Cannabidiol is of particular interest in the medical community today, with many studies showing its efficacy in the treatment of epilepsy. A broad spectrum of pre-clinical research in other fields further suggests that CBD has therapeutic potential for many other conditions and health complaints.
As public and medical interest in the compound increases, so does the need for an effective method of isolating it. In this article, we examine methods for extracting and isolating CBD from cannabis plants and discuss the important role of short path distillation in obtaining high purity CBD.
Cannabidiol, commonly known as CBD, is one of many cannabinoid compounds found in the cannabis plant. The compound has found recent popularity after several studies have indicated its potential for the treatment of numerous medical conditions. CBD’s potential to treat epilepsy is of particular interest, but recent evidence suggests it may exhibit useful analgesic, anti-inflammatory and antipsychotic effects suitable for the treatment of a broad range of conditions.
In 2018, the World Health Organisation published a critical review of cannabidiol. The review noted that CBD has been demonstrated as an effective treatment of epilepsy in multiple trials, has the potential for the treatment of other conditions, and exhibits a good safety profile with no indication of abuse or dependence potential.1 The therapeutic potential of CBD is currently of great interest within the pharmaceutical and medical community. As this interest level grows, so too does the importance of effective and efficient methods for extracting and purifying CBD for therapeutic use.
CBD can be obtained from many varieties of cannabis plants, including those that contain low quantities of THC, the compound responsible for the psychoactive effects of cannabis. Plants with low or zero THC content are colloquially known as hemp. The ability to derive CBD from hemp is important: many countries, including the USA, exercise strict legal control over plants containing high concentrations of THC, but the growth of hemp and subsequent extraction of CBD generally remains legal. In the USA, for example, pure CBD derived from a THC-rich plant is illegal, but a chemically identical product derived from hemp is legal.2 Consumers, and regulations require a high purity CBD with testing that proves potency, no presence of residual solvents, heavy metal, or pesticides just to name a few. Because of the growing market and the consumer demand for a good product, many manufactures have researched and refined how CBD products are produced.
Isolation of CBD and other cannabinoids from both high THC containing plants and Hemp requires six main steps: extraction, winterization, solvent recovery, decarboxilcation / devolatized, fractional distillation, and isolation. CBD compounds can be extracted from the plant via a solvent. The product recovered from the extraction can be consumed as is, but it is an impure mixture of lipids, terpenes, possibly chlorophyll, and multiple cannabinoids. Other steps, including fractional distillation, allows for a chemical purity that is wanted or required by medical/pharmaceutical applications.
Fractional Short Path Distillation is a widely-used technique throughout the chemical industry – especially in petrochemicals. This is a process which separates a liquid mixture into its components on the basis of boiling points. Due to the different boiling points of the various compounds (“fractions”) present in a mixture, they evaporate at different temperatures, allowing fractions to be isolated.
Short path distillation is a technique where the distillates are only required to travel a very short distance between the evaporation vessel and the condenser, so the compounds present are exposed to high temperatures for the shortest possible amount of time.
Distillation of cannabinoids is complicated by the fact that CBD is prone to heat degradation.4 This makes ordinary distillation difficult, as the heat required to boil each fraction of the extracted oil can degrade the cannabidiol. One solution to this is to carry out short-path distillation at a lower pressure.
Fractional Distillation of CBD via short path distillation at low pressure (under a vacuum) minimizes the exposure of CBD to higher temperatures that would be needed without a vacuum and thus maximizes its yield. Lowering pressure in the distillation vessel reduces the boiling temperature of the distillates, thus reducing the temperature required to separate any given fraction. Carrying out short path distillation at low pressure allows for manufactures to obtain high purity CBD without the need for high temperatures that could degrade the product which in return loses the manufacture money.
An additional advantage of short path distillation at a low pressure is the small size of the required equipment, giving a very small footprint in labs where space is valuable. Short path distillation can achieve yields of up to 99.9% CBD while taking up a fraction of the space of conventional fractional distillation equipment.5,6
Glas-Col manufactures a variety of high-quality equipment suitable for short path distillation of CBD and other compounds. As the first company to manufacture heating mantles, Glas-Col understands the importance of precise and uniform heating in chemical procedures. Glas-Col heating mantles are built for safe and efficient heat transfer, and the StirMantle™ has an inbuilt electromagnetic stirrer which is ideal for evenly distributing heat within a distillation vessel to achieve controlled temperatures.7 The motor-driven StirMantle™ can stir very viscus substances, like crude oils, which works perfectly with CBD manufacturing. Glas-Col also manufactures a range of precise digital temperature controls which can be used in conjunction with mantles to provide accuracy of 1.0 °C, enabling equipment to be used for precise distillation procedures.8
Glas-Col offers only part of what is needed for the 6-step process to obtain a pure isolate. Glas-Col has information on turn-key set-ups if that is what you are looking for.
References and Further Reading
- Geneva. CANNABIDIOL (CBD) Critical Review Report - World Health Organisation.
- Now That Hemp Is Legal, Is Cannabidiol (CBD) Legal Too? | Psychology Today. (Accessed: 21st March 2019)
- The Cannabis Workflow and the Importance of Temperature Control - Julabo Temperature Control. Nahler, G., Grotenhermen, F., Zuardi, A. W. & Crippa, J. A. S. A Conversion of Oral Cannabidiol to Delta9-Tetrahydrocannabinol Seems Not to Occur in Humans. Cannabis Cannabinoid Res. 2, 81–86 (2017).
- What is Short-Path Distillation? Available at: https://www.azom.com/article.aspx?ArticleID=17242. (Accessed: 21st March 2019)
- The Benefits of Short-Path Distillation. Available at: https://www.glascol.com/benefits-of-short-path-distillation. (Accessed: 21st March 2019)
- Aluminum Housed Stir Mantle. Available at: https://www.glascol.com/series-tm-stirmantle. (Accessed: 21st March 2019)
- Glas-Col Precision Controls. Available at: https://www.glascol.com/precision-controllers. (Accessed: 21st March 2019)