cbd extract crystalDecember 15, 2021
Now that our extract has been winterized, filtered and decarbed, we can perform distillation. There are short path and wiped film distillation apparatuses on the market, for the sake of this article we will use wiped film distillation.
An additional option that some manufacturers complete to change the structure of the CBD isolate is to subject it to a crystallization process. This process results in a final product that is still 99.9% CBD but has a crystalline structure.
Winterization is the process of removing the fats, waxes and chlorophyll from the extract. Not removing these will lower the percentage and purity of the targeted CBD compound we are trying to capture. To achieve winterization you are essentially cooling down the extract to sub-zero temperatures with a solvent. Then, maintaining that chilled environment for a period of time in order for the lipids (fats and waxes) to coagulate and separate from the crude oil – now termed ‘miscella’.
Depending on what end product you’re trying to make you may prefer to use a CBD isolate powder when manufacturing lotions, edibles, beverages, etc. In order to make a powder you are simply taking the CBD isolate crystals and grinding them down into a powder-like substance.
This crystallization process is started by putting the CBD oil into a large vat, or reactionary vessel, with a stirring attachment. The mixture is heated while constantly being stirred. Then, the temperature is lowered and the rate of stirring is slowed down. Once the mixture has cooled and nucleation starts to occur (the initial stages of crystallization), the stirring rate is drastically increased, which causes the crystals to separate from the solution. After this, the crystals are rinsed with pentane, or another chemical solvent, to remove any remaining unwanted impurities.
Step 3: Filtration.
Making CBD isolate requires more steps than creating a CBD oil, as you have to remove every other element, such as phospholipids and flavors, from the product. While the process is more complex and requires additional equipment, it creates a totally pure end product that is free of anything besides CBD.
CBD isolate is 99% pure CBD, often in the form of a white powder that can be mixed into drinks or taken sublingually. This option is often popular among people who are just beginning to explore the use of cannabis or hemp derived products or looking to avoid the euphoric high associated with THC. It is also a great option for people who want hyper-accurate doses of CBD and the flexibility to create their own customized mixtures in their preferred carrier oil or liquid.
Once winterization has been completed it is necessary to now quickly filter those fats and waxes we coagulated from the miscella. A filter press is used with the assistance of a vacuum pump to pull the miscella mixture through a series of filter plates. Fats, waxes, etc are collected in one vessel and the desired miscella in another.
In order to achieve optimal CBD content, decarboxylation is a critical step prior to distillation. The process of decarboxylation is to remove carboxylic acid and CO2 from cannabinoids present in the cannabis extract. Converting the acidic cannabinoid (CBDa) to its neutral form (CBD) ensures the end product contains all of the several benefits the cannabinoid has to offer. Furthermore, failure to remove CO2 from the extract will also affect the ability to properly form a vacuum in your distillation apparatus. The decarboxylation process is achieved through the application of heat in a reactionary vessel.
While under vacuum, the extract is loaded into the feed tank where it passes over a heated rotating plate. From there, the heated oil then enters a secondary vessel where there are spinning wipers and a thin film is created around the heated, jacketed vessel. A long condensing coil in the middle of the vessel, cooled with recirculating fluid, recondenses the vapors back into liquid form. Receiving vessels then collect the CBD (known as ‘main body’) from the terpenes, volatiles and high boiling point cannabinoids (known as ‘heads’ and ‘tails’).
To make any concentrate you first have to extract. Manufacturers can use either a hydrocarbon solvent, like butane or propane, or ethanol solvent. Typically, we see ethanol used for the production of CBD isolate often with the use of a larger commercial extraction system – like a centrifuge. Smaller extraction systems can be used, it just depends on your throughput goals.
As system integrators for cannabis and hemp processing labs, Precision brings solutions to all stages of how to make CBD isolate.
Step 5: Distillation.
Step 1: Extraction.
Typically, CBD isolate that has been crash cooled will require at least one recrystallisation (which is at least 2 steps in total) to achieve the desired CBD isolate purity, thus complicating downstream processing and reducing CBD isolate yields and throughputs.
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)
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.
The result is a less severe form of crash cooling, but still far from ideal: CBD isolate precipitates out of solution and other components become entrapped in the CBD isolate crystals. These may include THC, pesticides, solvent, and/or any other components that were present in the original CBD distillate.
Can you perform seeded, cooling crystallization in batch stirred tanks?
Fig 1: Example solubility curve for CBD in a solvent system.
NiTech ® continuous crystallizers are for Step 5 – the crystallization of CBD isolate : the crystallization of CBD molecules from CBD distillate, to form CBD isolate.
If you also require assistance with step 6, the filtration, washing and drying of CBD isolate, we recommend our friends at Alconbury Weston Ltd (AWL)
In a NiTech ® continuous crystallizer, the combination of optimal mixing, enhanced heat transfer and the addition of seeds, the operator can keep the CBD concentration in solution inside the metastable zone throughout the crystallization process (see Fig 2.).
Precipitation occurs when a solute in a solvent becomes supersaturated to such an extent that it nucleates and spontaneously comes out of solution.
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.
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.
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.
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.
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.
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.
This method is fast and simple but is not an efficient means of crystallizing CBD isolate as the precipitate forms rapidly and entraps other components. These may include THC, pesticides, solvent, and or any other components that were present in the original distillate. In addition, when CBD isolate is formed via precipitation, the particle size is small and results in the material becoming more compacted and harder to filter effectively, as well as caking on the side of the reactor/stirrer. Due to the small particle size, material is also lost during filtration and washing.
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.
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.
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.
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.
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.
How is it made?
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.
Fig 3: ‘Crash cooling’ crystallization.
Fig 2: Crystallization pathway (superimposed on the solubility curve) when performing seeded, cooling crystallization of CBD isolate in a NiTech® continuous crystallizer.
Crystallization is the desired method for isolating a compound from a system.
There are three zones:
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.
At NiTech, we are always careful to differentiate between precipitation and crystallization. In chemistry, precipitation is the formation of a solid phase. So, all crystallizations are a sub-set of precipitation processes. It is common to call rapid solid formation precipitation and slow, control formation of a crystalline solid phase crystallization. The difference between the two can cause some confusion for two reasons:
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.