eindreizig
Rising Star
Does anyone have any good alternatives to using a Buchner Funnel for filtration?
-
Members of the previous forum can retrieve their temporary password here, (login and check your PM).
Buchner Funnel
- Thread starter eindreizig
- Start date
69ron
Rising Star
Sometimes you can use a normal funnel with a cotton ball in it placed on a filter flask with vacuum applied to it. That works really well for filtering certain things that would normally clog filter paper in a Buchner funnel.
Sometimes, especially when filtering extremely volatile solvents like DCM, the filter paper in the Bucnher funnel will NOT stay put.
What I’d like to know is: are there any funnels like a Buchner funnel that can clamp down the damn filter paper to keep it firmly in place instead of relying on a wet vacuum seal?
Sometimes, especially when filtering extremely volatile solvents like DCM, the filter paper in the Bucnher funnel will NOT stay put.
What I’d like to know is: are there any funnels like a Buchner funnel that can clamp down the damn filter paper to keep it firmly in place instead of relying on a wet vacuum seal?
Strange, I've never had that problem?.?.?
My filter papers are always tight fitting in the Buchner funnel, they have to be firmly pushed down into the top, so the paper is being held in by friction too. I also give it a couple of vacuum pumps as soon as there is enough liquid in the top to cover all of the holes, but not nearly even 1/8 full yet. This pulls the paper against the bottom of the funnel pretty tight. I then continue pumping the vacuum pump as I'm pouring the liquid into the top of the Buchner funnel. Not too much though, or you'll bust the paper with too high of vacuum pressure, too soon.
I've never had em move at all in fact.
Sometimes, depending on what it is that I'm filtering, I use a small coffee filter instead of a true filter paper. They are not the right size for the funnels at all, so I use a jar or something with a broad bottom to push the coffee filter down flat into the funnel and fold any excess paper over the top edge of the funnel. This gives the [coffee] filter paper "sides", so even if it were to float up, whatever is being filtered out will remain in the filter paper, not spilling down into the flask.
To be fair, I've never had to try & filter anything out of DCM.
Hope there's something helpful in there somewhere.
WS
69ron
Rising Star
SWIM has the same experience. They work well, except when using DCM specifically.
It's only a problem with DCM. All the other solvents manage to keep the paper in place. DCM has very poor surface tension. I think that's why the paper doesn’t stay well with it. Also, as soon as the DCM passes through, the paper is bone dry because it evaporates SO FAST, so there's no liquid to hold the paper there so it always loses it's seal at that point. It's a real hassle.
It's only a problem with DCM. All the other solvents manage to keep the paper in place. DCM has very poor surface tension. I think that's why the paper doesn’t stay well with it. Also, as soon as the DCM passes through, the paper is bone dry because it evaporates SO FAST, so there's no liquid to hold the paper there so it always loses it's seal at that point. It's a real hassle.
that is a hassle!!
have you tried some kind of tiny but very heavy weight/s, like a small piece of lead or something? I don't know how that would react with your DCM but I think you can get these kind of things, covered in a type of rubber or plastic from lab supply companies. There is something like that (I think called a stir rod) that is placed in the bottom of a flask so when you swirl the liquid in the flask, the little plastic covered, metal rod helps to mix the contents. I think you can get them in different sizes & weights. One or two of them might be enough to hold your paper down, but not cover more than a couple of holes in the Buchner.
Or maybe find yourself an "o-ring" (probably would need to be metal so it fits tight) that fits the inner diameter of the Buchner. After placing the paper down in the funnel, push the O-ring down on top of it, holding down the outer sides of the paper.
just a few ideas.
WS
SWIM thought of making an improvised poor-man´s vacuum filtration system, due to having lack of funds lately..
First, make a water bottle with a little tube/hose attached to it´s side (or just a hole on the side). Then attach a funnel to the top, with the filter (or a cotton, as mentioned above). Then just use a vacuum cleaner to make the vacuum on the hose.. BUT.. as 69ron pointed out to me sometime, vacuum cleaner is way too strong, so the trick would be to keep the vacuum cleaner a bit farther away from the hose (or the hole on the bottle), so that it has a vacuum but not too much.
SWIM might try this in an extraction this weekend
First, make a water bottle with a little tube/hose attached to it´s side (or just a hole on the side). Then attach a funnel to the top, with the filter (or a cotton, as mentioned above). Then just use a vacuum cleaner to make the vacuum on the hose.. BUT.. as 69ron pointed out to me sometime, vacuum cleaner is way too strong, so the trick would be to keep the vacuum cleaner a bit farther away from the hose (or the hole on the bottle), so that it has a vacuum but not too much.
SWIM might try this in an extraction this weekend
69ron
Rising Star
I found one made by Whatman called the 3-Piece Filter Funnel:
They cost about $200 for a 9 cm one which takes normal filter paper. This should work but it’s SO PRICEY!
The 9 cm model is 1950-009. It has a 200 ml reservoir.
It comes with an acrylic support plate for the filter paper. You'll spend another $100 for a PTFE support plate which is needed if using DCM or chloroform (which both dissolve acrylic)
The good thing is that this unit uses normal cheap filter paper.
Doesn't someone else make the same thing cheaper?
They cost about $200 for a 9 cm one which takes normal filter paper. This should work but it’s SO PRICEY!
The 9 cm model is 1950-009. It has a 200 ml reservoir.
It comes with an acrylic support plate for the filter paper. You'll spend another $100 for a PTFE support plate which is needed if using DCM or chloroform (which both dissolve acrylic)
The good thing is that this unit uses normal cheap filter paper.
Doesn't someone else make the same thing cheaper?
69ron
Rising Star
benzyme said:
But you can't use a 1PS filter paper in those. A 1PS filter allows only non-polar solvents to pass through. That setup above is just for normal filtering and will work for DCM, but will allow all solvents the pass through. The 1PS filter would allow DCM to pass, but not water.
ahhh
ok.
like SWIY said, learn something new everyday
ok.
like SWIY said, learn something new everyday
endlessness said:
it worked very well! SWIM used this way for drying crystals after freeze precipitation, and it was IMMEDIATE! In 1 minute the crystals were completely dry! The vacuum from the vacuum cleaner did not break the filter (but SWIM did not use this for filter-clogging things such as mimosa powder or syrian rue xtraction, SWIM only used for drying DMT crystals from freeze precipitation.
SWIM took the freeze precipitation container out of the freezer, scraped the crystals from the bottom/sides using a razor blade, so it all got suspended but not dissolved in the still cold naphtha.. Then SWIM poured the naphtha in the improvised vacuum filter, turned on the vacuum pump and the crystals dried immediately and stayed nicely on top of the filter!