Supercritical fluid extraction is a new type of extraction and separation technology.
It uses a supercritical fluid, that is, a fluid in a thermodynamic state at a temperature higher than the critical temperature and a pressure higher than the critical pressure, as an extractant. Extract specific components from liquid or solid to achieve the purpose of separation.
- The extractant is a gas at normal pressure and room temperature, and it is easy to separate from the raffinate phase and the extraction group after extraction;
- It operates at a lower profitability, and is particularly suitable for the separation of natural substances;
- It can adjust the pressure , Temperature and attractive entraining agent can adjust the dissolving ability of the transboundary fluid, and can gradually extract the components into the desired product through the gradually density and temperature and pressure.
Supercritical fluid extraction process flow Supercritical fluid extraction is the most advanced physical extraction technology in the world, referred to as SFE (supercritical fluid extraction).
At lower temperatures, when the pressure of a gas is continuously increased, the gas will be converted into a liquid. When the pressure is increased, the volume of the liquid will increase. For a particular substance, there is always a critical temperature (Tc) and a critical pressure ( Pc), above the critical temperature and critical pressure, the substance will not become a liquid or gas, this is the critical point.
In the range above the critical point, the state of matter is between gas and liquid, and the fluid in this range becomes supercritical fluid (SF).
Supercritical fluid has strong penetrating power similar to gas, large density and solubility similar to liquid, has good solvent characteristics, and can be used as a solvent for extraction and separation of monomers. Supercritical fluid extraction is a high-tech emerging in modern chemical separation. SFE combines traditional distillation and organic solvent extraction, and uses the excellent solvent power of supercritical CO2 to effectively separate, extract and purify the matrix and the extract.
Supercritical CO2 extraction
SFE uses supercritical CO2 to extract the material. CO2 is a safe, non-toxic, and cheap liquid. Supercritical CO2 has a gas-like diffusion coefficient, liquid dissolving power, and zero surface tension. It can quickly penetrate into solid materials and extract its essence. It has high efficiency, is not easy to oxidize, Pure natural and no chemical pollution.
Supercritical fluid extraction and separation technology is based on the use of the solubility of supercritical fluids and their density, and changes the density of supercritical fluids by changing the pressure or temperature.
In a supercritical state, a supercritical fluid is contacted with a substance to be separated, so that it selectively extracts components with different polarities, high and low boiling points, and relative molecular masses in order.
Supercritical fluid (SF) is a fluid between gas and liquid that is above the critical temperature (Tc) and critical pressure (Pc). Supercritical fluids have the dual characteristics of gas and liquid.
The density of SF is similar to that of liquid, and the viscosity is similar to that of gas, but the diffusion coefficient is about 100 times larger than that of liquid. Because the dissolution process involves intermolecular interactions and diffusion, SF has a strong ability to dissolve many substances. These characteristics make supercritical fluids a good extractant.
Supercritical fluid extraction
Supercritical fluid extraction is a process that uses the strong dissolving ability characteristics of supercritical fluids to extract various active ingredients from animals and plants, and then releases them through decompression.
The process of dissolving and separating substances by supercritical fluid is called supercritical fluid extraction.
There are many substances that can be used as SF, such as carbon dioxide, nitrous oxide, sulfur hexafluoride, ethane, heptane, ammonia, etc. Among them, CO2 is mostly used (critical temperature is close to room temperature, and it is colorless, non-toxic, odorless, not easy) , Chemically inert, cheap, easy to make high purity gas).
The raw materials are loaded into the extractor after a series of pretreatments such as impurity removal, crushing or rolling.
The system is filled with supercritical fluid and pressurized. Under the action of SCF, the soluble components enter the SCF phase. The SCF phase flowing out of the extractor can be selectively separated from the SCF phase through decompression, temperature adjustment or adsorption, and the SCF is returned to the extractor for recycling after being tempered and compressed.
SC-CO2 extraction process consists of two parts: extraction and separation.
At a specific temperature and pressure, the raw material is fully contacted with the SC-CO2 fluid, and after equilibrium is reached, the extract is separated from the solvent SC-CO2 through temperature and pressure changes, and the SC-CO2 is recycled.
The entire process can be continuous, semi-continuous, or batch.
When supercritical extraction is used to extract natural products, CO2 is generally used as the extractant.
This is because:
- Low critical temperature and critical pressure (Tc = 31.1 ℃, Pc = 7.38MPa), mild operating conditions, and less damage to active ingredients, so it is particularly suitable for processing high boiling point heat-sensitive substances such as flavors, spices, oils, vitamins ;
- CO2 can be regarded as a non-toxic, cheap organic solvent similar to water; c) CO2 is stable, non-toxic, non-flammable, safe, and does not pollute the environment during use, and can avoid product oxidation:
- The extract of CO2 is free of nitrates and harmful heavy metals, and there is no residue of harmful solvents;
- During supercritical CO2 extraction, the extracted substance can be precipitated by reducing the pressure or raising the temperature of the supercritical fluid extraction machine without repeating the extraction operation, so the supercritical CO2 extraction process is simple.
Therefore, supercritical CO2 extraction is particularly suitable for the extraction and purification of biological, food, cosmetics and pharmaceuticals.
The characteristics of supercritical 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, the extraction of pigments, etc .;
Refining of natural and synthetic fragrances in the fragrance industry;
Separation of mixtures in the chemical industry, etc.
Specific applications can be divided into the following areas:
The traditional edible oil extraction method is ethane extraction, but the amount of solvent contained in the edible oil produced by this method is difficult to meet the requirements of food management law. Supercritical carbon dioxide extraction (SCFE) has been used to extract soybean oil in the United States, and the product quality is large Increased without pollution problems.
At present, supercritical carbon dioxide can be used to extract oil from sunflower seeds, safflower seeds, peanuts, wheat germ, palm, and cocoa beans.
The proposed oil contains neutral lipids, low phosphorus content, low coloration, and odorless taste. This method has a higher recovery rate than the traditional press method, and it does not have the problem of solvent separation in the solvent method.
Experts believe that supercritical carbon dioxide extraction can revolutionize the oil extraction process.
Caffeine contained in coffee is harmful to the human body due to excessive drinking, so it must be removed from coffee. The traditional method in industry is to use dichloroethane to extract, but not only does dichloroethane extract caffeine, but also the aromatic substances in coffee, and the residual dichloroethane is not easy to remove, affecting the quality of coffee.
The special technology developed by Dr. Zesst of the Max-plank Coal Research Institute in West Germany to extract caffeine from coffee beans with supercritical carbon dioxide has been industrialized by Hag in West Germany and has been widely adopted by countries around the world.
The biggest advantage of this technology is that it replaces the trace halogenated hydrocarbon solvents that are still harmful to the human body. The caffeine content can be reduced from about 1% to 0.02%, and the good selectivity of CO2 can be retained. Aromatic substances in coffee.
ADL company in the United States recently developed a method for extracting alcohol using SCFE technology, and also developed a technology to remove excessive oil from greasy fast food without losing its original color and fragrance, and maintaining its appearance and internal organization structure, and Applied for patent.
Medicines and Health Products
Professor Stahl of the University of Saarland in West Germany applied the SCFE method to many medicinal plants to achieve satisfactory separation of their active ingredients (such as various alkaloids, aromatic and oily components).
In the production of antibiotic drugs, traditional methods often use organic solvents such as acetone and methanol, but it is very difficult to completely remove the solvent without deteriorating the drug. If the SCFE method is used, it can meet the requirements.
The ADL company in the United States has extracted the active ingredients for treating cancer from 7 implants, making it truly applied in the clinic. Many scholars believe that taking fish oil and omega-3 fatty acids is good for health. These lipids can also be obtained from phytoplankton. The lipids obtained in this way do not contain cholesterol. J.K. Polak et al. Succeeded in extracting lipids from algae, and chlorophyll would not be extracted by supercritical CO2, thus eliminating the bleaching process of traditional solvent extraction.
In addition, ginkgo flavonoids extracted from ginkgo biloba leaves by the SCFE method, polyene unsaturated fatty acids (DHA, EPA) extracted from fish viscera, bones, seabuckthorn oil extracted from sea buckthorn seeds, lecithin extracted from egg yolk, etc. It has a unique effect on cardiovascular and cerebrovascular diseases. The Japanese scholar Gong Diyang and others extracted the effective ingredients from the medicinal plants She-Ci Zi, Mulberry Bark, Licorice Root, Lithospermum, Safflower and Evening Primrose.
Traditional Chinese medicine
The extraction of medicinal ingredients from medicinal plants began in the last five or six years.According to research and development practices, it is believed that the application of supercritical fluid extraction technology in the extraction and separation of Chinese medicine and the modernization of Chinese medicine has great potential and considerable prospects.
The SCFE method can not only effectively extract the aromatic components, but also improve the purity of the product and maintain its natural fragrance, such as extracting flower essence from osmanthus, jasmine, chrysanthemum, plum, milan, and rose, Cinnamon and mint extract spices, essential oils are extracted from celery seeds, ginger, mandarin duck seeds, fennel, amomum, star anise, cumin and other raw materials, not only can be used as seasoning spices, but some essential oils also have high medicinal value .
Hops are an indispensable additive in beer brewing, with unique aroma, freshness and bitterness. The hop extract produced by the traditional method does not contain or contains only a small amount of essential oils, which destroys the flavor of the beer, and the residual organic solvents are harmful to the human body.
Supercritical extraction technology has opened up broad prospects for the production of hop extracts. The American SKW company extracts hop oil from hops and has formed a production scale.
At present, the international demand for natural pigments is increasing year by year, and it is mainly used in food processing, medicine and cosmetics. Many developed countries have stipulated deadlines for prohibiting the use of synthetic pigments, and the ban on synthetic pigments in China is imperative.
Solvent-based pigments have poor purity, odor, and solvent residues, which cannot meet the demand for high-quality pigments in the international market.
Supercritical extraction technology overcomes these shortcomings. At present, the technology for extracting natural pigments (capsicum red pigment) by SCFE method has matured and reached the international advanced level.
Analysis of pesticide residues
Pesticide residue analysis includes the steps of extraction, purification, concentration, and detection of samples. Extraction, separation and purification are the key links of the analysis.
In traditional pesticide residue analysis, the pretreatment of samples is mostly extracted with organic solvents.
There are many disadvantages to solvent extraction
- First, the waste of solvents is serious and the environment is polluted;
- The second is time-consuming and tedious extraction and purification process;
- Third, the extraction rate is low.
At present, two methods of ultrasonic extraction and Soxhlet extraction are listed as the primary pesticide residue extraction methods in the world. However, the biggest disadvantage of these two extraction methods is the long processing time, which affects their application.
Advantages in the extraction of pesticide residues.
Supercritical fluid extraction technology has unique advantages in the extraction of pesticide residues.
According to the research of many scholars, the advantages of simple sample preparation, short extraction time, high extraction efficiency, high accuracy of extraction results and good reproducibility will greatly promote its application in pesticide residue analysis. For samples with large water content, just add an appropriate amount of desiccant during sample pre-treatment and mix well; for materials with greater polarity, add a certain amount of modifier or mix the fluid in the extraction process. Changes can be made to achieve effective extraction.
Each sample generally takes about 40 rain from sample preparation to completion, greatly reducing the extraction time, which is unmatched by conventional solvent extraction, Soxhlet extraction, and ultrasonic extraction. Previous research also found that the reproducibility and extraction accuracy of the results of supercritical fluid extraction are far better than other methods. Relevant scholars use SFE technology to achieve the extraction of pesticide residues. We also got relatively satisfactory results.
SFE technology is increasingly used in combination with multiple methods, and has great potential in the application research of pesticide residues, especially in pesticide multi-residue analysis, which can significantly improve the analysis efficiency. Some people have combined SFE with analytical instruments GC and MS to analyze organophosphorus pesticides and carbamate pesticides in animal tissues, and got very good results.