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Supercritical fluid extraction technology for herbal medicine

Definition

Supercritical fluid

A fluid (gas or liquid), when its temperature and pressure exceed its corresponding critical point value, the fluid in this state is called a supercritical fluid.

Supercritical fluid extraction

The process of using supercritical fluid as an extractant to extract dissolved substances from a solution is called supercritical fluid extraction, and this technology is called supercritical fluid extraction technology.

Supercritical fluid extraction of herbal medicine

The supercritical fluid extraction technology of herbal medicine is a new type of material separation and purification technology developed in recent years. It has aroused widespread interest in the fields of chemical industry, medicine, food, perfume, biochemical industry, etc. Today, as herbal medicine is gradually modernizing, Known as the high-efficiency extraction and separation technology of herbal medicine.

Features of supercritical fluid extraction technology

Supercritical fluid extraction technology combines the advantages of rectification and liquid-liquid extraction, that is, rectification uses the difference in the volatility of each component to achieve separation between different components, and liquid-liquid extraction uses the solubility of the extracted molecules. The difference separates the extracted components from the mixture, so it is a unique, high-efficiency and energy-saving separation technology.

Commonly used extractants

The commonly used extractant is CO2, which is non-toxic, tasteless, non-flammable, non-corrosive, inexpensive, easy to refine, and easy to recycle. It is regarded as an ideal substitute for harmful solvents.

Basic principles of supercritical fluid extraction

Characteristics of supercritical fluids

Density

The density of supercritical fluid is close to that of liquid.
Since the solubility of the solute in the solvent is generally proportional to the density of the solvent, the supercritical fluid has a dissolving ability equivalent to that of the liquid solvent.

Mass transfer rate

The diffusion coefficient of supercritical fluid is between gas and liquid, and its viscosity is also close to that of gas, so the mass transfer speed of supercritical fluid is closer to that of gas.

Therefore, the mass transfer rate of supercritical fluid extraction is greater than the extraction rate of liquid solvents.

Separation operation of supercritical CO2 fluid extraction

For fluids near the critical state, the enthalpy of evaporation will drop sharply with the increase of temperature and pressure. When it reaches the critical point, the gas-liquid two-phase interface disappears, the enthalpy of evaporation is zero, and the specific heat capacity tends to be infinite.
Therefore, the separation operation near the critical point is more conducive to heat transfer and energy saving than in the gas-liquid equilibrium zone.

As long as the pressure and temperature of the fluid near the critical point change slightly, the density of the fluid will change greatly, which will cause a considerable change in the solubility of the solute in the fluid.

That is, the supercritical fluid can perform supercritical fluid extraction of the extract at a higher density. At the same time, it can reduce the density of the solvent by adjusting the temperature and pressure, thereby reducing the extraction capacity of the solvent, and effectively separating the solvent from the extract.

Process principle of supercritical CO2 fluid extraction

First, let the solvent liquid CO2 reach the critical state through the CO2 high-pressure pump; then the supercritical CO2 fluid enters the extractor to contact the raw materials (solid or liquid mixture) inside for supercritical CO2 extraction;

The extract dissolved in the supercritical CO2 fluid leaves the extractor with the CO2 fluid and is then throttled and expanded by the pressure reducing valve to reduce the density of the supercritical CO2 fluid, so that the extract and the solvent can be effectively separated in the separator Then, the solvent is pressurized to a supercritical state by a pump or a compressor, and the above extraction and separation operation is repeated, and the CO2 fluid is circulated to reach the predetermined extraction rate.

Characteristics of supercritical CO2 fluid extraction process

  • Supercritical CO2 fluid extraction has the characteristics of both rectification and liquid-liquid extraction. The vapor pressure, polarity, and molecular weight of the solute are important factors that affect the solubility of the solute in the supercritical CO2 fluid. The difference in volatility between the separated substances during the extraction process and the force between them are two factors at the same time. Works. For example, the order in which the supercritical extracts are extracted is related to their boiling point order; the non-polar extractant CO2 has a higher extraction capacity for non-polar or weakly polar substances.
  • The extractant can be recycled. In terms of solvent separation and recovery, supercritical extraction is superior to general liquid-liquid extraction and rectification, and is considered an advanced technology with fast extraction speed, high efficiency and low energy consumption.
  • The operating parameters are easy to control. The extraction capacity of supercritical extraction mainly depends on the density of the fluid, and the density of the fluid can be easily controlled by adjusting the temperature and pressure, which makes it easy to ensure stable product quality.
  • Particularly suitable for separating heat-sensitive substances, and can achieve no solvent residue. The operating temperature of the supercritical extraction process is related to the critical temperature of the extractant used. At present, the critical temperature of the most commonly used extraction agent CO2 is 304.3K, which is the closest to room temperature, so it can not only prevent the degradation of heat-sensitive substances, but also achieve no solvent residue. This feature also makes the supercritical extraction technology used in the extraction and separation of natural products to become one of the current research hotspots.

CO2 is the most ideal extractant

The extractant for supercritical extraction can be divided into polar extractant and non-polar extractant according to its polarity.
Among them, the non-polar extractant CO2 is currently the most widely used extractant.

CO2 extractant has the following characteristics

  • The critical temperature of CO2 is close to room temperature (31.1°C). For heat-sensitive substances with high boiling point and low volatility, they can be extracted below their boiling point to avoid their degradation.
  • The critical pressure of CO2 (7.38KPa) is at a medium pressure. The current industrial level is also easy to reach.
  • CO2 has the characteristics of non-toxic, odorless, non-flammable, non-corrosive, cheap, easy to refine, easy to recycle, etc. Therefore, the supercritical CO2 fluid CO2 extraction has no solvent residue problem and belongs to an environmentally friendly process.
  • Supercritical CO2 fluid CO2 also has anti-oxidation and sterilization effects, which helps to ensure and improve the quality of natural products.

Application of Supercritical CO2 Extraction in Herbal Extraction

Application of supercritical CO2 extraction

  • In the pharmaceutical industry, it can be used to extract the effective ingredients of Chinese herbal medicines;
  • Refining of heat-sensitive biological drugs and separation of lipid and lipid mixtures;
  • In the food industry, the extraction of hops and pigments;
  • In the perfume industry, the refining of natural and synthetic perfumes;
  • Separation of mixtures in the chemical industry, etc.

Application of supercritical fluid systems

RangeType
Pharmaceutical IndustryExtraction of effective contents of Chinese herbs, concentration, refinement and precipitation of raw material drug, separation and refinement of fatty mixtures
Foodstuff IndustryExtraction of hops, caffeine removal from coffee berry, extraction of plant pigment
Cosmetics and PerfumeryIndustriesSeparation and refinement of natural and synthetic perfumeries, dealkalization of tobacco, extraction of raw material cosmetics
Chemical IndustrySeparation of hydrocarbon, refinement of organic synthetic raw material, separationof azeotrope, retrieval of raw materials of reaction, dehydration of water soluble powder of organic solution, water oxidation
OthersSuperconducting, semiconductor, ceramics, oil washing of petroleum core, enzyme catalytic reaction, preparation of materials, superfine granules, extraction of complex compound, supercritical dyeing technique, supercritical reaction,supercritical coating technique (pharmacy-making)

Specific applications

  • Extraction of biologically active molecules from medicinal plants, extraction and separation of alkaloids.
  • Anti-cancer substances are extracted from a variety of plants, especially paclitaxel is obtained from the bark and leaves of yew to prevent cancer.
  • Recover lipids from different microorganisms, or remove lipids from embryo sugar and protein.
  • Purify various active substances to remove unwanted molecules (such as removing pesticides from vegetable extracts) or residues to obtain purified products.
  • Processing of natural antibacterial or antioxidant extracts, such as string red, thyme, garlic, onion, licorice, fennel, etc.

Postscript

In short, supercritical extraction technology has entered the ranks of the world’s advanced technologies. With the rise of human “returning to nature”, the demand for natural medicines and herbal medicines will gradually expand, and herbal medicines will gradually be recognized by the world. The extraction of traditional herbal medicines generally uses water. Or the method of organic solvent extraction, most of the extracted substances are mixtures, which require further purification, separation and refinement.
In the post-processing process, there are shortcomings such as long heating time and difficult to completely remove residual organic solvents, resulting in degradation of heat-sensitive substances and loss of volatile components, which will inevitably affect the quality and stability of herbal products.

The success of supercritical CO2 fluid extraction technology has made the modernization of herbal medicine a historical necessity.

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