First, the principle.
Liquid-liquid extraction is the process of separating substances using the principle of solute partitioning between two immiscible liquids (usually one is an organic solvent). The solubility of solutes in both liquids is different, so at the interface of the two liquids, the solute is transferred from the less soluble solvent to the more soluble solvent. By constantly stirring and standing, the solute can reach equilibrium between the two phases, thus achieving the separation of the substance.
Solid-liquid extraction is the process of separating substances by using the adsorption between solid substances and liquid solvents. Solid matter adsorbents have different adsorption capacities for different components, so different components in the mixture can be adsorbed to varying degrees. With appropriate desorption agents or solvents, the components adsorbed to varying degrees can be desorbed down sequentially, thus achieving the separation of the substance.
Second, the operation method.
Liquid-liquid extraction is typically performed using a separating funnel or centrifugal extractor. First, the two immiscible liquids are mixed together, and the solute is fully exchanged between the two phases by stirring. Then let it stand and layer, and take out the upper and lower layers separately to obtain a pure substance. In order to improve the extraction efficiency, multiple extraction or reverse extraction methods can be used.
Solid-liquid extraction is typically performed with columnar adsorbents. The mixture is passed through the adsorption column, and the components are separated by taking advantage of the difference in the adsorption capacity of the adsorbent to the different components. Then use an appropriate desorption agent or solvent to desorb each component down in turn, and collect each component to obtain a pure substance. In order to improve the separation effect, the method of tandem column or parallel column can be used.
3. Scope of application.
Liquid-liquid extraction is widely used in chemical, petroleum, pharmaceutical and other fields, and is mainly used for the separation and purification of organic substances. For example, fuels such as gasoline and diesel are extracted from petroleum, and spices and pigments are extracted from plants. In addition, liquid-liquid extraction can also be used in hydrometallurgy, environmental treatment and other fields.
Solid-liquid extraction is widely used in environmental protection, food, pharmaceuticals and other fields, and is mainly used for separating and purifying inorganic substances. For example, the extraction of heavy metal ions from wastewater, the extraction of caffeine from tea, etc. In addition, solid-liquid extraction can also be used in hydrometallurgy, chemical analysis and other fields.
Fourth, the advantages and disadvantages are compared.
1.Separation effect: The separation effect of solid-liquid extraction is high, and relatively pure substances can be separatedHowever, the separation effect of liquid-liquid extraction is relatively low, and sometimes multiple extractions are required to obtain a purer substance.
2.Solvent consumption: Liquid-liquid extraction requires the use of large amounts of organic solvents, which can sometimes cause solvent residue problemsSolid-liquid extraction, on the other hand, does not require the use of organic solvents, making it more environmentally friendly and safer.
3.Ease of operation: Liquid-liquid extraction is relatively simple and easy to automateSolid-liquid extraction, on the other hand, requires certain technical means and experience, and is relatively complex to operate.
4.Applications: Liquid-liquid extraction is suitable for the separation and purification of organic substances;Solid-liquid extraction, on the other hand, is suitable for the separation and purification of inorganic substances. Therefore, there is also a difference in the scope of application.