Supercritical fluid extraction
Supercritical fluid extraction is abbreviated as SFE.
At lower temperatures, when the pressure of the gas is continuously increased, the gas will be transformed into a liquid. When the pressure increases, the volume of the liquid increases. For a certain substance, there is always a critical temperature (Tc) and a critical pressure ( Pc). Above the critical temperature and critical pressure, the substance will not become liquid or gas. This point is the critical point.
In the range above the critical point, the state of matter is between gas and liquid, and the fluid within this range becomes supercritical fluid (SF). Supercritical fluid has strong penetrating power similar to gas and larger density and solubility similar to liquid. It has good solvent characteristics and can be used as a solvent to extract and separate monomers.
Supercritical CO2 fluid extraction
Supercritical fluid extraction combines traditional distillation and organic solvent extraction, and uses the excellent solvent power of supercritical CO2 to effectively separate, extract and purify the matrix and the extract.
SFE uses supercritical CO2 to extract the material. CO2 is a safe, non-toxic, and cheap liquid. Supercritical CO2 has a diffusion coefficient similar to gas, liquid solubility, and zero surface tension. It can quickly penetrate into solid matter and extract its essence. It has high efficiency, is not easy to oxidize, and Pure natural, no chemical pollution and other characteristics.
The supercritical fluid extraction and separation technology utilizes the dissolving ability of a supercritical fluid to be closely related to its density, and the density of the supercritical fluid is greatly changed by changing the pressure or temperature. In the supercritical state, the supercritical fluid is contacted with the substance to be separated to selectively extract components with different polarity, boiling point, and relative molecular mass.
When supercritical extraction is used to extract natural products, CO2 is generally used as the extractant.
This is because:
- Low critical temperature and critical pressure (Tc=31.1℃, Pc=7.38MPa), mild operating conditions, and less damage to active ingredients, so it is particularly suitable for processing high-boiling heat-sensitive substances, such as essences, spices, oils, vitamins, etc.;
- CO2 can be regarded as a non-toxic and cheap organic solvent similar to water;
- CO2 is stable, non-toxic, non-combustible, safe, and does not pollute the environment during use, and can avoid product oxidation:
- The CO2 extract contains no nitrates and harmful heavy metals, and no harmful solvent residues;
- In the supercritical CO2 extraction, the extracted material can be precipitated by reducing the pressure or increasing the temperature, without repeated extraction operations, so the supercritical CO2 extraction process is simple.
Therefore, supercritical CO2 extraction is particularly suitable for the extraction and purification of biology, food, cosmetics and medicine.
SFE technology basic process flow
The raw materials are loaded into the extractor after a series of pretreatments such as impurity removal, crushing or flaking.
The system is flushed with supercritical fluid and pressurized.
Under the action of SCF, the soluble components enter the SCF phase.
The SCF phase flowing out of the extractor can be selectively separated from the SCF phase by decompression, temperature adjustment or adsorption, and the SCF can be returned to the extractor for recycling after temperature adjustment and compression.
The SC-CO2 extraction process consists of two parts: extraction and separation.
At a specific temperature and pressure, the raw materials are fully contacted with the SC-CO2 fluid, and after reaching equilibrium, the extract is separated from the solvent SC-CO2 through changes in temperature and pressure, and the SC-CO2 is recycled. The entire process can be continuous, semi-continuous or batch.