单元操作—萃取

1.Definition

-----It is a kind of method that transfers a material from a kind of liquid phase to another one.

-----Extraction ,also called solvent extraction or liquid-liquid extraction different from the liquid-solid extraction, is a kind of liquid extraction processing mutually dissolved two-component or components in order to realize a process of separating components from solution, and is a widely used

unit operation.

2.Principle----compatibility and similitude principle

(相似相容原理）

-----The use of compounds in the two immiscible (or slightly soluble) solvents of different solubility or partition coefficient, so that compounds are transferred to another solvent from one solvent. After repeating several times extraction, the great majority of compounds extracted.

3.compatibility and similitude principle

Similar "refers to the solute and solvent are similar in structure;" compatibility "refers to the solute and solvent immiscible with each other.

1----water molecules have a stronger hydrogen bonds between water molecules that can provide hydrogen atoms to generate hydrogen bond, and also because in which there is oxygen atom can accept lone electron pairs of other elements, hydrogen atoms, hydrogen bonds between water molecules is the main binding force. So, who can provide hydrogen to generate hydrogen bonds or acceptance of hydrogen solute molecules and water are "structure similar”.

2----For a class of structurally similar gas, the higher boiling point, and its larger intermolecular forces, the more close to the liquid, so the larger the solubility of liquids. The boiling point, such as O2's (90K) boiling point higher than the H2's (20 K), so the solubility of O2 in water is greater than the solubility of H2.

3----For a class of structurally similar solid solute, the lower melting point, its smaller intermolecular forces, the more close to the liquid, so the larger the solubility of liquids.

4.law of partition -----Distribution law is the main basis for the theory of

extraction method, material of different solvents have different solubility. At the same time, there are two immiscible solvents, by adding a soluble substances that can dissolve in the two kinds of solvents, respectively, the experiments show that under certain temperature, the compound does not occur with this two kinds of solvent decomposition, Electrolysis, association, and the role of solvents and so on, this compounds the ratio of two liquid layers is a fixed value. Regardless of how much the amount of added material, are true. (physical changes)

5.extraction agent（萃取剂）

Commonly used agent

------H2O , CCL4 , C6H6 Extraction agent the option of requesting 1. Solvent extraction agent and the former mutual immiscibility 2. Agent and solute does not react with each other 3. Solute solubility in the extraction agent is much greater than in the original Solubility

Related laws 1. Easy-to-organic solvent soluble organic solvents, polar solvents, polar

solvents dissolve easily 2. Use of "salting-out effect" to reduce the organic matter and extraction solvent

solubility in aqueous solution can often improve the extraction efficiency. In aqueous solution by adding a certain amount of electrolytes (such as sodium chloride)

6. Batch sheet level extraction 间歇式单级萃取

This is commonly used on the small scale in chemical labs. It is normal to use a separating funnel. For instance, if a chemist was to extract anisole from a mixture of water and 5% acetic acid using ether, then the anisole will enter the organic phase. The two phases would then be separated.

The acetic acid can then be scrubbed (removed) from the organic phase by shaking the organic extract with sodium bicarbonate. The acetic acid reacts with the sodium bicarbonate to form sodium acetate, carbon dioxide, and water.

7. Multistage countercurrent continuous processes 多级逆流连续过程

These are commonly used in industry for the processing of metals such as the lanthanides, because the separation factors between the lanthanides are so small many extraction stages are needed. In the multistage processes, the aqueous raffinate from one extraction unit is fed to the next unit as the aqueous feed, while the organic phase is moved in the opposite direction. Hence in this way even if the separation between two metals in each stage is small, the overall system can have a higher decontamination factor.

Multistage countercurrent arrays have been used for the separation of lanthanides. For the design of a good process the distribution ratio should be not too high (>100) or too low (<0.1) in the extraction portion of the process. It is often the case that the process will have a section for scrubbing unwanted metals from the organic phase, and finally a stripping section to obtain the metal back from the organic phase.

8. Ionic liquid extraction 离子液基萃取

Ionic liquid extraction of room temperature ionic liquids are used instead of volatile organic molecule solvent as diluent liquid (functional ion itself has the function of extraction) for extraction. To be a new green solvents.

9. Aqueous two phase extraction 双水相萃取

Using an Aqueous two phase system, it is possible to generate two immiscible water phases. This can then be used to extract proteins, which would denature if exposed to organic solvents.

10.supercritical fluid extraction 超临界萃取

Supercritical Fluid

---- Supercritical fluid is a liquid between the gas has neither the

non- liquid physical state, this substance can exist only in its temperature and pressure over the critical point . Density of supercritical fluid is similar to the liquid, but its viscosity is also closer to the viscosity of gas. Therefore, supercritical fluid extraction is a very good agent.

11.常见几种萃取设备

筛板萃取塔

转盘萃取塔

离心萃取器

12.Choice of extraction equipment

Selection principle 1. Stability and retention time 稳定性及停留时间 2.Theoretical stages required for 所需理论级数 3. Material dispersion and cohesion characteristic

s of the Department of 物系的分散与凝聚特性 4. Capacity 生产能力 5. Anti-corrosion and anti-pollution requirements

防腐蚀及防污染要求 6. Building site requirements 建筑物场地要求

members of the team

樊明哲 马睛玉 许伍 荣晓明 张帝