I. Overview
Extraction, also known as solvent extraction or liquid-liquid extraction (to distinguish it from solid-liquid extraction, ie leaching), also known as extraction (used in the petroleum refining industry), is a double solution that is immiscible with a liquid extractant. A component or multi-component solution, a mass transfer separation process that achieves component separation, is a widely used unit operation.
Using the principle of similar compatibility, there are two ways to extract:
Liquid-liquid extraction, separation of a component of a liquid mixture with a selected solvent. The solvent must be incompatible with the liquid of the extracted mixture, have selective solubility, and must have good thermal and chemical stability. And has little toxicity and corrosiveness. Phenols such as coal tar separated with benzene; petroleum fractions separated olefin with an organic solvent; of Br2 in water and extracted with CCl4.
Solid-liquid extraction, also called leaching, separating components in a solid mixture with a solvent, such as leaching sugar from sugar beets with water; leaching soybean oil from soybeans with alcohol to increase oil yield; effectively leaching with water from traditional Chinese medicine The ingredients used to make the extract are called "leaching" or "leaching". Although extraction is often used in chemical tests, its operation does not result in a change (or chemical reaction) in the chemical composition of the extracted material, so the extraction operation is a physical process. Extraction is one of the means used to purify and purify compounds in organic chemistry laboratories. By extraction, the desired compound can be extracted from a solid or liquid mixture. Here is a description of commonly used liquid-liquid extractions.
Second, the basic principles
The compound is transferred from one solvent to another by utilizing the difference in solubility or partition coefficient of the compound in two mutually incompatible (or slightly soluble) solvents. After repeated extractions, most of the compounds are extracted.
The law of distribution is the main basis for the theory of extraction methods. The substances have different solubility for different solvents. At the same time, when a certain soluble substance is added to two mutually incompatible solvents, it can be dissolved in the two solvents separately. Experiments show that the compound does not decompose with the two solvents at a certain temperature. The ratio of the compound in the two liquid layers is a constant value when electrolyzed, associated, and solvated. This is true regardless of the amount of material added.
Organic compounds generally have greater solubility in organic solvents than in water. Extraction of a compound dissolved in water with an organic solvent is a typical example of extraction. At the time of extraction, if a certain amount of electrolyte (such as sodium chloride) is added to the aqueous solution, the "salting effect" is used to reduce the solubility of the organic substance and the extraction solvent in the aqueous solution, and the extraction effect is often improved. To completely extract the desired compound from the solution, it is usually not enough to extract once, and the extraction must be repeated several times.
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