I’ve been running distillation for quite a while, but today I’ve run into a strange issue.
I’m distilling CBG extracted with subzero butane, 2 kilos in a 5l Glas-Col using hot condenser. Mantle double checked to be as high as 210°C with vacuum at 183 micron. Head temp was 150°C after crossing 185°C in mantle and was running smooth, but then stalled at 200°C with head temp dropping to 50°C.
I know vacuum is a little high, but has been consistent and is about where it normally is during a run on this setup, which has been smooth since beginning of the year. Double checked for any clogging, as my vacuum gauge is post cold trap, but found none.
How are the RPMs on your stir bar? Possible it spun out and is no longer doing its job? What kind of cold trap are you using? How cold is it and where are you taking your vacuum measurement from within the system?
Pushed to 35 on the Glas-Col Stir Control, 30 being where I usually set it at first signs of reflux. Definitely stirring well. Using a cold trap that is controlled by a polyscience set to -30° and is holding stable between -25 and -20. Same way it’s been ran since beginning of the year. Just broke it down and checked all connections and all looked good. The gauge is ran off the lineset adapter for the pump, so reads post cold trap, which I know I should switch at some point.
Thing is, before we were running with a dewar style cold trap last year and saw runs that went good even with pump approaching 300. We are getting better levels now and everything has ran smooth this year until today.
All seems well. Just a heads up running a trap less than -70c you’ll certainly be passing volatiles to your pump. We run either a -40c into a second -70c and still see rapid degradation of the pump oil. Have you tried helium at your joints to check for leaks in the system? I agree you should probably move your vac guage to reflect system depth more but it seems low enough you should be getting mains. I’ve had good results as high as 500 microns. I’ll ponder on it for a bit an see if I can think of anything else that may be helpful. I would certainly be pointing at a leak at either the head (where vapor point is monitored via thermocouple) or Boiling flask(where solution is monitored via thermocouple)
The only times I’ve experienced this are when I “lose” my reaction from too much, or too little, stirring. I try to create a very mild vortex to avoid that. Or it has happened when there is a vacuum leak and the system can’t equilibrate pressure. My vacuum leak occured specifically in my vac controller, which was super strange.
What your describing definitely sounds like the energy is getting trapped. Meaning your pot is hot and your solution is boiling at the bottom, but its unable to release the vapor from the oil matrix. Hence the drop in vapor temp.