173c At 8-10 Microns Of Vacuum Short Path Distillation

[EugeneOregon]

This is a work in progress but my new short path set up is working well enough to present here.

Chempub lists the boiling point of thc delta 9 as being 200C at 20 microns (VERY deep vacuum). On this run the sytem was clocking in at around 8-10 microns and the thc-9 was coming across well enough to load up and plug the short path head! lolz.

I checked online. Thin film evaporators publish on their site that their system operates between 100-300 microns. Others have posted distillation temps as high as 230C. This rig demonstrates and corraborates Pubchem insofar as 173C is more than adequate to pull a pure fraction if care is taken to pull a very deep vacuum. 173C is significantly below Pubchem's data but I have no way of knowing (yet) if this is azeotropic behavior, or if the deeper vacuum of 10 microns vs. the published 20 micron value is the reason. In any case keeping the temperatures as low as possible is my goal. Pubchem links reveal that thc delta 9 degrades with the application of heat. It lists no concerns for oxidation.

 

[Graywolf]

Greetings brother Eugene! I've seen you at SPR and about, but we've never directly engaged.

Good experiment! Some thoughts for the inquiring and scheming minds contemplating this to toss about.

In a previous lifetime, we got our equipment to sub-micron levels using a Rootes blower, mounted on top of a Stokes 412 vacuum pump, sitting on top of an oil diffusion pump, for the purposes of heat treating exotic alloys for defense and aerospace components. They were big parts, so we were using huge equipment relative to what we are doing here, but at some level it all relates to leak rate, versus pumping rate and ultimate pressure capability.

Nature hates a vacuum so deep vacuum values are elusive and hard to maintain, but things like rotary vacuum unions and tapered glass joints both leak some even when new, so most systems devoid of huge pumps operate at higher absolute pressure levels.

10 microns is actually pretty good and about what our vacuum interlocked inert atmosphere welding chambers pulled down to when properly maintained, but always a challenge to maintain, though in general, the lower the vacuum the greater the goodness.

Having provided the introduction, Brother Eugene, would you share how you're configured your system and what you are using for a pump to achieve those numbers?

 

[EugeneOregon]

Greetings brother Eugene! I've seen you at SPR and about, but we've never directly engaged.

Good experiment! Some thoughts for the inquiring and scheming minds contemplating this to toss about.

In a previous lifetime, we got our equipment to sub-micron levels using a Rootes blower, mounted on top of a Stokes 412 vacuum pump, sitting on top of an oil diffusion pump, for the purposes of heat treating exotic alloys for defense and aerospace components. They were big parts, so we were using huge equipment relative to what we are doing here, but at some level it all relates to leak rate, versus pumping rate and ultimate pressure capability.

Nature hates a vacuum so deep vacuum values are elusive and hard to maintain, but things like rotary vacuum unions and tapered glass joints both leak some even when new, so most systems devoid of huge pumps operate at higher absolute pressure levels.

10 microns is actually pretty good and about what our vacuum interlocked inert atmosphere welding chambers pulled down to when properly maintained, but always a challenge to maintain, though in general, the lower the vacuum the greater the goodness.

Having provided the introduction, Brother Eugene, would you share how you're configured your system and what you are using for a pump to achieve those numbers?

Greetings!

It is an Edwards model 28 vacuum pump I got used off of craigslist. It had been used with a vac oven for bho purging and the oil was contaminated badly. Two oil changes of grade 20 synthetic vacuum pump oil and an afternoon run with the gas ballast wide open and the vacuum pumps down now as advertised. I discovered that polymer hose of any type simply will not handle molecular distillation levels well so short length is critical.
It is a work in progress.

 

[Graywolf]

Edwards rates the EM28 at 22 cfm,making it a relatively large pump, and rate its ultimate pressure at 7.5 X 10-4 Torr, which is about .75 microns, so sounds like it is in good shape. At that pumping capacity, it would tolerate a lot of leakage running in the low micron range.