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Subcritical CO2 Extraction - Pros and Cons?

Hey everyone,

We have run several cannabis subcritical CO2 runs - mostly 45-60F at 1250PSI. It's not turning out much more terpy than our supercritical co2 runs. We only do nug runs anyway, so our terpene concentration is usually fairly high. However, i'd imagine we'd get a much terpy-er run doing subcritical. Are we doing something wrong?


  • Are you only looking at terpene content? THC potency should be observed as well. What conditions are you crashing out your components at? I have seen more volatile terpenes lingering in our CO2 after extraction and not crashing out with our concentrate.

  • edited August 2017

    The terp content and yield is not going to get any better with higher P and T as you observed and the majority of the terps will come out first no matter what phase your in. The goal is to limit the p/u of untargeted compounds with proper phase and flow (#of CO2 passed through the material). This technique is similar to how we ran CLS Hydrocarbons rigs which are liquid phase extractions. On the Eden 20L HI Flow, I run sub/liquid phase into an empty accumulator off the bottle, dump/recover the accumulator after it fills and do it again. I know exactly how much liquid CO2 I've passed through the material by what's come off the bottle in #. You'll find the point where that liquid phase stops producing. Xsact Xtract, Jon Baray is doing some really cool things with liquid phase CO2 extraction. I got a lot of ideas about the running this phase to it's fullest by following his IG feed. Happy extracting!!

  • 1250 psi is your problem, you are well past critical pressure. This is a sub critical extraction because you are past the critical pressure but below the critical temperature.

    If you want a terpene extraction from your Hi-Flo I would suggest a short low density 1800psi supercritical extraction.

    I run terpenes extractions at under 500 psi and we'll under 0c. These type of extractions won't fair well using a water cooled extractor.

    I would say that Marlin has the best method for a low pressure extraction in a Hi-Flo.
  • @jonaaronbray "These type of extractions won't fair well using a water cooled extractor."

    Why? Subzero is subzero no matter the method of cooling, ya?

  • Water cooling at those low temperatures would be expensive and wasteful. Direct refrigeration with r744 or another Freon based cooling is needed to keep such low temperatures for the duration of a extraction cycle.
  • @jonaaronbray I agree it's not very efficient. It's certainly not needed though, I've done it on my FX2 with water/glycol. I was replying to your statement that they wouldn't fair well.

  • Hey all, yes i've been experimenting with different pressures and temperatures to see if subcritical really makes a difference. I agree with @Marlin_Rando that if i'm trying to optimize terps, they'll come off first in any phase.


  • I run around 750psi with a water cooled condenser at 4C and can get about as much terpene yield as anyone would want. It's all about the system you're using and how you recover the extract when depressurizing.

  • null
    You don't have to collect extract while depressurizing. When you extract in a system that uses traditional distillation over of rapid pressure changes in a "separator".

    These "separators" were designed for the separation of solids from a gas stream. The cyclonic style separators have been used in supercritical machines because the thought was that the dense phase gas would drop solids out of suspension as the pressure and density lowered from expansion. This type of separation works well in till you get below 1056 psi.

    You can't easily purify a loaded supercritical steam because there is no liquid vapor equilibrium. The extractor must have a liquid form of solvent to distill before pure solvent can be recycled. Using a gas/solid separator to distill liquid co2 is less than ideal because you will have contamination that carries over ( intrained organics ) and taint you accumulator and eventually your storage tanks.

    Your small scale terpene extraction may work fine with a water cooled jackets (I never said it wouldn't). My point is that you wasted a lot of energy to cool water with refrigeration to cool the Co2 with water. You are exchanging heat from your system to your water. Your chiller is exchanging heat from you water to the air in your extraction room. That's not efficient or scalable.....
  • The extractor makes all of the difference in the world - not just parameters. The ExtraktLAB extractors run both sub & supercritical and produce as full of a spectrum as you want.

  • So we do our subcritical with the extractor heater off and keep the pressure between 900-1000psi. It does get a bit tricky as the separator pressure will equalize to extractor the longer it runs. So in the first 30mins to pull off the terps and we have had it come out liquid. The problem we run into is at the 45-1hr on some runs we have seen water come out although its subcritical when we know water should be soluble in supercritical. And going any longer then we start to get waxes/lipids, this is just the downside of the extractor of not able to keep the liquid chilled like jonaaronbray says.

  • @sensilabs this is exactly the same experience we've been having. Phew! I'll have to try chilling the extractor vessel further. We're having to run the machine at a reduced flow rate to avoid flooding the separators on our system.
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