volcanocowperson
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Oxidizing CO using KMnO4
Hoping someone here can help me out with this:
I'm going to be heating a 1-atm lab furnace to approximately 1260C to melt some pieces of volcanic glass, but I need to keep the samples in a constant
flow of CO-CO2 gas to prevent oxidation. Rather than just venting the CO-CO2, we're going to bubble it through a solution of KMnO4 to oxidize the CO
to CO2 before venting it out the fume hood.
Anyone have any experience doing this? I'd appreciate any input-- thanks!
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unionised
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I don't think that reaction's fast enough to be any use. If it were then gas analysis wouldn't mess about with solutions of copper (I) chloride in HCl
or ammonia as a CO sorbent .
[Edited on 15-5-2006 by unionised]
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12AX7
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Just run it through a burner. CO burns quite nicely in air.
Tim
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unionised
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A fine solution but be careful when setting up- you don't want the flame to flash back into the reaction vessel.
Is there a good reason to add CO? Just using CO2 would be a lot less hazardous.
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volcanocowperson
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Hmm, I think I did a poor job explaining this-- sorry 
The sample (pieces of volcanic glass) are going to be inside of a ceramic tube. Around the middle of the ceramic tube is a furnace-- so there's no
flame anywhere, and the top and bottom of the ceramic tube are sticking out in contact with air.
But both ends of the ceramic tube are sealed-- gas flows in from the bottom (at room temperature), and out through the top (considerably warmer than
room temperature, I'd imagine). We're using CO & CO2 to maintain the oxygen fugacity (partial pressure) such that my samples don't oxidize (in
"normal" air at these temperatures, the samples would oxidize).
So we have gas flowing out of the ceramic tube, and it's a mix of CO & CO2-- rather than venting this straight out, we're planning to have it
bubble through an Erlenmeyer with KMnO4 and water in it-- in theory, this gets rid of the CO (and our Environmental Safety people are happy).
My concern is that I'm not sure of the KMnO4 to water ratio, nor am I clear on how fast this reaction takes place (and thus, what volumes of gas flow
I can use here).
Sorry for being unclear the first time around
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garage chemist
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KMnO4 does not work, at least not fast enough.
Also, the manganese (heavy metal) waste from the KMnO4 is much more detrimental to the environment than some CO.
The environmental safety people obviously didn't think their idea through.
If you want to get rid of the CO, feed it into the air intake of a bunsen burner. That would be the best and most environmentally friendly method.
You wouldn' have to worry about flashback of the flame, since you have no oxygen in the furnace.
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unionised
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Carbon monoxide is quite capable of killing you in less time than it would take to safely purge the air from the apparatus if you get the set up
wrong.
The oxygen fugacity in clean CO2 is practically nil.
If you really need the CO to act as a reductant you might want to think about generating it in situ by putting carbon in the furnace as well as the
sample. Run CO2 through it cold until there's no air left, then heat the furnace so the C reduces the CO2 to CO and the sample melts in a reducing
atmosphere. Switch off the furnace and let it cool with the CO2 still running.
That way you don't generate CO any more of the time than you need.
In any event, KMnO4 simply won't work. You could try I2O5, but really just venting the stuff out of the window is the best bet- it's simple and
doesn't have any complicated bits to fail.
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The_Davster
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Why not just run argon through instead? It keeps molten titanium unoxidized when I arc melt it.
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midnite13
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| Quote: | Originally posted by volcanocowperson
I'm going to be heating a 1-atm lab furnace to approximately 1260C to melt some pieces of volcanic glass |
Hello, I just have a really newbie question pertaining to your lab.
What exactly is a 1-atm lab furnace? If you're going to be heating it to 1530K, according to Gay-Lussacs Law (Pi/Ti = Pf/Tf), wouldn't the pressure of
the lab furnance change?
Sorry for the newbie question (=
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12AX7
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Er, yeah, the gas expands, there is less density when heated. It's not hermetically sealed.
Tim
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I am a fish
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| Quote: | Originally posted by garage chemist
...feed it into the air intake of a bunsen burner... |
That wouldn't be the best method, as the flow rate of CO would affect the stoichiometry of the flame. CO is highly inflammable, and so it would be
better to merely use the burner as a pilot light.
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The_Davster
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From: Chemistry of the Elements by Greenwood
"I2O5 is notable in being one of the few chemicals that will oxidize CO rapidly and completly at room temperature
5CO + I2O5-->I2 + 5CO2
"
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