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Author: Subject: Effectiveness of activated carbon in non water solvents?
aromaticfanatic
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[*] posted on 29-11-2020 at 23:33
Effectiveness of activated carbon in non water solvents?


I see activated charcoal being used to purify an impure chemical dissolved in water pretty often. Mostly to remove trace impurities and color.

Some questions I have:

Can you use other solvents too (for ex. non polar solvents) or is the polar water a key part in the purification process?

How efficient is this process? I know activated charcoal absorbs impurities very well but it does absorb some of your product as well. I assume some chemicals are absorbed better and I know there was a SM thread on this a while back. What are the practical limitations? I don't think it wouldn't be able to replace distillation or recrystallization as it won't be able to really pull out impurities that are present in larger amounts but it seems to be good at absorbing smaller amounts of things.

My respirator filters use activated carbon. I think it is there to filter out a lot of organic vapors.

[Edited on 30-11-2020 by aromaticfanatic]




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Boffis
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[*] posted on 30-11-2020 at 09:01


I frequently use activated charcoal in low molecular weight solvent and have found it to be very effective at removing not only colour but also colloidal haze too. I sometimes mix it with cellite filter aid too to help with the removal when filtering.
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zed
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[*] posted on 2-12-2020 at 20:25


Ummm. The colored impurities you are attempting to remove, are generally polar.

Activated Charcoal likes to grab polar molecules.

Polar solvents, actually interfere with decolorization, by occupying sites that might otherwise "grab" your impurities.

At least, that is the way I remember it. Haven't utilized that theory lately.

Might have been a tip, extracted from Vogel. Or.... from a paper by Brown.

A good idea, but opportunities for practical utilization, might not be as common as we might like.

Perhaps carbon decolorization works best in non-polar solvents... But, quite possibly our product and our impurities, aren't soluble in non-polar solvents. Hmmmm.

[Edited on 3-12-2020 by zed]
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Fyndium
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[*] posted on 6-1-2021 at 11:23


The power of activated carbon in color removal is amazing.

I had a batch of KNO3 with some strong coloring agent, and although it has little effect on it, I decided to try out the carbon method when I was dissolving it for recrystallization. I put a tablespoon of alcohol grade activated carbon granules and stirred for 15 minutes, and after filtering it was completely colorless, and the fine crystals are now pure white and clear as glass.
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aromaticfanatic
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[*] posted on 6-1-2021 at 15:12


Quote: Originally posted by zed  
Ummm. The colored impurities you are attempting to remove, are generally polar.

Activated Charcoal likes to grab polar molecules.

Polar solvents, actually interfere with decolorization, by occupying sites that might otherwise "grab" your impurities.

At least, that is the way I remember it. Haven't utilized that theory lately.

Might have been a tip, extracted from Vogel. Or.... from a paper by Brown.

A good idea, but opportunities for practical utilization, might not be as common as we might like.

Perhaps carbon decolorization works best in non-polar solvents... But, quite possibly our product and our impurities, aren't soluble in non-polar solvents. Hmmmm.

[Edited on 3-12-2020 by zed]


You know what? I should do some small experiments putting that to the test. Might as well do something that would help out amateur chemists. I have a variety of solvents and I could test them out. If I decide to do this I will post the results.


Wait... come to think of it water is polar and it is the solvent most commonly used when pulling impurities from chemicals. Perhaps zed's claims only apply to organic polar molecules. This is really peaking my interest now. I will likely perform some tests using various coloring agents/impurities and solvents like water, ethyl acetate, naphtha, methanol, toluene and any other solvents I feel like trying out.

[Edited on 6-1-2021 by aromaticfanatic]




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Benignium
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[*] posted on 19-1-2021 at 10:41


I've had success using the information zed here provided. The first thing I tested the theory on was a compound called 1-piperidinocyclohexanecarbonitrile, which is very soluble in petroleum ether. A strikingly small amount of charcoal was required. Here's a before and after:





This is also the only way of completely decolorizing methaqualone that I know of so far. The difference in efficiency between base in toluene and salt in water is vast.





[Edited on 19-1-2021 by Benignium]
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zed
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[*] posted on 20-1-2021 at 01:05


Nice!
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