Supercritical extraction of CO2 as a single medium
Supercritical CO2 extraction
In SFE technology, supercritical CO2 extraction using CO2 as the extraction medium is the most widely used.
Supercritical fluid extraction with CO2 as a single medium is mainly used for lipophilic, non-polar materials with small molecular weight, which is mentioned in the solubility rules and Compounds that are miscible or highly soluble with supercritical CO2. If the components contained in the raw materials belong to the mentioned compounds, it is difficult to extract and remain in the raffinate.
Studies have shown that the extracts of supercritical pure CO2 are mostly mixtures of lipophilic chemical components such as volatile oil, grease, alcohol, ether, ester, resin, etc. Because supercritical CO2 extraction can achieve supercritical extraction near room temperature, it can avoid the problem of decomposition of heat-sensitive substances caused by high-temperature operation, and the solute separation is easy to avoid the problem of solvent residues, which is beneficial to guarantee and improve the quality of natural products. , Supercritical CO2 extraction is regarded as a green chemical technology
Pretreatment of raw materials includes crushing methods (grinding, slicing, etc.), particle size, raw material humidity limits, etc .; extraction operation parameters mainly include extraction pressure and temperature, extraction time, solvent-to-material flow ratio or solvent flow rate, etc .; separation operation parameters include Separation pressure and temperature, phase separation requirements, and solvent recovery and treatment during the process. The supercritical fluid cycle time depends on the solute extraction ability and separation factor of the supercritical fluid. Laboratory feasibility studies often use methods such as the least squares method, single factor test, or response surface method to study the effects of various factors on the extraction rate (or recovery rate) and selectivity of the target substance, so as to optimize and obtain appropriate operating parameters
For example, Guan et al. Compared supercritical CO2 extraction with clove oil with several traditional methods.
The results show that the oil recovery rate of SFE reaches 19.6% (mass fraction), which is nearly double that of steam distillation and water distillation. %, Mass fraction); at the same time, the extraction time of SFE is short (2h) without solvent residue, and the product is high-quality light yellow oil. The color of the essential oil obtained by distillation in water is dark, indicating that the heat severe decomposition, low oil recovery and solvent residues. When using absolute ethanol as a solvent, the extract obtained by Soxhlet extraction is a brown extract, which is difficult to obtain light yellow clove oil, which must be post-treated. The above results show that supercritical CO2 extraction of clove oil technology is far superior to other extraction methods
In addition, multi-stage extraction and multi-stage separation are also a type of process mode often used in supercritical fluid CO2 extraction.
Multi-stage extraction, also known as sequential or segmented extraction, refers to the method of gradually increasing the extraction pressure, so that the extracted components are sequentially extracted according to the polarity, boiling point, and molecular weight, in order to increase the target component purpose.
Multi-stage separation refers to the setting of different pressures and temperatures during the separation stage, so that the extracted components are sequentially separated according to the polarity, boiling point and molecular weight in order to increase the content of the target component.
Figure 1 shows a schematic diagram of the gas chromatogram of a typical natural product's chemical components. The types of compounds included are plant aromatic oils, higher terpene esters, free fatty acids, fats, waxes, resins, and pigments.
When supercritical CO2 is extracted under certain conditions (such as 60 ° C and 30 MPa), the extraction rate of the product can be increased due to the higher density. However, in addition to the plant aromatic oil, higher terpene esters, free fatty acids, fats and other components, some higher boiling waxes, resins and pigments were also extracted at the same time. Because some products have certain restrictions on the amount of wax, resin and pigment, the extracts under the above high pressure often do not meet the product requirements, as shown by the diagonal line 3 in FIG. Therefore, a multi-stage separation process can be used to achieve selective separation of the extracts.
For example, for supercritical CO2 extracts at 60 ° C and 30MPa, the pressure is first reduced to 10MPa, as shown by the diagonal line 2 in Figure 1.The high-boiling waxes, resins and pigments will And 10 MPa), the obtained fraction is mainly rich in wax and resin; when the pressure is reduced to 6 MPa, as shown by the diagonal line 1 in Fig. 1, the fraction obtained in the second stage separator (60 ° C and 6 MPa) is rich Contains terpene esters, free fatty acids, and fats; the remaining fractions are mainly rich in plant aromas and require a third-stage separator to be collected under lower pressure conditions; the fractions collected in stages can be further mixed in corresponding proportions To meet the quality requirements of different products.
Reverchon et al. Used supercritical COQ2 to study the extraction of sage oil by using two-stage separation. Volatile oil