Potassium Carbonate aquisition?

Hey Guys,

was looking for the easiest (or perhaps slightly complicated) method of synthesizing K2C03?

I have access to a few reagents such as NaOH, HCL, NaHC03, Na2C03, KOH, H2S04, Ca(OH)2, and a few others. (listed a bunch of reagents to give a variety of reactions i guess?)

A few equations, a procedure and method of extraction (as powder) would be much appreciated!

Thanks in advance ,

Fire away!!

Boonga

[Edited on 12-9-2011 by boonga]

Quote: Originally posted by hissingnoise

Treating a KOH solution with CO<sub>2</sub> or with carbonic acid and evaporating would seem the simplest route . . .

It's been several years since I've really lurked the forums (probably since the days of Rogue and Hive ) so I'm not sure on the current stand point of necro-posting but having Used The Fucking Google Search Engine Because The Site One Is Shit for quite some time I never found someone report their results on the rather straight forward sounding approach of: 2 KHCO3 -- heat --> K2CO3 + H20 + CO2.

I have had a hell of a time finding Potassium Carbonate anywhere in the country aside from one or two listings that were not only pretty damn expensive but also wanted my left testicle to post the stuff to me. I have a few times in the past made NaCO3 from NaHCO3 by just baking it in the oven (from memory around the 200C mark for 1.5 - 2 hours (don't quote me, it's been a while and I don't have my notebook handy - but I often did it at the same time as dehydrating MgSO4).

Now, Potassium Bicarbonate I can get from any brewing or wine making store but at a rather steep price! Problem is, no specific info is easily found, hell I even checked the Merck index in the end and no joy, Some places say 100C - 120C others say 110C - 400C and neither mention even a ball park figure for the time required. So, last week I decided "Screw it!" and just bought two 50g packs of the KHCO3 to do a couple of test runs. Here are my notes in the hopes it may help someone else in the future having the same sourcing issue:

Equipment used:
Scales accurate to 0.01g (or better)
A 25cm (10") square glass baking dish with low walls. Line the bottom with baking paper since K2CO3 is said to react with Aluminium (sorry forgot the source for that.
An electric kitchen oven (fan forced may be a bonus)
HDPE Bottles to store the K2CO3 in.

Stoichiometry to keep in mind:
2mols KHCO3 --> 1mol K2CO3 + H2O + CO2
KHCO3 = 100.11g/mol
K2CO3 = 138.20g/mol
H2O = 18.01g/mol
CO2 = 44.01g/mol

My 50g bag of "Wine De-Acid" weighed 51g on the scales (0.51mol) which means 35.24g K2CO3 + 4.59g H2O + 11.22g CO2 (0.255mol each) - This is the best way I had at my disposal at the time o check how the rxn was progressing. The KHCO3 was thinly poured over the baking paper ('wax paper in the U.S?) covering the bottom of the shallow baking dish and put into a pre-heated oven at 120C. After 30 minutes, no change in appearance was noticed, the course powder was stirred around a little and the oven temperature taken to 175C with the fan turned on (fan forced oven), after an addition 30 min at this temp no visual change was noticed (I expected to see a visual change due to my experience with Na's). So the temperature was raised to 200C, I look in 2 or 3 minutes later and most of the top layer was turning brown and some specs almost black, "Shit." I think so I open the oven door, drop the temp back to 140C - 150C and cool the baking dish a bit by sitting it on a wet towel for a minutes or so while stirring the powder around. It was placed back into the oven. Two hours from starting, the product still looked the same apart from the brown flecks, and was weighed at 36.17g which is 0.93g more than it theoretically should so it was returned to the oven at 150C with the fan on for another 30 min (Total time now = 2.5 hours) Weight dropped slightly to 36.02g (Still 0.78g heavier than theory. At this point it was bottled while still hot. After pouring it into a bottle I noticed with in a few seconds the odd tiny crystal clinging to the paper I used to transfer it had began to draw enough water from the air to melt itself.

The second 50g packet of the KHCO3 (51.68g - 0.516mol) was then spread over the same baking paper, in the same baking dish, but this time I kept the temperature to a maximum of 150C and cycled the oven fan so it was on for 30min - off for 30 min. After 2 Hours the product is still pure snow white with no visual difference to the starting material. At 2.5 hours the oven was turned off because 3am had come around fast and it was time for bed. The K2CO3 was weighed while it was pretty hot and dry @ 36.58g (0.93g over theory).

Notes I've taken from this:
* Don't heat KHCO3/K2CO3 mix over 175C due to discolouration.
* Possibly be able to run to completion in 2.5 hours @170C.
* K2CO3 is deliquescent (very hygroscopic) - Humidity wasn't excessive and small crystals were 'melting' themselves in seconds once cool.

Quote: Originally posted by CrimpJiggler

One thing I haven't learned to do yet is to deal with gases. I know how to generate CO2 gas but how to use a gas as a reactant I'm not so sure about.

Quote: Originally posted by Octavian

Now, Potassium Bicarbonate I can get from any brewing or wine making store but at a rather steep price! * Don't heat KHCO3/K2CO3 mix over 175C due to discolouration.