What is Cannabidiol
Cannabidiol, abbreviated as CBD, a type of cannabinoid, is the main chemical component in industrial cannabis, extracted from female cannabis plants.
The first feature of Cannabidiol is not addictive, and it has pharmacological effects such as antispasmodic, anti-anxiety and anti-inflammatory.
The second characteristic is that it can also eliminate the hallucinogenic effects of tetrahydrocannabinol (THC) on the human body, known as anti-drug compounds.
These two attributes determine the CBD’s greatest value for industrial cannabis.
The CBD was originally an organic compound isolated from Indian cannabis by Adams and Todd in 1940. In 1963 Mechoulam and Shvo measured their chemical structure. The chemical formula of CBD is C21H30O2 with a molecular weight of 314.46 Daltons.
From the structural point of view, CBD has optical activity and cis-trans isomers, and the natural CBDs are all left-handed trans-structures, namely (-)-trans-CBD.
Under normal temperature and pressure, the CBD is white or pale yellow resin or crystal, melting point 66-67 ° C, boiling point 463.9 ° C (760 mmHg), density 1.025 g / cm3, almost insoluble in water, soluble in organic solvents.
Because the chemical formula and molecular weight of CBD are completely consistent with THC, the physical and chemical properties of the two are very close, which leads to the difficulty in extracting CBD from industrial cannabis, which constitutes the technical barrier of the industry.
Cannabidiol extraction technology
At present, the main methods for extracting active ingredients (usually organic compounds) from plants include steam distillation, pressing and extraction.
Among them, the distillation method is suitable for substances with strong volatility, and the pressing method is suitable for extraction of eschar materials which are liquid at normal temperature.
Since the CBD has a boiling point of more than 400 degrees at normal temperature and pressure and is insoluble in water, the extraction method is the most suitable extraction method.
After reviewing the current CBD extraction methods, we can summarize the CBD enrichment/extraction process into the following process, which is divided into four parts, including pre-treatment steps such as pulverization and drying, extraction steps, and concentration after extraction.
A chromatographic purification step and a post-treatment step for the purified sample. Among them, extraction and purification are key steps.
The first step in the CBD extraction process is the selection of raw materials.
The content of CBD in the raw material has a direct influence on the yield and purity of the final extraction. The higher the content of CBD in the raw material, the higher the yield and purity under the same process conditions.
Similar to THC, the content of CBD in various parts of cannabis is usually decreased in the order of bracts, flowers, leaves, stalks and thick stems, and is highest in flowers and leaves of female flowers. Therefore, the processing of the CBD is usually carried out using the leaves.
In the treatment of raw materials, drying and comminution steps are usually included.
The water in the raw material is reduced to 8% or even 5% by heating or drying. The meshing number is usually about 50-200 mesh to increase the contact area with the extraction reagent during the extraction process and improve the extraction efficiency.
There are also companies that use cellulase, pectinase or complex enzymes after drying and pulverizing to destroy the cell wall of cannabis to further improve extraction efficiency.
However, the addition of enzymes also increases production costs.
From the perspective of industrial production, the addition of enzymes may require comprehensive consideration.
Current extraction methods commonly used in CBD include organic solvent extraction and supercritical carbon dioxide extraction.
In addition, there are individual companies that use subcritical water extraction. Most domestic companies use organic solvent extraction.
The main advantages of the organic solvent extraction method are simple operation, low requirements on equipment and low energy consumption. The disadvantages are that the organic solvent is liable to remain, the solvent dissolving ability is constant, and environmental pollution may occur.
Supercritical CO2 extraction
The main advantage of the supercritical carbon dioxide extraction method is that the separation range is wide, and the adjustment of the dissolution ability of the extractant can be achieved by changing the temperature and pressure, but the equipment requirements are high, the energy consumption is large, and the instrument cleaning is difficult.
At present, organic solvent extraction and supercritical carbon dioxide extraction are widely used, and subcritical water extraction is a new technology, which has not been used in industrial production of CBD in China.
Organic solvent extraction
The organic solvent extraction method can also be divided into soaking extraction, reflux extraction and ultrasonic extraction.
Soaking extraction is to directly extract and mix the organic solvent and the material for extraction, which takes a long time.
The reflux extraction is carried out by heating and distilling the leachate, distilling it and then condensing it, and then refluxing it back into the leacher to continue the extraction process. Although the extraction efficiency is improved, the continuous heating may cause the CBD. damage.
Ultrasonic extraction is a method that uses ultrasonic mechanical effects, cavitation effects, and thermal effects to improve extraction efficiency. Ultrasonic extraction can be carried out at a lower temperature, and the extraction speed is fast, the efficiency is high, and the solvent usage is small, which has certain advantages over the former two.
The traditional carbon dioxide supercritical extraction uses pure carbon dioxide gas to reach a critical state under a certain temperature and pressure, showing the characteristics of the fluid and extracting the material.
However, in practice, in order to improve the extraction efficiency, a mixed solvent, called an entrainer, is usually added to the superfluid, which is the main direction of the development of the supercritical extraction method.
CBD concentration and chromatographic purification
The extracted extract is usually concentrated by heating before being purified by a chromatography column, and the extraction solvent is evaporated and removed, and an extract composed of components such as CBD is left.
The effect of evaporation and concentration can remove some volatile impurities on the one hand, and replace the solvent with the mobile phase required for chromatography on the other hand, facilitating chromatographic purification.
The steps of replacing the solvent are more flexible, and the changes are different in different technologies. In some techniques, the method of water sedimentation is used for concentration, and in some techniques, the organic solvent is used for multiple dissolution and concentration.
The extract is dissolved in a solvent using a chromatographic mobile phase and then purified by a column. Purification of the column is carried out based on the difference in properties such as molecular weight and polarity of the different components.
Commonly used column packings include silica gel, macroporous adsorption resin, polyamide adsorption resin, etc., each of which can be subdivided according to chemical composition or crosslinking. Chromatographic elution solvents often use polar or non-polar organic solvents.
Different chromatography columns and different solvents can remove different impurities, and the recovery rates are not the same. In some technologies, a variety of chromatographic columns are combined to purify to improve the purity.
However, in the chromatographic process, the purity is usually not compatible with the recovery rate.
The selection of the column, the choice of the chromatographic solvent and the choice of the chromatographic purification method need to be comprehensively considered.
The chromatographically purified CBD solution also needs to be concentrated to remove the solvent to obtain a higher purity CBD oil or ester. The crystal of the CBD or the CBD sesame oil is then prepared by evaporation, drying or supersaturation.