The typical, legacy approach (“density method”) to increasing the rate of extraction of THC with supercritical CO₂ is to make THC more soluble by increasing CO₂ pressure and thus solvent density. Unfortunately, this also solubilizes a lot more of the undesired compounds which must be remediated post-extraction, leaving you with a Hobson’s Choice of either long extraction run times or tons of grueling work in post-extraction processing.
Green Mill’s Throughput Boost Method uses a different approach from density to achieve solubility, instead increasing the compound’s volatility or “vapor pressure” through higher temperature, while using a density that is actually lower than that of the legacy approach.
The method delivers a huge bump in efficiency in the extraction of THCa, while leaving behind the undesired compounds and producing a clean, pure extract requiring lower levels of post-extraction processing. It allows a processor to load the column with THCa, extract terpenes using low-density CO₂, then turn around and quickly and efficiently extract the THCa without the system becoming a bottleneck.
Feel like this is misleading for a number of reasons…
Didn’t mention that in addition to increasing the temperature, you also raised the extraction pressure from 1800psi to 3000psi.
Since when is 1800psi at 40C (104F) the industry standard? At that pressure/temperature, cannabinoids have little to no solubility in CO2 (with the exception of CBD).
Only two test conditions presented with drastically different extraction parameters.
No data presented for Δ9 yield/concentration. While it’ll occur very slowly, 70C toasty enough to decarb the material, especially if there’s any hotspots in the extraction vessel.
Not sure why the Perrotin-Brunel thesis is referenced as it does not cover THCA solubility (to the best of my knowledge, that research team has never posted a study of acidic cannabinoid solubility in CO2).
My biggest issue with this study (aside from it presenting only two test conditions) stems from the fact that cannabinoid solubility in CO2 does not always increase at higher temperatures. To quote the Perrotin-Brunel paper referenced by this study:
Another explanation for the differences in CO2 solubility may arise from the differences in melting point. It can be noticed that the liquid cannabinoids (CBD and CBN at 334 K, and 9-THC at all temperatures) show lower solubility in supercritical CO2 compared to the solid cannabinoids (CBD and CBN at lower temperatures, and CBG at all temperatures). This is consistent with the previous observation that melting results in a lower solubility of CBD and CBN in CO2 at higher temperatures.
The cross-over pressure of the different cannabinoids increases in the order of: CBN<CBD< CBG <9-THC. Interestingly enough, this shows the opposite trend with CO2 solubility i.e., the cannabinoid with the highest cross-over pressure has the lower solubility in CO2. This could also be the result of the melting point effect: the cannabinoid with the lowest melting point has the highest vapor pressure at given temperature. Because the crossing of solubility lines is a result of a trade-off between a density effect and a volatility effect, the cross-over pressure will be higher when the vapor pressure of a compound at given temperature is higher.
Unlike Δ9, THC-A solidifies at temperatures below 52C. Applying the same logic used by Perrotin-Brunel for non-acidic cannabinoids would suggest that a higher solubility of THC-A could be achieved by keeping the extraction temperature below the melting point and simply raising the extraction pressure to a reasonable value (2200 psi at 51C has a comparable CO2 density to 3000 psi at 70C). For instance, in the case of CBN, solubility actually decreases substantially when the temperature is raised above the melting point (note: not sure how the aromaticity factors into this, in general, cannabinoids with more C=C double bonds tend to have the highest solubility). I prepared a spreadsheet awhile back based on the data from the Perrotin-Brunel studies which shows the %change in solubility due to increasing the pressure or temperature (see image below).
Final note, I’ve heard a lot of claims regarding poor THC-A extraction efficiency relative to Δ9, but seen very little supporting data (if someone can point me towards a study on acidic cannabinoid solubility in CO2, please let me know). In fact, Supercritical carbon dioxide extraction of cannabinoids from Cannabissativa L. by Rovetto & Aieta seems to suggest the opposite, with THC-A being extracted quicker than Δ9 at 328K (130F) and 3000 psi (effect diminished at higher pressures).
Probably just what the Pennsylvania Marijuana program has in place…
Montana’s Medical Marijuana program has something similar where:
“a chemical extraction process using the solvent carbon dioxide, provided that the process: does not involve the use of heat over 180 degrees Fahrenheit”
1800psi at 40C is definitely on the low side for THCa extraction, I typically run extractions between 2200-2600psi at 50C to extract THCa. However, I have also done terp pulls at much lower pressures (1200-1600psi) and similar temperatures and found those extracts to contain anywhere from 5-20% THCa - it doesn’t seem inconceivable to me that you could extract THCa at 1800 psi although it would certainly take longer than higher pressures.
The thing that makes me really skeptical of this claim is the fact they didn’t speak to the composition of their extracts at all. I can’t say for sure, but in my experience if the yield vs time graph plateaus like theirs does for the “Density Method” that would indicate they have extracted most of the weight of compounds soluble at those extraction conditions. By bumping up the pressure and temperature, it doesn’t stand to reason that they’re getting out more of the compounds soluble at lower pressures, they’re probably pulling out compounds that weren’t solubilized until higher pressures/temps were reached.
That’s the most misleading part about this, they claim…
The method delivers a huge bump in efficiency in the extraction of THCa, while leaving behind the undesired compounds and producing a clean, pure extract requiring lower levels of post-extraction processing.
…although everything we know about chemical solubilities goes against this. Plus, their paper regular switches between using THC and THCa and its not clear which is being extracted in their experiment.
Personally, whenever I see something like this where they promise you can have everything you want without any drawbacks, I think it’s probably bullshit.
This has nothing to do with PA rules. I think that Greenmill is stating that 1800 psi is the standard because more people use those weak conditions than the more productive higher pressures. Ironically, I think it became the standard because the original Apeks and IES systems (~1,000 built) were built cheaply and they were not capable of going to the more standard equipment standard for other applications : 5,000 psi.
It’s better to run at high pressures and lower temperatures - you can get the THCa or CBDa using liquid CO2 as long as you go to high pressures. You can do this in ~90 min to 90% yield on a Thar Process 2x18. That’s not decarbed material and it’s still that fast.
Thar Sells systems up to 10k PSI. they claim the 5k-10k PSI systems can have the 2 hr run times that match the 4-10 hr run times on the 2k-5kPSI systems. they accomplish this due to the larger pump, with a Maximum CO2 flow rate: 2.7 kg/min on the 18L superfast, 40 kg/min on their 360L, 130-150 kg/min on their 1650L system.
Faster but not cleaner. Now that they are doing CO2 winterization then maybe they should run 55C. Are many companies still extracting hemp these days outside of Colorado?
Yeah well most hemp biomass is not going to be pretty regardless of the set conditions. Will take a good amount of time and patience if you want it to look decent.
Color remediation medias for CO2 work really well at those high temperatures and pressures.
There is at least a few CO2 cannabis manufacturers in the western states, both cannabis and hemp facilities.
But would solubility have to increase? If you are pumping sc/SC CO2 through the plant material you are going to push through any THCA in vapor state in the solvent tube, if you maintain in vapor state until it reaches the expansion vessel and deposits there, you have an extraction regardless of whether it dissolved in the solvent or not.
yeah, I know it’s an old post but I’m digging and bored.
