Tag Archives: Winterization

Recent Developments in Supercritical CO₂ Winterization

By Aaron Green
No Comments

Supercritical carbon dioxide (CO2) extraction is a processing technique whereby CO2 is pressurized under carefully controlled temperatures to enable extraction of terpenes, cannabinoids and other plant molecules. Once the extract is obtained the crude is often subjected to an ethanol winterization process to remove chlorophyll, fats and waxes.

Green Mill Supercritical is a Pittsburgh-based manufacturing and engineering company focused on cannabis and hemp extraction. The company offers a range of CO2 extraction equipment where users can tune and control their extraction methods. They recently announced  a technology advance enabling winterization in-process, which has the potential to remove the need for ethanol winterization.

We spoke with Jeff Diehl, director of marketing at Green Mill Supercritical, to learn more about the new process. Jeff was working in the tech industry in San Francisco in 2017 when he was invited to join Green Mill by his cousin, Jeremy Diehl, who is the founder and CTO.

Aaron Green: Before we get to your new technology, can you explain what industry trends you are watching?

Jeff Diehl: A big thing that I watch is the premium extract space. More and more consumers are demanding higher premium extracts. They want differentiated products. They want products that are safe and that have some kind of meaningful connection to the specific plant from which they came. Right now, CO2 plays a small role in the market for those products. Most premium products are generated through hydrocarbon extraction. So, I am watching how people are using CO2 to create the next generation of safe, premium products.

Aaron: What is the normal process for a CO2 extraction today?

Jeff Diehl, director of marketing at Green Mill Supercritical

Jeff: The current CO2 extraction process generally consists of two major phases to producing your final extract. In the first phase, you have extraction where you get your crude product. The second phase is post-extraction where you do cleanup to get your refined oil. Within that post-extraction phase, most operations include an ethanol-based winterization process.

Aaron: What does the winterization step do, exactly?

Jeff: Winterization is about removing waxes. Your main extraction is considered crude because it’s got a lot of materials from the plant that you don’t want. The large majority of unwanted material is waxes. Winterization is the process of using a solvent, traditionally ethanol, to separate the waxes from the cannabinoids. There are multiple challenges inherent in ethanol-based winterization that introduce cost, time and product loss. It’s terribly inefficient. Plus, there will always be residual ethanol left in your final product, and that’s not something consumers appreciate.

Aaron: You’ve recently announced a new process at Green Mill that moves the winterization step into the supercritical CO2 equipment. Can you explain how that works?

Jeff: With our process, which we call Real-Time Winterization, there is no ethanol involved in winterization anymore. It is all done with CO₂ during the primary extraction. That’s the major advance of our process and although it has been attempted before, no one has succeeded at doing it in a viable way. You take a process which is normally four days – one day for CO2 extraction and three days for ethanol winterization – and you do it all in less than a day. We have automated software, sensors and pumps that makes this all possible.

Aaron: How does the quality of the resulting product compare with the new process?

Jeff: You can see the difference right away, if you’re at all familiar with extraction. It just looks clean and bright. Lab analysis has been very positive thus far, but we continue to run tests. Our R&D team has done multiple tests, mostly on hemp and CBD. That’s because we don’t have a license for THC. We’re currently engaging with a licensed partner so that we can collect more data on THC-containing products, so we can give exact numbers. But with CBD, we’ve done multiple tests to validate the method and the technology, and are seeing consistently excellent results in regards to both purity of the product and efficiency of the process.

Aaron: How do yields compare between the processes?

Hemp CBD extract straight out of a Green Mill SFE Pro running Real-Time Winterization.

Jeff: From the data that we’ve seen in the industry, it looks like when you winterize with ethanol, you leave anywhere from 5 to 10% of your cannabinoids behind in the waxes. That’s just lost. With Real-Time Winterization using CO2 we have seen recovery rates as high as 99%. We are continuing to investigate that result with testing to make sure it was not an outlier, but in any case, recovery rates look promising.

Aaron: One of the other issues with ethanol is taxes and the ability to find food grade supply. Do you have any perspective you can share on that?

Jeff: There are a number of advantages to moving away from ethanol. The sheer quantity of ethanol is a factor. There are a lot of regulations and fire requirements around managing large quantities of ethanol. The ethanol winterization process itself is not just one process. There are multiple stages, from mixing, to freezing, to filtering, to removing the solvent. These are all opportunities for things to go wrong, so you’re always managing those risks. Multiple large pieces of equipment, including fume hoods, filter skids, cryo freezers and rotary evaporators, are expensive and require heavy management.

I think Elon Musk said the best process is no process. Anytime in an industrial process when you can remove steps in the process, that’s the direction you want to go in. And, that’s what we’ve done. With this recent work, we have effectively removed post processing for certain categories of end product.

Aaron: Do you have any patents on the new process?

Jeff: We have a patent pending on both the method and the equipment, which is allowing us to talk about this as much as we are.

Aaron: So, how does this work if somebody already owns an existing piece of Green Mill equipment? Is this something that can be retrofitted? Is it a software upgrade?

Jeff: There are two components. One is an equipment upgrade, which can be done retroactively for existing customers, and one is a methodology upgrade, which we assist our customers with. The automation software inherently can handle the settings that you need to run the methodology. In fact, it’s that software and the rest of our existing tech stack, the proprietary pump, the triple inline fractionation, the precision and stability of the overall system, that is what made this winterization advance possible.

Aaron: Where are you rolling this out first? And do you plan to go international?

Jeff: International is definitely in the plan, since we’ve already sold systems abroad. We are currently getting ready to announce the opening of our beta program with the new technology. So, we’re not ready to sell this widely at this time, but we are taking submissions from companies that want to get in early and join us at the forefront of CO₂ extraction innovation.

Aaron: Okay, great. Thanks Jeff, that’s the end of the interview.

extraction equipment

THC Remediation of Hemp Extracts

By Darwin Millard
1 Comment
extraction equipment

Remediation of delta-9 tetrahydrocannabinol (d9-THC) has become a hot button issue in the United States ever since the Drug Enforcement Agency (DEA) released their changes to the definitions of marijuana, marijuana extract, and tetrahydrocannabinols exempting extracts and tetrahydrocannabinols of a cannabis plant containing 0.3% or less d9-THC on a dry weight basis from the Controlled Substances Act. That is because, as a direct consequence, all extracts and tetrahydrocannabinols of a cannabis plant containing more than 0.3% d9-THC became explicitly under the purview of the DEA, including work-in-progress “hemp extracts” that because of the extraction process are above the 0.3% d9-THC limit immediately upon creation.

The legal ramifications of these changes to the definitions on the “hemp extracts” marketplace will not be addressed. Instead, this article focuses on the amount of d9-THC that is available in the plant material prior to extraction and tracks a “hemp extract” from the point it falls out of compliance to the point it becomes compliant again and stresses the importance of accurate track-n-trace protocols at the processing facility. The model developed to support this article was intended to be academic and was designed to follow the d9-THC portion of a “hemp extract” through the lifecycle of a typical CO2-based extract from initial extraction to THC remediation. A loss to the equipment of 2% was used for each step.

Initial Extraction

For this exercise, a common processing scenario of 1000 kg of plant material at 10% cannabidiol (CBD) and 0.3% d9-THC by weight was modeled. This amount, depending on scale of operations, can be a facility’s total capacity for the day or the capacity for a single run. 1000 kg of plant material at 0.3% d9-THC has 3 kg of d9-THC that could be extracted, purified, and diverted into the marketplace. CO2 has a nominal extraction efficiency of 95%, meaning some cannabinoids are left behind in the plant material. The same can be said about the recovery of the extract from the equipment. Traces of extract will remain in the equipment and this little bit of material, if unaccounted for, can potentially open an operator up to legal consequences. Data for the initial extraction is shown in Image 1.

Image 1: Summary Data Table for Typical CO2-based Extraction of Phytocannabinoids

As soon as the initial extract is produced it is out of compliance with the 0.3% d9-THC limit to be classified as a “hemp extract”, and of the 3 kg of d9-THC available, the extract contains approx. 2.8 kg, because some of the d9-THC remains in the plant material and some is lost to the equipment.

Dewaxing via Winterization and Solvent Removal

Dewaxing a typical CO2 extract via winterization is a common process step. For this exercise, a wax content of 30% by weight was used. A process efficiency of 98% was attributed to the wax removal process and it was assumed that 100% of the loss can be accounted for in the residue recovered from the equipment rather than in the removed waxes. Data for the winterization and solvent recovery are shown in Image 2 and 3.

Image 2: Summary Data Table for Typical Winterization of a CO2 Extract
Image 3: Summary Data Table for Solvent Removal from a CO2 Extract

Two things occur during winterization and solvent removal, non-target constituents are removed from the extract and there is compounded loss from multiple pieces of process equipment. These steps increase the concentration of the d9-THC portion of the extract and produce two streams of noncompliant waste.

Decarboxylation & Devolatilization

Most cannabinoids in the plant material are in their acid form. For this exercise, 90% of the cannabinoids were considered to be acid forms. Decarboxylation is known to produce a mass difference of 87.7%, i.e. the neutral forms are 12.3% lighter than the acid forms. Heat was modeled as the primary driver and a process efficiency of 95% was used for the conversion rate during decarboxylation. To simplify the model, the remaining 5% acidic cannabinoids are presumed destroyed rather than degraded into other compounds because the portion of the cannabinoids which get destroyed versus degrade into other compounds varies from process to process.

Devolatilization is the process of removing low-molecular weight constituents from an extract to stabilize it prior to distillation. Since the molecular constituents of cannabis resin extracts vary from variety to variety and process to process, the extracts were assumed to consist of 10% volatile compounds. The model combines the decarboxylation and devolatilization steps to account for complete decarboxylation of the available acidic cannabinoids and ignores their weight contribution to the volatiles collected during devolatilization. Destroyed cannabinoids result in an amount of loss that can only be accounted for through a complete mass balance analysis. Data for decarboxylation and devolatilization are shown in Image 4.

Image 4: Summary Data Table for Decarboxylation and Devolatilization of a CO2 Extract

As the extract moves along the process train, the d9-THC concentration continues to increase. Decarboxylation further complicates traceability because there is both a known mass difference associated with the process and an unknown mass difference that must be calculated and justified.


A two-pass distillation was modeled. On each pass a portion of the extract was removed to increase the cannabinoid concentration in the recovered material. Average data for distilled “hemp extracts” was used to ensure the model did not over- or underestimate the concentration of the cannabinoids in the distillate. The variables used to meet these data constraints were derived experimentally to match the model to the scenario described and are not indicative of an actual distillation. Data for distillation is shown in Image 5.

Image 5: Summary Data Table for Distillation of a Decarboxylated and Devolatilized Extract

After distillation, the d9-THC concentration is shown to have increased by 874% from the original concentration in the plant material. Roughly 2.2 kg of the available 3 kg of d9-THC remains in the extract, but 0.8 kg of d9-THC has either ended up in a waste stream or walking out the door.

Chromatography – THC Remediation Step 1

Chromatography was modeled to remove the d9-THC from the extract. Because there are several systems with variable efficiency rates at being able to selectively isolate the d9-THC peak from the eluent stream, the model used a 5% cut-off on the front-end and tail-end of the peak, i.e. 5% of the material before the d9-THC peak and 5% of the material after the d9-THC peak is assumed to be collected along with the d9-THC. Data for chromatography is shown in Image 6.

Image 6: Summary Data Table for d9-THC Removal using Chromatography

After chromatography, a minimum of three products are produced, compliant “hemp extract”, d9-THC extract, and noncompliant residue remaining in the equipment. The d9-THC extract modeled contains 2.1 kg of the available 3 kg in the plant material, and is 35% d9-THC by weight, an increase of 1335% from the distillation step and 11664% from the plant material.

CBN Creation – THC Remediation Step 2

For this exercise, the d9-THC extract was converted into cannabinol (CBN) using heat rather than cyclized into d8-THC, but a similar model could be used to account for this scenario. The conversion rate of the cannabinoids into CBN through heat degradation alone is low. Therefore, the model assumes half of the available cannabinoids in the d9-THC extract are converted to CBN. The entirety of the remaining portion of the cannabinoids are assumed to convert to some form of degradant rather than a portion getting destroyed. Data for THC destruction is shown in Image 7.

Image 7: Summary Data Table for THC Destruction through Degradation into CBN

Only after the CBN cyclization step has completed does the product that was the d9-THC extract become compliant and classifiable as a “hemp extract.”

Image 8: Summary Data Table for Reconciliation of the d9-THC Portion of the Hemp Extract

Throughout the process, from initial extraction to the final d9-THC remediation step, loss occurs. Of the 3 kg of d9-THC available in the plant material only 2.1 kg was recovered and converted to CBN. 0.9 kg was either lost to the equipment, destroyed in the process, attributable to the mass difference associated with decarboxylation, or was never extracted from the plant material in the first place. All of these potential areas of product loss should be identified, and their diversion risk fully assessed. Not every waste stream poses a risk of diversion, but some do; having a plan in place to handle waste the DEA considers a controlled substance is essential. Without a track-n-trace program following the d9-THC and identifying the potential risk of diversion would be impossible. The point of this is not to instill fear, instead the intention is to shed light on a very real issue “hemp extract” producers and state regulators need to understand to protect themselves and their marketplace from the DEA.