Planning On Experimenting With Sfe Co2 Machine For A Cryogenic Co2 Expanded Ethanol Extraction

So subzero ethanol extractions r becoming increasingly popular recently and is probably where large scale processing is going right now. and I’ve been researching co2 expanded solvents (CXS) and realized how easily i could modify my machine for this process method. I have a jacket pressure vessels and large tanks of co2; all i think i would need is a large condenser, a cheap vac pump and the liters of high proof ethanol i would need (which is expensive here in cali but fortunately part of my design is a large vacuum still lol).

Let me explain my idea without all the minutia first;
Take ethanol that has been chilled(x) and add to my main vessel which has been prechilled to the same temperature (x) then dissolve co2 in cold ethanol (x) then add plant matter to the mixture (x) then filter into 2nd vessel (x) and distill most solvent under moderate vacuum (x) yielding a concentrated ethanol cannabinoid solution (x)
ill end the abridged version there cause the final steps depend on what product ur going for and the exact parameters of the extraction. but almost always include purging of all the solvent at some point.

Take ethanol that has been chilled(as much as u can) and add to my main vessel which has been prechilled to the same temperature (I could use solid or pressurized liquid co2 do this by pressurizing-depressurizing cycles or I could make a cryo-liquid coolant out of iso or acetone and dry ice and pump thru the jacket) fill only ~40% full to leave room for both expansion and plant matter. Then dissolve co2 in cold ethanol (I would add dry ice to ethanol then seal chamber and let the pressure build to start then i can also add co2 gas into the system from the bottom of the vessel. co2 gas becomes more soluble in ethanol as it gets colder so this has to be done till all the ethanol is at lowest temp) then depressurize the system and add plant matter to the mixture (after addition reseal vessel and wait 30-45 mins) this is where the real unknowns start so ill be general. then filter into 2nd vessel (piping co2 gas into to top pushes ethanol thru filter and into next vessel or using the built up pressure) let solution warm to room temp then slowly raise to 40c to drive off co2 and distill most solvent under moderate vacuum (apply at least enough vacuum so that ethanol can be distilled with hot water pumped thru the jacket and in addition to a condenser an ice trap with dry ice cryofluid i also us a pusedo capilary tube action to prevent bumping) yielding a concentrated ethanol cannabinoid solution (stronger vacuum can be applied to the vessel and left on low heat to fully purge or may be collected then purged in a vac oven) from what ive read u could also grow thca crystal from this if ur starting material is high quality.

i might be able to do this all at atmospheric pressure when at -75c but if thats not true i hav 2 options, i could experiment with pressure and i hav good resources on the properties of the co2+ethanol mixture from 0f+ at pressures up to 1100psi just not for extracting cannabinoids. or i can just do a cryogenic ethanol extraction

One of the biggest benefits of this process over co2sfe is crystallizing of thca from freshly harvested and frozen (wet) cannabis recently given the term “live” extractions or thru the well documented liquid-liquid extraction of the thca. ive also seen this referred to as the Polar-NonPolar (Pnp) or acid/base (A/B) extraction of thca. similar techniques r know for co2 but r much harder to adapt to my machine.
Other potential benefits are yield and purity. and the yield is almost guaranteed to be better from what i understand its just if that yield is worth the decreased purity and process cost.
The biggest absolute negative is reduction batch size. i am basically making the solvent in situ and adding the plant matter to that so the material and the solvent both hav to fit. instead of just packing the with as much as can fit lik co2sfe.
This process might also be limited by how much can be dissolved it that volume of solvent which depends on the ratio of co2 to ethanol to water.
Another big negative is purging. i use to make bho so i know how fucking annoying purging oil is and how much time and overhead it adds. with co2 i dont ever hav to purge and i can always say my oil is solvent free.
and the setup cost is minimal and is for the same stuff i would need to buy to winterize my oil.


Hey! Did you ever try anything?

I have little experience actually doing any real CXE (yet) but am very familiar with eden machines etc as well as alcohol extraction.

One question I have is what are your goals? What are you trying to improve over normal CO2 extract?

With your method, I would be worried that you might add too much CO2 and cause the solvent to be too nonpolar, which might only matter if the feedstock hasn’t been activated (decarbed).

You might consider pulling a vacuum on your accumulator, and then sucking in alcohol to that, and then pressurizing/expanding that with CO2, and trying to run your system kind of normally after that until the accumulator is empty, and at that point you could push the remaining alcohol out of the plant matter with neat liquid co2 from a cylinder or some such.

I would think perhaps a better way would be to get a cosolvent pump CXE retrofit kit (@Jonaaronbray) where you would run your extractor like normal, but the pump would also add a specific ratio of ethanol (perhaps chilled) to increase yield over time without significantly changing selectivity. I think he was also talking about including additional condensing coils or something to get the thermo to still work right. After you got the extract, you could winterize it, and then come back for a crystallization step if that’s what you’re into.

My understanding is that you could extract under non-decarboxylating conditions and get good yields of potent product in a (comparatively) shorter amount of time by using a cosolvent pump.

Either way I would love to hear if you ended up trying anything, or if not, if your ideas have evolved over time.

Using ethanol as a co modifier is an excellent way to extract cannabinoids that are a little stubborn to solute in co2, thca being the most common. Use a 2.5% to 5% injection after your low pressure fraction and you can clean up and pull out before it gets too messy on the higher end of things. I recommend a purpose built extractor for this though as an accident at those pressures could be catastrophic to operator blah blah blah.

You may want to add the CO2 after you have added the material to be processed. If you have ethanol with CO2 disolved in it and then you add the material to it, it may foam up just like when you add something to soda pop especially if it is soluble, the object will present vaporization nodes and then if the material has a stronger affinity to any of the solvents (CO2 or ethanol) than the other solvent then the gas will be displaced bubling off.

u have a good point but there a few reasons to choose this “order of operations” . the main one is that c2 dissolve into ethanol rather slowly “the lower the temperature the better " so when u add the trim to the etoh before carbonating ud basically just be doing a typical ethanol extractions which have aggressively sharp diminishing returns after the first 30 min of extraction, because few in those few seconds at that points too point over 95% of the trim’s target material” been already been extracted off already that means for those first few seconds its gonna pickup chlorophyll and other stuff lik the water and all it’s solubles that can come over at the very quickly if any part falls above water’s freezing point. i consider the fizzing but so far it hasnt interfered to much with the process especially cause f the -40 -(-60f) temps change how it behaves . the vaporization nodes dont hinder the process either cause i feed the exhaust back into the chamber through a dip tube so the more it bubbles the more it agitates itself while maximizing the cooling power of both dry ice or compressed gas or both.

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The key is to never have pure modifier touch the biomass. Injecting small amounts into the Co2 solvent stream prevents any pure modifier from coming into contact with the biomass.


I don’t understand the reason to bubble co2 into the ethanol. The alcohol already has a really high solvency rate on the cannabanoids…

In theory addingb the co2 you can selectively extract terpenes and cannabinoids than if you used co2 or ethanol by it self. Also the co2 can be used as an anti-solvent which can be used for making crystals/diamonds.


So pulling the cannabanoids and turpenes out of the ethanol? I’d assume with relative extraction time, the ethanol has a way higher affinity for this kinda stuff than the co2 does. How would you get it to stick to the co2 Instead?

CO2 is “tunable”. by adjusting temp & pressure.

@JonaaronbrayAzoth is refering to the ethanol as a cosolve.nt (he makes awesome CO2 extractors). Others I believe refer to the CO2 as an “anti-solvent”.

All I know is the object of the game is to skip the ethanol recovery by selectively dropping out the targets by modifying the solvent properties. via temp, pressure, and the magic that is CO2.

you might be swapping a CO2 phase change for an ethanol phase change, but it still looks like a win from here.


His(/her) original post talked about solvent evaporation as a near final step in the process. Occuring under same time under vacuum as solvent evaporation.

I’d assume you’d need to run the whole thing liquid co2? You wouldn’t hit supercritical when the system is under 38c. I don’t think the liquid co2 is going to have a high enough affinity to any compounds other than maybe some of the turpenes? The fact that you need to run supercritical co2 over top the plant mass for 3-20h (pending on pump flow); to get thc extraction equivalent of 20m on chilled etoh, makes me think the co2 wouldn’t pull much out a la LLE principle?

I could see this potentially pulling some of the monoturpenes that form an azeotrope with the etoh.

Am I missing something? I don’t know how you could achieve the polarity differences while trying to manipulate the temperatures required for the polarity tuning.

If you went the other way, and had the system warm, the etoh would be highly polar, and the supercritical fluid non-polar. Maybe this would work?

*I’m baked, so gonna re-read this tomorrow and re-asses;

Extract everything in cold etoh to avoid chlorophyll and wax.

While cold, put in high pressure liquid co2, offgas the turps (if the co2 has a stronger affinity) into collection tube. The cold temperature ethanol loses some of it’s polar properties, so the co2 would be more polar?

Warm the mixture to get the co2 to supercritical, and the etoh into a more polar solvent. My only thought is the etoh is displays properties of a both polar and non-polar solvent. The supercritical co2 would need to be very highly non-polar-ly tuned to have a higher affinity for the cannabanoids than ethanol? Then potentially Let the co2 offgas into collection chamber.

End up with clean etoh in one chamber, sub and supercritical extract in other chamber?

Unless the super/sub critical co2 formed some kind of azeotrope with the etoh at the varying pressure/temps?

There are two sides of Co2 chemistry that I use. Using Co2 as your primary solvent with suspended liquid solvents (modifiers) mixed with the liquid Co2 in small ratios to increase the solvency power of the primary solvent (co2).

The flip side of that is when your primary solvent is a traditional liquid solvent (ethanol) and the liquid co2 is used in small ratios to cause less soluble compounds (acid forms, waxes) to crash out of the primary solvent (ethanol). The vessel used for this antisolvent reaction must be pressured to at least 150psi for this reaction to be a true antisolvent reaction.

If you try a antisolvent reaction with liquid Co2 in a non pressurized vessel then you are simply cooling your primary solvent using Joules Thompson cooling. This is a direct expansion refrigeration cycle and is very useful in quickly cooling the primary solvent down to cryogenic temperatures in minutes.

All three applications above are extremely useful and can eliminate bottlenecks from extraction solvent processing.


CO2 expanded pentane is something I would love to try.


Can you explain what you mean by acid forms?
In reference to the co2 as the anti-solvent; What kind of pressures would you use and to what end?

Does what I say above make sense? Is there a way to use the co2 and etoh tunability to avoid evaporating off the etoh entirety and use it in a pseudo LLE style extraction?

*Feel free to tell me if I’m asking too much detail :stuck_out_tongue_winking_eye:

Acid forms meaning mainly THC-a but to a lesser extent the other cannabinoids in acid form also.

The pressure vessel for a antisolvent reaction needs to be at least 600psi. The higher pressure vessels allow for more co2 to be added to the solvent. The more co2 you add the stronger the antisolvent reaction becomes. Once the desired amount of antisolvent (co2) is added to the solvent the temperature can be reduced by lowering the pressure of the reaction vessel. As the pressure lowers in the reaction vessel the solvent temperature will lower as the antisolvent evaporates.


Is what your saying more specific to a near evaporated alcohol/oil solution? Then using the co2 to help form crystals? Or would you do this with the alcohol directly off the extraction?

Generally I add the co2 to a CXE extraction that has had the liquid Co2 removed. The CXE crude tends to be 1:4 oil to alcohol so it is rather saturated already with the addition of liquid co2 back into the CXE crude at low pressures causes instant perception which can then be filter using the pressure of the co2 addition to push through a 5 micron filter.


Oh man that sounds pretty slick :slight_smile: I’ll give it a go.

So the thc-a & friends stay on top of the filter? With clean etoh on the other side? Do you know how efficient it is in the thc-a removal? Multiple passes needed or just the one?

Is it ambient temperatures? I would guess it would be better off at super low temps?

Thx :slight_smile: this is really exciting stuff

Edit I’m going through your posts to see if you’ve answered some of this already :stuck_out_tongue:

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The percipitate will be caught in the filter. If it’s a clean extraction or winterized then the percipitate is mostly THC-A. If there are high amounts of CBD-A it will accumulate also but to a much lesser degree than the THC-A.