How vacuum distillation of cannabis is performed
CBD is growing in popularity and accessibility. Forbes reports that the market for CBD sales is expecting to surpass $20 billion by 2024. Manufacturers are developing increasingly sophisticated processes to increase production quality and quantity of this oil distilled from cannabis. While the process of distilling CBD oil from cannabis is similar to that of other products such as essential oils, the unique properties of cannabis require special treatment.
Vacuum Distillation: Improving CBD Production
Vacuum distillation is a short path molecular distillation similar to the processes used for food oil purification. The goal is to isolate the cannabinoid components and remove the terpenes. This ensures that the oil retains its potency for antianxiety and other medicinal purposes, but is odorless, flavorless, and does not have psychoactive effects.
Using vacuum to turn THCA into THC
Before distillation can begin, the THCA (tetrahydocannabinolic acid) must be decarboxylated, producing THC. This is accomplished by holding the cannabis oil at 110c to 135c for up to an hour. Higher temperatures result in higher reaction rates, but this can cause other undesired effects.
Decarboxylation can be done in air at atmospheric pressure, but the THC produced then oxidizes at these higher temperatures. This reduces yield and produces other unwanted cannabinoid compounds. Decarboxylation under vacuum prevents this oxidation by removing most of the oxygen from the reaction environment. This produces high quantities of CO2 gas as a product daughter of the reaction. Only a slight vacuum is required for this step, and it can easily be achieved with a regenerative blower.
Related: Want to find out more about how vacuum pumps contribute to medical cannabis distillation? Click the button below to download a free copy of our eBook, How Vacuum Impacts Cannabis Processing.
The distillation is done at vacuum to reduce the temperature needed to vaporize heavier cannabinoid molecules. There are two distinct parts to the vacuum distillation step:
- The terpene cut (the "first pass").
- The cannabinoid cut (the "second pass").
The First Pass: Cutting Terpenes
Why cut terpenes?
- Terpenes are lighter hydrocarbon molecules that occur naturally in the cannabis plant. There are many different terpene species, each of which has unique characteristics. It is the terpenes that give a particular strain of cannabis a certain flavor or aroma profile.
- Terpenes also are widely thought to affect the medicinal properties of cannabis and are widely believed to create differences in the psychoactive effects that a particular strain has on the user.
- Terpenes are both loved and hated because of their odor. For those people who like the aromas of cannabis when smoked, they are highly desirable. For those who do not like the aroma of cannabis smoke or smell of the raw plant, the terpenes are a huge turn-off. As cannabis oils become more mainstream, it is likely that the majority of consumers will not want the aromas. Therefore, the terpenes must be stripped out of the bulk oil.
Things to consider when cutting terpenes
- Most terpenes are stripped from the cannabis oil at pressures between 200mtorr and 500mtorr depending on at what temperature the cannabis oil is held in the evaporator during the process.
- The terpenes represent a substantial fraction of the total oil makeup and therefore can outgas quite a bit of vapor during this process. High outgassing means you need much higher speeds of vacuum pumping to maintain the pressures in the target zone.
- You also need to consider how restrictive your vacuum lines are at this point.
- Additionally, if your measurement instruments are located in the wrong place, flow restrictions between the gauge and the evaporator can cause the actual pressure to be misreported. As this is a crucial measurement, be sure to arrange this equipment effectively.
Optimizing your equipment
Many small distillation systems (usually blown glass type short path, wiped film systems) have very small vacuum pumps backing a 50mm inlet diffusion pump. Diffusion pumps are meant to pump at high vacuum — that is at pressures less than 1mtorr (1micron or 1 x 10-3 torr). In fact, when pressures at a diffusion pump inlet are higher than 50mtorr, the diffusion pump will not operate effectively. At these pressures, the pump will tend to both backstream oil into the inlet piping due to high turbulence and fore-stream the diffusion pump oil into the backing pump. This results in an expensive loss of oil.
To add insult to injury, the backing pump—which is connected to the diffusion pump exhaust—is often the only roughing pump in the system. This means that all of the gases pumped by this pump must pass through the small and complicated geometry inside the diffusion pump, which is a huge restriction in the pumping speed. This causes a radical restriction in how much outgassing from the terpenes can be pumped through the roughing pump, thereby severely restricting the feed rate of bulk oil through the system during the first pass.
Be aware that the terpenes are condensable and are thus best pumped by condensing them. However, achieving the condensing conditions that raise throughput of the system is often either overlooked or difficult to achieve or maintain. A very good condenser with excellent cooling capacity and some means to slow or remove fouling of the condensing surfaces could have a profound effect on the efficiency of the system during the terpene cut.
To optimize the operation of your system, it is advisable to consult with someone like a Leybold engineer. They can help you improve the use of your current equipment rather than buying all new equipment. Find out more about the tailor-made vacuum solutions our engineers can advise on, on our Vacuum Systems product page.
Decrease production time on the first pass and increase profits
Optimizing your system could mean faster and more efficient production. This provides an opportunity for substantially higher profits.
The terpene cut (or first pass) can take roughly as long as the cannabinoid cut (or second pass) when using the small vacuum pumps usually equipped on these small systems. Reduce the cycle time of the terpene cut by raising the throughput on the roughing pump and by installing a dedicated roughing line. This will radically reduce the overall distillation cycle time, maybe by 30 to 40 percent.
If production throughput on the distillation system is expanded by one extra kilogram per day, at $5K per kilogram, that adds up to potentially $1.8M per year in extra productivity ($5,000 x 365 days per year).
Related: Read about how freeze drying has impacted cannabis production in our blog post, Drying Cannabis for Retail or THC & CBD Oil Extraction.
The Second Pass: Cutting Cannabinoids
Cannabinoids are isolated through this process to create a pure and potent product.
The cannabinoid cut has a target pressure of 0.1mtorr to 10mtorr, again depending on the temperature of the oil in the wiped film evaporator. The lower the temperature, the better the THC oil quality. The lower the pressure, the lower the temperature in the wiped film.
Here the condenser becomes more problematic as the THC oil becomes more viscous. At the cold temperatures of the condenser, the THC oil can create fouling issues that can radically reduce the condensing efficiency of the condenser, which then reduces the throughput of the system overall. A degrading performance of the condenser results in oil being drawn into the diffusion or turbo pump. Cannabinoid oils that are drawn into vacuum pumps during the distillation process, whether it be diffusion pump, turbo pump, or roughing pump cannot be used and is discarded.
A diffusion pump or turbo pump is recommended at this point to provide a pressure that will allow for evaporation of the THC oil from the wiped film evaporator at a sufficiently low temperature to ensure the best final product quality. Having adequate pumps and condensers decreases the waste produced in the second pass, meaning you gain more sellable product.
Vacuum Distillation: the Competitive Edge
As the market for CBD oil and other cannabis products is rapidly expanding, so is the competition. Vacuum distillation is the next step toward creating a high-quality product at a rate that will keep up with demand. Leybold can help you assess and improve your current system to increase productivity and improve the purity of your product at the same time. See a customer success story that shares how we did just that in our blog post, The Green Rush.
Get in touch with our customer service team today for expert advice and creative solutions and join the Leybold network. Click the button below to begin the conversation.