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Author: Subject: What vacuum funnel porosity to get?
evil_lurker
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[*] posted on 6-1-2006 at 07:51
What vacuum funnel porosity to get?


May sound like a simple question... but I don't have any first hand experience so some advice would be greatly appreciated...

Course, medium, or fine porosity?
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Magpie
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[*] posted on 6-1-2006 at 09:27


I like the ceramic Buchner funnel with the fixed holed plate. You then place a filter paper of your choice over this. This way your porosity options are unlimited.

Is this what you are asking?

I don't think I would buy a fritted glass funnel unless that was the only option - too hard to maintain.




The single most important condition for a successful synthesis is good mixing - Nicodem
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evil_lurker
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[*] posted on 6-1-2006 at 10:02


No not really. Honestly I was thinking that the vacuum might suck the material through the paper if the holes were too big or that it might interfere with the rate of filtration.

I agree on staying away from the fritted glass funnels. I was however thinking of snagging a new medium porosity 24/40 350ml glass buchner funnel with vacuum take off for $40... similar models list for well over $100.

I already snagged a brand spanking new 20ml 24/40 dean-stark trap with teflon stopcock and overflow for $36 this morning... I'm on a roll.
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Magpie
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[*] posted on 6-1-2006 at 15:27


I just received a 15cm (6") Coors Buchner funnel won on eBay for $20. This would cost 4 to 5 times that amount from a science supply house. Praise be to eBay! :D

I can usually get by fine with my 7cm Buchner for the regular small scale organic systhesis, etc. But when you run into a tough to filter material where you need to spread out a lot of diatomaceous earth the larger filter will be much better. It has 4 times the area (and capacity) of the smaller one.




The single most important condition for a successful synthesis is good mixing - Nicodem
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Fleaker
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[*] posted on 6-1-2006 at 17:12


I bought a 6" from ebay for about $32 then when I opened up the package the seller had sent me a 4" too! Apparently she wanted to get rid of it b/c of the small crack on the lip and the fact it took a week for her to send it to me!

Just use a strong filter paper for Buchner/vacuum filtration and you shouldn't have too much worry about ripping it. Again, choose the right paper for the job, just calling the people at Whatman can be very beneficial.

Fritted glass funnels are nice, but expensive. Cleaning them isn't exactly fun, although they're great for getting every last bit of precipitate providing you have a lot of time to spend watching it filter.
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bio2
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[*] posted on 7-1-2006 at 00:18


My 90mm pyrex buchner w a medium frit almost always gets paper anyway and the regular perforated glass plate one gets used much more.

Those frits are a major pain in the ass to clean and learned my lesson by filtering
some Fe sludge, I think it was, when it was real new. Man, that was a mistake, took days to get the shit out and have used paper on it every since.

If you get one of these keep the gunky stuff far away from them or you will regret it.
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Ephoton
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[*] posted on 7-1-2006 at 05:54


yep ill second that I once had a lovley funnel damb al sludge
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mick
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[*] posted on 15-1-2006 at 10:43


I have used stuff called Decon 90 and other stuff called Lipsol in the UK to clean sintered glass funnels. After soaking neat for 2 or 3 days and pushing water up through the sinter they have cleaned the funnel better than conc nitric.

mick
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neutrino
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[*] posted on 15-1-2006 at 12:59


I've got a question about cleaning glass frits. Is simply soaking the frit in <b>dilute</b> nitric acid of any use? That's what my chemistry teacher said to do, but I personally don't see how this would help, especially because the acid doesn't seem to reach the interior of the frit.
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