how to grow cbd crystalsDecember 15, 2021
The remaining solvent from the mixture needs to be evaporated, so it is placed within the roto-vape again, where it crystallizes. Afterwards, in order to make the crystals consumable, they go through a series of chemical washes, filtrations and roto-vaping.
While it is certainly possible to draw out extracts that are extremely high in THC and CBD with CO2 and hydrocarbon extraction and distillation, but THC-A and CBD crystalline opens up different potentials for storage and consumption to the market. For instance, storage is much more convenient when using crystalline isolate, less messy when dabbing, and easier to incorporate into foods and topicals (presuming you have decarboxylated your crystals). Did I mention that it is also very pretty to look at?
The only caveat to this is that you will not have the accompanying terpenes, and therefore will not experience the “entourage effect” that cannabis flower provides. However if you are intent on re-creating such an experience, you can reintroduce cannabis terpenes into your crystalline, or simply soak it within “terp sauce”.
Post chromatography, the crystals are dissolved in methanol and then filtered and then roto-vaped to remove the methanol. Afterward, pentane is used to remove the smallest bits of non-THC or non-CBD material and then roto-vaped for the last time. The results, white crystals testing at 99.97% cannabinoid.
For some this high-potency offering may seem excessive, but for many it is rather attractive. Medical marijuana patients are actively seeking the benefits of higher doses while veteran smoker may be looking for a new level of high. No matter the use, crystalline isolate is an exciting development within the chemistry of cannabis and the development of novel methods of consumption devoid of any harmful solvents and carcinogens.
So How Do They Make This Stuff?
In order to further purify the extract, chromatography is used in order to separate impure elements of the solution from the desired cannabinoids. Chromatography (sounds complicated but isn’t really) is a chemical process where different materials and mediums are used to separate different components within a solution based on its affinity to the different filter mediums and density (kind’ve like your standard water filter). In the instance of THC-A, chemists add Sephadex-LH20, dichloromethane and chloroform in order to further clarify the cannabis extract into majority cannabinoids and solvent devoid of any plant material.
You may be familiar with extractions, and if you’re not feel free to check out this article here discussing the two main types to refresh your knowledge, either way, in order to form crystals you must start with a cannabinoid-rich cannabis extract.
Ideally, in order to maximize on time and resources, A-grade flower with a high THC-A or CBD count (depending on what you’re isolating) will be blasted with CO2 or butane/propane in order to extract the greatest yield of cannabinoids from the plant material. The crude oil that is extracted isn’t completely “clean” and will typically have a fair amount of waxes and lipids emulsified within the oil. Once the crude oil is winterized and the major waxes and lipids are filtered we would be left with cannabis extract that could be placed within a vape cartridge or dabbed on a rig. However, this oil will range from 65-90% THC or CBD and still exist within a viscous/fluid state. In order to solidify the cannabinoids out of the remaining non-cannabinoid material, we must take the cannabis extract add different solvents in different stages and run it through a number of different filtrations.
Crystalline Isolate is an extremely pure form of cannabinoid that is extracted using CO2 or butane/propane. Available in both THC-A and CBD, crystalline can contain up to 99.97% THC or CBD depending on the application.
The first step is to take your cannabis extract and mix it with acetic acid and hexane, the combination of chemicals will act as a solvent to separate the dissolved plant matter from the THC/CBD. After the mixture has had time to settle, it is put through a filter and then the remaining fluid is placed within a roto-vape where the acetic acid and hexane are evaporated off. The remaining mixture will be primarily Delta-9 THC-A or CBD-A.
*Disclaimer, this post is for informational purposes only, the chemicals mentioned above are caustic and dangerous. We do not recommend you try this. This is not a tutorial.
Crystallization occurs when the solute dissolved in a solvent is supersaturated (but not precipitating spontaneously). An external stimulus, e.g. the presence of seeds, is used to initiate nucleation in a controlled manner. Crystallization is the controlled growth of crystals, often from seed crystals. The seed crystals act as de facto catalysts, which lower the energy barrier of crystallization: it is easier for solute to crystallise on an existing crystal surface than to form its own new solid phase, at relatively levels of low supersaturation.
Fig 3: ‘Crash cooling’ crystallization.
Precipitation occurs when a solute in a solvent becomes supersaturated to such an extent that it nucleates and spontaneously comes out of solution.
In the case of CBD isolate, the approach is the same. CBD present in CBD distillate, is diluted with hydrocarbon solvent (typically pentane or heptane) and then cooled so that the CBD molecules crystallize as CBD isolate crystals.
In addition, when using batch-based cooling crystallization, the CBD isolate particle size is small and results in the material becoming more compacted, and harder to filter effectively. Due to the small CBD isolate particle size, material is also lost during filtration and washing.
Cannabidiol (CBD) isolate is hemp-industry nomenclature for crystalline cannabidiol. It is cannabidiol in its purest form and its appearance (when pure) is that of an off-white crystalline solid. It is referred to as CBD isolate because CBD is one component of a multi-component extract that has been ‘isolated’ from all the others.
We hope you have found this page useful. We have explained the science behind crystallization and how it applies to CBD isolate production. We also explained how CBD isolate manufacturers can overcome the limitations of established, batch-based crystallization equipment through the application of NiTech’s proprietary continuous crystallizer.
NiTech ® continuous crystallizers are for Step 5 – the crystallization of CBD isolate : the crystallization of CBD molecules from CBD distillate, to form CBD isolate.
Batch stirred tanks are severely limited by heat and mass transfer (i.e. the ability to heat or cool their contents and the ability to mix effectively), particularly at larger scales, leading to significant batch to batch variation, reduced CBD isolate yield and purity.
Although the phase of the product is the same (i.e. a solid), the characteristic of the product and the mechanism by which it is formed is different between the two processes.
There are three zones:
In the case of CBD, this can mean THC, pesticides, solvent and other cannabinoids becoming entrapped in the CBD crystals, requiring resource-intensive recrystallization operations to achieve the required purity.
To perform a cooling crystallization, the solute must be sufficiently soluble in the solvent at the start (higher) temperature, and insoluble in the solvent at the end (lower) temperature. The more insoluble at lower temperatures the better, as this improves the theoretical yields over a practical temperature change by driving more of the solute out of solution.
To understand this, we first have to explain crystallization. At its base level, crystallization is the isolation of a solute from a solvent by causing it to form a solid. This is achieved by manipulating the solute’s solubility in the solvent. The most common way to achieve this is through the manipulation of temperature. This is referred to as a cooling crystallization and this is what is used to crystallize CBD isolate from CBD distillate.
Can you perform seeded, cooling crystallization in batch stirred tanks?
Fig 2: Crystallization pathway (superimposed on the solubility curve) when performing seeded, cooling crystallization of CBD isolate in a NiTech® continuous crystallizer.
Below is an illustration of a solubility diagram (Fig. 1) which demonstrates the important relationship between CBD concentration (y axis) and temperature (x axis), and the affect of temperate on CBD phase-behaviour.
At larger scales, mixing is less efficient and more energy intensive. Non-uniform mixing causes temperature and concentration gradients to form in the vessel, for example, areas close to the walls of the vessel will be colder than at the centre of the vessel. This leads to areas where, simultaneously within the same vessel, material is both spontaneously precipitating and re-dissolving.
Controlled crystallization in a COBC is gradual and forms large, uniform particles with high purity and yields and makes downstream processing simpler and more effective.
Fig 4: Seeded, cooling crystallization in large batch stirred tanks (Note: wider arrows are used to illustrate the temperature gradients within the fluid inside a large stirred tank caused by poor mass and heat transfer properties of this equipment)
It is possible to attempt seeded, cooling crystallization in batch stirred tanks; like the operation of a NiTech® continuous crystallizer. B/R Instrument’s blog provides a comprehensive explanation of this process: how to crystallize cbd.
What is the difference between precipitation and crystallization?
The enhanced control of crystallization pathway in a NiTech ® continuous crystallizer results in a high CBD isolate yield (close to the theoretical maximum) and a high-purity product with a uniform crystal size for simpler downstream processing.
There are several steps required to take the cannabis biomass ‘from crop to crystal’. These steps will vary depending on the user’s preferred extraction method, but typically the steps are as follows:
For these reasons, although quick and easy, precipitation is not an effective or desirable means of isolating a compound from a solution due to poor process performance.
Fig 1: Example solubility curve for CBD in a solvent system.
CBD isolate is often produced using crash cooling (this is precipitation). As demonstrated in Fig 3:
Precipitation is rapid and forms a large quantity of small particles, as rate of formation of new solids greatly exceeds the rate of crystal growth. Also, due to the speed of precipitation, other components become entrapped in the precipitate, resulting in a lower purity material; these can include the solvent as well as other components present in the solvent system at the time.
At larger scales, there is proportionally lower surface area available to transfer heat to the contents of the vessel. This is known as ‘decreasing surface area to volume ratio’. This means that it takes longer to heat or cool the contents of the reactor, making it impossible to respond quickly to dynamic processes, such as crystallization, to keep the vessel’s contents at the correct temperature.