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Medical

Cannabis Oil Distillation

Pharmaceutical cannabis contains hundreds of therapeutic compounds. Used for millennia, the plant offers healing and relief for a wide variety of ailments, and research has shown that  the different components work together synergistically to provide more medical benefits than one component alone [1],[2].

 

However, the ability to distill cannabis extract holds many useful applications. Separating terpenes, phytochemicals, waxes, starches, and cannabinoid compounds has been crucial in studies linking substances to specific beneficial effects. Distilled cannabinoids and other chemical components of the plant can be used to create medicines with precise and standardised dosages. This also allows for the recombination of cannabinoids and terpenes based on desired synergistic effects.  Furthermore, oils used for vaping can be purified of harsher ingredients and become harmless to inhale.  Purified cannabinoids have been shown to have bronchial dilatory effects, providing relief for asthma and other lung conditions [3].

 

Cannabis oil distillation usually refers to the process of “short path” distillation, which is an evaporation/condensation process performed under vacuum, with a short distance between the evaporator and the condenser.  Operational efficiency is maximised by this “short path” due to the relatively heavy molecular weight of the cannabinoids.  Variations in system design can affect flow rate, the amount of material capable of being processed at one time, and the amount of time the target compounds are exposed to heat.

 

Although some complex distillation systems are capable of yielding small amounts of THC or CBD isolates, they are not practical because of the very similar boiling points of these compounds.  THC has a boiling point of 157°C, while CBD vaporisation occurs between 160-180°C.  The most effective way to truly isolate a single compound from among the hundreds found in cannabis resin is through a technique called Centrifugal Partition Chromatography (CPC), which we will explore in detail in next months issue. Here, we explain the chemistry behind the entirely different process of distillation, discussing various methods and their suitability according to one’s production goals.

 

 

Starting Material

 

The starting material for any distillation  is a full-spectrum cannabis concentrate, which may have been extracted with or without the use of solvents. If this “crude” oil was extracted using alcohol or hydrocarbon based solvents, a rotary or falling/wiped film evaporation process should already have been applied to purge the solvent and recover it for further use.  This evaporation and recovery of solvent used in the initial extraction is often misrepresented as distillation.  However, with the exception of CO2 and solvent-less extracts, there will always be trace amounts of solvent still contained within the extract after this evaporation process.  Short path distillation rids the concentrate of all solvent.  The process also requires no additional solvent, as it runs at temperatures above 120°C; the concentrate flows easily when heated to these levels.

 

Waxes, lipids, phytochemicals, starches, and terpenes are separated from cannabinoids in distillation.  If a crude extract has already been “winterised” (a process described in detail in our previous extraction articles), a large portion of the waxes and lipids will have already been removed.  Distillation of a winterised extract will result in a cleaner, clearer, and more concentrated oil, with less passes necessary through the distiller, compared to starting material which has not been winterised.

 

 

Batch Mode Distillation

 

A “batch-mode” short path distillation set-up is the simplest and cheapest way to produce distillate.  In this system, an evaporator flask loaded with the starting material is attached to a condenser head and vacuum pump.  The condenser is connected to multiple collection   flasks at different distances.  The first collects the most volatile materials with the lowest boiling points, the residual solvent and monoterpenes. Another flask captures the cannabinoids, and a third chamber receives the waxes, lipids, chlorophyll and other compounds which have the highest boiling points.

 

Although this method is the most simple, the concentrate must be exposed to heat for an hour or more in order to achieve efficient separation. This long “residence time” in the evaporation stage will contribute to the thermal degradation of the target compounds. Also, batch mode does not allow for a “continuous flow” system, in which starting material can be continuously added.  Large batch-mode set-ups also lose efficiency and require even more evaporation time to process all the material.

 

Falling/Wiped Film Distillation

 

Falling and Wiped Film distillation technology address many of the issues with typical batch-mode processes.  These designs feature a cylinder in a heat jacket, so that the inner wall acts as the evaporator, and an internal condenser runs down the middle of the cylinder.  The distance between the evaporator and internal condenser is very small.  As the crude concentrate enters the evaporator, it begins to “fall” down the inner wall due to gravity.

 

By spreading the feed material as thinly and evenly as possible over the inner wall, surface area is maximised and more target molecules are vaporised and can travel the short distance to the condenser.  In a falling film system, small rollers are used to spread the concentrate evenly over the evaporator.  Wiped film improves upon the rollers by using “wipers”, built with slight downward angled slots, optimising thin film turbulence, and propelling the material in a circular and downward path across the evaporator.

 

Terpenes and residual solvent are the first substances to vaporise.  In falling and wiped film processes, these compounds are captured and fed into a separate condenser unit, kept at a lower temperature than the condenser in the main column.  The residual solvent is directed and condensed into a cold trap, while the terpenes condense at a slightly higher temperature and are collected in a different vessel.

 

In the main column, cannabinoids are vaporised and condensed by the internal condenser, while the waxes, lipids, and starches remain on the evaporation wall, due to their higher boiling point. These non-cannabinoid materials fall into a one collection vessel, while the cannabinoids collect in a different chamber.

 

These set-ups allow a continuous flow rate of feed material, so one can process more material in a shorter amount of time. Multiple passes in these machines will increase the cannabinoid purity of the final product.  After two or three passes, purities of 90-97% are achievable.  If one wishes to separate THC or CBD at this stage, filter-dryer systems can be  used which yield crystallised isolate [4].

 

 

Spinning Band Distillation

 

Spinning band distillation is the most complex and expensive system design for distilling cannabis oil.  The apparatus utilises a fractionating column with a spinning helical band.  As the feed material evaporates, it travels upward, and the rapidly rotating band forces close contact between the vapour and any liquid which has condensed onto the band.

 

As usual, terpenes and residual solvent are the first compounds to vaporise; they are collected in a similar way as in the falling and wiped film systems.  The remaining vapour consists of one or more target components with similar boiling points, while the condensed liquid will be a mix of cannabinoids and undesired compounds such as chlorophyll, waxes, etc. The intimate contact between vapour and liquid caused by the spinning band, creates zones of equilibrium between the liquid and vapour, called “theoretical plates”.  The higher the number of theoretical plates, the more precisely and efficiently separation occurs.  The liquid refluxes back into the boiling flask while high purity vapour travels to the condenser and collection vessel.  Once back in the evaporator, the liquid is vaporised again, and more pure cannabinoid vapour can travel to the collection chamber.  This process repeats until the cannabinoids are fully separated from the other substances.

 

Because of the multiple distillations occurring in a single cycle using this system, material usually does not require multiple passes to achieve 90+% cannabinoid purity, as in batch mode or falling/wiped film methods.  However, if one wishes to isolate THC or CBD, one can take the product from the first spinning band distillation, and run it through another spinning band apparatus tuned to the right temperature to separate these compounds from each other.  Because the boiling points of THC and CBD are so close, the system must be capable of very precise temperature tuning, and the yields will be small.

 

 

By Sama’a Djomehri

 

References

 

[1] Ryuichi Murase, Rumi Kawamura, Eric Singer, Arash Pakdel, Pranamee Sarma, Jonathon Judkins, Eiman Elwakeel, Sonali Dayal, Esther Martinez‐Martinez, Mukkanti Amere, Ramesh Gujjar, Anu Mahadevan, Pierre‐Yves Desprez, Sean D McAllister; “Targeting multiple cannabinoid antitumour pathways with a resorcinol derivative leads to inhibition of advanced stages of breast cancerBritish Journal of Pharmacology,Volume171, Issue19, October 2014, p. 4464-4477

 

[2] Sandra Blasco-Benito, Marta Seijo-Vila, Miriam Caro-Villalobos, Isabel Tundidor, Clara Andradas, Elena García-Taboada, Jeff Wade, Stewart Smith, Manuel Guzmán, EduardoPérez-Gómez, MaraGordon, Cristina Sánchez; “Appraising the ‘entourage effect’: Anti-tumor action of a pure cannabinoid versus a botanical drug preparation in preclinical models of breast cancer”; Biochemical Pharmacology, Vol. 157, November 2018, pgs. 285-293

 

[3] Grassin-Delyle S1, Naline E, Buenestado A, Faisy C, Alvarez JC, Salvator H, Abrial C, Advenier C, Zemoura L, Devillier P.; “Cannabinoids inhibit cholinergic contraction in human airways through prejunctional CB1 receptors”, British Journal of Pharmacology, 2014 Jun; Vol. 171(11), pgs. 2767-77

 

[4] https://www.popeinc.com/still-products/nutsche-filters-dryers/

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