metalresearcher
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Strongly heating K2CO3 + C foams ?
In order to try a 19th century experiment (and commercial production of sodium with similar Na2CO3 + C in that era) I mixed some K2CO3 with powdered
charcoal.
I put the mixture in a 316 stainless steel retort with its neck dipped in mineral oil. The same setup as I used successfully with KOH + Mg which
indeed yielded some K balls in the oil.
Now I heated it to 1200 C (checked with an infrared pyrometer on the bright orange body of the retort) for a few minutes until bubbling ceased.
It was 21g K2CO3 and 3.5g charcoal powder.
The 316 stainless appears to be rather resilient even at 1200 C, but is is only for short times. It is still in good condition after several heats
over 1000 C.
Above 1100 C this reaction takes place:
K2CO3 (liquid) + 2C (powder) => 2K (vapor) + 3CO (gas)
140 (21g) 24 (3.5g)
The threaded opening of the retort was sealed with Teflon tape which did work despite it decomposes (probably the carbon leftover) at such
temperature. There were barely any leaks as I did not see flame discoloration due to purplish K+ ions.
After opening and dumping the retort into water I heard a few small explosions inside the tube but the top part was full of foamed stuff. Weird,
because the lower (hot) part of the retort was only filled half full at the beginning with the charcoal powder with the pre-dried K2CO3 on top. Now it
was empty. The top part contained black frozen foam.
What did actually happen ? It appears that the liquid K2CO3 started to foam with the charcoal powder as CO gas appears.
On the pictures, the furnace running and the retort after use.
  
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Alkoholvergiftung
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How long did you heat it? Old book describe time of 12 hours and whithe glowing heat , first came burning gases over and at last the Potasium. They
mention to use excess potash because it forms dangerous Potasiumcarbonmonoxide and black substance that explodes. With Sodium there is non such
reaction. Maybe the black foam is this explosive substance?
Castner reduction with Ironcarbid (ironfillings heated with tar or very Carbonrich Iron) works on 800C and only 1 1/2 to 2 hours. That was the first
industrial methode of making Alkali metals.
[Edited on 4-10-2025 by Alkoholvergiftung]
[Edited on 4-10-2025 by Alkoholvergiftung]
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metalresearcher
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I heated it a few minutes until the bubbling in the jar with oil stopped.
The Potasiumcarbonmonoxide story can be an explanation of the explosions I heard.
Maybe next time heating with excess K2CO3 ?
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Alkoholvergiftung
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I would use the excess because more of the old sources state the danger of an explosible black potassium compound.
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metalresearcher
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Where did you get this info from ?
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Alkoholvergiftung
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from the book: Darstellung Chemischer Preperate, and Metalle und ihre Reihndarstellung.
The yield was bad too 2-3 parts Potassium from 14 parts Potassiumcarbonat.
The book has an discription with pictures for the apperatus too. Mostly they used musket barrels as retorte. I think they are to many side to make
photos and post it here and they are in german.
Oh and favorite starting material was Potassiumtartarat heated in an closed fessel with an lid so only an mix of carbon and potassiumcarbonat remains.
[Edited on 4-10-2025 by Alkoholvergiftung]
Castner reduced KOH with Ironcarbid an mistake i made bevore.
The book "Reine Metalle" labeld the black substance as potassiumcarbonyl.
[Edited on 4-10-2025 by Alkoholvergiftung]
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bnull
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Is this Darstellung the one by Hugo Erdmann?
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Alkoholvergiftung
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Its from Dr. G. C. Wittstein. Munic 1857.
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Alkoholvergiftung
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You need to cool the condensor with ice water that what they wrote and the Stove (Destilling) system looked something like this.
Attachment: Kalium2.pdf (69kB)
This file has been downloaded 29 times
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Alkoholvergiftung
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I ve put all files in one together hope it works this time.
Attachment: Kalium.pdf (542kB)
This file has been downloaded 31 times
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bnull
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Thank you.
Edit: I found a copy of Darstellung at Internet Archive: https://archive.org/details/anleitungzurdars00witt/page/n3/m.... Potassium starts on page 423.
[Edited on 4-10-2025 by bnull]
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metalresearcher
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This old book (1844) is really interesting, some incorrect formulas (potassium oxide as KO instead of K2O and water HO).
This is a different and far more complex setup, in a simple setup this will clog the distiller as the K freezes in the pipe leading to the oil.
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Alkoholvergiftung
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The book is good because there are lot of tips what you could do wrong. I know that its outdated but if someone trys to make same basic chemicals by
yourself this book is perfect.
Modener books write about Vakuumdestillation of CaC2 and KF or KF reduction with Mg (grieß). But who has an Vakuumdestillation setup for higher
temperatures
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