How to extract cbd?

Preparation for Cannabis Extraction

Carbon Dioxide (CO2) extraction of cannabis is becoming more prevalent as the extract market grows with the spread of medical and recreational legalization. However, due to the historically underground nature of working with the substance, little true scientific experimentation and process development has occurred; even less has been published. Those new to the field have limited guidance.

Feedstock selection

Material selection, especially when starting extraction work, may be determined by availability. However, once there are options the following criteria should be considered.

Strain

Although there is an incredible variety of cannabis grown in the US, there are three basic distinctions:

  • Cannabis indica—induces full-body relaxation, used to treat pain or insomnia, more resinous material
  • Cannabis sativa—induces creativity, used to treat depression, more woody material
  • Cannabis Hybrid—any combination of the above two

The number of cannabis strains continues to increase as plants are bred to optimize specific traits such as:

  • Yield
  • Hardiness
  • Concentration/balance of certain cannabinoids (generally THC and CBD)
  • Flavor
  • Effectiveness at treating specific ailments
  • Effectiveness at inducing certain effects

Grower

The extract can only be as good as the starting material, and that is almost completely determined by the grower. This person or company has been responsible for nurturing the plants through months of growth, harvesting, and in many cases, drying or curing the material. If the grower has used pesticides, herbicides, or fungicides, or has used them at the wrong time, those residues will be in the feedstock and will be concentrated in the extract. If the plant has been inadequately tended it may not fully develop the expected characteristics. Poor harvesting and storage techniques can lead to mold. Inferior curing techniques do not preserve the terpenoid content of the plant.

Feedstock type

The cannabis feedstock is available as whole plants, branches, buds, and trim (leaves, stems, and perhaps some small buds). It is available both fresh and dried. Any of these variants can be CO2 extracted, but with differing results.

Fresh material

Freshly harvested cannabis is quite fragrant due to terpenes, the compounds responsible for scent and flavor. Extract derived from fresh material has a higher terpene content than that made from dried material. It, therefore, has more flavor and demands a higher price.
Relatively few manufacturers use fresh material however due to the following issues:

  • The scent of fresh feedstock tends to be intense, causing issues for discrete transport
  • It is very perishable and must be refrigerated, frozen, or processed quickly, usually within 24 hours of harvest
  • It requires more processing than dried material because of the inherent water content. Increasing the number of processing steps and, the overall processing time not only adds to manufacturing costs, but also generally results in reduced yield and some level of product degradation.
  • The resulting extract tends to be sticky and hard to work with
  • Acquisition costs tend to be much higher per pound than for dried material (even though a substantial portion of what you are buying is water weight)
  • To get fresh material you usually need to buy the whole plant
Dried material

Terpenes are highly volatile and dissipate quickly, especially when heated or exposed to circulating air for curing. Although dried material will have a lower concentration than fresh material, the dried feedstock is more readily available, has a lower cost per pound, is

more stable, and takes up less storage space than the wet version. Growers that dry and store with care will preserve more cannabinoid and terpene content than less experienced or less skilled growers.
Extract derived from dried material makes up the majority of the market.

Bud/Flower

This most expensive part of the plant has the highest concentration of cannabinoids and will produce the highest yield. Optimizing the bud has been the goal of growers throughout the history of cannabis cultivation in the US.

Trim


This is the green material trimmed from the plant to expose the bud/flower consisting of the leaves, non-woody stems, and immature buds (popcorn). High-quality trim will be free of any woody material and have an abundance of popcorn. Low-quality material will be full of stems and devoid of popcorn.
Cannabinoid concentration depends on the quality of trim and extraction yield will be between flower and stem.

Stem and roots

The stems and roots are the most fibrous parts of the plant and they contain the lowest concentration of cannabinoids. They are difficult to process.

Whole plants

Plants from an indoor nursery tend to be of manageable size with stems that are pliable and of small diameter. Outdoor-grown plants, although usually healthier, can be more than ten feet high and ten feet in diameter. Processing this mass of material can be challenging, especially since the stems can be quite woody. Drying whole plants is difficult as it is hard to get consistent airflow throughout the plant, so whole plants tend to be used fresh.

Preparing the feedstock

While it is possible to stuff any kind of feedstock material into the extraction vessel as is, there are a number of reasons why this is almost never done:

  • Large pieces of material have limited surface area, and therefore require large volumes of CO2 solvent for full extraction
  • Loading unevenly shaped items into the extraction vessel, even if the material is compactable and strongly tamped down, will inevitably lead to air pockets that will ensure channeling (having the CO2 flow through one channel in the load rather than evenly throughout the load)
  • Loading weights will vary as the feedstock material is non-homogeneous
  • Preloading charges of material will be impossible

Both efficiency and yield are greatly improved by first breaking down the material into small particle sizes.

Grinding

The goal of grinding is to break up the plant material into very small pieces that are as homogenous as possible without degradation. This can be done using any kind of equipment that does the following:

  • Cuts rather than compress the feedstock
  • Keeps the feedstock moving so that it does not heat up and release terpenes

In small-scale production, a consumer-grade food processor works well. In larger-scale production a commercial kitchen grade food processor is appropriate. When using a food processor, make sure to loosely pack the grinding chamber so that the machine can fully break down the feedstock without binding up, thus heating the material. It is better to have more batches and cool material than fewer batches and warm material. At pilot-scale production (with the NPX units) an industrial grinding unit will allow flow through processing without heating.

Grinding generates cannabis dust. It should be done in a hood. If a hood is not available then personnel in the area should wear a mask and lab coat. Personnel should always wear lab gloves when handling cannabis.

Preparing charges

Pre-making extraction charges enable processing efficiency.

Prepare a form

  • Get a tube (PVC, stainless steel, or other non-reactive material) that has a slightly smaller ID (inner diameter) than the extraction vessel ID.
  • Measure the internal height of the extraction vessel.
  • Mark that height on the tube.
  • Cut the tube to be longer than that height by at least two inches.

Select charge sleeves

  • The sleeve should hold the material with minimal leakage, be flexible, be non-reactive, and allow CO2 to flow through.
  • When filled, the sleeve must fit into the extracted vessel without wrinkles or gaps as those would encourage channeling.
  • Some common sleeves are women’s stockings, cotton bags, cheesecloth bags mesh bags, and mesh baskets.

Grind the material (in fume hood wearing gloves from this point on)

  • Grind the quantity of material that you will use in one day. The terpenes that remain in the dry material will dissipate quickly once the surface area has been exposed; the longer the material sits after grinding the lower the terpene concentration will be.
  • Keep the ground material sealed in its container except when you are actively using it.

Create the first charge (note, should be done with each new feed material)

  • Put the tube into the charge sleeve with the height marking at the top.
  • Tare a container that will hold more than enough volume of ground cannabis to fill the tube when compacted.
  • Fill and weigh the container (weight1).
  • Carefully transfer as much of the material in the container as possible into the tube, tamping down firmly to compress the ground cannabis to get rid of any air pockets, until the tube is filled to the height marking.
  • Weigh the container holding the remaining ground cannabis (weight2).
  • The load weight for each of the additional charges will be (weight1 – weight2).
  • Carefully lift up the tube while pushing the ground contents into the sleeve. A flexible plunger with the same ID as the tube will help greatly.
  • Remove the tube from the charge sleeve leaving the ground cannabis in the sleeve.
  • Seal the open end of the sleeve by tying it off or using a cable tie.
  • Put the completed charge sleeve into a sealed container until ready to use.

Create remaining charges

  • Put the tube into the charge sleeve with the height marking at the top.
  • Weigh out the charge (weight1 – weight2)
  • Carefully lift up the tube while pushing the ground contents into the sleeve. A flexible plunger with the same ID as the tube will help greatly.
  • Remove the tube from the charge sleeve leaving the ground cannabis in the sleeve.
  • Seal the open end of the sleeve by tying it off or using a cable tie.
  • Put the completed charge sleeve into a sealed container until ready to use.

A Complete Guide to the CBD CO2 Extraction Process

Supercritical CO2 Extraction of Cannabis Oil
Figure I
Supercritical CO2 applied to the extraction of cbd oil
Figure II
CO2 extraction process
CO2 extraction process

Bucking and Drying

Hemp or cannabis biomass preparation starts with removing the flower from the stems. This process is often referred to as bucking and can be accomplished with a bucking machine or by hand.

Bucking machines eliminate the labor-intensive part of obtaining the flower. One alternative to bucking is to chop the entire plant (stock, stem, seed, and flower) in a commercial combine. However, including the entire plant reduces extraction throughput by as much as a third, and may produce low-quality isolate and distillate.

Drying

Hemp or hemp biomass breaks down more easily when the moisture content is less than 10%. To dry hemp biomass, we recommend hanging the whole plant upside down in a 40 square meter, humidity, and temperature-controlled room for 24-48 hours. A control room of this size can service cannabis greenhouses of up to 4000 square meters.

On the other hand, a hemp dryer will dry a lot of material. Drying equipment used in this case may include a fluidized bed, rotary kiln dryers or belt-driven infrared dryers. As an alternative to machinery, many cannabis growers let their crops dry in the fields. This method works well as long as the harvest time is cool and dry.

Bucking

Hemp or cannabis biomass preparation starts with removing the flower from the stems. This process is often referred to as bucking and can be accomplished with a bucking machine or by hand.

Bucking machines eliminate the labor-intensive part of obtaining the flower. One alternative to bucking is to chop the entire plant (stock, stem, seed, and flower) in a commercial combine. However, including the entire plant reduces extraction throughput by as much as a third, and may produce low-quality isolate and distillate.

Grinding

Once the hemp or cannabis has been bucked and dried, it is granulated. In general, smaller particles (200-1000 microns) are desirable and tighter particle diameter distributions are better for extraction throughput. Also, sticks, stems, and seeds that made it through the bucking process should be removed before grinding. Several kinds of mills are available on the market to accomplish these goals including hammer mills, shear mills, and cone mills.

Depending on the desired processing volume, a typical grinding operation will include a hammer or a cone mill. The mill is assisted with vacuum cyclone collection.

Once the materials are milled, they can be extracted or further processed to convert the acidic forms of CBD or THC into neutral molecules. This further processing is known as decarboxylation and the resulting biomass is referred to as decarb material.

Conversion of the acidic to the neutral form is desirable from the standpoint of throughput and for formulation reasons. However, acid forms are also desirable for specific types of formulations.

Decarboxylating before extraction has the advantage of speeding up the extraction process and allowing the gentle collection of pure, full-spectrum terpenes, which do not have any cannabinoids using fractional distillation with a cold trap condenser. Because decarboxylation involves the use of heat and vacuum pressure, the evaporation point of the terpenes is low enough to be removed from the biomass without damaging the terpenes themselves. Once removed, the cold trap chilled condenser will collect full-spectrum terpenes that would otherwise be unobtainable further down the processing line.

Full Spectrum terpenes are completely natural and easy to dilute into formulations. Processing terpenes earlier, rather than later, is a huge advantage for formulations and aroma engineering.

Terpenes

When choosing your system, it is important to consider terpene retention during the extraction process. You can increase the terpene yield by properly prepping the material and also by adding a vapor condenser or cold trap to the system.

  • Load extraction vessel with biomass.
  • Bring each vessel to working pressure using CO2 from supply cylinders.
  • Create supercritical CO2 fluid.
  • Alter pressure and temperature, depending on what’s being extracted and the goals of the extraction.
  • Pass the supercritical CO2 through an extractor containing the plant matter itself.
  • In Extraction Vessel, compounds are pulled from biomass into solution.
  • Solvent (CO2) is boiled out of solution in Separator 1.
  • Evaporated CO2 is condensed into liquid and stored in Accumulator.
  • Pass the new solution through a separator to quickly and easily remove (and recycle!) the liquid CO2.
  • After allotted run time, the system is depressurized by releasing CO2 through Separator 2 or 3. (Popular CO2 machines are often equipped with 3 separators: Waxes separation and Light oil separation in 1st separator. Light oil separation in 2nd separator. To trap lightest and volatile compounds in 3rd separator.)

If you look closely at the picture on the left, the color of Figure I and Figure II is different, much darker.

This is not the reason for the light, but the supercritical CO2 fractionation process of BIT in Figure II, which removes a part of the wax and more chlorophyll during the extraction process, so its color is much lighter.

At the same time, in the subsequent winterization process, cost and time are saved.

Note: In the CO2 extraction process, CO2 is recycled in the machine, and the large CO2 extraction machine is also equipped with a CO2 recovery system to save production costs. Of course, some gas will be lost, about one-third of the weight of the extract.

Dewaxing (Winterizing )

How to make winterized oil: Winterization is typically needed to remove extracted heavy waxes; the resulting oil is referred to as dewaxed oil or winterize oil.

Winterizing is usually accomplished by dissolving the extract in a small amount of food-grade ethanol, cooling the ethanolic extract to – 20ºC, and then filtering. At -20ºC, the precipitation of wax in ethanol can take up to 24 hours to complete. However, many operators process materials prepared the day before in a first-in-first-out manner.
Sub-critical CO2 extraction methods can also be used to remove the need for winterization and is popular for producing terpene-rich oils.

Filtration with large filter funnels offers a high throughput means of separating the precipitated wax from the ethanolic oil.

Ethanol is then removed and recycled with a thin film evaporator or a rotovap. Two advantages of a thin-film evaporator are: it is continuous and has a high throughput.

Distillation

How to make distillate: Distillation can be accomplished with short path distillation equipment or wiped film evaporation equipment. A distillation machine is typically used to improve the potency and color of the extract. Potency is typically improved 10- 30% while the color of the oil is converted from an opaque dark amber – to a light amber – then to a clear light yellow.

Chromatography

Chromatography is a separations method necessary for the remediation and isolation of various compounds into their individual components. This is essential for remediating THC from CBD products, identifying and removing unwanted materials, and isolating cannabinoids for specific downstream product formulations.

In the hemp and cannabis extraction industry, chromatography allows manufacturers to distinguish a list of compounds in the cannabis plant and create a specifically formulated product that’s both legal and tailored to the marketplace demands.
Chromatography is also effective at identifying and removing unwanted pesticides, and other residual chemicals. These are essential factors in creating a healthy, safe, desirable product for the end-user making supercritical chromatography an essential part of your production.

CBD Crystals or THC Crystals

How to make isolate: CBD crystals are made by precipitation in a nonpolar solvent, which involves dissolving distillate into the solvent, cooling the solvent down to induce precipitation of CBD, washing the crystals, and then removal of the nonpolar solvent. When using jacketed stirred reactors, crystallization and precipitation processes can be used to produce several hundreds of kg of crystal CBD isolate.

Just like in the winterization process, the amount of solvent used is less than when compared to the solvent required for extraction. Crystal production rooms can be designated as separate control areas, making the amount of solvent in the room and building more manageable.

THC crystals are made by similar precipitation. Typically, an ethanolic extract is subjected to very low temperatures thus causing precipitation of the crystals. Just like CBD crystals, they’re washed, and then the solvent is removed.