stoichiometric_steve
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hybrid pump/vane pump questions...
the book "Organikum" suggests that when combining a conventional rotary vane oil pump with a diaphragm pump, one can omit the cold trap, as the dia.
pump constantly evacuates the oil pump.
i can hardly believe this.
does anybody have experience with this kind of setup?
i'm trying to figure out how to run a rotary vane pump without the hassle of liquid nitrogen, which i have no means of storage for. i was shooting for
CO2(s)/Acetone for the trap, while i mostly distill organics in the range of bp. 150-300deg@(760mmHg).
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bio2
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For that temperature range even an ice trap is sufficient
as long as the vacuum is adjusted so that the distillation
is conducted say 30-50 degrees over the cooling water
temp.
Just change the oil when completed to remove any
solvent traces. Solvents should be removed with an aspirator
unless of course you have an efficient low temperature
cold trap.
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stoichiometric_steve
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thanks bio2!
do you mean to remove the solvents with an aspirator from the oil? or removing solvents in general with an aspirator (rotavap e.g.)? i will certainly
use my diaphragm pumps for rotavap purposes.
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bio2
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No, I meant the reaction pot but that's actually quite
a good idea. Clean, solvent contaminated vacuum oil could be saved up and then periodically remove the solvent for reuse.
If using a resistant diaphragm pump then keeping of the condensing temperature high enough, as I described ,will
prevent half the solvent going through the pump when a low temperature trap is not available.
There a diaphragm pumps actually designed to recirculate the vapor.
A ice/salt bath trap is sufficient as long as the distilling vapor
is kept say at least 30 degrees. Packing in the trap helps condensing as well.
[Edited on by bio2]
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bio2
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Also I would mention that when a 2stage rotary vacuum pump gets laden with solvent that the oil level rises and then the oil
& condensed solvent fluid will spit out of the exhaust port.
If your diaphragm pump is in series downstream, and can't
handle this then you need some type of vapor/liquid separator.
I suppose that when the distillation is over, if the valve is closed,
upstream of the rotary, that the diaphragm will eventually
distill all of the solvent out as your article indicates.
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chemrox
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The problem with this is that contaminated oil doesn't achieve the same vacuum so as the oil gets solvent laden the pressure changes. This means your
distillation temp changes unless you have a manostat in line. If you have a manostat why not a cold trap as well? My manostat works on liquid vapor
pressure so the cold trap is necessary or the manostat will also get contaminated and not work properly. They're pretty simple to make ... dry ice
and acetone makes a nice cold liquid .. you can get a dry ice maker or by it at Baskin-Robbins
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