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Does anyone know of Pros/Cons of vacuum freezing to precipitate

C

ChickMicklin

Rising Star
Would this have any significant effects on yield and or crystal growth? also, assuming the vacuum wasn't pulled until the chamber was already freezing, would there be any potential danger of solvent gases entering the vacuum pump and causing disaster?
 
When applying vacuum to solvent, it's best practice to use a cryogenic trap to prevent solvent vapours from entering the pump, particularly with pumps that contain oil, as the solvent will cause vacuum oil to lose its performance and may even be dangerous.

Why would you pull a vacuum on a freeze precipitation vessel anyway? And how cold is your freezer? Other than that, it depends on your aims with crystal growth. Sure, pulling off a bit of solvent might increase the yield slightly, maybe at a small expense of purity. Reduced oxygen concentration may limit polymerisation, but you may as well use argon or nitrogen for that.


You'll have to say very specifically how you intend to set this up, otherwise it's sounding like some kind of Schnappsidee.
 
SWIM has a freeze drier and was trying to think if there was any way that the fancy expensive machine would be useful in an extraction. probably still use it for the freeze precipitation because it gets much colder than the freezer even without a vacuum pulled. The only other application I thought it may have use in an extraction would be to soak the root bark powder in water and then freeze dry it to try and burst the cell walls, may be more effective than some of the newer TEKs with an early freezing cycle. Just spit balling ideas, not everything is a nail but some people have some cool hammers laying around.
 
It's worth noting that slower cooling makes bigger crystals when freeze precipitating. Tests have shown that the residual amount of DMT in naphtha at typical deep freeze temperatures of around -22°C is fairly minimal (~109mg/100mL), although results which quantify any additional yield (or the corresponding diminution in solubility) at lower temperatures would be very welcome.

Figures here:
DMT Chemical and Physical Properties
 
I can confidently say you will destroy your vac pump if used on solvent laden product.

I opened a JB industries DV85 that the previous owner had used on an ammonia refrigerant system and it had seized the vanes and rotor solid to the housing.

You might have some luck with a diaphragm pump like the KNF Neuberger N022AN18, but the vac in inches of Hg will be less and the volume of air moved is much less so it will take longer.
The diaphragm pump has an aluminium head with SS valves, so ingesting any caustic soda particles will corrode the valve seat area and also render the pump useless.
 
61pete said:
I can confidently say you will destroy your vac pump if used on solvent laden product.

I opened a JB industries DV85 that the previous owner had used on an ammonia refrigerant system and it had seized the vanes and rotor solid to the housing.

You might have some luck with a diaphragm pump like the KNF Neuberger N022AN18, but the vac in inches of Hg will be less and the volume of air moved is much less so it will take longer.
The diaphragm pump has an aluminium head with SS valves, so ingesting any caustic soda particles will corrode the valve seat area and also render the pump useless.
Click to expand...
Hence the comment:
Transform said:
When applying vacuum to solvent, it's best practice to use a cryogenic trap to prevent solvent vapours from entering the pump,
Click to expand...
It's imperative to mention, utmost care should also be taken to avoid inadvertent production of liquid oxygen if using liquid nitrogen to cool the trap. Co-condensing flammable solvent vapours with liquid oxygen presents an extreme explosion risk.
 
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