Since supercritical fluid extraction is a rare environment-friendly separation technology, a lot of research is being carried out in the world to continuously improve and broaden this technology, so that the application of supercritical fluid extraction technology is more scientific, more effective and more efficient. To be extensive and more profitable.
Among them, the more eye-catching researches include complex extraction, microemulsion extraction and reverse micellar extraction. Fractional distillation extraction, subcritical extraction, ultra-high pressure extraction, development of new supercritical fluid and enhancement of carbon dioxide extraction, etc.
Supercritical Fluid Extraction (SFE)
In the standard SFE process, the sample is placed in an extraction vessel, and supercritical CO2 is passed through it. The CO2 dissolves the target compounds from the sample, and the resulting mixture is collected in a separate vessel. The extracted compounds are separated from the CO2 by decreasing the pressure, which causes the CO2 to return to its gas phase and leaves the extracted compounds behind.
This process is commonly used to extract nonpolar compounds from a sample, such as essential oils, fatty acids, and terpenes. The advantages of using supercritical CO2 as a solvent include its high selectivity, high purity, and low toxicity.
What is Supercritical Fluid Chelating Extraction
Supercritical Fluid Chelating Extraction is the use of complexing agents and charged ions to form electrically neutral, stable, and easily soluble complexes in supercritical fluids through coordination bonds, and then enter the supercritical fluid phase through mass transfer and interact with the original matrix A separate method of separation. In the early 1990s, Laintz et al. first carried out the research on complex extraction of copper ions from aqueous solution.
Application: In recent years, research on supercritical complexation extraction has mainly focused on environmental governance, metallurgy, electronic materials and ceramic production.
At present, the complexing agents used for supercritical complexation extraction mainly include crown ethers, diketones, organic phosphines, organic amines, diethyldithiocarbamate and its derivatives. Diethyldithiocarbamate (DDC) is one of the most widely used complexing agents.
The solubility, concentration and stability of the complexing agent, temperature, pressure, pH value, matrix, modifier, and the existing form of the extracted elements all have an impact on supercritical complexation extraction. Under supercritical conditions, the stability of complexing agents and metal complexes in aqueous solution is another important factor affecting complex extraction in aqueous solution.
Surfactant and Supercritical Microemulsion Extraction
Supercritical microemulsion process
The supercritical microemulsion process is a new topic in the development of supercritical fluid technology. Supercritical microemulsion is a quasi-homogeneous solution composed of water droplets surrounded by surfactants dispersed in supercritical fluid. The key to forming a microemulsion solution is that the surfactant has amphiphilicity with water and carbon dioxide, first of all, the affinity between the tail of the surfactant and carbon dioxide. Among the currently used surfactants, the fluorine-based tails account for the vast majority, and the hydrophilic head of the surfactant is generally nonionic or anionic. Among the surfactants used in carbon dioxide microemulsions, PFPE (fluorosurfactant perfluoropolyether ammonium bolate) has been reported more, and pressure, temperature, surfactant and water content all affect the phase behavior of the system.
Advantages of supercritical microemulsion
The supercritical microemulsion process organically combines supercritical technology and microemulsion technology. Supercritical fluid is sensitive to changes in state parameters, and can easily realize emulsification and demulsification. The microemulsion contains a water core, which realizes the existence of a large number of polar microenvironments in a nonpolar environment, and makes up for the deficiency that carbon dioxide cannot extract polar substances. Many gases and organics can be dissolved in supercritical fluids, and the solubility can be easily controlled. The whole microemulsion system is pseudo-homogeneous, with small heat and mass transfer resistance. The most distinctive feature of the application of supercritical microemulsion is the use of special surfactants to achieve specific separation of proteins.
Supercritical Fractional Distillation Extraction
Usually, supercritical fluid extraction is mostly simple extraction, and the processed materials are mainly plants, and the crude extraction mixture is almost not pure. In order to obtain high value-added products with higher purity, more and more researches have been done on supercritical fractional distillation extraction. The current research systems include sterol-vitamin E, citrus oil and various unsaturated fatty acids. The research contents include phase equilibrium, theoretical calculation, determination of theoretical plate height and mass transfer unit height, optimization of process conditions, extraction column concentration distribution. Energy consumption estimation, extraction column design, etc.
CO2 subcritical extraction
The main advantages of subcritical fluid benzene are low working pressure and simple process. For example, the working pressure of carbon dioxide subcritical extraction is 3-7MPa, and the working temperature is 20~30°C, which greatly reduces equipment investment, improves safety, and still maintains the advantages of supercritical fluid extraction, such as environmental friendliness , no stripping operation is required, and another advantage is that fluid circulation can be realized by variable temperature method, which reduces the demand for high-pressure conveying equipment. Subcritical extraction is especially suitable for extracting highly volatile substances, such as flavor and fragrance compounds.
Ultra-high pressure CO2 extraction
Thermodynamic studies have shown that the higher the pressure, the higher the dissolving capacity of the supercritical CO2 fluid. Taking the extraction of soybean oil as an example, when the pressure is lower than 30MPa, the solubility is generally about 1‰, but when the pressure is increased to 80MPa and the temperature is about 70℃, the oil and carbon dioxide is almost miscible, and the solubility reaches more than 30%. This results in greatly reduced recirculation of hard dioxide and shortened extraction times. Taking the extraction of sunflower seed oil as an example, 30MPa, 60°C, extraction for 60 minutes, the extraction rate is only 60%, while 70MPa, 80°C, extraction for 6 minutes, the extraction rate can reach 90%, and the amount of carbon dioxide is also reduced by 10 times. According to preliminary estimates, the processing capacity of a set of 15L ultra-high pressure extraction equipment is about the same as that of ordinary 120L equipment, and the operating cost is also greatly reduced.
Supercritical Fluid Chromatography (SFC)
Supercritical fluid chromatography (SFC) is a type of SFE that involves using a supercritical fluid as the mobile phase in chromatography. In SFC, the sample is injected into a chromatographic column, and the supercritical fluid is used to separate the components of the sample.
SFC is useful for separating and purifying a wide range of compounds, including chiral compounds, peptides, and pharmaceuticals.
Supercritical Fluid Reaction Extraction
Supercritical fluid reaction extraction involves using supercritical fluids as both a solvent and a reaction medium. The sample is placed in a reaction vessel, and supercritical fluids are used to dissolve and react with the sample.
This process is useful for conducting chemical reactions, such as hydrogenation, oxidation, and esterification, in a supercritical environment. It is commonly used for the synthesis of pharmaceuticals, fine chemicals, and polymers.
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