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Squibble
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[*] posted on 10-6-2024 at 12:26
Vacuum regulation


Hi. My first post here after many years lurking.

I have a rotary vane pump I'm wanting to use for distillations such as high boiling oils or higher boiling solvent removal. What is the best way to regulate the vacuum? Is it possible to get any kind of reasonable regulation by simply having a bleed valve allowing it to draw in some air? Do I absolutely need a regulator of some kind? Are refrigeration re-gassing regulators any use? If there are any other options, could you recommend one?

All this with the understanding that my budget is seriously limited!!

The only time I've run a vacuum distillation in the past was using the inlet of an air compressor, but it didn't reach a strong vacuum and fluctuated a lot.

Many thanks!
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Sulaiman
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[*] posted on 10-6-2024 at 19:22


If your reactants and products are not too sensitive
An air leak in the form of a bubbler in the boiling pot allows some range of pressure adjustability,
and prevents bumping.




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[*] posted on 11-6-2024 at 06:18


OK. Now you mention it, I've heard of that before. I was thinking of a bleed in the tube to the pump, but this is better. Thanks!

When you say sensitive, you mean to the atmosphere?
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Sulaiman
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[*] posted on 11-6-2024 at 06:46


Yes, sensitive to components of the atmosphere.
Oxygen, water vapour, carbon dioxide etc.




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walruslover69
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[*] posted on 11-6-2024 at 06:56


My old lab used to have a comically oversized rotary vane pump connected to our rotary evaporator. When we tried evaporating anything with a boiling point below 70C it would flash boil and bump out of control.

The solution we came up with was to connect the vacuum pump to the rotary evaporator with flexible vinyl tubing. We then placed a C clamp on the tubing to restrict it and reduce the vacuum flow rate. sometimes up to 3 clamps were needed when evaporating solvents like DCM, but it worked surprisingly well.
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Mateo_swe
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[*] posted on 11-6-2024 at 12:18


There are vacuum regulators on some rotovaps.
Maybe you can get such a vacuum regulator, a used one.
I think they usually are a separate box with a display and sone buttons.
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Rainwater
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[*] posted on 11-6-2024 at 18:18


There are two working options in this post
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

Easiest is the $70 controller.
Cheapest is a glove, jam jar and some tubing.




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Sulaiman
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[*] posted on 11-6-2024 at 19:32


Quote: Originally posted by walruslover6  
We then placed a C clamp on the tubing to restrict it and reduce the vacuum flow rate. sometimes up to 3 clamps were needed when evaporating solvents like DCM, but it worked surprisingly well.
just curious:
Why would you want to use vacuum with DCM, bp<40oC,
and how did you condense it?

EDIT: Thanks for the explanation you gave below. Unexpected, but logical.

........................
I like the idea of the jar, funnel and membrane regulator,
but I'd connect the regulator independently to the jar to reduce pulsing of the supplied pressure/vacuum.

[Edited on 12-6-2024 by Sulaiman]




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[*] posted on 12-6-2024 at 03:56


Thanks for the ideas everyone!
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walruslover69
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[*] posted on 12-6-2024 at 05:37


@Sulaiman I wish I had an old picture to show, the whole system was insane. For some background This was a materials lab with a lot of money to throw around but no experienced benchtop chemists.

The roto water bath was really over sized with an undersized heating element, so it was drastically quicker to just start the vacuum from room temp and distill over that way. For the collection, we had a large cryogenic chiller that got down to -80C.

it was a situation where we just had tons of oversized equipment cobbled together.

Writing this now makes me look back on how surreal of a setup it was....
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