There are as many ways to extract essential oils from a plant material as there are recipes to make bread from grain. Developing your Standard Operating Procedure (SOP) means defining three main considerations;
1. Capacity per hour,
2. End goal or use of extract, and
3. Variety, condition, and harvest method of biomass.
There are as many ways to extract essential oils from a plant material as there are recipes to make bread from grain. Developing your Standard Operating Procedure (SOP) means defining three main considerations; 1. Capacity per hour, 2. End goal or use of extract, and 3. Variety, condition, and harvest method of biomass.
Capacity – The guide below is based on processing 500 lbs of dry biomass per hour. Therefore, this SOP might not apply directly to the SOP of a system that is processing 10-20 lbs per hour.
End Goal – We designed our system to produce isolate in the most energy efficient way, while maintaining end product quality. For example, if the end goal is non-winterized crude as a direct retail product ingredient, a different SOP is used.
Biomass Quality – Hemp strain, concentration of cannabinoids, harvest methods, drying methods, post harvest handling/shipping, age of biomass, etc., all play a role in developing how it’s extracted.
Entrainment, also known as Washing or Primary Extraction, this step involves soaking the biomass in ethanol and agitating the hemp and ethanol mixture. Our extractor has a basket inside the tank much like a Navy sized top-load clothes washing machine. 400-500 lbs of biomass is loaded and 400-500 gallons of ethanol for each batch. After 15-30 minutes of agitation, the ethanol is drained out of the tank and the wet biomass is spun at 250-350 RPM to remove as much of the ethanol as possible. The centrifugal force of the spinning removes 99% of the ethanol from the biomass. After 15-30 min of the spin cycle, the hemp is removed, a fresh batch of hemp is loaded, and washing starts again.
Primary Extraction can be processed at room temperatures, or using pre-chilled ethanol and a chiller on the jackets of the vessel to keep the whole extraction process super-cooled. Cold Primary Extraction limits the extraction of fats, sugars, lipids, chlorophyll, etc., but the cost of chilling massive amounts of ethanol before and during the process is extreme in a mass production facility. This is where defining your end goal is important in developing your SOP.
The entrained solution is pumped through a filter to remove dirt, insects, rocks, and anything else that came from the farm along with the hemp. From the filter, the solution goes into a holding tank for the Falling Film Evaporator (FFE). The main job of the FFE is to separate the extracted oil and the ethanol. The ethanol solution (~20:1 ethanol to oil) is fed into the top of Column 1 (C1) in the FFE where it is rapidly heated causing the ethanol to vaporize. From there, the ethanol vapor and oil enter the expansion column (C2) allowing room for further separation. Oil travels down into a collection tank, and ethanol vapor travels up to the top of the condensing column (C3) where the ethanol vapor is condensed back into liquid ethanol. This recovered ethanol is now sent back to be reused in another extraction batch in Step 1: Entrainment.
The oil that is collected in the receiver is further heated to decarboxylate the cannabinoids and any residual ethanol is purged. At this point the extract is raw crude hemp oil.
Winterization is the first step in refining the extracted raw crude oil to its desired potency of cannabinoids (CBD, CBG, CBN, etc). At this point the cannabinoid concentration is 50-60% and the winterization process helps in removing fats, lipids, waxes, and some chlorophyll that were extracted in Step 1 along with the cannabinoids. The term “winterization” comes from the idea of taking the crude down to very cold temperatures until the fats, lipids, and waxes solidify to a point where they can be filtered out of the crude oil. A warm, or ambient temp wash will end up with a higher level of waxes in the crude. We developed a robust winterization system to deal with those higher level of waxes the crude. Our theory is that we’d rather chill the extract down to cryogenic temperatures instead of chilling the primary extraction solution because the volume is 20 times smaller.
The first step is to take the crude down to -90C where the waxes solidify. This usually takes 12-16 hours to get down to temp. Because of the massive variety of hemp in the market, there can be huge differences in the amount of waxes to remove. If processing low (4%) CBD content hemp, 4x the amount of hemp needs to be processed hemp to get the same yield of CBD oil from high (16%) CBD hemp. This also means that 4x the waxes will be produced for the same CBD yield.
Once the tank reaches -90C the jacketed and insulated filter array must be pre-chilled and filtering out the solids can begin. The filter array starts with a “6-pot” 100 gallon (380 liter) first stage filter that catches 95% of the waxes with six 10 micron filter bags. After the majority of the waxes are removed, the crude is run through a single bag 1 micron filter to catch the rest.
Distillation is the next step and our equipment for that is Short Path Distillation (SPD) to take the purity up to 70-75%. Fully explaining fractional distillation is beyond the scope of this simple tutorial, but the basic concept is not beyond the grasp of a non-chemist enthusiast. If you look at a graph showing time vs. temperature of heating ice until it becomes steam at atmospheric pressure, one can see the basis of fractional theory. Starting with heating -40C ice, the heat works to raise the temp of the ice until it reaches it’s melting point, 0C. Once the ice reaches that melting point, the heat energy goes into the phase change of melting the ice and the temperature levels out until the last bit of ice is melted. At that point the temperature rises until the water starts boiling and again the graph levels out while the heat works toward a phase change instead of raising the temperature.
For this conceptual illustration we’re going to sidestep the effect pressure has on the process. But it’s important to understand the fundamentals in learning how our equipment functions. A kitchen pressure cooker uses pressure to raise the boiling point of water. In the same way, vacuum lowers the boiling point. Our SPD operates at a vacuum that is close to a deep space vacuum so we can lower all the boiling points of the fractions we’re after. By lowering the boiling points with vacuum, we’re preserving cannabinoid profiles that can be damaged or changed with the application of heat.
Winterized crude contains over 100 different components, each component or compound has it’s own boiling point. The hot side of the SPD slowly heats the crude oil a chemist will monitor for those flat spots in the heating curve. Each plateau represents one component or “fraction” vaporizing from the crude. These fractions’ boiling points can be less than 1/4 degree apart, and identifying them takes multiple temperature probes feeding into a Programmable Logic Controller (PLC) that can identify and data log every point for the chemist operating the system. The SPD is able to capture the fractions and the result is 70-75% CBD distillate. In this burgeoning industry, this is referred to “Full Spectrum” or “Broad Spectrum” Distillate because it contains many cannabinoids that are close to the boiling point of CBD. These nearby compounds can have beneficial effects when consumed with the primary component, often referred to as the “Entourage Effect”.
Isolation or Crystalization is the final refinement of CBD into it’s purest form. The 70-75% distillate is diluted with another solvent, chilled overnight to -40C in a specialized tank built for nucleation of crystals. The crystals grow about 2” thick on every stainless surface in the tank.
If you’ve ever made sugar crystals on a string from supersaturated sugar water, it’s the same basic idea.
This is a picture of isolate from 16% CBG dominate hemp strains and the crystals form in a needle like shape. It also has a very slight pink tint that is removed during further stages of crystallization purification.
Isolate powder has a very diverse set of uses in the retail market. Because it is 99.9% pure, there are none of the other cannabinoids, including THC.