The cannabis plant, by nature, possesses inconsistent and unpredictable qualities. Depending on strains and evolution within strains, taste, smell and THC/CBD potency may vary greatly. These inconsistencies will flow into any end product, thereby causing undesirable variations.

In order to produce a consistent product, the THC and CBD components must be isolated and separated from other cannabis components and then infused into the product. Via distillation, this is possible.

 Cannabis distillation is a post-processing extraction technique done subsequent to an initial solvent-based extraction.

In practice, and by way of example, the raw oil (sometimes referred to as “crude” oil) from the cannabis plant will first be extracted via the use of a PX1 or PXP system. Depending on a number of factors, that crude oil will have a THC/CBD concentration of 60-80%.

What is not THC and CBD in the crude oil will be a blend of flavors and smells, known as terpenes, and a variety of other plant-based components from vitamins, antioxidants and additional consumable substances.

In order to further purify the oil, it will then be subject to the distillation process with a specialized commercial distillation unit such as the CDU 1000. The distillation process isolates specific compounds, such as THC and CBD, thereby producing a refined oil (or “distillate”) of over 90% purity.

The remaining terpenes and other non-THC/CBD compounds will have an insignificant effect on the flavor and smell of the product. By targeting THC and CBD, for example, one can see how flavor, smell and potency may not be controlled by the producer.

With the cannabis market raking in $6.7 billion in 2016 in the U.S. and Canada and the market expected to hit $20.2 billion by 2021, processors are looking for the best ways to increase their product quality and grow profit margins.

To produce the highest-quality products, processors are looking to more traditional methods of extraction and isolation. Using techniques long established in the botanical, chemical and distilled spirits industries, cannabis processors have several options to improve their manufacturing techniques.

Applying Rotary Evaporator To Cannabis Processing

A fixture in many labs, the rotary evaporator is a common tool for solvent removal. The process allows the solvent to be removed in a controlled manner under vacuum.

It’s also easily scalable, ranging from smaller bench top flasks up to 5 liters to pilot scale, using flasks of 20 liters and more. This flexibility makes it very adaptable when processing cannabis.

As the pressure is reduced using a vacuum pump in the rotary evaporator, the boiling point of the solvent, ethanol in this case, is lowered.
Typically, the distilling flask (A) is filled to 50% volume. The water bath (B) is heated to 30-40°C. The condenser temperature (F), controlled by a recirculating chiller, is set to -10°C to 0°C. Once the water bath and condenser have reached the set points, the distillation flask is rotated from 150-200 rpm. This creates a thin film on the upper surface of the glass cylinder, which increases the solution surface area and enhances the solvent evaporation rate. Applying an appropriate vacuum to the system (H) lowers the boiling point.

To achieve a recommended target, set the vacuum to achieve an ethanol vapor temperature of 15-20°C. As the ethanol evaporates, it will condense and collect into the distillate flask (G). Optimization of the parameters allows for easy reproducibility.

Things To Watch For When Using Rotary Evaporators

While it may be tempting to try to tweak the process by increasing the evaporation rate by lowering the vacuum and/or increasing the water bath temperature, this will cause capacity overload on the condenser. Doing this actually causes the evaporation rate to exceed the condensation capacity of the recirculating chiller.

This causes ethanol vapor to pass through the condenser and into the vacuum pump. Cannabis extracts require lower water bath temperatures to minimize thermal decomposition. So the condenser temperature of -10°C to 0°C will require a chiller with adequate cooling capacity at those low temperatures.

There are other ways to increase throughput while still maintaining quality. There are a variety of options for automatic vacuum control and refilling accessories, both manual and automated, that can be added to rotary evaporators.

To learn more about improving your cannabis processing, read our whitepaper, “The Cannabis Workflow and the Importance of Temperature Control.”