Supercritical CO2 Extraction Process:
Basics, 7 Advantages, 7 Features, 4 Applications

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 special 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.

The whole process of extracting roses by supercritical CO2 extraction process

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 clearly 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

Supercritical state data for common molecules

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.

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.

What is supercritical CO2 extraction?

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 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 techniques, it can be used to the extraction of spices, herbs and flowers using food grade CO2.

Principle of 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 state, supercritical carbon dioxide is brought into contact with the substance to be separated, so that it selectively extracts the components with different polarity size, boiling point height and molecular weight size 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 by means of pressure reduction and temperature increase, and the extracted substances are completely or basically precipitated out, so as 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 featuress 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:

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

7 Advantages of 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, and 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 human 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 in order 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 own 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#: Less 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 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 really 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 not only extracts more botanical compounds faster but also 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.

Applications of CO2 Extracts

The parameters of some CO2 extraction processes in the following examples are from the laboratory and need to be adjusted if they are suitable for industrial production.