What Is Solvent Extraction?
Solvent extraction is a method where chemical compounds are isolated based on their solubilities. This process requires using a particular solvent in the form of fluid to separate and dissolve another substance.
Solvent extraction is used in many different industries from food to vegetable oils, perfume to manufacturing, mining to processing of minerals, pharmaceuticals, and cosmetics. The main purpose of solvent extraction is to isolate hazardous materials from the sediments and sludge or separate the useful components from debris.
Professional extractors use many different solvents to concentrate the essential oil. Ethanol, butane, and propane are the most common solvents used by extractors. Yet, not all solvents and extraction methods are created equal. Some, like ethanol and CO2, are safer for consumers and processors alike. However, even these two processes can produce dramatically different products.
What is Ethanol Extraction?
“Ethanol/alcohol extraction is optimization for high throughput because it generally has the lowest electrical costs per pound, and almost always a lower labor cost per pound of biomass processed. It is likely the cheapest equipment to scale, especially when safety concerns are taken into consideration.”
Compared to other extraction methodologies such as hydrocarbon extraction, ethanol extraction can help an extractor pull a broader range of compounds from the plant, and can provide operators with higher throughput, ethanol has been used as a solvent in pharmaceutical and food processing industries. Ethanol extraction equipment requires a lower upfront investment compared to other processes without sacrificing high extraction efficiency.
As such, cost and extract profile are some of the major factors to bear in mind when considering different types of ethanol extraction.
Note that other alcohols may be used in cannabis extraction as an alternative to ethanol. For example, isopropanol is particularly popular among producers.
Ethanol is, simply put, alcohol. In ethanol extraction, alcohol is used as a solvent. Unlike other solvents, like butane, ethanol is considered a safe and clean solvent that poses little risk of toxicity. Apart from solventless extractions, ethanol is considered one of the safest solvents to use in consumer goods.
As a solvent, ethanol is highly efficient. Alcohols are polar in nature, allowing ethanol to form bonds with both water-soluble and fat-soluble plant compounds alike.
Ethanol is also often mixed with other solvents to produce extracts with specific properties. For example, the alcohol is frequently used at the end of a BHO or CO2 cycle to “winterize” the product by pulling out unwanted waxes. The end product will often be more translucent, with a light amber coloration.
advantages of Ethanol Extraction
- Compared to other extraction methods, ethanol extraction provides the quickest run times on the market.
- Able to easily store large volumes of ethanol, operators can store more of the ethanol solvent so they can process higher volumes of biomass per day.
- Ethanol is very efficient at separating cannabinoids and terpenes from the plant, removing the need for winterization or dewaxing.
- Due to strict compliance regulations of other solvent types, ethanol extraction can simplify the licensing process to get a business off the ground quickly without compromising safety and compliance.
- Ethanol extractions run at lower pressures and use approved organic solvents.
- Low risk of toxicity since ethanol evaporates quickly, is affordable and is a food-grade solvent that is safe for lab use.
Disadvantages of Ethanol Extraction
- Ethanol is a polar solvent and will pull more water-soluble components from the plant such as chlorophyll, and create lower purity products.
- Ethanol has a much higher boiling point than Butane or Propane making the recovery process generally slower and more difficult.
- Post-processing for ethanol extraction is much more labor-intensive than hydrocarbon and involves, requires additional purification and refinement processes, and the use of several different methods of refinement and filtration, meaning an increase in labor, time, and cost.
- Ethanol is limited in the products it can produce making items like shatter or “sauce” nearly impossible.
- Food-grade ethanol can have a higher cost than CO2.
- Most importantly, ethanol-derived chemical contaminants10that remain in the extracted oil after removal of the ethanol may increase the risk of safety and health for the consumer. For example, some of the residual contaminants listed in the specially denatured ethanol recipes have a higher boiling point compared to ethanol and are not removed from the oil during distillation. Furthermore, solvent analysis for contaminants is not always included in a typical certificate of analysis.
The ethanol extraction process of CBD oil
The ethanol is loaded into vessels. The ethanol is brought down to below-freezing temperatures using chillers and jacketed vessels. The ethanol is sprayed from the tank to the extractor, to completely soak the hemp biomass. The ethanol is circulated to complete the run. The extract solution is pumped out through the filter assembly into a separate collection vessel.
These two types of extraction follow the same basic steps. But, because of the difference in the temperature of the ethanol, they will yield different results. Both can be carried out using a relatively simple setup without requiring specialized equipment. Here are the main steps involved:
- The raw cannabis plant material is placed in a suitable vessel. It might be left loose or placed inside a bag (think of a very large teabag). The plant matter is completely covered with ethanol and left to soak. Soaking time will depend on the ethanol temperature and the desired profile of the product.
- During soaking, the ethanol will solubilize the cannabinoids (including THC and CBD) and possibly other compounds present in the plant, such as terpenes, pigments, and plant lipids. The specific compounds and their quantities will depend on the temperature of the ethanol, as well as various aspects of the plant matter, including strain, plant part, and condition of the raw material.
- After soaking, the plant material is separated from the ethanol solution. If a bag is used, this step might be as simple as removing the bag from the vessel. If loose plant matter is used, some type of filtration will be applied.
- The next stages will depend on a few factors including the temperature of the ethanol and the desired final product. For example, a winterization step is often included to remove undesirable plant lipids from the extract. For some extracts, in particular, those using cold ethanol, the solution will be accepted as is.
- Now it’s time to remove the ethanol from the extract. This is often carried out using vacuum distillation in a rotary evaporator, but other methods include a falling film evaporator (often used in larger-scale production).
- Although most of the ethanol may be removed using those methods, there will usually still be an unacceptable level of ethanol in the extract. A vacuum oven is often used to purge the remaining alcohol, but a hotplate stirrer is another option.
Features of room temperature
By extracting at room temperature, an extractor can achieve a robust plant profile without the need for heating or cooling equipment.
An extractor will likely end up with some plant lipids in the room temperature extract, which, if undesirable, will need to be removed by a winterization step. This involves washing the extract with cold ethanol, allowing plant fats and waxes to precipitate out of the solution, and then filtering to remove them. Multiple winterization steps may be required to reach the desired final product.
When you opt for cold extraction, you have the task of keeping the mixture cold (usually below -30°C) for a long period of time while the plant soaks in the alcohol. This can be difficult if you want to work with larger quantities but are limited in terms of equipment. That said, one of the benefits is that cold ethanol won’t pull out plant lipids and pigments. This means you can avoid having to deal with a winterization step and may achieve a more optimal flavor profile.
Warm ethanol extraction
Ethanol extraction processes can be performed under cold or warm temperatures. A warm ethanol extraction method is the Soxhlet technique.
The raw plant material is placed in a special piece of equipment called a Soxhlet extractor. Warm ethanol is passed over the material multiple times, and the solvent is recycled. Once the extraction is complete, additional steps such as winterization are carried out as needed and the ethanol is removed, usually via a rotary evaporator.
With warm ethanol extraction, an extractor can solubilize a border range of compounds from the plant matter. This means it can be a good choice if you want a full-spectrum extract. However, with high temperatures, you’ll solubilize pigments such as chlorophyll, which tends to have a bitter taste. You may also cause damage to sensitive compounds such as terpenes, further impacting the flavor of the extract. Removal of undesirable compounds is possible but can require multiple steps and a longer overall process.
Some processors prefer this warm ethanol approach because it is time-efficient and requires a relatively low solvent-to-biomass ratio.
What is the CO2 Extraction Process?
Carbon dioxide is a gas at room temperature and pressure.
When compressed under high pressure (2,000 to 5,000 PSIG) the substance becomes what is known as a supercritical fluid.
A supercritical fluid is a phase in which the molecules have the density of a liquid but still have the movement properties of a gas. Fluid in this state can penetrate deep into a botanical matrix, can pass through tightly packed beds of botanical material, and can dissolve a substantial amount of non-polar substances.
Supercritical CO2 extraction technology provides an efficient extraction method that provides good extraction efficiency, low operating cost, and a product that can be marketed as both “green” and organic.
Like ethanol extraction, CO2 extraction is considered one of the safest forms of extraction possible. CO2 products pose little risk of toxicity to consumers, which is perhaps one of the reasons that vapor cartridges filled with CO2-extracted essential oils have become so widespread.
Additionally, CO2 extraction produces extracts that are of high-quality and thus require less post-processing than extracts produced by ethanol extraction. While CO2 extraction can produce extracts of excellent quality, the equipment comes with a high cost to purchase and operate, especially at small to moderate scale.
Extraction Efficiency
Supercritical fluids, including CO2, have unique properties that simultaneously give them liquid-like density and gas-like movement properties. Combined, these qualities make them incredibly effective at solvating botanical material and result in high extraction efficiency.
Extraction Selectivity
Supercritical CO2 is a highly non-polar solvent of moderate strength and will effectively extract non-polar compounds from plants such as fats, terpenes and others.
CO2 is a solvent that possesses tunable extraction strength and selectivity. By manipulating extraction pressure and temperature operators can produce a wider variety of extracts than is possible with ethanol extraction. Lower pressures result in extracts that are lighter in color and flavor.
Higher pressures result in faster, more complete extractions, but at the cost of a darker extract color.
CO2 has good market value because it has good purity, and lacks troubling contaminants such as sugars, proteins, gums, and other more polar molecules.
co2 vs ethanol extraction of CBD oil
Each extraction method uses a different solvent to pull essential oils out of the biomass.
While each method carries its pros and cons, supercritical CO2 extraction has emerged as the leader for demanding customers while driving high throughput and low operating costs, with the optimization quality, purity, and consistency of essential oils produced.
The following table compares the pros and cons of CO2
| Parameter | Ethanol Extraction | Supercritical CO2 Extraction |
| Organic Oil | Organic ethanol is required. | No special requirements for approved organic solvents. |
| Cannabinoid Recovery | 50-80% typical cannabinoid recovery including carbon scrubbing. The method may require carbon to remove chlorophyll. Carbon absorbs THC and CBD which lowers recovery. Carbon is a high-cost consumable. | 85-95% typical cannabinoid recovery. No carbon is required. |
| Solvent Recovery | Ethanol is expensive and therefore needs to be recovered. Typically, 90-95% recovery of ethanol leads to high operating costs. Losses come from ethanol remaining in biomass and in the extract. | No need to recover CO2 other than recycling within a run or batch due to the low expense of CO2. |
| Reuse of Extracted Biomass | Biomass extracted with ethanol is hazardous waste until the ethanol is removed to negligible levels, and may be flammable and/or toxic due to the type of ethanol used. | Biomass extracted is clean and is a source of food-grade essential amino acids. Transportation is not regulated. |
| Winterization | Winterization may be avoided if extraction is at < -20o | Winterization may be avoided with subcritical extraction. However, extraction is much slower at low pressure. |
| Safety | Significant fire hazard risk for indoor deployment. | Inert. No fire hazard risk.Static and asphyxiation risks are mitigated with proper installation. |
| Infrastructure Cost & Requirements | High cost for hazardous building occupancy and special room classifications and limitations. | Minimal requirements. May operate in industrial building (F2) classification. |
| Equipment Cost | $2-3M USD for 1 ton per day | $3-4M USD for 1 ton per day |
| Operating Cost | High variable costs and overhead due to ethanol cost, losses of ethanol, consumables, reduced recovery, high insurance premiums, hazardous waste disposal, and energy costs. | The very low variable cost for CO2. No difficulty getting business insurance. |
| Scalability | Scalable easily to 10 tons per day in less than 450 m2 with hazardous (H2,3) occupancy, with about ~7000 amps, 230V, 3 phase cooling capacity, and C1D2 special rooms. | Scalable easily to 10 tons per day in less than 450 m2 in F occupancy with ~2400 amps 230V 3 phase. |
| Solvent Sourced Cross-Contamination Risk | Herbicide, pesticide, solvent contamination, extraction byproduct contamination, and build-up risk.b | CO2 is not generally used across lots. No risk of cross-contamination. |
| Solvent Sourced Cross-Contamination Risk | Herbicide, pesticide, solvent contamination, extraction byproduct contamination, and build-up risk.b | CO2 is not generally used across lots. No risk of cross-contamination. |
| Cost of Solvents | Food-grade ethanol is safest and comes with little to no chemical contamination risk but with a higher cost. Specially denatured solvents are less expensive but carry a myriad of non-food grade contaminants. | Low price per kg. |
| Terpenes for full spectrum flavor and aroma | Lost during processing. | Harvested during processing. |
| Environment | The high carbon footprint to produce ethanol, tons of cooling capacity needed to cool to <20o | The byproduct of existing industrial processes, non-toxic, nonecotoxic, renewable, recaptured. Considered a green solvent by the American Chemical Society. |
Estimated Difference in Solvent Cost for a 1 ton per day Ethanol and CO2 system.
| Ethanol | CO2 | |
| Approximate Equipment Cost | $2,000,000 | $4,000,000 |
| Required Solvent Start-Up Cost | $7,000 | $500 |
| Solvent Loss Cost per Day | $3,500 | $115 |
| COMPARISON | ||
| 1 Year Solvent Loss Cost | $1,260,000 | $42,048 |
| 10 Year Solvent Loss Cost | $12,260,000 | $340,000 |
Ethanol extraction vs co2 extraction: which one is better?
Which extraction method is better for consumers and producers? There is not an easy answer. In fact, there is no optimization method overall. Ultimately, it depends on what the producer needs to create. Here, we cover the most important factors to consider when making the choice between ethanol vs. CO2 extraction.
Costs
Out of all the methods available to producers, carbon dioxide is by far the most expensive method in terms of upfront costs. Processors must pay a steep price for a CO2 extraction system compared to lower-priced, entry-level ethanol and hydrocarbon units. Hydrocarbon systems that use butane and propane can be the most affordable.
An entry-level CO2 extraction system can start at about $100,000. In addition to the cost of the equipment, processors may need to invest more in employee training to handle the specialized machinery. Ethanol requires a lower upfront investment and will not require as much intensive training for operators.
In terms of operating costs, there are a few variables to consider for each method. Ethanol extractions can include high variable costs and overhead due to the solvent price, ethanol losses, insurance premiums, hazardous waste disposal, and lower recovery. CO2 has low variable costs. Business insurance is not hard to get with CO2.
Food-grade ethanol is relatively safe and can reduce the likelihood of chemical contamination but it comes at a higher price. Denatured ethanol solvents are more affordable but include a wide range of non-food grade solvents. In comparison, CO2 has a low price per kilogram.
Ethanol as a solvent requires additional infrastructure investment due to the limits on ethanol storage, requirements for alarm lights, deflagration alarms, detectors, and a complete alarm system for gas detection. CO2 does not require any of these additional expenditures since there is no limit on the amount of CO2 that a facility can store on site.
Overall, CO2 extractions may cost more initially but can have lower operating costs that may pay for themselves in the long run. In the battle between ethanol extraction vs. CO2 extraction, it is hard to choose the optimization method in terms of cost.
Quality
For operators looking to make high-potency distillate, ethanol extraction is the way to go. Ethanol can extract a high amount of active compounds quickly to create a high-quality extract. For processors that want to create full-spectrum extracts featuring high concentrations of terpenes and cannabinoids as well as flavonoids and carotenoids, CO2 extraction may work for them. This method can help them produce a product that more closely resembles the plant material.
For many producers and consumers, CO2 extractions may reduce the risk of the carbon dioxide ending up in the final product compared to other methods that may leave behind residual solvents. When processors want to create pharmaceutical-grade products, CO2 may be a viable option.
Safety
Ethanol extraction is flammable, but not nearly as much as light hydrocarbons such as butane and propane.
However, for those that want peace of mind, CO2 can offer more safety than other extraction methods since carbon dioxide is not flammable and less toxic than ethanol. In addition, there is a lower risk of ending up with residual solvents in the end product.
Ethanol extraction can run the risk of leaving behind chemical contaminants that can increase the health risk for consumers (medical and recreational), especially when using denatured ethanol that includes non-food-grade chemicals.
While the process occurs at high pressure, peer-reviewed systems are designed to handle any risks associated with the high-pressure process.
However, CO2 is not entirely risk-free. If there is a leak in the room, it could replace the oxygen and suffocate operators. An adequate alarm system and sensors to detect leaks can offset these dangers.
In terms of solvent recovery, ethanol extraction requires more investments in the recovery process. Generally, CO2 extractions do not need to recover the solvent. However, they may want to recycle the carbon dioxide within a run or batch due to the affordability of CO2.
In terms of its effect on the environment, ethanol has a higher carbon footprint. The higher footprint comes from the production of the ethanol solvents, the high amount of energy needed to cool the system down to cool temperatures, and the environmental costs of disposing of the hazardous biomass waste.
CO2 extraction uses CO2, a byproduct of many industrial operations that is currently in the atmosphere. CO2 is non-toxic, renewable, and able to be recycled for use. CO2 is also considered a green solvent by the American Chemical Society.
CHOOSING A SYSTEM
Ultimately, the type of system a processor chooses will depend on their budget and specific production needs. If companies have the budget and want to create full-spectrum products with slightly lower yields, then CO2 is a good option. For companies that want to get their operations off the ground quicker and for a lower upfront investment while still producing quality CBD from hemp, ethanol extraction may be the optimization option.