What is the specific concept of fractionation? What is the difference with distillation?

Fractionation is an important method for separating and purifying components of liquid-organic mixtures with small differences in boiling points.

Fractionation: If the mixture of two volatile liquids is distilled, at the boiling temperature, the gas phase and the liquid phase reach equilibrium, and the resulting vapor contains more volatile components, and the vapor is condensed into a liquid, and its composition is equal to that of the gas phase (that is, it contains more volatile components), and the residue.

However, the residue contains a large amount of high boiling point components (difficult to volatile components), which is a simple distillation.

If the liquid condensed by the vapor is re-distilled, that is, the gas-liquid equilibrium is carried out again, and the composition of the volatile substances contained in the vapor produced again increases, and the composition of the volatile substances in the liquid obtained by condensation of the vapor is of course higher, so that we can use a series of systematic repeated distillation, and finally we can obtain two liquids close to the pure components.

Although two liquids close to the pure composition can be obtained by applying such repeated simple distillation many times, it is a waste of time, and the loss in repeated distillation operations is very large, and the equipment is complex, so it is usually the use of fractionation column for multiple gasification and condensation, which is fractionation.

In the fractionation column, when the rising vapor is in contact with the falling condensate, the rising vapor partially condenses and releases heat to vaporize the falling condensate, and heat exchange occurs between the two, as a result, the volatile components in the rising vapor increase, and the high boiling point components (difficult volatile components) in the falling condensate increase. This results in a high ratio of volatile components near the top of the fractionation column and a high ratio of high boiling point components (refractory components) in the flask. This allows the fractionation column to be completely separated as long as the fractionation column is high enough.

The industrial rectification column is equivalent to the fractionation column.

Difference Between Distillation and Fractionation:

1.The number of distillations is different.

Distillation only performs one vaporization and condensation, and fractionation is a method that uses a fractionation column to vaporize multiple times and condense the process in one operation. Thus, fractionation is actually multiple distillations.

2.The purity of the substances separated is different.

The substances separated by distillation are generally pure, such as distilled water made from natural water.

and from industrial alcohol.

Absolute ethanol is prepared in China.

The substances separated by fractionation are still mixtures with different boiling point ranges. It is more suitable for separating and purifying liquid-organic mixtures with little difference in boiling point.

Principle of fractionation:

Fractionation is carried out with a fractionation column, and after the solvent being fractionated is boiled in the distillation flask, the vapor evaporates from the round-bottom flask into the fractionation column, where it partially condenses into a liquid. The boiling point of this liquid is lower than that of the liquid in the distillation flask due to the higher content of low-boiling components.

When another part of the vapor in the flask rises into the fractionation column, it is heat exchanged with the condensed liquid, causing it to re-boil, while the rising vapor itself is partially condensed, so that a new liquid vapor equilibrium is created, and as a result, the low boiling point component in the vapor increases. As this new vapor rises in the fractionation column, it is condensed into a liquid, and then boiled by heat exchange with the other part of the rising vapor.

As the rising vapor is constantly condensed and evaporated in the fractionation column, each condensation and evaporation increases the low boiling point components of the vapor. Therefore, the ascent of the vapor in the fractionation column is similar to a simple distillation that has been repeated many times, so that the components of the low boiling point in the vapor are gradually increased.

1. The number of distillations.

Distillation is performed only once for vaporization and condensation, and fractionation is a method of using fractionation columns to complete the process of multiple gasification-condensation in a single operation. Thus, fractionation is actually multiple distillations.

2. The purity of the separated substance.

The substances separated by distillation are generally pure, such as distilled water from natural water and absolute ethanol from industrial alcohol;

The substances separated by fractionation are still mixtures with different boiling point ranges. It is more suitable for separating and purifying liquid-organic mixtures with little difference in boiling point.

With the increasing depletion of the first-class industry and the increasing competition in the oil market, how to make full use of limited oil resources and enhance the core competitiveness of enterprises has become the focus and core of the development of China's petroleum industry. In order to promote the sustained and healthy development of the petroleum industry and provide strong support for China's national economy, we must vigorously enhance the development of the petroleum industry, and the stability of the oil industry is the key. In the process of stabilization, it is worth mentioning the process technology of fractionation.

If the mixture is heated to boiling, and the vapor phase and the liquid phase are in close contact for a long time, and the vapor-liquid two phases reach an equilibrium state, and finally the two phases are moved into the separator for separation, this operation is called equilibrium distillation.

Features: It is only partially separated, and cannot meet the separation requirements of high purity.

Scope of application: only for rough separation or as preliminary processing.

1.Distillation

The process of heating a liquid mixture to boiling it into vapor and then condensing it into a liquid.

Distillation is one of the most commonly used methods for separating and purifying liquid organic compounds. It can also be used as a method to identify organic matter and judge the purity of substances.

2.The basic principle of fractional distillation is similar to that of distillation. The difference is that there is an additional fractionation column on the device, and the process of using the fractionation column to make the vapor state and cold the condensation is improved from one time to many times.

To put it simply, fractionation is the distillation of multiple times.

3.Distillation and fractionation are both important methods for separating and purifying liquid organic compounds. Distillation is mainly used to separate two or more liquid mixtures with large boiling points (at least 30 or more), while fractionation is to separate and purify liquid mixtures with small differences in boiling points, and now the most sophisticated fractionation equipment has been able to separate mixtures with a difference in boiling point of 1 2.

Fractionation has been widely used in laboratories and in the chemical industry.

First, the principle is different.

1. Distillation principle: use the difference in the volatility of each component in the liquid mixture to partially vaporize the liquid mixture, and then condense the vapor part, so as to realize the separation of its components. It is a unit operation that falls under the mass transfer separation.

It is widely used in petroleum refining, chemical industry, light industry and other fields. The principle is based on the example of separating a mixture of two components. The volatile components were enriched in steam, and the non-volatile components were enriched in the remaining liquid, which realized the separation of the two components to a certain extent.

2. Principle of fractionation: Fractionation column is used for fractionation, and after the solvent to be fractionated is boiled in the distillation flask, the steam evaporates from the round bottom flask into the fractionation column and condenses the liquid in the fractionation column. Due to the high content of low-boiling components, the boiling point of the liquid is lower than that of the liquid in the distillation flask.

When another part of the steam in the distillation flask rises to the fractionation column, it exchanges heat with the condensate to boil it again, while the rising steam itself partially condenses. As a result, a new liquid-vapor equilibrium is created, resulting in an increase in the low-boiling component of the steam.

Second, the device is different.

1. Distillation device: distillation flask (with branch pipe), thermometer, condenser tube, horn tube, alcohol lamp, asbestos net, iron frame, branch Erlenmeyer flask, rubber stopper.

2. Fractionation device: gas lamp, fractionation column, asbestos net, tripod, round bottom flask, condenser tube, horn tube (liquid receiver), Erlenmeyer flask, thermometer.

Distillation: The process of vaporizing a liquid and then condensing it.

Dry distillation: A series of complex chemical changes occur when air isolation strengthens heat.

Fractionation: The process of multiple distillations.

Dry Distillation:The whole process of heating a substance under the condition of isolation from the outside world to pyrolyze the substance and produce volatile low-molecular compounds is called dry distillation; For example, coal dry distillation, the products are coal coke and coal tar

In connection with common experiments, dry distillation can also be said to be a processing method for the decomposition of wood and coal under the condition of isolating air. After dry distillation, the composition and aggregation state of the raw material will change, and the product will be solid, gaseous and liquid. Dry distillation of wood can obtain charcoal, wood tar and wood gas; For coal dry distillation, coke, coal tar, crude ammonia, and coke oven gas can be obtained.

The process of dry distillation is a chemical process.

Fractionation:It is distilled many times; It is the process of heating and cooling and separating a mixture into relatively pure single substances according to the different boiling points of each component in the mixture------ such as the fractionation of coal tar; Fractionation of petroleum

Distillation:It is a joint operation of the two processes of heating a liquid substance to boiling and turning it into vapor, and cooling the vapor into a liquid. This operation can be used to separate, remove impurities, and purify substances; Fractionation, like distillation, also uses the different boiling points of each substance in the mixture to strictly control the temperature to separate the lead or purify the substance.