SPD troubleshooting woes

Greetings. First, thank you to everyone here, this place is an incredible resource and the only reason I’ve made it this far. We have a 2l SPD set up that we have been building over the last couple months that we can’t get to produce any volume of distillate.

Our process is as follows:

-Dry ice is added anhydrous food grade ethanol until temp stabilizes at approx -80c
-Cannabis (trim, small buds, so on) is added (in a 50micron bag) at a ratio of 1/10 cannabis to ethanol and lightly agitated for 5-10 minutes
-The cannabis bag is removed and the bag is pressed to to recoup as much extract as possible
-The Resulting extract (usually approx 10 liters) is filtered via buchner through 2.5 micron qualitative filter paper, collecting a sizable amount of epicuticular wax, this also forces remaining CO2 out of solution, stopping the mild bubbling
-The extract is then held overnight in a normal commercial freezer (-10c), then again filtered through qualitative filter media
-The extract is then rotovapped until all ethanol is removed and the resulting oil has the consistency of room temperature molasses
-The oil is then transferred to a 2l double neck flask and attached to a SPD head> three neck cow > three 250ml flasks. The cow has a vacuum take off running to a cold trap using black thick walled tubing, which then runs into a small vacuum manifold made out of a triclamp 1.5in tube and 1/4in adapters. the 2 stage rotary vane pump rated at 12.5CFM. The pump pulls 15 micron with the yellow jacket gauge screwed directly into it, 150 microns directly into the vacuum manifold, and 250 microns in the whole setup.

-The heating mantle is raised in increments of 5c at 250 micron. at approx 100c distillate appears to coalesce in small amounts on the vigreux fingers

  • The temperature is raised very gradually until the mantle maxes out at 300c and the material becomes charred. The Kangaroo thermometer at the head reads room temp until well into the 200s, and even then only very light, clear fractions come over in very small amounts

-Our license requires that I use ethanol
-I’m aware that various aspects are made much easier with much more expensive equipment (jacketed cryo centrifuges, et cetera), however I can’t justify those expenses until the benchtop scale is proven to higher ups.

My theories (uneducated as they may be):

  • The lack of long cryo exposure in something like a medical freezer is leaving more large molecular weight compounds in the extract, leading to more BTUs needed to cause vaporization and that thermal reality is above the point at which everything becomes a charred mess
  • 250 micron is too high of a vacuum to be feasible in this process
    -Processing with adsorbents could yield a lower molecular weight (Ihave carbon, mag-sil, bentonite and so on. But I am unsure as to which to use for this particular remediation.
  • I have not sacrificed a lab assistant to Enthalpus, Lord of Vacuum Distillation, and as such he has cursed my endeavors. I am aware this is hubris on my part but I only have two assistants and can’t spare one right now.

Any ideas, oh learned men of the dark weed arts? I’m at a loss.

Forgot the decarb step! The oil is heated on a heated stirrer in a round bottom flask in an oil bath until bubbles stop. Testing determined that all THCA was converted to THC, so I’m confident the offgassing of CO2 is not causing a higher vacuum


You should never be hitting 300c. You need a pump that is appropriate for the task.


Are you using a stirbar at all?

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Thank you for your reply. I hear this a lot on similar threads, but what I’m trying to determine is what is appropriate maximum vacuum. 500 micron? 5?. Part of my issue is that the 2000$ pump is a much bigger ask from a budget standpoint than the 500$ one I currently have.

large oval stir bar at max stirring.

At 250 micron you should definitely be getting something over to the otherside. What rpm is your stirbar set to? Do you check to see it’s actually spinning? You need a better pump. You need to at least straighten your lines if not replace them with a wide bore set up and you need a Gauge before your cold trap which I hope you are using.


Your vac level is entirely different before and after cold trap


How hot is your decarb step?

That’s super useful, thank you. In order to eliminate as much tubing as possible there are only two lines, one from the glass cow to the trap and one from the glass trap to the manifold. I’ll see about switching to a larger gauge of tubing.

The vacuum reads 160 or so without the cold trap attached, but that is at room temp, no process running.

The bar does appear to be moving, but there isn’t a terribly large amount of material in that 2l, about 300mg as a test. Is it possible that the area of empty glass is acting as too efficient a condenser, turning the whole shebang into a complicated reflux rig? I have a very large amount of flower, a very large amount of anhydrous ethanol, should I try with way more material or a way smaller flask (or both).

Decarb is 115c to stoppage of bubbling. Testing came with THCa below LOQ

You generally want your boiling flask half full, more if you’re doing second pass with the volatile removed. Insulate the the top half of your flask with fireplace rope. Wrap it around it like a coil. Make sure your stir bar isn’t to large for you flask it could be spinning but not at its target speed. Larger gauge of tubing will increase your pumps ability to pull a vacuum. But once again and I can’t stress this enough you need a better pump.


300ml should still distill over. You should be running larger but in no case should you ever get your flask as hot as you are currently. If you don’t see anything by 200-210c just shut it off.


I have a fiberglass tape with PID I use in other reactions that I could use as an insulator and perhaps even apply a gentle heat with that as well. Thanks I’ll try that.

With the pump issue, what about the better pumps remediates this situation? Other posts have seemed to suggest that 12.5 cfm is a bit overkill for 2l. Is this process simply not doable at 200-300 micron? Or is there another metric I’m not taking into account? This process working essentially lets me buy the more expensive stuff, so not having a great first or even second pass isn’t a deal breaker for me, I just need… well, any pass at all.

It looks to me like you’re dealing with two issues

First you’re under loading the system. Until you’re more experienced you should avoid under loading by too many % below 50%. Probably 25% full (1.25kg/5L flask) is the minimum I would do. This becomes more important with small systems.

Second when you are selecting a vacuum pump you need to look at both the CFM and the ultimate vac for the pump. You need the factory specs to be between 1 and 10 micron in my experience to have good success. Then select a CFM that will pull the system down fast enough. 3cfm pumps with a 1 micron ultimate vac will pull just as fast as 3cfm pumps with a 500micron ultimate vac. You might be able to get away with an Edwards8 on that little system.


That makes a lot of sense. Do you suppose it makes more sense to extract 1l and put it into the 2l or get a say 500ml double neck and test say 250ml to give the pump less total volume to work with?

Which pump? if you get an edwards8 or edwards12 you’re in good shape I think.

Here’s the issue with under loading:
The environment around your system provides a certain amount of wind which cools the system. Cool distillation heads condense material in the head and drip it back down, preventing it from exiting the boiling flask. The glass sitting above the mantle starts cold so it has to be heated to allow material through. If there is no material in your flask there is no way for the glass to efficiently heat up and allow a fraction through.


Got it. The heat that is very efficiently being transferred through the glass into the material is equally efficiently leaving the glass through the large empty volume. I didn’t realize the loss was so great but it makes sense explained like that. I’ll likely go with the E2M-12 you linked, I wasn’t aware the secondhand market was that much cheaper.

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Happy to help.

I’d also recommend looking around on eBay for a couple of days there are very good deals and sometimes they come with guarantees and with tested gear. This linked one looks only semi tested. You might want to look around more

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Sent you a PM

300 gram?

300mg is a big dab…if that’s all you loaded you aint getting anywhere.

(300ml. got it :wink: )

do you have a mantle that will fit such a flask. putting the wrong size flask in the mantle doesn’t do you any favors.

that pump you have will work with a smaller system, and I’ve heard tell of folks getting by above 500um

yeah, not enough in there…

you might also want to invest in a panda (cheaper than your pump). you’re leaving a lot behind with your current extraction.

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