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.
Supercritical CO2 extraction process
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
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.
Supercritical fluid extraction is a green process and nature friendly techniques used for the extraction of spices, herbs and flowers using food grade CO2.
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.
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.
5 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#: Without toxic solvent residue
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.
Advantages 2#: 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.
Advantages 3#: 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; 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#: 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; therefore, the technology is short, time consuming and small in size, and is really friendly to the environment. It is a truly “green” production process.
Advantages 5#: 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.