chucknorris
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Vacuum distillation flask limits
My friend warned that using larger than 500ml flasks in vacuum distillation is very hazardous and may cause instant implosion of the system. Is this
true or is he just over careful? The glassware I have in use is high quality german brand, bought new and therefore should contain no micro-fractures
as I havent rough handled them.
So, the question is, is that safe to drive 5-15mbar vacuum pressures using 2000, 4000 and 8000ml round bottom flasks with water ejector pump?
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kristofvagyok
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Quote: Originally posted by chucknorris  | | My friend warned that using larger than 500ml flasks in vacuum distillation is very hazardous and may cause instant implosion of the system.
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I have distilled some N-methyl-aniline from a 2000ml flask 1 month ago and I'm still alive and the vacuum was at circa 70torr as I remember.
The only important thing is to use some shielding (e.g. a plexiglass), because if the large glass breaks under vacuum it could hurt.
[Edited on 18-7-2012 by kristofvagyok]
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zoombafu
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Ive pulled a vacuum on a 2000ml flask no problem.
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simba
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http://osum.ucr.ac.cr/sites/default/files/documentos/CUIDADO...
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BromicAcid
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Routinely distill out of 72L flasks under full vac (ca. 1-3 mm Hg in the pot). My work is a stickler for safety and they have no problem with vacuum
on any sized round bottom flask apparatus. They recommend against pulling full vacuum on a flat bottomed flask, Erlenmeyer side arm, or 20-L glass
carboy however it is done from time to time. I have never seen an implosion. The only time I heard of anything going wrong was full vacuum on a
flask where the material fell below one of the zones of the heating mantle. The heating mantle put it's full heat on the glass itself with nothing on
the inside to wick it away and the glassware very nicely began to implode slowly until it was far enough away from the mantle to where it
re-solidified.
Keep in mind this is all with name-brand Ace glassware. Your mileage may vary with off-brands.
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chucknorris
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Thanks for the answers!
Im having trouble driving high vacuum with aspirator. I dont know the exact pressure of the water network at here, but the temp is around 15 degs.
Water merely boils in 20C room temp. The problem is, that when I try to distill some stuff with higher temperature, the temp wont just rise, no matter
what I do when the system is at vacuum, even though I have 2kW heating plate!
Could I use hot air blower to aid the heating?
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zoombafu
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Are you using oil baths with RBFs, or flat bottomed glassware?
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chucknorris
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I had sand bath before. I tried oil bath, but it caught fire and almost destroyed my glassware. I tried brake fluid, but it started to smoke and smell
like a hell. Now I actually tried to cut aluminium can bottom off and fit it just over and around the plate and the rbflask comes in the middle, with
5-10mm space between the plate surface and the flask, and now the system heats up very nicely. So, I could put it this way, the problem is solved.
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zoombafu
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how did your oil bath catch fire?
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chemrox
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How high a temperature are you trying to achieve? I have dibutyl pthalate in my oil bath and it gets up to over 200 without smoking. Break fluid
should be DOT 5, silicone based. Expensive to initially fill but a lot easier to manage than sand.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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chucknorris
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The oil bath autoignited. My 2kw cooking plate seems to get at LEAST 400 degrees c temps, my thermometer reaches only 360C in graduations and it
skyrockets high past that when put on top of the hot plate.
I tested DOT 5 brake fluid. Could not use, it started to smoke like hell. I will use the aluminium-air containment system by now. No mess with baths
and shit.
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starman
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Well you are" messing with a bath". Old fashioned AIR bath.Metal beads such as Lab armor or even BBs are reported as being very good.
Chemistry- The journey from the end of physics to the beginning of life.(starman)
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