Extraction technology is constantly evolving each year, which helps drive down associated costs, increase output volumes, and improve product quality. While these advancements are promising, the method you choose, how you operate, and which post-extraction processing steps you deem necessary will all determine the quality of the final product and what type of product you want.
Ethanol versus Hydrocarbons and Carbon Dioxide
There is a place in the cannabis world for every style of extraction. Butane and propane are the most common solvents used in hydrocarbon extraction. The non-polarity of these hydrocarbons allows extractors to easily draw cannabinoids and terpenes out of plant material without also accidentally stripping unwanted chlorophyll into the extract. Butane and propane are favored over other longer-chain hydrocarbons because of their low boiling points, enabling these hydrocarbons to be readily evaporated from the final product once extraction is complete.
Hydrocarbon extraction is considered one of the best methods available for making cannabis concentrates; it is especially well-suited for creating live resin concentrates that use freshly harvested cannabis that has been frozen immediately at harvest to preserve the maximum amount of terpenes. This fresh-frozen biomass naturally has a much higher water content than the cured cannabis used in other extraction operations, and so an extraction that can be done at sub-zero temperatures while still removing terpenes efficiently — as with hydrocarbon extraction — will have the added benefit of keeping water-soluble components (such as anthocyanin pigments) ‘trapped’ in the frozen biomass and away from the extract.
Despite these advantages, the flammability and combustibility of hydrocarbon solvents present elevated safety risks if a leak or a fault is to occur while large volumes of the solvents are in use. Many jurisdictions also impose limits on the allowable total volume of flammable hydrocarbon solvent that can be stored on-site, and on the type and size of storage containers that can be used. Furthermore, only a limited number of hydrocarbon system manufacturers are producing Good Manufacturing Practice (GMP)-compliant equipment, and there are no pharmaceutical GMP-approved hydrocarbon extraction systems to date.
To minimize or otherwise avoid these problems, many extractors use supercritical carbon dioxide (CO2). In this method, CO2 gas is subjected to temperatures and pressures that transform it into a supercritical fluid: a state of matter that has the properties of both a liquid and gas. The gas-like qualities allow for the CO2 to permeate through the plant material, extracting cannabinoids and terpenes from the material as a liquid solvent would do.
This method, while effective, requires significant upfront costs in terms of equipment and employee training. To complicate matters further, ethanol is sometimes employed as a cosolvent in CO2 extraction to increase performance, and so, if a cosolvent is being used, then suitable ethanol solvent storage facilities need to be maintained on-site regardless. Additional post-processing efforts are also a common requirement since if ethanol is used as a co-solvent, the ethanol will have to be removed anyway.
For these reasons, many high-volume cannabis extractors run ethanol-based extraction methods. While the method can be done under hot or cold conditions, the colder, “cryogenic” ethanol extraction technique is becoming increasingly popular. Ethanol extraction has been used in herbal medicine preparation long before legal cannabis. It’s one of the safest methods to scale up while affording a good throughput with minimal post-processing steps, thereby providing a savings of people-hours and equipment that can offset the higher solvent cost. Ethanol extraction also bodes well for cannabis processors looking to adhere to different levels of GMPs (e.g., nutraceutical, pharmaceutical).
Cryogenic Ethanol Extraction
The heart of this technique is the chilled ethanol, which requires the use of industrial chillers and freezers to cool the solvent to temperatures below a minimum of -40°C for most cannabinoids like cannabidiol (CBD), or -60°C for high-quality delta-9-tetrahydrocannabinol (THC) extraction. Below this temperature, undesirable compounds such as chlorophyll and waxes become insoluble and will not make it into the final extract.
Once the chilled ethanol has been prepared, it is ready to be combined with the cannabis or hemp biomass inside the extraction vessel. The biomass is submerged in the chilled solvent and steeped for several minutes, thereby extracting desirable cannabinoids. Classic extraction principles can also be used where the biomass is quickly washed with cold solvent so that only the trichomes are dissolved.
Post extraction, the raffinate is processed through centrifugal force or steam replacement to leave the raffinate free of residual solvents. The extract and ethanol mixture can be loaded into a rotary evaporator, falling film evaporator, or a membrane filter to recover up to 97% of the solvent. This leaves you with a crude extract that’s ready to use or be further refined through distillation. Many advanced systems like DEVEX are all-in-one solutions. If you are scaling, you can easily start with equipment that does 100 pounds a shift and scale up to 1000 pounds a shift before getting into customized industrial systems. Notably, this scalable size does have stated extra equipment needs (e.g., chillers) and temperature requirements which add to the ancillary costs and contribute to the total cost of operation, not to mention the ethanol cost itself.
Benefits of Ethanol Extraction
Cold ethanol extraction reaches the perfect balance between efficient extraction and optimal safety, which is what makes it such a powerful method for the modern extractor.
Unlike butane and CO2, ethanol does not need to be stored under pressure. And while ethanol is still flammable, it presents less of an explosion risk than butane — meaning it can be stored responsibly at room temperature and pressure in an appropriate non-flammable container. This risk is even further reduced when ethanol is stored at 0°C or cooler.
Not only is the initial cost of purchasing equipment much lower than other methods, but the continuous running costs of ethanol extraction are also comparably economical. According to Anthony DeMeo, professor of extraction at Oaksterdam, ethanol extraction has operational costs around $15 per pound of biomass (not including recapturing ethanol), CO2 around $12 per pound, and hydrocarbon around $11 per pound, assuming an 80% recovery. Again, despite the lower solvent usage costs, you have to keep post-processing costs in mind and niche products you may want to develop. Additionally, high-quality ethanol can be bought slightly diluted with water to reduce costs. Ethanol can be reclaimed via solvent recovery (e.g., rotary evaporator or falling film evaporator) and recycled multiple times before it needs to be replaced with fresh ethanol.
While CO2 and hydrocarbons seem to have cheaper operating costs, it is important to always keep your end products in mind. In a medical market, and specifically in a pharmaceutical market, the products must have a consistent chemical purity. With ethanol, undesirable compounds can be inhibited from co-extracting, resulting in lower operating costs through reduced labor and equipment costs.
Post-Extraction Processing
After performing cryogenic ethanol extraction, you will want to purify the crude oil. Some distillation machines like the VTA 100 can process 3 to 3.5 liters an hour and are designed to run continuously with minimal operator needs. Through distillation you can typically achieve 80% or higher total cannabinoid purification in one run, depending on starting biomass potency. These levels are excellent for formulations in an herbal pharmaceutical market or for more precise formulations in a recreational market.
However, to ensure the purity of medical-grade products for single cannabinoid formulations for pharmacological applications, this end product can be further refined using chromatography to generate higher purity (> 95%) of cannabinoids like THC or minor cannabinoids like cannabichromene (CBC).
As an extractor, trying to match your budget, skill level, and desired output are all important when deciding which style of extraction equipment you want. The need for post-extraction equipment and clean-up processes will play a major role in the quality and costs. Extraction time and throughput plus proper staffing should all factor into your decision-making.
