Roadmap to Hemp Oil Processing
The hemp oil processing facility is a relatively new discipline in the chemical and industrial engineering landscape. Although many aspects of CBD extraction and purification can draw from the maturity of other natural products, there are numerous nuances that require careful consideration from the outset; failing to address these crucial design and processing elements can be catastrophic to a fledgling business. In order to understand the nuances of hemp oil processing and CBD extraction, one must first understand the process and in doing so, the basic chemistry of solvents, CBD, lipids, and pigments. Herein, we will discuss the basic science of CBD and how these properties can affect our decisions regarding extraction solvent, facility layout, equipment selection, and safety considerations.
Cannabidiol in its natural form
The hemp plant does not produce cannabidiol per se, but rather cannabidiolic acid (CBDA). As you can see from the two structures below, CBD and CBDA differ only by the presents of 4 atoms: COOH.
Technically known as a carboxylic acid group, this appendage of the molecule determines the physiological activity of CBD. Simply put, unless this -COOH group of CBDA is removed (decarboxylated) before ingestion, our bodies will not benefit from CBD because CBDA is not physiologically active. Thus, at some point during hemp oil processing and CBD purification, CBDA must be decarboxylated. Currently, the most efficient method to decarboxylate is by delivering enough heat to break the bond connecting the carboxylic acid to CBD. The details of decarboxylation will be addressed later.
What is the best CBD extraction solvent?
This is a million-dollar question because there are many factors that can limit your solvent options. The short answer is ethanol, for reasons we discuss shortly but the justification for this answer is a compromise between three key factors: selectivity, cost, and safety. Safety also happens to be the X-factor by virtue of the exponential effect it can have on cost.
Solvent selectivity
Molecules and solvents can be classified by their polarity: polar vs nonpolar (or somewhere in between). CBD is very nonpolar. Water is very polar. Adhering to the very old and very true adage, “like dissolves like”, we can correctly assume that water is ineffective for CBD extraction. While you may have heard of water (or “bubble”) hash, this is actually a physical separation of the trichomes from the rest of the plant. The potency of this extract peaks at around 45% CBD and is unsuitable for crystallization whereas solvent extracts reach 90% CBD and can be further processed to reach 99% after crystallization. For this reason, we will omit water hash from the discussion of high-throughput hemp processing.
Clearly, nonpolar solvents are chemically ideal for CBD extraction so does that mean ethanol is a nonpolar solvent? No. Ethanol is considered “somewhere in between” on the scale of nonpolar vs polar. Thus, it has the disadvantage of extracting polar molecules such as pigments, sugars, and- you guessed it- water. If ethanol is so much less selective than a common industrial nonpolar solvent such as butane or hexane, why would we use it? You guessed it- cost and safety.
Before we weigh the pros and cons of solvent safety, another common nonpolar extraction solvent deserves honorable mention- carbon dioxide.
When carbon dioxide is under enough pressure and temperature, it transitions to a fourth state of matter- a supercritical fluid. Extraction using carbon dioxide is called SFE (supercritical fluid extraction). In SFE, carbon dioxide is purchased very inexpensively in its liquid state and the pump on the CO2 machine brings it up to supercritical pressure while heaters bring it up to supercritical temperature. The pump must be very robust to achieve these pressures as well as the vessels and tubing in order to withstand these conditions safely. The end result is a SFE machine that is cost prohibitive for most start-ups. A “high capacity” SFE machine starts at $500,000 and can only extract approximately 25 pounds per hour whereas a similar throughput ethanol extraction unit costs about 10X less. That being said, carbon dioxide is the safest of the relevant extraction solvents being used in the industry today. But, you may ask, isn’t safety the X-factor? The answer is yes, but SFE has a major caveat: carbon dioxide also extracts lipids (AKA waxes and fats). Removal of lipids requires the painstaking and costly step of precipitation or “winterization”. Not only is this process inefficient but it negates the safety advantage of CO2 by requiring the use of ethanol. Is ethanol unsafe? No, it is again “somewhere in between”. Ethanol is more dangerous than carbon dioxide (after all, carbon dioxide is a fire extinguisher) but less dangerous than hydrocarbon solvents (i.e., hexane or butane).
Safety
For the sake of argument, let’s pretend that your hemp processing start-up company has the technical and engineering expertise to build a safe, reliable extraction facility with the equipment, infrastructure, and safeguards necessary to prevent a catastrophic accident involving the volatile solvent hexane or the gaseous butane or propane. Is your Fire Marshal willing to send his or her men and women into an explosive situation just so you can beta-test your cannabis facility in your proof-of-concept business venture? If you are a first-mover in that Fire Marshal’s jurisdiction, the answer is probably no. If entrepreneurs have already tried this and the result was a fire or explosion, the answer is a resounding NO. Per the NFPA codes, closed-loop light hydrocarbon extraction using butane or propane requires C1D1 construction which is very stringent and very high cost.
Let’s take this hypothetical situation one step further and assume that your Fire Marshal does in fact allow hydrocarbon extraction. Let’s also assume you aren’t using butane or propane due to the limitation in throughput inherent in pressurized batch extraction. That leaves us with pentane, hexane, or heptane- all of which behave almost identically with the exception of boiling point (this detail is inconsequential in regards to extraction but has significant implications in the crystallization process, more on that later). With the multitude of ethanol extraction and evaporation equipment on the market today, one might be tempted to reappropriate said equipment for use with, say, hexane. While this in theory may seem perfectly reasonable, the devil is in the details. There are many fittings and seals in this equipment and some of them aren’t trivial (ie, a centrifugal seal or evaporation plate exchanger). The manufacturer designs and sells this equipment for use with ethanol and therefore the seals are designed to be chemically compatible with ethanol, not hydrocarbons. Case in point- use of 190 proof ethanol denatured with heptane will void the warranty of most centrifuge extractors because even 5% hydrocarbon by volume will destroy the seals.
By now, we have made a case for ethanol based on selectivity and safety but it is a scant case at that. If we reduce the solvent temperature to below zero degrees Celsius, however, selectivity and safety become significantly better.
Here’s why cryo-ethanol improves selectivity and safety:
Temperature affects the rate at which processes occur
Cold ethanol does not have a higher affinity for CBD nor a lower affinity for pigments and lipids. Lower temperature slows down the rate at which molecules move from the solid material (hemp) into the liquid material (ethanol). This rate is called the mass transfer coefficient. CBD, pigments, and lipids all have their respective mass transfer coefficients at a given temperature. The great thing about CBD is that its mass transfer coefficient is still quite high at very low temperatures. This is not the case for lipids and pigments such as chlorophyll. So by manipulating the temperature and halting the extraction until just after the bulk of the CBD has entered the solvent, we can improve de facto selectivity.
Just as low temperature slows down the rate of mass transfer, low temperature slows the rate of evaporation. As you probably know, it is not the liquid itself that is flammable but rather the vapor and its access to oxygen in the atmosphere for combustion. Thus, cryo-ethanol is much less flammable and likewise much less explosive than at room temperature. In fact, at -40 C there are so few ethanol molecules evaporating from the liquid surface, if a match were struck just above the surface (not recommended), it would not ignite. Since there is no reason to have ethanol in open use, a closed-loop system allows for safe and efficient transfer of solvent in the extraction and evaporation room. The NFPA code for closed-loop ethanol extraction calls for C1D2 (as opposed to C1D1 for butane) which significantly brings down costs and complexity.
Finally, ethanol is safer not just in terms of a fire hazard but also in terms of consumer safety. Ethanol is classified by the FDA as a Class 3 solvent with low toxicity. It can be present at concentrations up to 5000ppm and still be considered safe for consumption. Moreover, ethanol can be certified as food grade, Kosher, and Halal.
Cost
Ethanol may be one of the more expensive solvents to choose from but its high cost can be managed in some ways and mitigated in other ways. The largest savings can be accomplished through ethanol recovery in the evaporation process. This is essentially ethanol distillation and has become standard procedure in the cannabis industry. A major disadvantage of ethanol distillation is the formation of an ethanol-water azeotrope which prevents the recovery of pure 200-proof ethanol. Regardless of the source of the water- in the plant, in the air, or condensation in cold vessels- the azeotrope is extremely difficult to break, resulting in recovered ethanol of less than 185 proof. As more water comprises the ethanol, the solvation strength for CBD decreases. This is another often overlooked detail that can have a drastic effect on the cost of consumables. There are solutions for reproofing ethanol, such as molecular sieves and reproofing stills. The best solution, however, may be the choice of evaporation equipment which could avoid the problem altogether (see Evaporation Equipment section).
The next best way to maximize your ethanol savings is by using the same volume of ethanol multiple times for extraction. The reason behind this is simple- at a typical 1:1
hemp(lb):ethanol(gal) extraction ratio, the solvation capacity of ethanol far exceeds what will be extracted in the first batch of biomass. The number of batches which can be extracted by the same volume of ethanol depends on the CBD potency of the biomass, of course, but typically 7% biomass can be extracted at least three times before the ethanol nears saturation and solvation strength diminishes. Note: extraction of pigments and waxes also diminish solvation strength so cryo temperatures must be maintained in order to reuse the ethanol several times.
Another way to cut ethanol costs are through purchasing 190-proof denatured ethanol. Denatured ethanol does not incur the federal excise tax so the cost is significantly cheaper than 200 proof. It is important, however, to use ethanol denatured by n-heptane which is a food-grade denaturant but be aware that the EPDM seals most likely in your extraction and evaporation equipment are not compatible with heptane. Another option is to purchase non-denatured 190-proof ethanol (w/ 5% water) but the small savings compared to 200-proof does not justify the dilution.
The final cost factor that makes ethanol extraction the best choice is the price of equipment. Being non-volatile, ethanol extraction equipment is designed to operate at atmospheric pressure, allowing for much more affordable materials, closures, valves, and safety measures. Furthermore, the highly competitive market of ethanol equipment drives the prices down.
Hemp Oil Processing Facility Layout
A hemp oil processing facility must be thoughtfully designed such that every objective can be accomplished safely and efficiently. Many times, objectives that are assumed a necessity on-site are later relegated to an off-site location, delegated to the farmer, or outsourced entirely. For example, milling of biomass in the processing facility utilizes valuable processing space, creates a huge amount of dust which is also a fire hazard, consumes power, and produces a great deal of noise. This responsibility should not fall on the processor, since it is a practice closely associated with agriculture. If the processor has the space and equipment, they may offer this service for a fee, but it is by no means obligatory.
On the other hand, many operators overlook the importance of in-house analytical testing, instead relying on 3rd party laboratories for their routine QA/QC tests. While this may be a good strategy for the more technical analysis such as pesticides and heavy metals which require very expensive instruments and full-time scientists to operate them, simple potency analysis is imperative to have on-site due to the need for speedy results and the relative simplicity of the instrument.
Once the scope of the processing facility has been defined, the rooms and hallways can be laid out according to your equipment and process flow. Here is a general flowchart for a cryo-ethanol processing facility:
Your facility will probably have a roll-up door which will serve as the entrance for the biomass and essentially the beginning of the process. The biomass will most likely be transported in super sacks common to the agricultural industry. These can be brought in through the roll-up door with a forklift or pallet jack. These should be kept in an enclosed room to allow for climate control and prevent infestation. With most extraction machines, fine mesh bags are used to contain the biomass, separate from the solvent during draining, and allow for easy loading and unloading. It is in this first room where the milled biomass is transferred from supersack to extraction bags.
Freezer
The biomass is stored at room temperature but the ethanol is introduced into the extraction machine at -40 C and is necessary to remain at
-40 C throughout the entire extraction run. Clearly, submerging 30 pounds of 25 C biomass in 30 gallons of -40 C ethanol is going to raise the temperature of the ethanol to the point where pigments and lipids are co-extracted. Therefore, a freezer is needed to stage and store the loaded bag prior to extraction. Depending on your throughput, a few cryo freezers may give you the cubic feet of capacity needed to prevent a bottleneck. However, if you are intending on processing over 1000lbs in a 24-hour period, a walk-in freezer may be more practical. A -40 C walk-in freezer is neither a trivial nor cheap item, however. Complicating the design is the frequent opening of the door, requiring a refrigerated parlor in order to buffer the extremely cold air escaping and ambient air entering.
Extraction, Evaporation, & Decarb- oxylation Room
This is the first C1D2 room (Class 1, Division 2 per NFPA code). Due to the use of ethanol in this room, many design considerations must be implemented ranging from sparkless lights, light switches, and outlets to C1D2 rated equipment. Walls must also be fire rated according to the amount of solvent present in the room at any one time. Fire sprinklers should be installed at the proper density required by the NFPA code. Any wall penetrations for hosing, piping, or conduit must be sealed with fire proof caulking. Vessels that hold flammable solvent which is transferred to and fro must be grounded to discharge static electricity generated by the flow of liquid. Furthermore, the HVAC system must exchange enough air deemed necessary by the Fire Protection Engineer (FPE).
Extraction
Since ethanol can be conserved by extracting several batches of biomass with the same volume of ethanol “tincture”, it makes sense to have at least two extraction machines because you will ideally transfer the tincture from extractor #1 directly into extractor #2, rather than holding the solvent in an auxiliary vessel while exchanging the raffinate with a new bag.
Extraction Centrifuge
Filtration
The fine mesh extraction bags restrain most of the biomass but not all. These fine particles of hemp (and sometimes dirt if poorly harvested) flow out of the bag with the tincture and must be filtered out prior to evaporation. Even at -40C a small amount of lipids and pigments are co-extracted and need to be filtered and adsorbed, respectively. Rather than having a stand-alone filter or cartridge for each purpose, it is practical to use a four stage filtration skid for which there are numerous options on the market. The first stage is typically a course bag filter, followed by a diatomaceous earth lenticular filter, followed by a carbon lenticular filter, and finally a fine bag filter. Make sure that the skid is equipped with a pneumatic pump that is compliant with a C1D2 room.
4 Stage Filtration Skid
Evaporation & Decarboxylation
Once the tincture is filtered, the ethanol may now be evaporated. The options for evaporation in a C1D2 room are limited to rotary evaporators (rotovaps) and falling film evaporators (FFE). When dealing with a high-throughput operation, rotavaps are impractical due to the batch nature, unscalability, fragile glassware, and multiple peripheral components for each unit. One advantage of rotavaps is the redundancy of multiple units- if one fails, you are still operational. Another advantage is the ability of the rotovap to evaporate up to 99% of the ethanol from the crude oil.
A stainless steel FFE, on the other hand, sacrifices 5-10% residual ethanol in the crude for the much higher evaporation rate- many models can handle 50 gallons per hour and the newer versions boast over 100 gph evaporation rates. The 5-10% ethanol left in the crude is easily justified by the fact that terpene evaporation and decarboxylation are the very next steps and both require heat and vacuum. Furthermore, crude oil is very viscous and resistant to flow through piping and housing. Some residual ethanol lowers the viscosity, enabling the oil to easily flow into the decarboxylation vessel. Last but not least, a big advantage of the FFE is the fact that the remaining 5-10% ethanol in the crude oil contains much of the azeotropic water. That means that the vast majority of the ethanol used in extraction (and recovered by the FFE) never falls below 190 proof, thus obviating the need for reproofing via molecular sieves or a reproofing still.
Once the crude oil is transferred to the decarboxylation machine, the jacket is heated progressively hotter while the vacuum is applied progressively deeper. The result is 3 sequential processes in the same vessel: 1) evaporation of the remaining 5-10% ethanol/water, 2) evaporation of terpenes which must be removed before CBD distillation, and 3) decarboxylation of CBDA to CBD. Regarding the equipment, the most important elements from a safety and compliance standpoint are the explosion-proof vacuum pump and mixer motor. Also, because C1D2 rated glycol chillers and hot oil circulators are inordinately expensive, it makes sense to place them in an adjacent room and run hosing to the condenser and decarb vessel jacket, respectively.
Decarboxylation System
Hazmat Room
Proceeding along the process flow, a Hazmat Room should be adjacent to the Extraction Room. The Hazmat Room is where the bulk containers of ethanol and other flammable solvents are stored. This is the second C1D2 room and shall have the same C1D2 safety elements with the additional requirement of secondary containment in case the bulk container spills or leaks. The secondary containment must also be able to accommodate water from the Hazmat Room fire sprinklers for 15 minutes in case they discharge.
Depending on the proximity of the bulk ethanol container to the extraction machines, it may be possible to install piping that would allow direct transfer of ethanol to the cooling tower of the solvent chiller. This would avoid the need to manually fill kegs and haul them in and out of the extraction room. Caution- this will generate a great deal of dangerous static charge if not properly grounded.
Distillation Room
The next room in the facility should be home to the distilling equipment. There are only a couple options as far as the types of distillation equipment: short path distillation (SPD) and wiped-film distillation (WFD). Similar to the trade-offs between rotavapor and FFE, SPD offers redundancy by virtue of its small but fragile batch capacity whereas WFD offers continuous processing by way of fully automated stainless steel components and gear pumps to keep the oil moving throughout the still. Crude oil, distillate, and residue are all non-volatile and non-flammable so the Distillation Room can be a non-classified location per the NFPA code.
One major disadvantage of SPD can now be viewed as a selling point- the crude oil sits in a hot boiling flask for a long time compared to WFD which can lead to isomerization of cannabinoids. The conversion of CBD to delta-8-THC using SPD is currently in a legal gray area which many processors are exploiting with haste before the loophole is closed.
The product of distillation is >80% CBD distillate. The non-selective nature of extraction solvents as well as distillation result in THC levels that are concentrated to levels above the legal definition of hemp (<0.3%) and is regarded as “hot” distillate. Therefore, it is necessary to either formulate consumer products in-house such that the dilution factor will bring the THC to under 0.3% or further purify the distillate to remove the egregious THC.
Thin Film Distillation
Crystallization
Crystallization of CBD to form isolate is the simplest way to remove THC because CBD readily crystallizes at high concentrations whereas THC does not.
The most challenging part of crystallization is doing it safely due to the hydrocarbon solvents needed. One can mitigate the risk slightly by choosing heptane over pentane at the expense of purging efficiency. Or a compromise could be made to allow for the washing of the crystals with pentane but crystallization with heptane. The downside of this is the complicated housekeeping of another solvent. Whichever solvent is chosen, the crystallization and filtration vessels should be closed-loop and located in a C1D2 room. Hydrocarbon solvent is transferred using an inert gas such as nitrogen and vessels shall be properly grounded. The receiving crystallization vessel should be pre-purged with nitrogen gas to account for when the vessel fills with solvent, the headspace will be accumulating flammable vapor and create a hazardous environment inside the crystallization vessel. Likewise, as the headspace nitrogen/solvent vapor mixture is vented from the vessel as the liquid solvent displaces the headspace, it must pass through a cold trap to condense the vapor and prevent it from entering the ambient air in the room. Similar headspace management should be employed when the crystal slurry is transferred to the filtration vessel.
The crystallization and filtration equipment itself should be constructed of stainless steel, have an explosion-proof mixer motor, and all seals should be made of PTFE. Both vessels should be jacketed so that the solvent/distillate mixture can be cooled down in the case of crystallization and so the isolate cake can be warmed to accelerate purging in the filtration step.
Crystallization System
Remediation
If your business model includes selling bulk distillate, the THC must be remediated in order to be sold legally. This involves a very technical and expensive process known as flash chromatography. These systems are slow, low throughput, and require large amounts of solvent and, in turn, evaporation. A skilled technician is needed to operate these instruments as well as verify the efficacy of the remediation method. This verification is done by high-performance liquid chromatography (HPLC) and is an indispensable tool in a hemp oil extraction and processing facility. Remediation instruments are normally placed alongside the HPLC chromatography machine in the Analytical Room.
Analytical Room
As stated previously, many of the highly technical analyses can be outsourced to a 3rd party lab, but every hemp oil processing facility should have the ability to perform routine potency analyses in-house. An HPLC is a small, inexpensive instrument that is relatively straightforward assuming the person is properly trained. Results can be acquired within one hour of taking a sample from the process flow. The analytical equipment should be placed in a clean, secure room and occupied by authorized personnel only.
Formulation & Packaging
White labeling and private labeling is a valuable service to offer customers, not to mention a great alternative to remediation. A formulation and packaging room should have enough room to accommodate several hotplates, homogenizers, and an ultrasonicator if beverages are desired.
Storage/Vault
Besides the storage of consumables and miscellaneous items, the facility should have a vault for secure storage of high-value end products such as distillate, isolate, and consumer packaged goods. Key card access and security monitors are highly recommended.
Employee Break Room and Bathroom
Not only is it good management, but it is also a federal law to provide employees with a room to eat meals, store food, change into uniforms, and use the lavatory.
Hire Professionals to Complete a Hemp Oil Processing Facility
Building a processing facility is a very costly project often undertaken by brave entrepreneurs with little to no experience on the subject. While it may be tempting to cut costs by DIY engineering, early mistakes can be irreparable in many cases. Therefore, it is imperative that you build a qualified team from the start. Here is a list of positions you should fill and the main services they provide:
Lead Scientist
This person should be a trained chemist or engineer with experience in extraction, distillation, analytical chemistry, and laboratory safety. Most equipment purchasing decisions are made by the Lead Scientist and the technical specifications are communicated by the Lead Scientist to the General Contractor and Architect. The Lead Scientist is the main point of contact for the FPE and the Peer Review/Field Verification Engineer.
Architect
The architect is responsible for organizing the plethora or design and logistical details for the project into a concise and professional blueprint for the General Contractor, Fire Department, and the local government office that issues building permits.
General Contractor
The General Contractor is the main contact point between the Lead Scientist, Architect, subcontractors, local permit department, Fire Department, inspectors, and owners. The subcontractors provide the MEP drawings to the GC, architect, and lead scientist. MEP refers to mechanical, electrical, and plumbing specifications. The mechanical drawings are supplied by the HVAC technician, the electrical schematics are supplied by the electrician, and the plumbing diagram is provided by a licensed plumber & fire water specialist. This set of MEP drawings is the playbook for the entire project and contains thousands of specifications.
Fire Protection Engineer (FPE)
The FPE is a Professional Engineer (P.E.) certified by the state where the facility is located. The FPE takes all the information about the solvents, quantities, floorplan, exits, egress, etc to make recommendations on sprinkler head locations, Hazmat room specs, fire extinguisher locations, and ventilation requirements. This information is compiled into a comprehensive Hazardous Analysis Report and shared with the Fire Marshal.
Peer Review/Field Verification Engineer
This P.E. is a versatile scientist with the authority to peer review any pieces of equipment that were not already peer-reviewed by the manufacturer. They will also review the entire facility and provide verification to the Fire Marshal that all the equipment is installed and situated in a safe manner. Finally, they will peer review the Process Piping to verify that the hosing, piping, tubing, and conduit are all satisfactory for the purpose they serve. The Fire Marshal often relies on the Field Verification Engineer to provide objective assurance that the facility is safe.
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Conclusion on How to Extract CBD from Hemp Oil
Hemp oil processing and CBD extraction is an exciting new industry but not for the faint of heart. Rapid innovation, regulation, and market volatility require management that is knowledgeable, flexible, aggressive, and patient. Establishing a roadmap early in your venture will greatly increase your chance for success.
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