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Author: Subject: Vacuum pump problem
Readytorock
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[*] posted on 14-3-2012 at 15:40
Vacuum pump problem


I have a rotary vacuum pump. I set up for a standard distillation of dcm and triethylamine. I put the distallation flask on a oil bath and set the hot plate to 100c.

Now my problem is the vacuum pump is freezing the flask :s.. I have no idea why. Im trying to boil the solvent + triethylamine off but the vacuum pump keeps freezing the flask.. Any one know why?
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Readytorock
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[*] posted on 15-3-2012 at 05:41


bump!.. any one?
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chemx01
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[*] posted on 15-3-2012 at 12:21


I don't know if I understand you corectly but as I understand your boiling DCM and TEA under vacuum on oil bath.
Well the boiling point of DCM at this pressure could be as low as -30°C so it's probably condensing moisture on the flask and freezing it therefore the "frozen flask".

If I didn't understand you corectly please elaborate and one advice don't rush it people usually don't take that very kindly.
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garage chemist
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[*] posted on 15-3-2012 at 13:34


You seem to be pulling the solvent vapors straight into your vacuum pump. This will contaminate the oil and quickly destroy the pump. Immediately disassemble the pump completely, clean it and fill it with fresh oil.

DCM and triethylamine are best removed by distillation at atmospheric pressure. If you insist on using vacuum, you will either have to put a cold trap cooled with dry ice or liquid nitrogen between your distillation setup and the pump and have the solvent condense there, or buy a chemically resistant diaphragm vacuum pump that lets you condense the solvent vapors at the pump outlet at atmospheric pressure and with a water-cooled condenser.
I have such a chemically resistant pump, the MZ2C from Vacuubrand, and I can only recommend that you don't use your rotary vacuum pump in the chemical laboratory.

[Edited on 15-3-2012 by garage chemist]




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Magpie
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[*] posted on 15-3-2012 at 13:58


What's the point in a vacuum distillation and a 100C oil bath to remove a low boiling solvent like DCM? It seems like gross overkill.



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zoombafu
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[*] posted on 15-3-2012 at 14:39


You don't need to be doing a vacuum distillation (unless I'm missing something) typically you only use vacuum distillation for high boiling liquids (such as essential oils)



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Readytorock
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[*] posted on 15-3-2012 at 18:23


Quote: Originally posted by chemx01  
I don't know if I understand you corectly but as I understand your boiling DCM and TEA under vacuum on oil bath.
Well the boiling point of DCM at this pressure could be as low as -30°C so it's probably condensing moisture on the flask and freezing it therefore the "frozen flask".

If I didn't understand you corectly please elaborate and one advice don't rush it people usually don't take that very kindly.



Thanks :)
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Readytorock
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[*] posted on 15-3-2012 at 18:27


Quote: Originally posted by garage chemist  
You seem to be pulling the solvent vapors straight into your vacuum pump. This will contaminate the oil and quickly destroy the pump. Immediately disassemble the pump completely, clean it and fill it with fresh oil.

DCM and triethylamine are best removed by distillation at atmospheric pressure. If you insist on using vacuum, you will either have to put a cold trap cooled with dry ice or liquid nitrogen between your distillation setup and the pump and have the solvent condense there, or buy a chemically resistant diaphragm vacuum pump that lets you condense the solvent vapors at the pump outlet at atmospheric pressure and with a water-cooled condenser.
I have such a chemically resistant pump, the MZ2C from Vacuubrand, and I can only recommend that you don't use your rotary vacuum pump in the chemical laboratory.

[Edited on 15-3-2012 by garage chemist]


Thanks :)
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