Low Temperature Short Contact Distillation Path

by | Aug 10, 2018

Various Extraction techniques are used to separate the bioactive components of cannabis plants and remove them from the plant matrix. The cannabis extraction techniques are often used to isolate specific desirable compounds.

The cannabis (marijuana, hemp) plant has been used for medicinal purposes for millennia. In addition to terpenes and flavonoids, over 100 types of therapeutically active compounds known as cannabinoids have been identified in these plants. The two most important and well-known cannabinoids are tetrahydrocannabinol (THC) and cannabidiol (CBD).

CBD is non-psychoactive and has been clinically demonstrated to have analgesic, antispasmodic, anxiolytic, antipsychotic, antinausea, and anti-rheumatoid arthritic properties. THC is psychoactive and, as such, can be used recreationally.  It is, however, also an extremely potent therapeutic compound, which is used, for example, by cancer patients to reduce nausea, vomiting, pain, and to stimulate appetite.

Due to the significant synergy between different cannabinoids and terpenes, it is considerably more beneficial to utilize natural cannabis-based preparations, rather than any single purified or synthetic cannabinoid and hence a nonselective extraction method is advised.

In recent years, concentrated extracts of cannabis plants (shatter, crumble, budder, wax, oil) have become very popular because they allow many convenient routes of administration. Concentrates are viscous and frequently very sticky substances that can be produced by extraction with solvents such as petroleum hydrocarbons (e.g., propane, butane, hexane, petroleum ether, naphtha), subcritical or supercritical CO2, and alcohols (e.g., ethanol, isopropanol).  Extraction is followed by solvent evaporation, which yields the “pure” and very potent concentrate. 

Several common forms of cannabis extraction rely on a solvent. In brief, the cannabis plant material is soaked in solvent or a solvent system, the plant material is then removed, the liquid filtered, and the solvent is removed with some form of evaporation.

It is imperative that, whatever the method followed for the extraction, the solvents are to be removed to get a highly concentrated extract which can exert significant pharmacological effect and can be easily formulated into a drug delivery route. There are several separation techniques, including conventional distillation, for extracting heat sensitive compounds from herbs. However, some compounds may have high boiling points at which other compounds might be adversely affected.

|Low Temperature Short Contact distillation path|

We, at Clean Green Biosystems, developed a PLC-SCADA based method of separating the bioactive molecules from herbs and from cannabis, called Low-Temperature Short Contact distillation path, which is a combination of forced circulation evaporation and molecular distillation process.

Once the Solid-Liquid extraction is completed, the miscella is collected in a tank. This miscella contains all the phytochemicals of the cannabis plant and the solvent/solvent system. This miscella is taken from the evaporation through the forced circulation evaporator and molecular distillation system. Depending upon the miscella volume, one can have a single stage, double stage or multiple stage system.

In forced circulation evaporation the miscella is circulated through tubes or tube bundles which are enclosed in a shell at high pressure by means of a pump. Steam is introduced into the calendria to heat the miscella in the tubes or tube bundles. A pump sends the liquid to the tube with a positive velocity. As the liquid moves up through the tube it gets heated and begins to boil. As a result, the vapor and liquid mixture rushes out of the tubes at a high velocity. Forced circulation of the miscella creates some form of agitation. When the miscella leaves the tubes and enters the vapor head, the pressure falls suddenly. This mixture strikes the deflector to effective separation of liquid and vapor. This leads to the flashing of super heated miscella. Thus the evaporation is effected.

Figure 1. Forced Circulation Evaporation

The vapor enters the cyclone separator and leaves the equipment through a condenser. The solvents thus collected shall be reused for the next cycle of extraction. The concentrated liquid enters the pump for further evaporation. Finally, the concentrated product is collected.

Sufficient liquid height (submergence) is maintained above the liquor inlet on the vapor body and above the heat exchanger tubes to suppress mass boiling in the inlet and prevent boiling at the tube surface. This is necessary to prevent precipitation in the tubes which would lead to fouling of the heat transfer surface.

A high circulation rate is provided for adequate tube velocity to achieve good heat transfer. Therefore, lower temperature rises are assured which minimize super saturation of the solution.

The output of forced circulation evaporation is concentrated miscella, which contains high amount of cannabis phytochemicals. This is further concentrated in the molecular distillation unit.


Figure 2. Molecular Distillation

Molecular distillation is an advanced vacuum distillation method performed by short-path evaporators. The distance between the evaporator and condenser is extremely reduced, which results in minimized pressure drop. Heat sensitive material meets heat for a short time under high vacuum, thus low, or no decomposition occurs.

Molecular distillation is considered the safest mode of separation and to purify the thermally unstable molecules and related compounds with low volatility and elevated boiling point. The process distinguishes the short residence time in the zone of the molecular evaporator exposed to heat and low operating temperature due to vacuum in the space of distillation.

The molecular distillation process is carried out at a very low pressure so that the distance between hot and condensing surface is less than the mean free path of the molecules. The number of stages of molecular unit integration depends on the volume of miscella to be processed.

Molecular distillation is applied to thermally sensitive high molecular weight materials (range of 250 – 1200). The molecular weight of cannabinoids is 628.938; THC 314.45, Cannabidiol 314.46) The contact times in commercial units may be low as 0.001 seconds. The film thickness is of the order of 0.05 – 0.1 mm which is created by suitable vipers which are rotated on the cylindrical vessel.

A molecular distillation unit has a feed distributor, which distributes the miscella evenly as a thin film by the vipers , which increases the evaporation surface. The evaporated solvent is condensed in the internal condenser using chilled water and the thick/concentrated miscella is sent out by means of the vapers.

The solvent /solvent system is collected through an external vent condenser and used to extract further materials. The highly concentrated cannabis extract is thus collected for further processing or direct usage.

This method gives a highly bioactive cannabis extract which contains intact cannabis phytochemicals as the overall process sequence is done in low temperature and short residence time with heating elements.

The entire process is controlled by PLC-SCADA software with all process control systems like temperature control, flow control, vacuum control and product viscosity.