Loptr - 23-7-2018 at 06:26
I have recently gotten my glassware back out and started experimenting again. Last night I followed a procedure in the attached paper to prepare
nickel peroxide, a mixture of oxides that should contain Ni2O(OH).
This stuff is incredibly difficult to filter and it just clogs up the sintered funnel forcing me to leave the vacuum pump running for a periods adding
up to a few hours. I am using a medium frit, which works very slowly. I am afraid to leave my pump running that long. I think I can finish the
filtration today after work, but this started yesterday a little after noon. This would have been impossible without a vacuum pump!
Any suggestions or tips to more efficiently filter solids that form a sticky mass in the filter?
EDIT: Added attachment
[Edited on 23-7-2018 by Loptr]
Attachment: jo01052a026[1].pdf (567kB)
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CobaltChloride - 23-7-2018 at 06:31
I've had success using a 100ml syringe with a piece of cotton wool stuffed in it's lower part to filter Zn(OH)2 produced by the reduction of sodium
metabisulfite by zinc powder. In order to do this I had to press hard on the plunger so that all the liquid drained from the Zn(OH)2. In order to make
the plunger move easier in this situation I sprayed some silicone grease on it.
You might also be able to remove the precipitate by letting the solution stand for a few days so that the nickel oxide settles. This method worked for
removing CaCO3 precipitate made by the reaction of Ca(ClO)2 and Na2CO3 (which couldn't be removed by neither gravity filtration, nor vacuum filtration
efficiently). In the case of this reaction I kept the solution in the freezer away from light so that the sodium hypochlorite didn't degrade as the
precipitate was settling.
[Edited on 23-7-2018 by CobaltChloride]
Boffis - 23-7-2018 at 10:08
If the conditions are too aggressive to permit the use of fine paper filter then I tend to go for glass fiber filter papers in a good old-fashioned
Buchner funnel. These glass papers are very expensive but they occasionally crop up on Ebay at a reasonable price 5.5 and 7cm seem to be the most
common sizes.
Loptr - 23-7-2018 at 11:46
Thanks, guys.
@CobaltChloride, I could take a look into that at some point. I was hoping to prepare a few hundred grams of it for a couple reactions that I have in
mind.
@Boffis, yes that sounds like a good idea. I was thinking that I would pull holes through the filter paper if I tried, and have to start over. Now
that I think of it, I have some nylon filter paper supports somewhere around here. They are the same size as the filter papers, but go under them
against the Buchner funnel itself. They might help, actually.
Boffis - 24-7-2018 at 07:31
With very fine precipitates it is often better to use very gentle suction at first to reduce the tendency to blind the filters. I find that the fibre
glass paper are perfectly happy provided the holes in the Buchner funnel are less than 1.5mm wide.
chemplayer... - 13-5-2019 at 22:09
We've just been playing with this - it's very like fine 'chemical' manganese dioxide from the potassium permanganate / manganese (II) sulfate
reaction. Paper filter + buchner funnel is possible for small amounts, and then once its a paste on the filter we found that an acetone mix/wash
worked quite well to help dry it a bit better and get the water out of the paste. Really hard to dry properly though.
For larger quantities this would be a huge pain in the ass though. Some potentially interesting oxidation properties for organic substrates though.
Would be interested to see if you had any follow-up success?
S.C. Wack - 14-5-2019 at 19:27
There are few things that glass wool packed into a kitchen funnel hasn't filtered well for me. Paper and bleach and hydroxide and time and oxidizing
precipitate is not a good combination.
For acids this has been done in one pot from a catalytic amt. of Ni salt and bleach. For aldehydes a mixture with alumina has been used; one could use
it as a filter aid, but this might complicate Ni regeneration too much.
[Edited on 15-5-2019 by S.C. Wack]