Nitrox2
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Vacuum distillation
In the depiction, how are they monitoring the temperature?
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Radiums Lab
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See that probe dipped in water? It measures the temp of the bath.
Water is dangerous if you don't know how to handle it, elemental fluorine (F₂) on the other hand is pretty tame if you know what you are doing.
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Nitrox2
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Yes, but that is not the temperature of the bath, not the vapor.
??
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Texium
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Sometimes you don’t care about the temperature of the vapor. In that case, they’re distilling DMSO, a common solvent, so they probably only care
about recovering whatever was dissolved in it. As long as the vacuum is strong enough for the DMSO to distill at a reasonable temperature, they
couldn’t care less what the exact boiling point is.
If I was in their situation, I’d consult a pressure/temperature boiling point chart for DMSO, find the pressure that my vacuum pump can pull, and
set the oil bath temperature 10-20 degrees above the corresponding boiling point to ensure a speedy distillation.
You only really need to measure the vapor temperature when you’re distilling something that doesn’t have a well-documented pressure/temperature
curve.
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RU_KLO
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I do not have the corresponding glassware, so when I need to check the temperature inside the flask I check the temperature of the bath and then
adjust.
From experience (the temperature in the bath (liquid) vs in the solution is aprox 1º-2º C and changes with time - gets smaller as you increment the
bath time) You could check it by making a simple experiment with water, 2 beakers + 2 thermometers.
1) "calibrate" the thermometers (by inserting both of them, side by side, bulb very closed - in water. start at 0ºC (glass of water with a lot of
ice) and start heating till it boils.
take notes every X min (5?)
2) note the difference. so you can adjust later. (for example I have an alcohol therm. that at 0ºC marks 8ºC and at 100ºC marks 96ºC. So any read
I know to add 4ºC (or 2 lines). I put a label in the thermometer indicating this. (I also done this with every temp meassuring device - I got only 2
therm. but 10 cheap bimetal probes for cheap tester (that can meassure temp.)
3) do the same experiment but with one thermometer in the bath and the other in the solution. (try different flasks) also dipping or lifting the
beaker inside the bath.
I think its a good practice to know your hardware. How much it takes to boil water, the induction time, how much it takes to get to XºC, etc
Go SAFE, because stupidity and bad Luck exist.
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BromicAcid
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As others have said they're not measuring the head temperature. Couple of possible reasons:
1) They don't care - they're just trying to rip off the DMSO and they know that at the vacuum applied and the temperature of the bath their product
is going to stay behind.
2) They don't care (again) - they're going to flash everything over to get away from non-volatile impurities and will more carefully fractionate it
later.
3) They don't care (yet again) - they actually don't know where their product is going to come out. They're going to flash over their DMSO and then
check the DMSO fraction and any pot residue to see where the product ended up and design a purification from there.
4) They don't know better - they have no clue what they are doing, they should probably have a head temperature but don't realize that it's
important.
5) They don't have a thermowell or vacuum tight thermometer adapter - they're risking air exposure and bad vacuum by rigging a thermometer in place
and they're missing the right pieces so they intend to wing it.
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Sulaiman
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For the setup in the photo, the bp is reduced to 70oC,
but I see no significant vapour cooling provision,
I would expect a lot of dmso vapour to enter the vacuum system
I guess there should at least be an ice bath around the receiving flask.
or maybe a very slow distillation in a cold lab ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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