CO2 Extraction vs. Solvent 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 is, simply put, alcohol. In ethanol extraction, the 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.

What is CO2 Extraction?

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.

Take CBD OIL extraction as an example

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 essential oils produced.

The following table compares the pros and cons of CO2

ParameterEthanol ExtractionSupercritical CO2 Extraction
Organic OilOrganic ethanol required.No special requirements, approved organic solvent.
Cannabinoid Recovery50-80% typical cannabinoid recovery including carbon scrubbing. 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 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 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 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 install.
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.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 little to no chemical contamination risk but with 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.
EnvironmentHigh carbon footprint to produce ethanol, tons of cooling capacity needed to cool to <20oByproduct of existing industrial processes, non toxic, non eco toxic, 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