Common solid-liquid separation methods and their applicable conditions

Common solid-liquid separation methods and applicable conditions are as follows:

The main factors affecting solid-liquid separation are the difference of solubility between two phases, temperature, contact area, stirring and so on.

Extraction, also known as solvent extraction or liquid-liquid extraction, is a unit operation to separate the mixture by using the solubility of each component in the solvent. That is, the method of transferring solute substances from one solvent to another by using the difference of solubility or distribution coefficient of substances in two mutually insoluble (or slightly soluble) solvents.

Widely used in chemical, metallurgical, food and other industries, generally used in petroleum refining industry. In addition, the operation of separating two immiscible liquids after extraction is called liquid separation.

Solid-liquid extraction, also known as leaching, is to separate the components in the solid mixture with solvents, such as leaching sugar from beets with water; Soak soybean oil in soybean with alcohol to increase oil yield; The effective components in traditional Chinese medicine are leached with water to make fluid extract, which is called "leaching" or "leaching".

Although extraction is often used in chemical experiments, its operation process does not change the chemical composition (or chemical reaction) of the extracted substance, so the extraction operation is a physical process.

Extraction is one of the methods used to purify and purify compounds in organic chemistry laboratory. By extraction, the desired substance can be extracted from a solid or liquid mixture.

Principle:

Distribution law is the main basis of extraction theory, and substances have different solubility in different solvents. At the same time, soluble substances can be dissolved in two solvents by adding them into two mutually immiscible solvents. The experiment shows that at a certain temperature, when there is no decomposition, electrolysis, association and solvation between this compound and these two solvents, the proportion of this compound in the two liquid layers is a constant value.

Method:

An extractant insoluble (at most partially soluble) in the solution to be separated is added to form two liquid phases. Using the solubility difference between the original solvent and extractant (including dissolution after chemical reaction). Such that they are unevenly distributed in the two liquid phases, and then these components are separated by the separation of the two liquid phases. For example, the aqueous solution of iodine is extracted with carbon tetrachloride, and almost all iodine moves into carbon tetrachloride, so that iodine can be separated from a large amount of water.

Application:

Compared with other methods for separating solution components, extraction has the advantages of operating at room temperature, saving energy, not involving solids and gases, and convenient operation.

It is usually advantageous to use extraction in the following situations:

The boiling points of each component of the feed liquid are similar, and even a * * boiling substance is formed, which is difficult to rectify, such as the separation of alkanes and aromatics in petroleum fractions and the dephenolization of coal tar; For the separation of low concentration and high boiling point components, distillation consumes a lot of energy, such as dehydration of dilute acetic acid; For the separation of various ions, such as the separation and purification of mineral leaching solution, if chemicals are added for partial precipitation, not only the separation quality is poor, but also the filtration operation is carried out, and the loss is great; Separate unstable substances (such as heat-sensitive substances) from fermentation broth, such as penicillin.