Multi-stage extraction & multi-stage separation
Multi-stage extraction and multi-stage separation are a type of process mode often used in supercritical fluid CO2 extraction.
Multi-stage extraction, also known as sequential extraction or segmented extraction, refers to the method of gradually increasing the extraction pressure for extraction, so that the extracted components are extracted in sequence according to the polarity, boiling point, and molecular weight, so as to increase the content of the target component purpose.
Multi-stage separation refers to setting different pressures and temperatures in the separation stage, so that the extracted components are separated according to polarity, boiling point, and molecular weight in order to increase the content of target components.
Schematic analysis of gas chromatography
The figure above shows a gas chromatographic schematic diagram of the chemical components of a typical natural product. The types of compounds contained include plant aromatic oils, high-grade terpene esters, free fatty acids, fats, waxes, resins and pigments.
When supercritical CO2 is extracted under certain conditions (such as 60℃ and 30MPa), the higher density can increase the extraction rate of the product.
However, in addition to plant aromatic oils, higher terpene esters, free fatty acids, fats and other components, some higher boiling waxes, resins and pigments are also extracted at the same time.
Because some products have certain restrictions on the amount of wax, resin and pigment, the above-mentioned extracts under higher pressure often do not meet the product requirements, as shown by the diagonal line 3 in the figure.
Therefore, a multi-stage separation process can be used to achieve selective separation of extracts.
Multi-level separation example
For example, for the supercritical CO2 extract at 60°C and 30MPa, the pressure is first reduced to 10MPa, as shown by the diagonal line 2 in Figure 35, then the high boiling wax, resin and pigment will be in the first stage separator (60°C). And 10MPa), the obtained fraction is mainly rich in wax and resin;
When the pressure is increased to 6MPa, as shown by the slash 1 in the figure, the fraction obtained from the second-stage separator (60°C and 6MPa) is mainly rich in terpene esters, free fatty acids and fats;
The remaining fractions are mainly rich in plant aromatic oils and require a third-stage separator to collect them under lower pressure conditions;
The fractions collected by classification can be further mixed in corresponding proportions to meet the quality requirements of different products.
Research on Extraction of Sage Oil
In the study of supercritical CO2 extraction of sage oil, two-stage separation was used, so that the wax was analyzed and separated in separator I with a higher pressure (8.5MPa), and a higher content of volatile oil was obtained in separator II.
Multi-stage extraction and separation of supercritical CO2 extraction
Multi-stage extraction and separation in supercritical CO2 extraction is a technique used to enhance the efficiency and selectivity of the extraction process. It involves the use of multiple stages or steps to optimize the extraction and separation of desired compounds from the target material. This approach allows for better control over the extraction parameters and enables the extraction of a broader range of compounds with varying solubilities in supercritical CO2.
The multi-stage extraction and separation process in supercritical CO2 extraction typically includes the following steps:
- Pre-treatment: The target material is often subjected to pre-treatment steps before the extraction process. This may involve grinding, milling, or drying the material to increase its surface area and facilitate better contact with the supercritical CO2.
- Multi-Stage Extraction: In the extraction stage, the supercritical CO2 is passed through the extraction vessel containing the target material. This process is typically carried out at specific temperature and pressure conditions to achieve the desired extraction efficiency. However, in multi-stage extraction, the process is divided into several stages or steps to enhance the overall extraction performance.a. Countercurrent Extraction: In countercurrent extraction, the supercritical CO2 is introduced at one end of the extraction vessel while the target material flows in the opposite direction. This allows for efficient mass transfer, as the supercritical CO2 contacts fresh material during each stage, maximizing the extraction efficiency.b. Cascading Extraction: Cascading extraction involves passing the extracted supercritical CO2 from one extraction vessel to another, sequentially extracting different compounds with varying solubilities. This approach allows for the extraction of a broader range of compounds from the target material.
- Separation and Fractionation: After the multi-stage extraction, the mixture of supercritical CO2 and extracted compounds is directed to a separation unit. Here, the pressure and temperature conditions are adjusted to separate the supercritical CO2 from the extracted compounds. The separation process may involve reducing the pressure, allowing the CO2 to return to its gaseous state and leaving behind the extracted compounds as a liquid or solid.
- Recycling and Reuse: The separated supercritical CO2 can be recycled and reused in the extraction process. It is typically purified and pressurized before being reintroduced into the extraction vessel. This recycling of CO2 reduces waste and contributes to the sustainability of the overall process.
The multi-stage extraction and separation approach in supercritical CO2 extraction offers several benefits:
- Enhanced Extraction Efficiency: By dividing the extraction process into multiple stages, more efficient mass transfer is achieved, allowing for improved extraction yields and enhanced extraction efficiency.
- Selective Extraction: Different compounds have varying solubilities in supercritical CO2. Through multi-stage extraction, it becomes possible to selectively extract specific compounds based on their solubility characteristics, leading to higher selectivity in the extraction process.
- Wide Range of Applications: Multi-stage extraction and separation can be tailored to different target materials and desired compounds, making it suitable for a wide range of applications, including natural product extraction, food processing, and pharmaceutical production.
Overall, the multi-stage extraction and separation approach in supercritical CO2 extraction enables better control over the extraction process, improved selectivity, and enhanced extraction efficiency, making it a valuable technique for obtaining high-quality extracts from various sources.
Supercritical fluid extraction (SFE) is the process of separating one component (the extractant) from another (the matrix) using supercritical fluids as the extracting solvent.
Supercritical CO2 extraction (SCFE) is used particularly in the food, beverage, cosmetics and pharmaceutical industry for extracting natural substances, aromas, fats, oils, waxes, polymers, enzymes and colourants in their supercritical physical state.
CO2 is a natural and environmentally-friendly solvent which has advantages over synthetic and harmful media such as n-hexane when it comes to sustainability.