The CBD extraction and purification process
The extraction of Cannabis plant material and the purification of distinct fractions will be a step-wise process. Each step will result in a smaller amount of material in an increasingly purified form. We will produce pure CBD extract free of all of the possible contaminants in the plant (i.e. other cannabinoids, terpenes, waxes, chlorophyll and any other chemicals). It will also be possible to isolate other cannabinoids (e.g.THC, etc.) from the original extracted material. It is important that the extraction processes are undertaken at low temperatures (<60oC) to retain cannabinoids in their acid form (i.e.to minimize decarboxylation).
Stage 1. Selection and development of the appropriate plant cultivar.
The most appropriate cannabis cultivar will be grown under greenhouse conditions. For CBD isolation and purification, these plants will probably be clones of a cultivar with high CBD (>5%) and low THC (<0.5%). The selection and cultivation of the appropriate cannabis cultivars have been established.
Stage 2. Harvesting of the bud material from the mature Cannabis plants.
The Cannabis plants will be harvested at the time when the level of cannabinoids in the bud material is maximal. The fresh stems (along with the leaf and twig material) are harvested at the optimal time. This material will contain >5% CBD (wet weight).
Stage 3. Drying and milling of the bud material.
The bud material from the Cannabis plants will be carefully dried (50oC for 8-12 hours) to produce a product containing <10% moisture. The dried plant material will then be milled and sieved to a fine powder (1-2mm screen). Each batch of dried Cannabis powder will be mixed to homogeneity, vacuum packed, labeled and stored at 4oC. 100Kg of fresh Cannabis plants will produce about 10Kg of dry leaf material. This material will contain up to 50% CBD and about 1% THC (dry weight).
Stage 4. Primary extraction of the dried and milled Cannabis plant material.
The dried and milled plant material will be extracted at room temperature with a proprietary gaseous solvent to generate a liquid extract of the Cannabis plant (â€œgreen goopâ€). This crude extract will contain the cannabinoids, the terpenes and the waxes (along with chlorophyll and other chemicals). 100Kg of Cannabis plants will produce about 2.5L of this green goop. This material will contain 50-70% CBD (w/w) and 5-7% THC. Alternative solvents include other gaseous solvents (e.g.propane, butane, CO2,etc.) or liquid solvents (e.g. ethanol, methanol, acetone, hexane,etc.). Solvent-extracted material needs to be concentrated by the evaporation of the solvent from the extract. With gaseous solvents, this occurs automatically as the product is returned to atmospheric pressure. With liquid solvent extracts, the solvent needs to be carefully evaporated in order to concentrate the extract. Careful processing conditions (e.g.minimal heating) must be employed to retain the cannabinoids in their acid forms. The choice of the primary extraction solvent requires consideration of the extraction efficacy (getting a large proportion of the cannabinoids out of the plant material), selectivity of extraction (getting the cannabinoids out of the plant material without unwanted components like chlorophyll), etc.The choice of this proprietary gaseous solvent is based on the comprehensive extraction and the minimal presence of residual extraction solvent at the completion of the process. As with many extraction solvents, the green goop obtained contains a significant amount of chlorophyll that will need to be removed as the product is further purified. It may be possible to reduce the amount of chlorophyll by extracting the plant material under cold conditions.
Stage 5. Removal of chlorophyll from the Cannabis extract.
The green goop contains a large amount of chlorophyll that complicates the isolation and purification of other more important groups of phytochemicals from the Cannabis extract. The green goop can be mixed with a solvent (e.g.ethanol) and applied to a resin (e.g.charcoal, alumina, silica) that binds some of the chlorophyll from the crude extract while leaving most of the terpenes, waxes and other chemicals unbound.
Stage 6. Removal of plant waxes from the Cannabis extract.
When the decolourised extract in 5 volumes of ethanol is cooled to –20oC for 2-3 days in a sealed container, the waxes will solidify and can be removed with filtration of the cold ethanol solution.
Stage 7. Fractionation and concentration of CBD from the cannabinoid-enriched material.
There are a number of processes that could be applied to the cannabinoid-enriched material to isolate a CBD-enriched product. These include Supercritical Fluid (CO2) Extraction (SFE), Centrifugal Partition Chromatography (CPC), Crystallization, Molecular Distillation, etc. Ultimately, we are seeking to produce an extract that contains at least 98% CBD.
|Adsorption Chromatography||Low capital cost, Easily Scalable to 1-10Kg of â€œgreen goopâ€ per run||Difficult to achieve 98%+ purity in a single adsorption step.|
|Supercritical Fluid (CO2) Extraction (SFE)||May be able to achieve 98%+ purity in a single step||High capital cost.|
|Centrifugal Partition Chromatography (CPC)||May be able to achieve 98%+ purity in a single step||No experience with this process. High capital cost.|
|Molecular Distillation||May be able to achieve 98%+ purity in a single step||No experience with this process. High capital cost.|
|Crystallization||May be able to achieve 98%+ purity in a single step||No experience with this process. Probably needs a process prior to crystallization. Time to achieve a high purity crystal. Might need several crystallization repeats|
Author Dr. Craig Davis