1. distillation principle: the liquid mixture is partially vaporized, and then the vapor is partially condensed, thus realizing the separation of its components. Belonging to the unit operation of mass transfer and separation.

Widely used in oil refining, chemical industry, light industry and other fields. Its principle is to take the separation of two-component mixture as an example. Volatile components are enriched in steam and non-volatile components are enriched in residual liquid, which realizes the separation of the two components to some extent.

2. Fractionation principle: Fractionation is carried out by fractionating tower. After the fractionated solvent boils in the distillation flask, the steam evaporates from the round bottom flask to the fractionating column, where it condenses into liquid. Because of the high content of low-boiling components, the boiling point of liquid is lower than that of liquid in distillation bottle.

When another part of the steam in the distillation bottle rises to the fractionator, it exchanges heat with the condensate to make it boil again, and the rising steam itself is partially condensed. Thus, a new vapor-liquid equilibrium is generated, which leads to the increase of low-boiling components of steam.

Second, the equipment is different.

1. Distillation device: distillation bottle (with branch pipe), thermometer, condenser pipe, trumpet, alcohol lamp, asbestos mesh, iron shelf, conical bottle with branch mouth and rubber stopper.

2. Fractionation device: gas lamp, fractionator, asbestos mesh, tripod, round-bottomed flask, condenser tube, flare tube (liquid receiver), conical flask and thermometer.

Extended data:

Fractionation is carried out under normal pressure to obtain a low-boiling fraction, and then a high-boiling fraction is obtained under vacuum. Each fraction also contains various compounds and can be further fractionated.

Fractionation is actually repeated distillation, which is more suitable for the separation and purification of liquid organic mixtures with similar boiling points. For example, the fractionation of coal tar; Fractionation of petroleum When the boiling points of substances are very close, with a difference of about 25 degrees, simple distillation cannot be used, but fractional distillation can be used. The small tower of fractionator can provide large surface area for steam condensation.

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