Extraction is one of the unit operations for separating liquid mixtures in industrial production.

　　Extraction is the use of substances in two immiscible or slightly soluble solvents in the solubility or distribution coefficient of the difference, so that the substance from a solvent within (original solvent) transferred to another solvent (extractant), after a number of operations, the vast majority of the

　　The method of extracting the majority of the substance.

　　Extraction, also known as solvent extraction or liquid-liquid extraction, also known as extraction, is a liquid extractant to deal with the immiscible two-component or multi-component solution, to achieve the separation of the components of the mass transfer unit operation.

　　Liquid-liquid extraction using the principle of similar solubility, with a selected solvent to separate a component of the liquid mixture, the solvent is separated from the mixture of liquids with the ability to selectively dissolve, and must have good thermal and chemical stability, toxicity and corrosiveness should be small.

　　And must have good thermal and chemical stability, toxicity and corrosiveness should be very small.

　　Solid-liquid extraction (i.e., leaching) is different from liquid-liquid extraction, liquid-solid extraction is a solvent to separate the components of the solid mixture, such as water leaching sugar in sugar beets, ethanol leaching of soybean oil in soybeans, water leaching of active ingredients from traditional Chinese medicine, etc..

　　Generally, in the liquid mixture (raw material liquid, denoted by F), the components that are soluble in the solvent are called solutes (denoted by A), the components that are difficult to dissolve in the solvent are called proto-solvents (denoted by B), and the selected solvent is the extractant (denoted by S).

　　The extractant should have the largest possible solubility of the solute in the raw liquid, and the original solvent should be completely immiscible or partially immiscible. If the extractant is completely immiscible with the original solvent, the extractant mixed with the feedstock liquid will become two phases, one of which is dominated by the extractant and dissolved in the solvent.

　　Extractant-based, dissolved in more solutes, known as the extraction phase (expressed as E); another phase of the original solvent-based, dissolved solutes are not extracted, known as the extraction phase (expressed as R).

　　If the extractant of the original solvent partially soluble, the extractive phase also contains the original solvent, the extractive phase also contains the extractant. The extractant in the extractive phase is removed and the liquid obtained is called the extractive solution (expressed as E'); the extractant in the extractive phase is removed and the liquid obtained is called the extractive solution (expressed as E').

　　The liquid obtained after removal of the extractant is called the extractant (indicated by R').

　　The extraction operation is generally carried out at room temperature, mainly used for the occasions which are not suitable for distillation operation (such as the volatility of the separated components is close to the concentration of the components to be separated is low, etc.), but also particularly suitable for the separation of heat-sensitive materials or non-volatile substances.

　　The extraction process does not cause changes in the chemical composition of substances, commonly used to purify and purify compounds, can be used to separate and purify a large number of substances, but also suitable for the separation of trace or trace substances, enrichment. With the recent development of analytical chemistry separation

　　With the development of modern analytical chemistry separation technology, liquid-liquid extraction is combined with photometric method, atomic absorption method, electrochemical method and so on, which is widely used in metallurgy, electronics, environmental protection, biochemistry and medicine and other fields.

　　Usually, extraction devices with relatively large diameter are collectively called tower extraction equipment, or extraction tower for short. In order to ensure good extraction results, the extraction tower should have:

　　① dispersing device to provide good contact conditions between the two phases;.

　　② The top and bottom of the tower should have enough separation space for the stratification of the two phases. According to the two-phase mixing and dispersion of different measures, the structure of the extracting tower in a variety of forms.

　　Commonly used in the industry extraction tower spray extraction tower, packing extraction tower, turntable extraction tower, sieve plate extraction tower and so on.