What Is Supercritical Extraction?

Supercritical fluid is a supercritical fluid, which is a state of gas and liquid that is neither gaseous nor liquid. This kind of substance can exist only when its temperature and pressure exceed the critical point. The density of a supercritical fluid is larger, similar to that of a liquid, and its viscosity is closer to that of a gas. Therefore, supercritical fluid is an ideal extractant.

Chinese name: Supercritical extraction
Foreign name: supercritical fluid extraction

Application area: Extraction of volatile oil, perfume industry, etc.
World's first: American Philo Power Station

Overview of supercritical extraction

English name of supercritical extraction

supercritical fluid extraction

Introduction to supercritical extraction

The solvent strength of a supercritical fluid depends on the temperature and pressure of the extraction. Utilizing this characteristic, simply changing the pressure and temperature of the extractant fluid, the different components in the sample can be extracted according to the solubility in the fluid, and the weakly polar substances at low pressure are extracted first. The increase in pressure, the more polar and large molecular weight substances and basic properties, so the supercritical extraction under the program pressure increase can obtain different extraction components, but also can play a role in separation.

The change in temperature is reflected in two factors that affect the density of the extractant and the vapor pressure of the solute. In the low temperature region (still above the critical temperature), the temperature rise decreases the fluid density, and the vapor pressure of the solute does not increase much. The temperature increase during the dissolving capacity can cause the solute to be precipitated from the fluid extractant. When the temperature is further increased to the high temperature region, although the density of the extractant is further reduced, the vapor pressure of the solute is increased and the volatility is increased. Increasing trend.

In addition to pressure and temperature, adding a small amount of other solvents to the supercritical fluid can also change its ability to solute. Its mechanism of action has not yet been fully understood. Usually the added amount does not exceed 10%, and most of the polar solvents are methanol and isopropanol. Adding a small amount of polar solvent can further extend the application of supercritical extraction technology to more polar compounds.

Supercritical fluid extraction

Substances exist in three forms: gas, liquid, and solid, and can be phase-converted under different pressures and temperatures. When the temperature is higher than a certain value, any large pressure cannot convert the pure substance from the gas phase to the liquid phase. The temperature at this time is called the critical temperature Tc; and at the critical temperature, the gas can be liquefied. The minimum pressure is called the critical pressure Pc. When the temperature of a substance is higher than the critical temperature and the pressure is greater than the critical pressure, the substance is in a supercritical state. In the pressure and temperature diagram, the region above the critical temperature and critical pressure is called the supercritical region. If the fluid is heated or compressed to a state above its critical temperature (Tc) and critical pressure (Pc), the gas is transferred to the state. Pressurized, the gas will not liquefy, but the density increases, it has similar liquid properties, while still retaining gas properties. A fluid in this state is called a supercritical fluid.

Principle of supercritical extraction technology

The principle of the supercritical CO2 fluid extraction (SFE) separation process is based on the relationship between the solubility of a supercritical fluid and its density, that is, the effect of pressure and temperature on the solubility of a supercritical fluid. In a supercritical state, a supercritical fluid is brought into contact with a substance to be separated, so that it selectively extracts components having a polarity, a high and a low boiling point, and a large molecular weight in turn. Of course, the extracts obtained for each pressure range cannot be single, but the conditions can be controlled to obtain the optimal proportion of the mixed components, and then the supercritical fluid is turned into an ordinary gas by means of pressure reduction and temperature rise. Complete or basic precipitation, so as to achieve the purpose of separation and purification, so the supercritical CO2 fluid extraction process is a combination of extraction and separation processes.

Supercritical extraction process

Vent CO2

Cooling water CO2 low temperature bath high pressure pump preheater extractor separator product ^[1]

Supercritical extraction characteristics

1. Supercritical extraction can be performed at near room temperature (35-40 ° C) and under the cover of CO2 gas, which effectively prevents the oxidation and escape of heat-sensitive substances. Therefore, the active ingredients of medicinal plants are maintained in the extract, and high boiling point, low volatility, and easily pyrolyzed substances can be extracted at a temperature far below its boiling point;

2. Using SFE is the cleanest extraction method. Since no organic solvent is used in the whole process, the extract has no residual solvent substances, thereby preventing the existence of harmful substances to the human body and environmental pollution during the extraction process, and guaranteeing 100%. Pure nature

3. Extraction and separation are combined into one. When the saturated dissolved CO2 fluid enters the separator, due to the pressure drop or temperature change, CO2 and the extract quickly become two-phase (gas-liquid separation) and immediately separate. Not only the extraction efficiency is high and the energy consumption is small, which improves the production efficiency and reduces the cost;

4. CO2 is an inactive gas, no chemical reaction occurs during the extraction process, and it is a non-flammable gas, which is odorless, odorless, non-toxic, and very safe;

5, CO2 gas is cheap, high purity, easy to prepare, and can be recycled in production, thereby effectively reducing costs;

6. Both pressure and temperature can become parameters for adjusting the extraction process. The purpose of extraction can be achieved by changing the temperature and pressure. The pressure can also be separated by changing the temperature. On the contrary, the temperature is fixed and the extract can be reduced by reducing the pressure Separation, so the process is simple and easy to grasp, and the speed of extraction is fast.

Application of supercritical extraction technology

The characteristics of supercritical CO2 extraction determine its wide application range. For example, in the pharmaceutical industry, it can be used for the extraction of active ingredients of Chinese herbal medicine, the purification of heat-sensitive biological products, and the separation of lipid mixtures; in the food industry, the extraction of hops and the extraction of pigments; Refining of synthetic fragrances; separation of mixtures in the chemical industry, etc. Specific applications can be divided into the following areas:

1. Extract bioactive molecules from medicinal plants, and extract and separate alkaloids;

2. Lipids and lipids from different microorganisms, or used for lipid lipid recovery, or remove lipids from sugars and proteins;

3. Extract anti-cancer substances from a variety of plants, especially to obtain paclitaxel from yew bark and branches and leaves to prevent cancer;

4. Vitamins, mainly the extraction of vitamin E;

5. Purify various active substances (natural or synthetic), remove unnecessary molecules (such as removing pesticides from vegetable extracts) or "residues" to obtain purified products;

6. Processing of various natural antibacterial or antioxidant extracts, such as basil, string red, thyme, garlic, onion, chamomile, paprika, licorice and fennel.

Difference in supercritical extraction

Subcritical, similar to supercritical extraction, refers to the condition of the existence of substances, which refers to substances that exist at a temperature higher than their boiling point but lower than the critical temperature, in the form of a fluid and at a pressure lower than their critical pressure. When the temperature does not exceed a certain value, pressurizing the gas can liquefy the gas, and above this temperature, no matter how much pressure is added, the gas cannot be liquefied. This temperature is called the critical temperature of the gas. At the critical temperature, the pressure necessary to liquefy the gas is called the critical pressure.

1.Supercritical extraction of carbon dioxide solvent

This extraction method is low-temperature processing, which can extract effective ingredients with good quality without solvent residue. However, the equipment has a large investment at one time, because the extraction is carried out under high pressure, the volume of the extracted tritium is small (maximum 1000 liters), the production capacity is limited, and industrialized large-scale production cannot be formed, and the product cost is high.

2. Subcritical (butane, etc.) low temperature extraction

The entire production process of this method is carried out at low temperature, the nutritional components of the material will not be damaged, and the yield is high, and the product's condition is good. The quality is comparable to carbon dioxide supercritical extraction. Large-scale production can be formed with less investment in disposable equipment. Low production costs. energy saving. This technology has been well applied in the fields of precious oils, red pigments such as capsicum and marigold lutein.