CO2 vs Ethanol Extraction

co2 extraction method vs solvent method

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 best 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.”
Ethanol extraction can help an extractor pull a broader range of compounds from the plant than when using other solvents. Although, this is sometimes considered a drawback.
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

  • Removes the need for winterization or dewaxing
  • Super efficient at separating cannabinoids and terpenes from the plant
  • Food grade solvent that is safe for lab use
  • Able to easily store large volumes of ethanol
  • Affordable solvent
  • Can create full-spectrum hemp extracts
  • Low risk of toxicity since ethanol evaporates quickly

Disadvantages of Ethanol Extraction

  • Ethanol polarity means it can also remove water-soluble compounds such a chlorophyll and create lower purity products
  • Slower recovery process due to ethanol’s higher relative boiling point compared to hydrocarbons
  • May require additional purification and refinement processes after the initial ethanol extraction process, meaning an increase in labor, time, and cost
  • May produce a limited variety of products and unable to produce popular varieties including shatter or terp sauce
  • 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 are not always included in a typical certificate of analysis.

Room temperature and cold ethanol extraction of CBD oil

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:

  1. 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.
  2. 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.
  3. 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.
  4. The next stages will depend on a few factors including the temperature of the ethanol 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 acceptable as is.
  5. 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).
  6. 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

Warm or hot ethanol extraction typically requires special equipment. One popular 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 lengthy overall process.

What is 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. A 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 wide-spread.

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 best quality, purity, and consistency of essential oils produced.

The following table compares the pros and cons of CO2

ParameterEthanol ExtractionSupercritical CO2 Extraction
Organic OilOrganic ethanol is required.No special requirements for approved organic solvents.
Cannabinoid Recovery50-80% 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 RecoveryEthanol 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 BiomassBiomass extracted with ethanol is hazardous waste until the ethanol is removed to negligible levels, 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.
WinterizationWinterization may be avoided if extraction is at < -20oWinterization may be avoided with subcritical extraction.  However, extraction is much slower at low pressure.
SafetySignificant fire hazard risk for indoor deployment.Inert. No fire hazard risk.Static and asphyxiation risks are mitigated with proper installation.
Infrastructure Cost & RequirementsHigh 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 CostHigh 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.
ScalabilityScalable 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.bCO2 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.bCO2 is not generally used across lots.  No risk of cross-contamination.
Cost of SolventsFood-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 aromaLost during processing.Harvested during processing.
EnvironmentThe high carbon footprint to produce ethanol, tons of cooling capacity needed to cool to <20oThe 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.

 EthanolCO2
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