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Author: Subject: Vacuum distillation flask limits
chucknorris
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[*] posted on 17-7-2012 at 19:48
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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[*] posted on 18-7-2012 at 05:43


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.


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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[*] posted on 18-7-2012 at 11:45


Ive pulled a vacuum on a 2000ml flask no problem.



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simba
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[*] posted on 18-7-2012 at 16:15


http://osum.ucr.ac.cr/sites/default/files/documentos/CUIDADO...
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BromicAcid
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[*] posted on 18-7-2012 at 16:21


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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[*] posted on 19-7-2012 at 15:40


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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[*] posted on 19-7-2012 at 15:46


Are you using oil baths with RBFs, or flat bottomed glassware?



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chucknorris
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[*] posted on 20-7-2012 at 01:16


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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[*] posted on 20-7-2012 at 04:57


how did your oil bath catch fire?



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chemrox
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[*] posted on 20-7-2012 at 09:47


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.



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chucknorris
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[*] posted on 20-7-2012 at 15:37


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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[*] posted on 20-7-2012 at 17:31


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.



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