CBD isolation is the final step in a long process of extracting and manufacturing CBD products. The steps that are involved in the isolation process are as follows:
1. Selection of drying and processing of high CBD hemp biomass;
2. Decarboxylation of hemp;
3. Extraction of CBD oil from hemp;
4. Refinement of CBD oil to remove contaminants;
5. Distillation of refined CBD oil for a more concentrated mixture;
6. Chromatography for pure CBD from distillate;
7. and crystallization of CBD to further purify.
• When selecting hemp biomass, farmers look for the best plants and flowers that will provide the highest CBD concentration.
• If chromatography is used, available methods include supercritical CO2 chromatography, High-Pressure Liquid Chromatography (HPLC) using solvents such as pentane, flash chromatography, and rotary chromatography. Using CO2 is preferred because it doesn’t leave behind any toxins.
• Then, the refined CBD oil is distilled by way of winterization or short path distillation. Sometimes this step comes before chromatography.
◦ During winterization, elements that are harder to get rid of such as fats, waxes, and lipids are removed from the extract. Here the oil is mixed with 200 proof alcohol, and placed in a deep freezer overnight. It is then run through a filter paper the next day to remove unwanted substances.
◦ In short path distillation, the extract is heated and each compound is separated due to different boiling points.
• After this process of separating the CBD and refining it to very high levels by removing impurities such as THC and terpenes, further purification is done and the CBD is crystallized so that the CBD is collected in solid form.
More on Chromatography
Chromatography is one of the most common methods used to CBD extract from hemp, especially in large scale production operations. Only in smaller productions is it usually excluded because it requires access to specialized equipment and a safe environment. Distillation processes, like short-path distillation and winterization, are used both before and after chromatography, to increase the purity of the end product.
To Do or Not to Do Chromatography
• Chromatography is used for the extraction / isolation CBD from hemp. It also “takes out all the terpenes, which are responsible for both scent [and] flavor,” and removes all/most plant matter.
• This methodology separates and purifies chemical compounds “taking advantage of their differences in properties.” It is a “practical and straightforward way to purify a substance from a complex mixture.”
• Four of the most common types of chromatography that were mentioned earlier are: supercritical CO2 chromatography, high-pressure liquid chromatography (HPLC), flash chromatography, and rotary chromatography. Of these, only the first type does not involve the use of “toxic solvents such as pentane or hexane to isolate the product.” Both HPLC and flash chromatography use pentane as a solvent in the process, while a special liquid solvent mix is used in the rotary method.
• Another form of chromatography is called centrifugal partition chromatography, which one researcher stated is “the key to achieving high-purity, high-throughput cannabidiol production.” The same researcher stated that, because of the impact of using solvents and the expensive consumable silica resin, those methods are not ideal CBD production, especially for human consumption, whereas this is not an issue with centrifugal partition chromatography.
• The choice to use either chromatography or skip it and use only distillation processes (like multiple short-path distillations) depends on multiple factors such as how much product is being used and what equipment is available to the producer. Side Note: using distillation-only processes is significantly cheaper and requires less specific machinery and supplies than chromatography making it ideal for smaller operations. Skipping the chromatography step can result in a less-refined product.
Purpose of Distilling CBD Oil Before/After Chromatography
• CBD isolate production involves extraction processes followed by distillation procedures (more distillation steps results in a more refined the product) followed by chromatography. Then, tests are performed to what ‘extras’ are still in the products and other distillation methods may be used to extract other compounds from the distillate.
• Distillation procedures can take place both before and after chromatography (or in place of for smaller operations), if the engineer/chemist has the equipment and is seeking a truly refined product. In fact, “distillation can be performed multiple times to increase purity levels.”
• Short-path distillation, also known as molecular distillation, is one of the most common and most efficient ways to purify CBD products. This process results in hemp distillates that can be up to 99% pure.
• Winterization, another type of distillation process, is also used, often before short-path distillation. As discussed earlier, this process removes the extras or undesirable elements from the CBD oil through an alcohol-and-freezing process.
Additional Purification for CBD Isolate
• After the initial extraction process, the concentrated CBD is still full of all the plant material so a purifying process is needed. First, all plant material is filtered out of the extract. Next comes winterization, which further removes impurities – and produces the fine, white powder that is 99% pure CBD.
• These filtrations and distillations are repeated until the end-product is as pure as possible.
CBD Crystallization
CBD crystallization is a long process involving a solvent (like pentane) and other steps such as stirring, heating, and cooling.
• Starting material is CBD that has been winterized and distilled. It should be clear (without the cloudiness indicative of contaminants). If it is still cloudy, it should be re-distilled until it is clear, as crystallizing oil with contamination will lead to poor yields.
• Extracted CBD is then added to a glass jacketed vessel with stirring capabilities. A heating/cooling bath is also connected to the vessel for temperature control. In some cases, pentane is used as the solvent.
• To start the process, add three parts CBD to one part pentane into the vessel, turn on the stirring mechanism, and set the temperature to 45 degrees C (or 113 degrees F). Once the solution reaches that temperature and the oil has dissolved, lower the temperature to 5 degrees C and reduce stirring speed. The solution will cool and become more viscous. Once this happens (it’s called “precipitation”), adjust stirring speed to 120 RPM. This forces the CBD crystals to spontaneously form or ‘crash out’ of the pentane solution. Continually reduce temperature to fully crystallize the solution. Crystal growth depends on the temperature used, so testing is necessary to reach optimum crystal production.
• After the precipitation phase, the CBD crystals can be collected from the vessel, and the slurry removed. The crystals are then rinsed in ice-cold pentane to rinse impurities from the crystal surfaces. More rinses that will improve color but reduce yield.
• If the starting CBD distillate is 70 – 75% pure, crystallizing can produce isolate that has a purity rate of 90% or higher. If the starting distillate is less than 70%, the crystallized isolate will have 85+% purity. CBD crystals can be redissolved and then recrystallized to improve the potency even further.