Cannabidiol (CBD), an extract that many use as an anti-anxiety or relaxation tool, comes from the Cannabis sativa plant and cannot be divorced from this original source. Cannabis sativa has many different variations, and not all of these contain significant amounts of CBD. Prior to the gradual ending of cannabis prohibition in many locales, CBD was practically eliminated from the commercial black market to maximize profitability of the psychoactive cannabinoid content of the plants through selective breeding, according to many of the black-market growers I have spoken with throughout the years. The reason CBD is now widely accessible is most assuredly due to the change in social perceptions of this once-outlawed plant and the legalization of this plant in many locales. Without cannabis legalization, CBD would be difficult to acquire—and there would be no testing to ensure that consumers receive the product they are paying for.
Before any CBD oil, THC tincture, weed butter or cannabis concentrate can be bought, first, it must be extracted. This is the job of cannabis extraction equipment, the machines that remove the coveted cannabis compounds from the plant’s matrix .
And just like any other piece of kit, an inevitable question arises when considering extraction machines: which one’s the best value for money?
Cannabis Extraction Equipment
Since its invention in 1950, the rotary evaporator has been a ubiquitous scientific tool for the use of solvent removal. The rotary evaporator enables the removal of solvent in a controlled manner under vacuum. Sizes range from bench top (to 5 L flasks) to pilot scale (20 L and up). Reducing the pressure in the rotary evaporator by a vacuum pump lowers the boiling point of the solvent to be removed; specifically ethanol in the case of cannabis extract processing.
Typically, the distilling flask is filled to 50% volume. The water bath is heated to 30-40°C. The condenser temperature, 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 round glass flask, which increases the solution surface area and enhances the solvent evaporation rate. Applying an appropriate vacuum to the system 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. Optimization of the parameters allows for easy reproducibility.
Things to watch for: Increasing the evaporation rate by lowering the vacuum and/or increasing the water bath temperature can lead to capacity overload on the condenser. The evaporation rate can exceed the condensation capacity of the recirculating chiller. In this case, ethanol vapor will pass through the condenser and into the vacuum pump. Cannabis extracts require lower water bath temperatures to minimize thermal decomposition.
Thus, the condenser temperature of -10°C to 0°C will require a chiller with adequate cooling capacity at those low temperatures.
Rotary evaporator manufacturers have multiple options for automatic vacuum control and refilling accessories (manual and automated) to increase throughput.
Falling Film Evaporation
Large volumes of cannabis ethanol extract can be concentrated utilizing a falling film evaporator. Falling film evaporators are essentially vertical shell and tube heat exchangers. While placed under vacuum the ethanol solution flows down an externally heated tube or tubes causing the ethanol to vaporize. The ethanol vapor collects in a condenser / cold trap while the higher boiling cannabis extract flows down the walls of the tube into a collection vessel.
This method provides a high capacity evaporation rate with a short heat exposure time to the extract. Benefits of this evaporation method include limited heat exposure to the extract and the possibility of continuous operation.
This apparatus requires properly sized heating circulators to facilitate the ethanol vaporizationand chillers to condense the ethanol vapors.
Isolation of high purity THC or CBD for medicinal and recreational applications requires additional processing. For CBD, various cannabis plant strains now produce higher amounts of CBD. Alternatively, hemp can be used as the starting material. Reduction in THC content is important to eliminate the psychoactive high effect to yield a product rich in CBD for anti-inflammatory, anti-seizure and other indications.
Distillation methods can isolate enriched component fractions of extracts. Since terpenes, THC, and CBD have high boiling points (156-250°C; 312-482°F), distillation under atmospheric conditions is undesirable. Exposure to oxygen at these high temperatures can promote oxidation and prolonged heat exposure leads to thermal decomposition. By applying a vacuum, the boiling points are lowered. Vacuum conditions remove oxygen, thus eliminating product oxidation while lowering the boiling point temperature to lessen heat exposure.
A short path distillation apparatus with a multi-position receiver facilitates component isolation. The oil is heated in a flask under vacuum (typically with a magnetically stirred hot plate) with a short path distillation attachment. The condenser is cooled with a recirculating chiller to provide cooling for condensation of the component vapors. As the vapor temperature increases, indicating a new compound/mixture fraction, the multi-position receiving flask is adjusted to isolate the different fractions of terpenes, THC, and CBD.
To improve results over the short path method, a longer fractionating column can be installed between the vessel with heated oil and the condenser apparatus. This can consist of various types of columns (Vigreux, Oldershaw, etc.), enabling finer separation of the components. The added length of the fractionating column with protrusions, trays, or packing material causes the vapor to equilibrate with the liquid state, thus providing a refined separation of the components.
Wiped Film Distillation
This variation of short path distillation can operate in batch or continuous modes. While under vacuum, the oil is introduced to the top of a heated vertical cylinder. As the oil enters the cylinder, it encounters rotating wipers or rollers that create a thin film on the heated surface. A long, slender condenser in the middle of the apparatus, cooled with recirculating fluid, condenses the vapor. Receiving vessels collect the condensate and the high temperature residue at the bottom.
Reduced exposure time of the oil to high temperature conditions is the key benefit of this technique. It can also increase productivity if the apparatus is configured to operate in a continuous mode.
A recirculating heater provides temperature control of the feed container and outer jacketed wiped film body. Refrigerated circulators cool the condenser and vacuum trap.
Process optimization of the feed rate, vacuum and temperatures must be conducted to yield the desired component composition in the distillate.
All vacuum distillation fractions might require further refinement by repeating the distillation process to achieve the desired purity and composition.