With interest increasing into the benefits of plant extracts, many companies are seeking better methods to use for extraction.
Though traditional processes present advantages, the use of harmful solvents can have a drastic effect on the quality of the finished oils. CO2 extraction provides an alternative that allows for excellent retention of valuable plant compounds.
Many target compounds are delicate and can be easily destroyed by heat, whereas CO2 extraction offers a delicate method, allowing companies to produce a broad-spectrum oil that most closely resembles the flavor and aroma profile of the original plant material.
Plant compounds that are difficult to extract or too fragile for steam distillation can be extracted using a number of solvent based solutions. Solvents are substances that dissolve a given solute.
In this case, the solutes are the compounds within the plant matrix.
Common solvents currently used are:
Solvents are passed through the chamber and its contents, diffusing through the material and dissolving compounds. If processed incorrectly, several of these solvents can leave behind traces of unwanted chemical residue. Though standards for oils for consumption have become more stringent and require quality testing, there remains a perception among consumers that oils derived from these methods are lower quality or potentially harmful if consumed.
Ethanol is a safer solvent and has many advantages including processing time. However, there are significant disadvantages. Operating costs – given the price of the solvent and the extra infrastructure required to support large volumes of ethanol – can be problematic for many processors. As well, ethanol has poor retention of terpenes, and to avoid co-extraction of chlorophyll, ethanol must be chilled to less than 40 degrees Celsius. This can take a significant amount of energy and time.
This is where CO2 extraction can prove to be a superior solution.
Extraction using carbon dioxide has many advantages, including selectivity. Subcritical CO2 provides a fantastic option for the preservation of delicate terpenes and flavonoids, while supercritical CO2 – having properties of both a liquid and a gas, can be an efficient solvent for the recovery of cannabinoids.
Carbon dioxide is an excellent solvent as a supercritical fluid because:
- It can have a near liquid density
- It has low viscosity and diffuses quickly like a gas
- After depressurizing, it leaves no solvent residue.
Through CO2 extraction, delicate compounds are retained through the process, and a broad-spectrum plant profile can be retained.
MASS TRANSFER & SOLUBILITY
Extracting the compounds of interest from a feedstock’s matrix is most easily accomplished with the assistance of a solvent. Regardless of what starting material is to be loaded into the extraction chamber, success in extraction begins with ensuring the selected solvent and conditions of extraction are a suitable match for the components of interest the operator wishes to target.
Each solute of interest will have a set of ideal solvent conditions for its extraction based on two main areas of characteristics. These are:
- the qualities about the compound of interest that can be targeted to help coax it into solution
- those that help provide the impetus to favour the compound of interest leaving its position in the plant matrix.
In other words, there are both pull factors and push factors governing the behaviour of solutes which can be capitalized upon to help optimize their mass transfer (that is, their movement) from the plant matrix to the solvent.
Carbon dioxide, a non-polar solvent, has compatible characteristics for the solutes of interest in the cannabis industry. Further, it boasts a very wide range of pressures and temperatures at which it maintains appropriate density to act as a solvent while still providing advantages in diffusivity to increase efficiency of plant matrix penetration. Finally, it also lends itself well to dynamic extractions.
Capitalizing on all these factors for a solvent-solute pair will take into account;
- A polarity match between the solute and the solvent;
- Maximizing chemical potential by renewing the volume of solvent in the extraction chamber, that is, ensuring to maximize the natural phenomenon of diffusion from areas of higher solute concentration (the plant matrix), to lower solute concentration (the renewed volume of solvent);
- Tuning pressure and temperature to:
- Find the ideal balance between solvent density and diffusivity;
- Impart enough kinetic energy unto the solute molecules to cause them to want to transition phase to a vapour (that is, to capitalize on their inherent volatility; note that the amount of energy required will be different for each and every compound);
- Ensure conditions are mild enough to avoid thermal alteration of the solutes.
Other factors of importance that will impact and extraction’s efficiency include;
- Structure of the plant matrix;
- Size of the feedstock particles and other pre-processing considerations.
For an extraction orchestrated by a skilled operator, and carried through to completion, carbon dioxide can provide a representative profile of the original components present in the plant. It also imparts a massive advantage in solvent removal in the primary product as it is collected from the extraction equipment.
At the end of the day, CO2 extraction gives consumers an excellent opportunity to experience a satisfying, broad-spectrum product.