How rapidly does KOH absorb CO2 from the atmosphere and transform into K2CO3?woelen - 20-12-2012 at 23:53
Quite fast. if you leave a solution standing in contact with air, then within several hours you already have a noticeable carbonate content.elementcollector1 - 21-12-2012 at 08:40
But if the solution is freshly prepared, for instance, and immediately boiled down to dryness and stored, then carbonate content remains low?Pyro - 21-12-2012 at 08:50
sure, if you don't boil it for hours. and use disposable glass or metal.elementcollector1 - 21-12-2012 at 11:52
Definitely using metal.elementcollector1 - 21-12-2012 at 12:48
Well, shoot. Seems I underestimated the solubility of sodium sulfate in water. It says it's insoluble in alcohol, while potassium hydroxide is, so
could I extract these with isopropyl alcohol? (There is a precipitate of sodium sulfate, it's just not as much as I expected, and I'd really like as
little impurity as possible in this KOH so I can use it for some elemental potassium making.)elementcollector1 - 21-12-2012 at 20:13
Actually, is it possible to boil KOH down in glass if one keeps the temperature below 406 degrees C (MP of KOH)?Oscilllator - 22-12-2012 at 00:38
sure, if you don't boil it for hours. and use disposable glass or metal.
So long as you boil the KOH at a decent rate and preferably in tapered neck vessel (such as an erlenmeyer) I think that the steam being driven off
will prevent any significant quantity of carbon dioxide reaching the KOHsimba - 22-12-2012 at 08:08
Actually, is it possible to boil KOH down in glass if one keeps the temperature below 406 degrees C (MP of KOH)?
Yes, but keep in mind KOH attacks glass even when not melted, but much slower also. I've already done reactions with solid NaOH at 150ºC in glass
container with no serious damage, but using a magnetic stirrer, the center of flask became 'scratched' after it.elementcollector1 - 22-12-2012 at 12:21
Well, I have some Ca(OH)2 for use in regenerating any KOH lost to K2CO3. Wiki suggests boiling a solution of carbonate/hydroxide with calcium
hydroxide, but in what form? Should the calcium hydroxide be in solid form (it doesn't tend to dissolve too much, so I assume that's what they mean)?
If so, wouldn't the calcium carbonate form a coating on the hydroxide, preventing further regeneration?
I'd like to find a serious steel or stainless steel container for boiling this down, but I have no idea where to look. Tin cans for soup are
plastic-coated, and unless someone has a very good procedure for removing this, I don't think these are going to work.m1tanker78 - 22-12-2012 at 12:33
I assume lime water is what's implied. When I need a stainless steel vessel to boil things down, I hit up the pet section at the grocery store or go
to a pet shop and buy a food/water dish. They're inexpensive and come in very handy sometimes.
Tankelementcollector1 - 22-12-2012 at 12:55
That's a lot of water, then. Time to get boiling.woelen - 22-12-2012 at 13:16
Be prepared to get contaminated KOH if you boil down in glass. You etch your glassware and the resulting KOH will contain silicate. You definitely
need something elso to boil down the material. if you go as high as 400 C or so, then I think that your glassware simply will dissolve!m1tanker78 - 22-12-2012 at 13:28
EC: Depending on the degree of carbonate contamination in your KOH solution, you may not need much lime water.
The only other 'easy' way I can think of is to add small portions of calcium chloride solution if you can accept calcium/chloride contamination in
your product. You'd pretty much be exchanging one form of contamination for another but it may be more acceptable (or not) for your purposes.
How are you filtering your solutions?
Tankelementcollector1 - 22-12-2012 at 13:39
My KOH is already horribly contaminated (attempted to boil it in a plastic-coated container)... this is more of a proof-of-concept.
What will the calcium chloride do, transform into calcium hydroxide? Not sure how that will help...m1tanker78 - 22-12-2012 at 13:53
The calcium chloride would sort of be a workaround to preparing lime water which suffers the same fate as KOH solution when exposed to CO2. Just
something else to try if you're doing proof of concept.
Tankelementcollector1 - 22-12-2012 at 17:13
Just found an old stainless steel crucible. It doesn't stick to a magnet, but the color is wrong for aluminum (and I distinctly remember buying it as
a "stainless steel cup"). It's a bit small, but I guess that'll make for more clumping together of whatever KOH does come out.
Anyway, if this does work, this'll be my method of preparing KOH (which is horribly inefficient, but all reagents are OTC):
1) KCl + H2SO4 -> K2SO4 + HCl
2) K2SO4 + NaOH / Ca(OH)2 -> KOH + Na2SO4/CaSO4
I've moved away from electrolysis because it never seems to produce a strong enough solution, takes longer, and isn't quite as easy to work with (my
car battery charger can be horribly temperamental).
