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Author: Subject: Activated carbon extraction?
Fyndium
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[*] posted on 28-7-2020 at 00:08
Activated carbon extraction?


https://www.youtube.com/watch?v=son8yyD-T_E

Could activated carbon be used to absorb dissolved compound from a solution and vacuum distill it off? Considering the solvent is of low molecular weight and the desired compound a high mw?

https://www.jstage.jst.go.jp/article/tanso/2015/269/2015_140...

[Edited on 28-7-2020 by Fyndium]
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Tsjerk
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[*] posted on 28-7-2020 at 00:14


I don't think so. As far as I know there is no way to reactivate activated carbon besides heating beyond the point where the absorbed compounds decompose.
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Fyndium
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[*] posted on 28-7-2020 at 01:54


I doubt that. I have used activated carbon to clean alcohol and when boiled and finally dried in oven, it releases a lot of smelly vapors. The odor evolution pretty much ceases above 200C after some time, indicating all the compounds it has adsorbed are of lower bp than that. I expect that everything that boils off rather than decomposes, will boil at some point, in a vacuum much more so, and what eventually decomposes, will gradually be reduced until only carbon and non-volatile elements are left.

Silica and carbon are aDsorbents, not absorbents, as far as I know the difference, and the molecules are practically glued or grabbed to their surface instead of dissolving into the crystal lattice (like carbon does to steel, or hydrogen to palladium, etc) and will be released when the energy to vapor pressure ratio grows large enough.

The key concept here was to adsorb a compound dissolved in a large amount of solvent to be filtered in a concentrated form which is a lot easier to distill off rather than evaporating the entire solvent first because carbon is passive, low energy element which does not boil or melt and hence only the residual solvent and the target compound need to be evaporated.

[Edited on 28-7-2020 by Fyndium]
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[*] posted on 28-7-2020 at 02:46


I guess the carbon you cleaned the alcohol with was moist with alcohol when you oven dried it? In that case there was a lot more alcohol than just the alcohol it adsorded.

It would be interesting to see if it still smells when you first air dry the carbon and then put in an oven.
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Fyndium
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[*] posted on 28-7-2020 at 05:04


The carbon was first washed and then boiled in water for half an hour prior to oven and that should get rid of most of the lower boiling compounds. The smell was not ethanolic at all, but most likely fusel oils and other junk, the smell is difficult to describe, but it's remotely sweetish or aromatic to say.

This was done to alcohol that was first stripped to 60% abv and then fractionated at 78.2C into foreshots, heads, hearts and tails and measured 95% with abv meter at ntp.
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DavidJR
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[*] posted on 31-7-2020 at 09:31


Thermal desorption cartridges containing activated carbon are routinely used for analysis of VOCs in atmospeheric air.
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macckone
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[*] posted on 31-7-2020 at 09:42


Short answer is yes, activated carbon can and is used for separating compounds.

Better answer is use column chromatography separation,
silica is often used as the stationary phase and is easier to work with.
Numerous other stationary phases are possible with activated carbon being one of the hardest as it has to be heated to release the compounds effectively. The heat required varies by compound which provides a good way to separate the adsorbed compounds.
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