No, this hardly will work. NaCl is slightly less soluble, so you could obtain a mostly KOH solution, but heavily contaminated with sodium chloride. Making KOH from NaOH hardly is feasible.

One way to make KOH is to try to obtain CaO or Ca(OH)2 (some cement's contain this, albeit in impure form). Making a solution of this, and adding a solution of K2CO3 does the job. CaCO3 is precipitated and KOH remains behind in solution. It should be possible to obtain reasonably pure KOH in this way.

mericad193724 - 11-10-2006 at 13:05

It seems that my proposed synthesis is impractical.

IIRC you can make CaO from CaCO3 by heating it to decomposition. (Coincidentally I made CaCO3 yesterday, 8 grams). Can I achieve sufficient temperature to decompose the CaCO3 completely if I put the CaCO3 in a copper pipe end cap and heat strongly with a propane torch? This could be a simple path to CaO.

Mericad

stricnine - 11-10-2006 at 13:34

Off my head, you need 1100ºC to decompose it into CaO. The propane flame should allow you to reach that temperature, but I am not so sure about the heat loss of your pipe "crucible", nor how efficient is the torch.

But yes, it would be a practical and easy path.

mericad193724 - 11-10-2006 at 17:21

I just tried taking 1 gram of Precipitated CaCO3 and heating it with propane on a ceramic wire gauze. First let me say DO NOT HEAT BARE WIRE GAUZE, it will glow red, sag and crack a bit upon cooling. But after the CaCO3 weighed .76 grams. There was some CaO produced because trying to dissolve it in water yield a solution with pH 13-14! Very little of the solid dissolved. I only heated for about 5 min.

Also, can you filter strong Alkali solution (NaOH and KOH) through regular paper filter paper or will it "eat it" as H2SO4 does???

Mericad

Magpie - 11-10-2006 at 17:42

I have purchased hydrated lime, Ca(OH)2, by the pound at weed & feed stores. I've also seen it for sale at Ace Hardware.

I purchased 5lbs of KOH off the internet in flake form. It should be more available now with biodiesel in vogue. But if you want to make everything yourself I understand. ;)

12AX7 - 11-10-2006 at 19:04

Classical method is to pile limestone blocks on top of a bed of say, charcoal or coke (I suppose coal would work too, but the volatiles might junk things up). This is done inside a lime kiln (naturally), which isn't much different from any other cylindrical pile of rock and mortar. The next day you kick out all the soft blocks of lime and slake it, to much boiling.

Tim

not_important - 11-10-2006 at 20:06

Slaked lime, Ca(OH)2, often labeled "type S lime" in the US, can be found in hardware and construction supply outlets in large bags of 10 to 25 Kg. It's cheap, and likely easier than making your own CaO.

If you do want to make CaO :
Around a 1000 C will do for making CaO, if you arrange things so that a current of air flows through the heated lime then you can run the conversion as low as 800 C and perhaps lower, but it will take longer. You're dealing with an equilibrium, CaCO3 <=> CaO + CO2, so removing the CO2 drives it to the right.

Use steel/iron pipe, copper will oxidise too much.


You will want to concentrate the KOH solution and let it sit in a sealed polyolefin plastic (not glass) bottle for some days, the calcium salts that were in solution will slowly settle out ; decant the KOH solution from the (hard to filter strong alkali) and toss the last bit of solution and ppt into the next K2CO3 + Ca(OH)2 reaction you do.


Edit - don't type while cooking...


[Edited on 12-10-2006 by not_important]

unionised - 11-10-2006 at 21:53

limestone + vinegar -> Ca acetate
Ca acetate + drain cleaner-> Ca(OH)2
Ca(OH)2 + K2CO3 -> KOH

dr. nick - 12-10-2006 at 09:14

how is that last step to be done?
got both Ca(OH)2 + K2CO3 and would like to try ...

12AX7 - 12-10-2006 at 09:18

Drain cleaner is either NaOH or KOH solution; seems redundant to me...

Tim

Maja - 12-10-2006 at 10:00

Drain cleaner is mostly NaOH prills ... Atleast in my country :)

mericad193724 - 12-10-2006 at 17:37

Don't get me wrong...I would LOVE to buy some hydrated lime, slaked Lime, or Limestone...its just not available in my area. My hardware store doesn't sell it (I work there, I would know). My area doesn't have any natural limestone either.

Does Home Depot, Ace, or Lowes (North America Stores) have Ca(OH) or CaO?

The one drain opener I found said "Contains Sodium Hydroxide and Potassium Hydroxide." Another one that only contained KOH was a dark green and low concentration.


Mericad

[Edited on 13-10-2006 by mericad193724]

Magpie - 12-10-2006 at 18:17

Do you have stores that cater to people with livestock like horses, etc. Check with them. I bought it by the lb for $0.60/lb at a place like that. I'd be very surprised if they didn't sell hydrated lime in rural NJ.

People who homemake liquid soap should be using KOH. Try to find one of their suppliers.

[Edited on 13-10-2006 by Magpie]

Froogle for potassium hydroxide. You'll find it quickly in 1, 5, and 50 lb quantities.

[Edited on 13-10-2006 by Magpie]

not_important - 12-10-2006 at 22:48

Quote:
Originally posted by mericad193724
...

Does Home Depot, Ace, or Lowes (North America Stores) have Ca(OH) or CaO?

...
Mericad



I have been informed that either Home Depot or Lowes, or possibly both, carry slaked lime - again likely to be labeled "type S lime". This was told to me by someone living on the West Coast, if you are in a heavly urbanised region you may have to get to stores in a more suburban setting.

It appears that for a Kg or less of KOH, going to ebay may be the best deal for people in the US.

I have done this before

Ephoton - 25-10-2006 at 16:31

it was in t old inorganic chem book and I was trying to go compleatly otc.

first I got potasium sulfate which is used for fert.
then I mixed it with calcium hydroxide with extra water.
I heated them for abour an hour then filtered out plaster of
paris adding extra water to wash out potasium hydroxide solution.
the bigest problem I got was distilling the water off of the solution.
best done under vacuum for sure do less damage to your glass
and make a purer product.

pritty easy so easy I dont buy KOH any more.

Endo - 26-10-2006 at 05:09

I recently purchased some lime at the grocery store. Just go to the canning section and look for Pickling Lime. It is cheap <$2 for 2lb.

denatured - 27-10-2006 at 01:40

"People who homemake liquid soap should be using KOH. Try to find one of their suppliers."

I make all the time , I either use KOH or something else they spell it as 'sliKa' or 'silica' I don't know if there is any silicon in it but I'm sure it is something basic ...

Just a note on potassium hydroxide soln.

I once prepared a very concentrated soln. of it and then I stored it in glass container, after say 16 days I don't remember I found the container broken and full of white flakes and no soln. when I tried to dissolve these flakes in water, the solubility was very weak if it dissolved at all ...

I'm not sure if it is KOH or something from the air reacted with the soln. it wasn't very air tight ...

BeerChloride - 27-10-2006 at 05:00

alnokta, your KOH had turned into potassium carbonate.

jimmyboy - 28-10-2006 at 01:50

this has already been covered in the sodium hydroxide threads... use the search engine.......

mericad193724 - 20-11-2006 at 17:37

I was just thinking...can't you simply produce KOH by the electrolysis of potassium chloride?

KCl is readily available and cheap in huge bags or it is also sold as a salt substitute. I know that under certain conditions electrolysis of KCl will yield potassium chlorate (hot solution) and IIRC a cold solution will yield potassium hypochlorite(KClO). Under what conditions does KOH form? The Cl needs to be driven off as Cl2 gas.

Mericad

The_Davster - 20-11-2006 at 17:44

Placing the electrode evolving chloring as near to the surface of the solution as possible will prevent the chlorine from dissolving in the increasingly basic solution. A cell separated by some sort of membrane or diaphragm may also be of use here.

Aqua_Fortis_100% - 27-1-2007 at 15:35

@ mericad ,
i have this KCl in fertilizer form (pinkish/redish impure powder) and at the momment i playing around purify it..when i dissolved this in boiling water a weak ammonia smell was observed, and i almost sure which contains NH4Cl what has a similar solubility compared to NaCl (even after cristalyzing this compound - nice white needles), because i added some NaOH pellets to dried "purified" powder material and a more stronger ammonia smell was observed.. i think which isn't too good to chlorate manufacture because of changes to form also NH4ClO3 highly dangerous contaminant to KClO3, maybe making a disappointing synth..

about the KOH:
what about mix stoichometricaly this in diluted sulfuric acid and boil off the HCl gas to make K2SO4 , then add a correct portion of Ca(OH)2 and fiter off the CaSO4 hydrate, concentrating the solution and recristalyzing the KOH ???
i interested because i have TONS of dilute H2SO4 here..free battery acid solves all problems haha :D

[Editado em 27-1-2007 por Aqua_Fortis_100%]

12AX7 - 27-1-2007 at 23:12

Wouldn't the NH3 component be eliminated during electrolysis?

Ca(OH)2 works for carbonate or sulfate, sure.

Tim

womble - 29-1-2007 at 00:40

look online for the people that supply the soap makers and the hobbyist essential oil market. The wholesalers will sell you bulk KOH and many other useful things.

picketfence - 31-1-2007 at 07:42

Quote:
Originally posted by mericad193724
Don't get me wrong...I would LOVE to buy some hydrated lime, slaked Lime, or Limestone...its just not available in my area. My hardware store doesn't sell it (I work there, I would know). My area doesn't have any natural limestone either.

Does Home Depot, Ace, or Lowes (North America Stores) have Ca(OH) or CaO?

The one drain opener I found said "Contains Sodium Hydroxide and Potassium Hydroxide." Another one that only contained KOH was a dark green and low concentration.


Mericad

[Edited on 13-10-2006 by mericad193724]



Try ceramic suppliers

UnintentionalChaos - 31-1-2007 at 08:41

If you're really desperate for limestone, you can make some of your own with much higher purity than you could buy as a fertilizer. Just look at the hardware store for CaCl2 ice-melt and combine it with dirt cheap washing soda to ppt the CaCO3. Excessive, yes, but the product is a paper white, ultrafine powder which reacts easily with even very dilute acids.

Try garden shops for limestone. It's used as a soil amendment. Also, any place stocking supplies for a horse farm would carry CaO or Ca(OH)2 due to its use as a disenfectant in stables. The lowes by me carries NaOH flakes, mixed solutions of KOH and NaOH, and KOH solutions.

[Edited on 1-31-07 by UnintentionalChaos]

chemrox - 9-2-2007 at 22:00

isn't K2 + 2HOH ==> 2KOH + H2 ? leaving a solution of KOH and water which could then be dehydrated...??

12AX7 - 10-2-2007 at 13:10

That sounds awfully counterproductive.