Supercritical CO2 Extraction Process

The objective of every food production is to achieve high quality, minimally processed, "natural", additive-free food with high nutritional value. Researchers have been trying to find the best alternative processes to minimize the environmental impact, decrease the toxic residues, efficiently use sub-products, and produce higher-quality foods. Oil extraction with supercritical CO2 fluids is an alternative method to replace or complement conventional industrial processes such as pressing and solvent extraction. 
The principle of the supercritical CO2 (carbon dioxide) fluid extraction and separation process is based on the use of the superior solubility of supercritical CO2 fluid for certain specific natural products, and the relationship between the solubility of supercritical CO2 and its density, i.e., the effect of pressure and temperature on the solubility of supercritical CO2 fluid.

What is Supercritical CO2 Extraction?

Supercritical CO2 fluid has emerged as a remarkable substance with diverse applications across various industries. As a supercritical fluid, CO2 exhibits unique properties that make it a versatile solvent for extraction, cleaning, and other processes.

Supercritical Fluid

With the change of temperature and pressure in the environment, some substances exist in three phases – gas phase, liquid phase, and solid phase, and the point where the three phases coexist in equilibrium is called the three-phase point. The point at which the interface between the liquid and gas phases disappears is called the supercritical point. The temperature and pressure at the critical point are called the critical temperature and critical pressure, and the pressure and temperature at the critical point vary for different substances. A Super Critical fluid (SCF) is a fluid whose temperature and pressure are higher than its critical point. When an object is in a supercritical state, it is called “supercritical fluid” because the properties of the gas and liquid phases are so similar that they cannot be separated. Read more: Supercritical carbon dioxide

Supercritical state data for common molecules

Molecular	Temperature (℃)	Pressure (atm)	Density (g/cm³)	Molecular	Temperature (℃)	Pressure (atm)	Density (g/cm³)
H2	-239.9	12.8	0.032	CF3Cl	28.8	38.7	0.579
N2	-147.0	33.5	0.314	NH3	132.3	111.3	0.235
Xe	16.6	57.7	1.110	CH3OH	240.0	78.5	0.272
CO2	31.265	72.9	0.468	CH3CN	274.7	47.7	0.237
C2H6	32.3	48.2	0.203	H2O	374.2	218.3	0.315
CF3H	25.9	47.8	0.526

What is Supercritical CO2 Fluid

Supercritical CO2 fluid: Carbon dioxide changes its properties at a temperature higher than the critical temperature Tc=31.26℃ and pressure higher than the critical pressure Pc=72.9atm. Its density is almost like a liquid, its viscosity is almost like a gas, and its diffusion coefficient is 100 times that of a liquid, so it has an amazing dissolving ability.

Supercritical CO2 fluid can dissolve a variety of substances and then extract the active ingredients from them, which has a wide range of application prospects.

Supercritical CO2 fluid is created by subjecting carbon dioxide to specific temperature and pressure conditions, surpassing its critical point. At this point, CO2 exhibits properties of both a gas and a liquid, resulting in unique characteristics that make it an exceptional solvent. The principles of supercritical CO2 fluid include:

• Supercritical State: CO2 becomes supercritical above its critical temperature (31.1°C) and critical pressure (73.8 bar). In this state, it possesses a density and solvating power that is intermediate between gas and liquid phases.
• Tunable Solvating Power: The solvating power of supercritical CO2 can be controlled by adjusting temperature and pressure, enabling the selective extraction of desired compounds from a range of substances.
• Non-Toxic and Environmentally Friendly: CO2 is non-toxic, non-flammable, and abundant in the atmosphere. Supercritical CO2 fluid extraction eliminates the need for toxic organic solvents, reducing environmental impact.

Three main characteristics of supercritical CO2 fluids

• The critical temperature of CO2 is 31.26°C and the critical pressure is 72.9 atm, so the critical conditions are easy to achieve.
• CO2 is chemically inactive, colorless, tasteless, and non-toxic, with good safety.
• Cheap, high purity, and easy to obtain.

Top 4 Advantages of Supercritical CO2 Fluid

Supercritical CO2 fluid offers numerous advantages over conventional solvents, making it a preferred choice in various applications. Some key advantages include:

• Selective Extraction: Supercritical CO2 fluid extraction allows for the selective extraction of target compounds by adjusting pressure and temperature parameters.
• Safety and Environmentally Friendly: CO2 is non-toxic, non-flammable, and readily available, eliminating the need for hazardous organic solvents.
• Mild Processing Conditions: The low operating temperatures and pressures of supercritical CO2 fluid minimize the risk of thermal degradation and preserve the quality of extracted compounds.
• Versatility: Supercritical CO2 fluid can extract a wide range of compounds, including essential oils, flavors, fragrances, pharmaceuticals, and natural products.

Applications of Supercritical CO2 Fluid

• Extraction of Natural Products: Supercritical CO2 fluid is utilized to extract natural compounds, such as essential oils, flavors, fragrances, and bioactive compounds from plants and botanical sources.
• Pharmaceutical Industry: Supercritical CO2 fluid is employed for the extraction of active pharmaceutical ingredients (APIs) from natural sources, offering a cleaner and more sustainable alternative to conventional extraction methods.
• Food and Beverage Industry: Supercritical CO2 fluid is utilized for the extraction of flavors, natural colorants, caffeine from coffee beans, and decaffeination of tea.
• Environmental Remediation: Supercritical CO2 fluid is used for the extraction of contaminants from soil and water, contributing to environmental cleanup efforts.
• Carbon Capture and Storage: Supercritical CO2 fluid is employed in carbon capture and storage technologies to capture and sequester CO2 emissions from industrial processes.

4 Factors Influencing Supercritical CO2 Fluid

Several factors influence the efficiency and success of supercritical CO2 fluid processes:

• Temperature and Pressure: Optimal temperature and pressure conditions are determined to achieve desired solubility, extraction efficiency, and selectivity.
• CO2 Flow Rate: The flow rate of supercritical CO2 influences mass transfer rates and extraction kinetics.
• Matrix Composition: The composition and characteristics of the material being processed impact the solubility and extraction efficiency.
• Co-Solvents and Modifiers: The addition of co-solvents or modifiers can enhance solubility and improve extraction efficiency for specific compounds.

Supercritical CO2 Extraction

Supercritical fluid extraction, particularly utilizing supercritical carbon dioxide (CO2), has emerged as a powerful and versatile technique in the field of extraction processes. By employing fluids in their supercritical state, these extraction methods offer numerous advantages over conventional methods, including enhanced selectivity, improved efficiency, and reduced environmental impact.

Supercritical fluid extraction

Supercritical fluid extraction is based on the principle of utilizing fluids above their critical temperature and pressure to obtain desired components from solid or liquid matrices. The critical point is where the fluid exhibits properties of both a gas and a liquid, resulting in unique solvent characteristics. The key principles of supercritical fluid extraction include:

• Supercritical State: The supercritical state is achieved when a fluid is above its critical temperature and pressure. This state provides fluid properties that combine gas-like diffusivity and liquid-like density, making it an excellent solvent.
• Selective Extraction: The solvating power of supercritical fluids can be adjusted by varying temperature and pressure, enabling the selective extraction of specific components while leaving unwanted substances behind.
• Environmentally Friendly: Supercritical fluid extraction methods, particularly with CO2 as the solvent, are environmentally friendly due to the non-toxic nature of CO2 and its ability to be easily separated from the extracted compounds.

Principles of Supercritical Fluid Extraction

Supercritical fluid extraction is based on the principle of utilizing fluids above their critical temperature and pressure to obtain desired components from solid or liquid matrices. The critical point is where the fluid exhibits properties of both a gas and a liquid, resulting in unique solvent characteristics. The key principles of supercritical fluid extraction include:

Supercritical State: The supercritical state is achieved when a fluid is above its critical temperature and pressure. This state provides fluid properties that combine gas-like diffusivity and liquid-like density, making it an excellent solvent.

Selective Extraction: The solvating power of supercritical fluids can be adjusted by varying temperature and pressure, enabling the selective extraction of specific components while leaving unwanted substances behind.

Environmentally Friendly: Supercritical fluid extraction methods, particularly with CO2 as the solvent, are environmentally friendly due to the non-toxic nature of CO2 and its ability to be easily separated from the extracted compounds.

Supercritical CO2 fluid extraction

Supercritical CO2 extraction is a process that extracts compounds from plant material using carbon dioxide. Carbon dioxide is used as a solvent, which is manipulated at high pressure and temperature to achieve a supercritical state, where it exhibits both gas and liquid properties. This method is commonly used to extract valuable compounds like terpenes, cannabinoids, and essential oils from plants.

Supercritical CO2 extraction presents an opportunity for users to extract their desired compounds without leaving behind harmful chemicals and solvents. The extracted compounds retain their natural aroma, flavor, and potency while limiting any alteration of chemical composition. The speed at which the process is carried out ensures that the quality of the extracted compounds remains intact, thus creating a cleaner, and higher quality extract.

Extraction Equipment and Method

Supercritical CO2 extraction equipment is designed to handle the pressure and temperature required to transform carbon dioxide into a supercritical state. The equipment is composed of three components: a solvent pump, extraction vessel, and a separator.

The extraction process occurs by loading the plant material into the extraction vessel. Next, carbon dioxide is pumped into the vessel to reach a supercritical state and to dissolve the desired compounds. The solvent is then separated from the oil-containing material in the separator, where flash evaporation takes place, leaving behind the extracted compounds.

Top 6 Benefits of Supercritical CO2 Extraction

• Selectivity: Supercritical CO2 extraction allows for selective extraction of target compounds by adjusting temperature and pressure, preserving their quality and purity.
• Safety: CO2 is non-toxic, non-flammable, and readily available, eliminating the need for potentially harmful organic solvents.
• Mild Extraction Conditions: The use of low temperatures in supercritical CO2 extraction minimizes thermal degradation of heat-sensitive compounds.
• Versatility: Supercritical CO2 can extract a wide range of compounds, including lipids, essential oils, flavors, fragrances, and pharmaceuticals.
• Environmentally Friendly: The process uses carbon dioxide, which is considered a green solvent since it is non-toxic and can be easily recycled without leaving a harmful residue behind.
• High-Quality Extracts: Supercritical CO2 extraction produces high-quality extracts with a pure flavor and aroma.

Applications of Supercritical CO2 Extraction

• Food and Beverage Industry: Extraction of natural flavors, essential oils, and bioactive compounds from botanicals, spices, and aromatic plants.
• Pharmaceutical Industry: Extraction of active pharmaceutical ingredients (APIs) from medicinal herbs, plants, and algae.
• Cosmetics and Personal Care Industry: Extraction of natural pigments, fragrances, and botanical extracts for use in skincare and cosmetic formulations.
• Environmental Remediation: Extraction of contaminants from soil and water for environmental analysis and purification purposes.
• Nutraceuticals and Functional Foods: Extraction of bioactive compounds with potential health benefits for dietary supplements and functional food formulations.

Process

CO2 extraction, also known as supercritical CO2 extraction, is a process that uses pressurized carbon dioxide to extract desirable compounds from plant materials. Here’re three steps of it works:

• The plant material is loaded into a chamber and pressurized with carbon dioxide until it becomes a supercritical fluid.
• The supercritical CO2 fluid is passed through the plant material, dissolving the desirable compounds, such as essential oils or CBD, and carrying them away.
• The CO2 and dissolved compounds are then passed through a separator, where the pressure is released, and the CO2 evaporates, leaving behind the desired compound.

This extraction method has advantages over other methods because CO2 is a clean, safe, and renewable solvent that doesn’t leave behind any residual solvent in the final product. Additionally, the process can be fine-tuned to be selective for specific compounds, making it ideal for creating high-purity extracts.

The process of supercritical CO2 extraction for CBD

Supercritical CO2 extraction is one of the most popular methods used to extract CBD from cannabis or hemp plants. It is an efficient and clean method that produces high-quality, pure extracts. Here is an overview of the process of supercritical CO2 extraction for CBD:

Top 7 Steps

• Crushing and Grinding: The hemp or cannabis plant material is ground down into smaller pieces to increase its surface area and facilitate the extraction process.
• Loading the Extraction Chamber: The ground material is then loaded into the extraction chamber of the supercritical CO2 extraction equipment.
• Pressurization and Temperature Control: Carbon dioxide gas is pressurized and heated until it reaches the supercritical state. Supercritical CO2 offers the ideal solvent properties for extracting the desired cannabinoids effectively. Also, the optimal temperature and pressure are set and maintained.
• Extraction: The supercritical CO2 is then passed through the plant material, acting as a solvent to extract the desired cannabinoids, mainly CBD.
• Separation: The CBD-rich extract mixture consisting of CO2 and other plant materials is then separated by depressurizing the mixture and allowing it to evaporate or separating it through a post-extraction separation process, such as distillation or chromatography.
• Purification: The final extract is then purified to remove any other undesirable compounds, including THC, terpenes, flavonoids, and waxes.
• Packaging: The pure extract is then packaged in its final form, either as a liquid or a solid concentrate.

summary

Supercritical CO2 extraction has emerged as a popular method for CBD extraction. It offers several benefits, including a higher yield of pure and superior quality cannabidiol oil, enhanced flavor, and reduced risk of unwanted impurities. The primary steps involved in CO2 extraction for CBD include preparation of plant material, loading of extraction chambers, pressurizing the CO2 to reach its supercritical state, extraction of CBD and other cannabinoids, separation, and purification. The final cannabinoid-rich extract can be refined into a crude oil, distillate, or isolate for use in a wide range of products, including topicals, edibles, tinctures, and vape cartridges.

Further Reading: What is the supercritical CO2 extraction process?

Supercritical carbon dioxide extraction is a commonly efficient separation method used method to separate various active ingredients from the plant due to it producing a pure.

Supercritical CO2 extraction, also known as CO2 extraction or Supercritical Fluid Extraction (SFE), is a process that uses carbon dioxide in a supercritical state, which means that it is at a temperature and pressure above its critical point, to extract desirable compounds from plant material or other materials.

Supercritical co2 solvent extraction is one of the gentlest, most flexible, dynamic, CO2 Extraction allows you to create a pure, clean, quality oil that is safe to produce with little-to-no post-processing. These are the products extracted at ambient temperatures and at high pressures to avoid loss of aroma and degradation of actives, also, since supercritical fluid extraction is a green process and nature-friendly technique, it can be used for the extraction of spices, herbs, and flowers using food grade CO2.

Supercritical CO2 extraction has the advantage of being a safe, non-toxic, and environmentally friendly method of extraction. It also allows the extraction of compounds with high purity and selectivity. This process is widely used in the food, pharmaceutical, and cosmetic industries to produce high-quality extracts.

Principle of the supercritical CO2 extraction process

By changing the temperature and pressure as well as flow rate, certain molecules will bond to CO2, allowing them to be separated from the plant. 

• In the supercritical CO2 extraction process, carbon dioxide is pressurized and heated, which converts it into a supercritical fluid that can be used as a solvent. The supercritical fluid is then passed through the plant material, which dissolves and carries away the desired compounds, such as essential oils, flavors, and fragrances.
• After passing through the material, the supercritical CO2 and the dissolved compounds are moved to a collection vessel, where the pressure drops, allowing the CO2 to return to its gaseous state, leaving behind the desired extract.

In the supercritical state, supercritical carbon dioxide is brought into contact with the substance to be separated, so that it selectively extracts the components with different polarity sizes, boiling point heights, and molecular weightiness in turn. Of course, the extracts obtained in each pressure range cannot be single, but the conditions can be controlled to get the best proportion of mixed components, and then the supercritical fluid is turned into ordinary gas using pressure reduction and temperature increase, and the extracted substances are completely or precipitated out, to achieve the purpose of separation and purification, so the supercritical fluid carbon dioxide extraction process is a combination of extraction and separation. Supercritical carbon dioxide extraction is a commonly used method to separate various components from the plant due to it producing a pure, clean, and safe product.

7 Features of the Solubility of Supercritical CO2 Fluids

In the supercritical state, the solubility of CO2 for different solutes varies greatly, which is closely related to the polarity, boiling point, and molecular weight of the solute, and generally has the following features:

1. Lipophilic, low boiling point components can be extracted below 104KPa (about 1 atm), such as volatile oils, hydrocarbons, esters, ethers, and epoxides.
2. Aroma components from natural plants and fruits, such as eucalyptus brain, muscimol, low boiling point esters from hops, etc.
3. The more polar groups ( such as -OH, -COOH, etc.) of a compound, the more difficult it is to extract.
4. The extraction pressure of strongly polar substances: sugar and amino acids should be above 4×104KPa.
5. The larger the molecular weight of the compound, the more difficult it is to extract.
6. Components with molecular weight in the range of 200-400 are easy to extract, and some low molecular weight, volatile components can even be extracted directly with CO2 liquid.
7. High molecular weight substances (such as proteins, gums, waxes, etc.) are very difficult to extract with CO2.

7 Advantages of the Supercritical Carbon Dioxide Extraction Process

Supercritical CO2 is used in large quantities for extraction because it has the following advantages in extraction technology:

Advantages 1#: Purity Promises, Without toxic solvent residue

In the health, nutraceutical, and personal care markets, consumers value product purity. Supercritical CO2 fluid is a colorless, odorless, and non-toxic gas under normal conditions. After separation from the extracted components, there is no solvent residue at all, which can effectively avoid the residue of solvent toxicity under traditional solvent extraction conditions. It also prevents the extraction process from being toxic to humans and polluting the environment, which is a natural and environmentally friendly extraction technology. So the CO2 extraction methods create CO2 essential oil, hemp/cannabis extracts, and CBD products that deliver on purity promises by eliminating harmful solvent residues and reducing unwanted compounds in the finished product.
Further, the Federal Drug Administration (FDA) has labeled CO2 safe for industrial extractions.

Advantages 2#: More beneficial unsaponifiable materials, Low-temperature extraction

The extraction temperature is low, the critical temperature of CO2 is 31.265℃ and the critical pressure is 72.9 atm, which can effectively prevent the oxidation, escape and reaction of heat-sensitive components and retain the biological activity of the biomass intact; meanwhile, it can also extract the high boiling point, low volatility and easy pyrolysis substances below their boiling point temperature.

The production of essential oils requires heat to distill the plant material. Even for cold-pressed citrus oils, some heat can be involved due to the friction involved. CO2 Extracts possess an advantage over essential oils because the botanical material and supercritical CO2 extraction process require much less heat. Low-temperature CO2 extracts generally contain the volatile (aromatic) components of the botanical that are soluble in liquefied CO2. Aromatic molecules each have their molecular weight. Some aromatic molecules are too heavy to be present in a steam-distilled essential oil. However, some of the heavier aromatic molecules are present in CO2 extracts. Therefore, CO2 extracts often smell closer to the aroma of a natural herb than some steam-distilled essential oils.

CO2 supercritical extraction isn’t limited to just the production of aromatic extracts. Low-temperature CO2 extraction can also be used to produce superior lipids (carrier oils) that contain more of the beneficial unsaponifiable materials of the plant that cold pressing isn’t able to extract. Additionally, the biomass(plant) is not subjected to extreme temperatures, so CO2 extract does not experience degradation as it does during other extraction methods.

Advantages 3#: Fewer steps and Easier, Extraction and separation in one

Extraction and separation are combined into one, when the supercritical fluid of carbon dioxide full of solubles flows through the separator, the CO2 and the extracted material quickly recover into two separate phases (gas-liquid separation) and immediately separate, there is no material phase change process, no need to recover solvent, easy to operate, and this makes processing quicker and more efficient; The yield using supercritical CO2 extraction process is higher than other extraction methods, the yield and quality of the product can easily be varied by adjusting the physical properties, not only high extraction efficiency, but also less energy consumption, cost saving, and in line with the trend of environmental protection and energy saving.

Advantages 4#: Truly “Green” Production, Extraction Operation is Simple

The extraction operation is easy, and both pressure and temperature can be the parameters to regulate the extraction process. Near the critical point, small changes in temperature and pressure can cause significant changes in the density of CO2, thus causing changes in the solubility of the material to be extracted, and the extraction can be achieved by controlling the temperature or pressure. The pressure is fixed and the temperature can be changed to separate the substances; conversely, the temperature is fixed and the pressure can be lowered to separate the extracted substances.

Unlike hydrocarbon solvents or ethanol extraction, the supercritical CO2 extraction process can be fine-tuned by adjusting temperature and pressure to achieve variable density, viscosity, and surface tension. This makes processing quicker and more efficient while also targeting only the desired compounds in the biomass such as hemp/cannabis. Therefore, the CO2 extraction process technology is short, small in size, and friendly to the environment. It is a truly “green” production process. Supercritical CO2 has become a favorite of eco-conscious producers of essential oils, cannabis & hemp extracts, and nutraceuticals due to its Green properties

Advantages 5#: Ultra-low Post-operation Cost

Supercritical CO2 is highly competitive with butane and ethanol extractions, particularly for large-scale industrial extraction facilities that are found in the hemp industry. At a large scale, solvent costs dominate the operating cost of the extraction facility and that is where supercritical CO2 excels. Bulk carbon dioxide costs $0.06-$0.10 per pound; no hydrocarbon or alcohol-based solvent can come close to that cost.
More and more processors are choosing to center their businesses around CO2 as a result.

Advantages 6#: Extract greater than 95% of Target Compounds, Wide range of options

The polarity of the supercritical fluid can be changed, and under certain temperature conditions, substances with different polarities can be extracted by changing the pressure or adding the appropriate entraining agent. Specifically, with manufacturers of products (CO2 essential oils, cannabis & hemp extracts) derived from botanical matter (plants), the supercritical CO2 is highly favorable because the supercritical CO2 fluid is highly efficient when targeting specific compounds within plants. The supercritical CO2 extraction process is often able to extract greater than 95% of target compounds in oils found in plants.

Advantages 7#: The efficiency of co2 extraction process can eliminate some post-processing steps

The supercritical CO2 extraction process extracts more botanical compounds faster and eliminates the need for some post-processing steps. Such as CO2 acts as a cleaning agent, so microbial bacteria, molds, and mildew are killed during the process.
This gets your CO2 extract into blends and final products — and on its way to the shelf — faster than other extraction methods, too.

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