LuckyWinner
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What Fritted Disk Pore Size to Select for Filtrations?
how would one determine the pore size needed for recrystallization filtrations?
there are a lot of pore sizes available.
you recrystallize something and want to drain the solvent to yield the crystals.
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Oxy
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Larger pore size means more space in the glass frit.
So the filtration will be faster, but if there are small particles in the solution, they can pass through the filter.
The size selection should be made when you see what you will be filtering. If the crystals are huge, perhaps the largest pore size can be chosen, but
if there are really small particles there, choose another that will hold solids.
Here you can find pore sizes https://adamschittenden.com/technical/frits/frit-size
The small pore diameter also means that the filter is easier to clog.
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Aloesci
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My buchner funnels have sintered disks with a porosity of 'Grade 3' which means that it has pores 15-40 microns across.
Grade 3 seems to have worked for everything I've ever needed to filter, especially after a re-crystalisation as generally my aim is to make nice
larger crystals of higher purity.
I found some info online about grades of disks, so here you go if you want to be picky about buying one for a particular reason:
(Porosity Grade:Size of pores in Microns)
0:150-250
1:90-150
2:40-90
3:15-40
4:5-15
5:up to 2
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Dr.Bob
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Most frits I have seen are marked in Cource, Medium, or Fine. Fine is great for trying to remove small particles from a solution you wish to keep
(like filtering activated charcoal. Medium is ideal for most uses, like keeping the solids as the main product, and course is best for either
filtering large chunks like sodium sulfate for drying, or for uses where you will put sand or silica gel in the frit also to prefilter something or
run a column.
My mediums also say 10-20 microns, so likely would match 3 or 4 in the above scale. Even 15-40 would be fine for most uses.
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Fyndium
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Chinese usually sell #3 frit, and that has served me well. I've got several of them and they do not clog easily, but will filter everything crystal
clear, even stuff that might be little shady when passed through paper.
I would probably stick with them. If I needed some super-fine filtering, I would get those membrane suction filters with single-use sterile pore
plates. They can be used down to 0.2um to sterilize stuff.
[Edited on 3-5-2021 by Fyndium]
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