Manipulating super critical co2 solvent density to target specific compounds in cannabis

Hash and Stuff Extraction
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Greetings hash wizards and warlocks,

In my never-ending quest to better understand the nuances of CO2 extraction, I wanted to direct some of my long-lasting questions to the CO2 extraction gurus within this forum to start a dialogue about methods and theories.

I have ~8 years of CO2 extraction experience with the legal industry space, but this experience has been mostly focused on the extraction of premium CO2 terpenes and highly potent oil in a production based setting, rather than any kind of R&D.

I am interested in doing some R&D to try to extract THCa from undecarbed plant material, but i dont know where to start. My question lies in the nature of manipulating solvent density to target specific compounds within the plant, namely THCa. I understand that changing solvent density is the single most important factor in determining what type of compounds are extracted, but my understanding of this concept is entirely practical and lacks the deeper theoretical understanding of this phenomena.

Can someone point me towards some academic articles that dive into the physics behind what is occurring when solvent density is manipulated? Why is it that terpenes and other volatile compounds are selectively extracted at a solvent density of ~0.2 - 0.35 g/m^3, while decarbed cannabinoids are extracted at higher SD, say ~ 0.6- 0.9 g/m^3. I get that it is a gradient and the compounds most soluble in the solvent will extract first, and less soluble compounds take more time, but I do not understand what is happening on a molecular level.

How is the polarity of the solvent changed as its solvent density is adjusted? Why are more polar compounds pulled at higher solvent densities, especially in supercritical settings? How is it that CO2, a non-polar molecule, can pull water during terpene-extraction parameters?

Finally, how can one approach finding the correct parameters to pull THCa from plant material while also not pulling waxes/lipids and other undesirables from the plant? I assume it will take some post-processing cleanup steps to try to isolate the THCa from the rest of the extract.

I am eager to hear your points of view on this topic, or if you can point me in the right direction to some resources that will help me better educate myself on this topic.

Thanks

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Nice ask!

Might find some starting points here Beyond CO2 density, "vapor pressure" method boosts THCa throughput

Pretty sure there are a couple of other discussions around here that have links to the primary literature. Probably in reference to terpene extraction…don’t recall a deep dive into the theory

Poke around a little, imo it’s pretty easy to see who the friendly CO2 wizards are…and it looks like you’ve been here for a bit.

Consider tagging individuals you think might have the knowledge you seek into the discussion directly…or simply asking if they have any suggestions for reading material when you figure out who they are…(they provide salient advice in another relevant thread)

wow! You seem to have a good handle on the theory, any chance you can point me at appropriate resources for getting there myself?

Maybe see

Manipulating super critical co2 solvent density to target specific compounds in cannabis

To get an idea where my head is?

I have absolutely seen crystalline THCa in an early Apex or Eden lab separator…

They thought it was so neat, they bought the thing to a high times event, and were offering dabs (apparently NOT from the THCa)

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Thanks for the response @cyclopath. I’ve perused through that thread and just about every other thread pertaining to this, but there are no specifics on the method or approach. Was hoping someone here who is a long-time CO2 user might be able to break it down a bit more than just the regular surface level explanation. @ExTek90 @JonaaronbrayAzoth @Photon_noir @Roguelab @Soxhlet @misterMR @GreenSolvent @TharProcess
Want to share any input on this?

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I have done supercritical for 9 years now. There are settings which will make the extraction yield mostly just terpenes, but I found that when extracting cannabinoids there isn’t a way to select for them (but there are different settings to make a high cbda extraction or high thca extraction faster). Since biomass is usually high in one or the other, the minor cannabinoids are still extracted by the time you are done extracting the primary cannabinoid. I also found that CO2 results in a higher decarb of THCa/CBDa

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I’ve heard that Ethanol is the Cannabinoid grabber and the C02 is the terpene grabber.

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@EverettMarm @Muzik_CO2tech in case they have anything to add.

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No hands on CO2 extraction experience here, but I am a fan of physical chemistry.

You are asking some tough questions, which can lead down as long of a rabbit hole as you are willing to explore. Tons of computational chemistry research is based around describing and predicting solubility on the quantum mechanical level.

Some non-cannabis specific journal articles I found on a quick Google search. SciHub is your friend if you hit a paywall

https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/cphc.201700434

https://pubs.acs.org/doi/10.1021/ar040082m

https://www.sciencedirect.com/science/article/abs/pii/S0896844622002480

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As soon as I left my job i basically forgot everything. Different pressures will extract different cannabinoids for sure. We had settings for thc, terpenes and cbd. For cbd, the setting was for when we ran crude cbd not extracting thc and cbd at the same time. I did run across settings in one of these threads on this site.

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Did you follow this

Here?

https://wnvnl.academia.edu/HelenePerrotinbrunel

If I’m hearing your question correctly, you want to understand why CO2 changes properties depending on where you are on the phase diagram & how that effects the solubility/extraction efficiency of the various molecules involved?

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If you are looking to target THCA don’t decarb the material first which is recommended by the equip mfgs for a better yield.

Whatever you extract without decarbing will contain THCA. You can dewax and recover the ethanol below decarb temps as well so you should be able to isolate from there if you use another solvent.

There are methods of getting THCA to form on the wall in a crystalline structure but it’s formed with all the other full spectrum stuff too so not necessarily an isolate

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I dont expect it to extract an THCa isolate, CO2 isnt specific enough to only target one cannabinoid (it’s always a gradient), but am looking for super or subcritical parameters that will produce a THCa heavy extract from undecarbed plant material. This is where fractionation comes into play.

I’ve heard other people insinuate that subcritical is better for this, and doing it at a low enough solvent temp that it doesnt incidentally decarb the THCa during extraction, but nothing specific beyond that.

This is my best guess at it so far: do a terpene pull first at normal supercritical parameters (we use ~1150psi, 105˚F solvent temp for a solvent density of ~0.269 g/cm^-3). Then increase the solvent density greatly to around 0.9 g/cm^-3 (subcritical) to try to target the cannabinoids. This would be around 1200psi and 50˚F solvent temp. Our cannabis is THCa dominate, so while it will extract many different cannabinoids and cannabinoid acids, hopefully it will be THCa rich. I’m expecting the supercritical fluid to pull waxes/lipids first, so i will likely need to harvest after 1 hour fraction increments at these parameters to see how the extract changes over time. Just not sure if it will pull a lot of other desirables like chlorophyll along the way as it is undecarbed.

going back to my original question, the @Photon_noir post about Extraction & van der Waals Forces is excelllent and extremely thorough and the closest thing i’ve come across on this website that describes what is going on at a molecular level. I’m still trying to decode it :thinking:. He say’s " Simply put, propane and CO2 are also, for these same reasons, harder and much harder , respectively, to induce into polarity". Nonetheless, supercritical CO2 will pull a significant water fraction during a terpene pull. I think this has to do with the “Debye force”, but not sure how to apply that in practice. Despite being a rigid non-polar molecule, it can definitely extract polar molecules, and therefore it is possible to tune the solvent to extact a relatively polar molecule like THCa…

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The interactions between scCO2 and solute are, I believe, more quadrupole-dipole than dipole-dipole as CO2 does have a quadrupole rather than a dipole moment.

THCA pulls can be done with lowish yields… the higher your solvent flow the better your yield will be because scCO2 is a shit solvent so recirculation is necessary. Like you want a system capable of 500 kg/hr or more for scale extractions. Also you’ll be pulling fats/waxes as well, so CRY media or similar is a good idea.

IMG_3536
IMG_35364032Ă—3024 2.41 MB

These are THCA from cured material. The center is with CRY CO2 media.

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If you turn up the volume you can hear the crystals clink. It’s all yellowish because I just mixed the terps straight with the yellow crystals.

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IMG_3416
IMG_34163024Ă—4032 2.21 MB

This one wasn’t blended well. You can see waxy chunks of you zoom in.

Looks ranged from this to baby shit without CRC. You could dial it in and get better product for sure.

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Apologies I have been absent several months, @Billiamaire ! So I’ll get straight to it…

I don’t recall if I said this in that Van der Waals force post or not, but although CO2 can ostensibly be tuned to extract polar molecules, it usually requires a “cheat” in the form of an adjunct (aka, “helper”* additive, usually in smaller quantity) solvent* that bridges the gap between non-polar and polar, such as an alcohol. Ethanol is a common SCO2 polarity “booster”* used to extract cannabinoids… especially in their original carboxylic acid forms.:nerd_face:

  • The most common term for this additional solvent in SCO2 is just dancing in my head and ignoring my hands trying to type it… Anybody want to help this doddering old fool’s recall with recognition? :face_with_spiral_eyes:

I think one of the most important aspects for SCO2 cannabinoid extractions is to work with gravity, not against it. Of course this will depend on your inlet and outlet configuration on the biomass column and on filter stages along the path to the collection aperture. While terpenes are rather volatile molecules and tend to travel with the SCO2 (although best with liquid CO2), the cannabinoids are decidedly NOT volatile, and have a tendency to literally fall out of solution, following gravity… aside from what little Brownian motion can do to suspend them in a supercritical fluid, that is. I suspect (total speculation, here) that the cannabinoids tend to agglomerate in the microsecond instances where CO2 becomes more gaseous in pockets amid the supercritical mass, and this produces cannabinoid particles (globules) that are too large for Brownian motion to have much effect on them. :melting_face:

I say all this because, from what I have seen, SCO2 systems that utilize gravity (downward outlets, cyclonic separators, etc.) have produced better products in higher yields on average, than those that do not (column top outlets, radial or arbitrarily oriented collection apertures, etc.)… the latter also have more problems with terpenes and other well-carried solutes escaping into the CO2 recycling system, it seems. :face_in_clouds:

As an aside: I used to address this volatile escapee problem with a coalescing filter I assembled with high-pressure components… and I must say that high pressure CO2 can really beat the shit out of fine stainless parts! Finding an effective and reasonably long-lasting stainless steel or other acceptable sanitary metal coalescing medium was no trivial matter! (oh the punnage) I cannot recall the exact alloy, but I can say it is important to use more ductile stuff… so 304 rather than 316, for example. Titanium alloy may have been one. Definitely not cheap in the necessary form factor, though! :money_mouth_face:

So use gravity as much as you can. Don’t fight it. :cowboy_hat_face:

Of course, after all that, using ethanol with the SCO2 makes it far more amenable to upside-down extraction flows being effective for cannabinoids (which are also alcohols). Keeping solutes in solution works better for extraction than randomly turning into gas and dropping them before reaching the collection point… whodathunkit?! :squinting_face_with_tongue:

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Oh! This is new to me and my curiosity is ever so piqued, @EverettMarm ! Afaik, a quadrupole is part of the ion detection system in a mass spectrometer, but I have not heard of quadrupolar molecular interactions! Can you explain to me the way you understand this concept? I will look it up, of course, but I am curious what YOU mean when you use the term! Very interesting! Is chemistry finally breaking free of the infernal perceptual dichotomy born of humanity’s bilateral symmetry?! Do tell! I’m all ears… err… eyes! :zipper_mouth_face:

Edit: This reads as if I am being sarcastic, but I assure you I am sincere! I really AM curious if this is a thing, now! Thank you for bringing it up!

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In the supercritical state carbon dioxide has an enhanced quadrupole moment - as in a nonuniformly spherical charge distribution about the nuclear axis - which can lead to increased favorability of quadrupole-dipole solvent/solute dynamics. Dipoles moments are separations of static spatial charges where quadrupole moments are caused by distortions of the nuclear charges themselves within the overall symmetry of the molecule.

https://pubs.acs.org/doi/10.1021/jp004359l

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I do have an old project draft about utilizing b-cyclo with cannabinoids and modulating the environment in a SCO2 system (temp, pressure, residence time) to solubilize hydrophobic compounds with known excipients, and always wondered if and when these systems would be refitted for other applications, especially chromatography, given how inefficient and wasteful the process is in this industry at scale. There’s an abundance of literature regarding this topic in drug delivery and formulation chem, and I know there’s been at least a few companies that tried a fractional extraction approach, especially with varins and acidic cannabinoids. I can pass along the literature I have regarding modulation of the xlogp for hydrophobic compounds, but also am curious if altering the mobile phase composition, rather than CO2 + eluents like EtOH, has been attempted here before, as it’d offer a much wider eluent range between collected fractions.

I also designed an equation with a variable that I made up called polarity*volume (PV) which can predict with high certainty when cannabinoids will elute out of a stationary phase. You just need to keep the stationary phase constant, but can alter mobile phases, flow rate, temp, pressure, etc with known eluent strengths at will, and scale from a UPLC to industrial FPLC systems like the 5.105 and remove the guess work and 3rd party testing of dozens of timepoints on industrial runs. I think that’d translate here, and I’ve proven the above several times, so it may parameterize exactly what variables, RRTs of the compunds of interest, etc when designing how to test this concept.

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Thank you for the references, @EverettMarm !

I am very interested to check out your equation @chempistry ! Is it somehow able to predict the RTs of different cannabinoids in mixture, or does it simply indicate which eluting volumes should be expected to contain cannabinoids in general? Fascinating!

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hi guys
there is this guy in uk who is quite obviously buying bulk thc-a isolate and terps or the thc-a sorbet ready mixed from canna refined (all the terps of his past menus match their products and he talks about the same laser vape they sell. also he mentioned they were coming out with a vape pen and that new product appeared on canna refined website)
the only mention of co2 on canna refined website is for the terps yet this guy is claiming his product he is selling is a single source thc-a extract made only with apex machines using co2 subcritical methods. I’m no scientist but from what i have gathered from my reading is that you can’t get thc-a isolate just from co2 extraction alone because you need further steps to turn it from a thc-a rich extract to isolate right?
i would have no problem with this guy but he’s targeting young uneducated medical patients and making very medical claims about a thc-a isolate with terps that is a very cheap and then selling it to them for £45-50 a g which is just daylight robbery.
he has been called out numerous times and made threats and silenced anyone who spoke up. we all know how cheap these products are in any sort of bulk.

anyway i will post his sales pitch so i can get an experts final word that he is a liar and a fraud ripping off sick desperate people and uneducated young stoners.
this is what he tells his customers when they ask how his product is made
A closed-loop CO2 cannabis extraction system uses pressurized carbon dioxide (CO2) to extract terpenes and THC-A from cannabis. Here’s a simple breakdown:

  1. Setup: The system is sealed (closed-loop) to prevent CO2 leaks and ensure safety.

  2. CO2 Pressurization: Liquid CO2 is pressurized and heated to a “supercritical” state, where it acts like both a liquid and gas, making it an efficient solvent.

  3. Extraction: The supercritical CO2 passes through cannabis material in an extraction vessel, dissolving and pulling out terpenes (aromatic compounds) and THC-A (the non-psychoactive precursor to THC).

  4. Separation: The CO2-cannabinoid mixture moves to a separator, where pressure and temperature are adjusted to release the CO2, leaving behind the extracted terpenes and THC-A.

  5. Collection: The extracted compounds are collected as a concentrated oil, while the CO2 is recycled back into the system for reuse.

  6. Purification: The extract may undergo further refinement (e.g., winterization) to remove impurities like waxes or chlorophyll.

This method is efficient, safe, and preserves the plant’s natural compounds without leaving harmful solvent residues.

and this is his sales pitch he has trying to get his customers to repost (man it makes me so angry reading this . in u.k you cannot make medical claims about this type of product at all)
Do you suffer from pain, anxiety, depression or other ailments and wish to avoid conventional medicines?

Medical cannabis has been legal in the United Kingdom since 2018 however, the way medical cannabis is produced here destroys terpenes and medical cannabis companies in the UK thanks to unneeded involvement from companies like GW pharmaceuticals, produce low quality products and actually break medical practice guidelines with their manufacturing processes. The plant is not respected and the medicinal benefits are lost!

Using some very clever loopholes within our own legal system, I was able to set up the company Nevski Exotics LTD with the aims to finally create the narrative and legalise cannabis for everyone to enjoy, responsibly!

We produce the worlds cleanest, strongest cannabis extracts which can be dabbed, smoked and vaporised in the same way you would with traditional extracts! Only mine are produced in California by artisans and extracted with C02 instead of harmful butanes and low cost methods. Our extracts can even be cooked into foods to make edibles which can be excellent for a host of benefits without the need for combustion.

We market them under THC-A which is a legal wording meaning the THC has yet to be decarbonised, think of it as water to ice.

While it is not technically legal to consume these products, what you do behind closed doors is up to you, we offer next day delivery Monday to Friday giving patients a much better and safer alternative to anything on the Cannabis medical market.

For more information you can check out

We also have a thriving discord which you can join with the link below to connect with our community of over 500 customers! (You may need to copy the discord link into google, download the app and follow instructions.

Meet new friends, get advice and lots of mental health support. The link will be in the comment section below!

We are revolutionary, we are real and we are here to help.