kenofken - 20-4-2012 at 14:12
I've never had much luck with the use of carbon to decolorize a product, but I'm told I need to be using a much finer grade of charcoal. Apparently to
filter that stuff, paper isn't nearly sufficient and you need something like Celite. The most common grade of Celite I see is 545. Is that good for
this sort of work and do I just build up a slurry/cake on top of filter paper in a buchner and then pour the charcoal-boiled rxn over it under vacuum?
What "grit" or grade of carbon is best?
Magpie - 20-4-2012 at 14:39
I've had good luck with the edible activated carbon I bought at a health food store. I just filter it using regular filter paper, sometimes even
without vacuum. Yes, it's slow.
Celite should help speed things up.
smaerd - 8-12-2012 at 06:58
Will diatomaceous earth work to replace celite for most general purposes? Such as filtration, and dry-loading chromatography columns?
oldflattop - 9-12-2012 at 09:02
I use 'decolourizing carbon'! Leaving the carbon to settle before decanting into the filter is a good way to speed up the actual filtration process. I
filter it through a paper filter first so as to remove most of the material, then do a second filtration through a sintered glass funnel. You can put
a piece of filter paper on the sintered glass disc if you like, to prevent the carbon from clogging the sintered glass itself. The 'pellets' of
decolourizing carbon don't work nearly as well as the powdered material, in my experience. I've never had occasion to use celite with decolourizing
carbon, and there are no residues whatsoever in the product: even after leaving the filtrate for several days there is no visible precipitate of any
material.
[Edited on 9-12-2012 by oldflattop]
S.C. Wack - 9-12-2012 at 15:22
Filter the charcoal in something with something first.
Check the label first on the DE.
Dr.Bob - 9-12-2012 at 21:03
Yes, you want to use activated charcoal or decolorizing charcoal, there are several grades, but a fresh bottle will absorb more stuff, as older
bottles will absorb stuff (solvent vapors, pollution, etc) from the air, which lowers their capacity. Celite is diatomaceous earth, and the 545 is a
good choice. I use that to filter out Pd on carbon from hydrogenations. I would agree that letting the bulk of the carbon settle out and gently
decanting the fluid off of the top will make the filtrations go much better.
I usually make a slurry of the Celite in the solvent (I like EtOH as the solvent in hydrog's) and then pour that into the Buchner on top of the
already wet filter paper, under either no vacuum or a weak one. Then once the solvent is mostly drained off to make a cake of Celite, I then pour in
the filtrate (you can put small piece of filter paper on top of it to help from having it create a hole in the Celite). About 1/2 of the volume of
the funnel top is ideal. Try to never let the cake dry out, as that will cause slower filtration.