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What is the multi-stage extraction and separation of supercritical CO2 extraction?

Multi-stage extraction & multi-stage separation

Supercritical CO2 extraction and fractionation equipment
Supercritical CO2 extraction and fractionation equipment

Multi-stage extraction and multi-stage separation are a type of process mode often used in supercritical fluid CO2 extraction.

Multi-level extraction

Supercritical CO2 fractionation equipment
Supercritical CO2 fractionation equipment with multi-stage extraction function

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-level separation

Three-stage separation vessel of supercritical CO2 extraction equipment
Three-stage separation vessel of supercritical CO2 extraction equipment

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

Schematic diagram of gas chromatogram of chemical components of natural products
Schematic diagram of gas chromatogram of chemical components of natural products

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.

What is supercritical fluid extraction

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.

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