What is the principle of rectification and what is the principle of rectification

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The principle of rectification.

Distillation is a method of partial gasification and partial condensation that is used multiple times and at the same time to separate the mixture more completely to obtain close to pure components.

Theoretically, high-purity volatile components can be obtained in the liquid phase by multiple partial gasification, and high-purity volatile components can be obtained by multiple partial condensation in the gas phase, but the product quantity is very small due to the production of a large number of intermediate components, and the equipment is huge. The rectification process in industrial production is in the rectification column.

The operation is achieved by organically combining part of the gasification process and part of the condensation process.

The flow of the distillation unit.

A typical distillation unit is a continuous distillation unit, including a distillation column and a condenser.

In the continuous distillation operation, the raw liquid is continuously fed into the distillation column, and the product (distillate, kettle residue) is continuously obtained from the top and bottom of the column at the same time, so it is a steady operation process.

The role of the distillation unit.

The distillation column is divided into two sections, the distillation section and the distillation section.

1. The role of the distillation section.

The column section above the feeding plate is the distillation section, and its function is to concentrate the concentration of volatile components in the rising gas phase plate by plate.

2. The role of the distillation section.

The following plates, including the feeding plate, are the distillation section, and the action of this plate extracts the volatile components in the liquid phase that have descended one by one.

3. The role of the tray.

The tray is a place for mass transfer and heat transfer in the two phases of gas and liquid. The gas-liquid phases on each tray carry out two-way mass transfer, and as long as there is enough plate number, the mixture can be separated into two purer components.

4. The role of the reboiler.

Its function is to provide a certain flow of upward vapor flow.

5. The role of the condenser.

Its role is to provide the overhead LC product and ensure proper LC reflux.

Reflux mainly replenishes the concentration of volatile components on the tray and is a necessary condition for the continuous steading of rectification.

Taking advantage of the different boiling points and volatilization capacity of each component in the mixture, through the reflux of the liquid phase and the gas phase, the gas and liquid phases are reversed to multi-stage contact, and under the constraint of thermal energy drive and phase equilibrium relationship, the volatile components (light components) are continuously transferred from the liquid phase to the gas phase, while the non-volatile components migrate from the gas phase to the liquid phase, so that the mixture is continuously separated.

Rectification is actually a combination of multiple simple distillations. In the distillation stage, the low boiling point components of the gas phase are continuously refined and continuously enriched in the gas phase during the rising process of the gas phase, and the low boiling point product is obtained at the top of the column. In the distillation stage, in the process of decreasing the liquid phase, the low boiling point components are continuously distilled, so that the high boiling point components are continuously concentrated in the liquid phase, and the high boiling point products are obtained at the bottom of the column.

Fundamental Difference Between Rectification and Distillation:

1.Rectification is a combination of multiple simple distillations.

2.The relative volatility between the components in the manual excitation system of the distillation to be separated is small, and the relative volatility of distillation needs to vary greatly.

3.The degree of distillation separation is higher, and distillation can only be separated simply. Rectification is usually done in the rectification column.

The gas-liquid phases are contacted by countercurrent to carry out interphase heat and mass transfer. The volatile components in the liquid phase enter the gas phase, and the non-volatile components in the gas phase transfer to the liquid phase.

Distillation (distillation method, preparation for excavation) imitation.

Distillation is a separation process that separates each component by using the different volatility of each component in the mixture, and the commonly used equipment is a plate distillation column.

and packed distillation columns. The principle and equipment flow of precision distillation are the same as those of ordinary distillation, but the relative volatility between the components in the system to be separated is small (<, so high-efficiency precision packing materials are used to realize the separation and purification of the components to be separated. There are often isomers in the raw materials for the production of mono fragrances, a natural refined and dry oil.

Coexisting conditions, such as citronellol and rose alcohol that are present in natural essential oils such as gerania oil, rose oil, rose grass oil, etc., are optical isomers. The boiling point difference of these isomers is relatively small, and it is difficult to achieve the effective separation of this single fragrance with the general distillation process, so precision distillation has a wide range of applications in the production of single fragrance fragrances. The high-efficiency packing materials used in precision distillation columns include Q

Bulk packing such as dixon filler and mcmahon filler, as well as structured packing represented by screen corrugated filler (sulyer filler). The specific surface of these packing materials is large, the wettability is good, the liquid holding capacity and fluid resistance are small, but the diameter of the bulk packing tower should not be too large, otherwise the mass transfer separation efficiency will drop sharply, which is the "amplification effect" of the packed tower. The amplification effect of structured packing is small, so the application of screen corrugated structured packing is becoming more and more extensive.

Distillation. Principles of distillation.

Rectification is usually carried out in a distillation column, where the gas-liquid phases are contacted by countercurrent to carry out interphase heat and mass transfer. The volatile components in the liquid phase enter the gas phase, and the refractory components in the gas phase transfer to the liquid phase, so that almost pure volatile components can be obtained at the top of the tower, and almost pure refractory components can be obtained at the bottom of the tower. The feed liquid is added from the middle of the tower, and the tower section above the feed port further enriches the volatile components in the rising vapor, which is called the distillation section; The column below the feed inlet, where the volatile components are extracted from the descending liquid, is called the distillation section.

The vapor drawn from the top of the column is condensed, and a part of the condensate is returned to the distillation column from the top of the column as a reflux liquid, and the rest of the distillate is the product of the top of the column. The liquid drawn from the bottom of the tower is partially vaporized by the reboiler, the vapor rises along the tower, and the remaining liquid is used as the product at the bottom of the tower. The ratio of the amount of liquid flowing back into the column at the top of the column to the amount of product at the top of the column is called the reflux ratio, and its magnitude affects the separation effect and energy consumption of the distillation operation.

A distillation method that uses reflux to separate liquid mixtures with high purity, is the most widely used liquid mixture separation operation in industry, and is widely used in petroleum, chemical, light industry, food, metallurgy and other sectors. Distillation operations are classified according to different methods. According to the mode of operation, it can be divided into continuous distillation and batch distillation; According to the component fraction of the mixture, it can be divided into binary distillation and multivariate distillation; According to whether additives affecting the vapor-liquid balance are added to the mixture, it can be divided into ordinary distillation and special distillation (including extractive distillation, constant boiling distillation and salt distillation).

If the distillation process is accompanied by a chemical reaction, it is called reactive distillation.

The separation of two-component mixtures is the easiest.

Distillation. Operate. A typical distillation unit is a continuous distillation unit, comprising:

Distillation column. Reboiler,

Condenser. Wait. The distillation tower is carried out by the vapor-liquid two-phase contact.

Interphase mass transfer. The condenser located at the top of the column partially condenses the vapor, part of the condensate returns to the top of the column as a reflux liquid, and the rest of the distillate is the top product. Situated.

The bottom of the tower. The reboiler makes the liquid part.

Vaporization. The vapor rises along the tower, and the remaining liquid serves as the bottom product.

Feeding. Added in the middle of the tower, the liquid in the feed and the liquid from the upper tower section descend along the tower together, and the vapor in the feed and the vapor from the lower tower section rise along the tower together. In the entire distillation column, the vapor-liquid two phases are in countercurrent contact for interphase mass transfer.

The volatile components in the liquid phase enter the vapor phase, and the non-volatile components in the vapor phase transfer to the liquid phase. For the system that does not form a constant boiling substance, as long as the design and operation are appropriate, the distillate will be a high-purity volatile component, and the bottom product will be a high-purity refractory volatile component. In the tower section above the feed port, the volatile components in the rising vapor are further concentrated, which is called the distillation section; The column below the feed inlet, where the volatile components are extracted from the descending liquid, is called the distillation section.

The combination of the two stages of operation makes the following:

Liquid mixtures.

The two components are relatively completely separated, producing the two products of the required purity. When to make.

When the N-component mixture is completely separated to obtain n high-purity one-component products, n-1 columns are required.

The reason why distillation can achieve a more complete separation of liquid mixtures lies in the application of reflux. The reflux includes the high-concentration volatile component liquid at the top of the column and the high-concentration refractory component vapor at the bottom of the column, both of which are returned to the column. The vapor-liquid reflux forms a vapor-liquid phase in countercurrent contact, resulting in a fairly pure one-component product at each end of the column.

The ratio of the amount of liquid flowing back into the tower at the top of the tower to the amount of product at the top of the tower is called.

Reflux ratio. It is an important control parameter for distillation operations, and its variation affects the separation effect of distillation operations. Energy consumption.

Under specific conditions, the reaction process is integrated with the distillation process so that:

A technique in which the reaction and distillation are carried out simultaneously in a distillation facility.

Features: The generated product is moved out of the reaction zone in time, and the chemical equilibrium moves to the reaction direction of the product for reversible and complex reactions, which can improve the conversion rate and selectivity of the reaction.

Due to the timely removal of the generated products, the total concentration of reactants increases, which is conducive to accelerating the reaction rate.

The heat of reaction is utilized, which reduces the energy consumption of the distillation process.

The reactor and distillation column are integrated into one, which saves equipment investment.

For some difficult-to-separate systems, one component can be reacted by reactive distillation and the other component can be separated.

Conditions: The requirements of both the reaction process and the distillation process must be met.

Reaction process – appropriate temperature, pressure, reactant concentration distribution and catalyst, etc.;

Rectification process – The volatile capacity of the reactants and the product is quite different.

Therefore, the reactive distillation should be based on the needs of different reaction processes and the properties of each component in the system, and the distillation process, feeding mode, plate structure and operating conditions should be selected.

The distillation unit consists of three parts: a heating and gasification part, a condensation part, and a receiving part.

Note: When distilling under reduced pressure, use a K-wire distillation head, a drained tube with a branch tube, or use a multi-ended drained tube.

It is necessary to replace zeolite with a capillary tube to prevent boiling.

Heating in a hot bath is required, and a thick-walled, pressure-resistant glass instrument is required.

Principle. The difference in the volatility of each component in the liquid mixture is used to partially vaporize the liquid mixture and subsequently condense the vapor part, so as to achieve the separation of the components contained in it. It is a unit operation that belongs to mass transfer separation. It is widely used in oil refining, chemical industry, light industry and other fields.

The principle is based on the separation of a two-component mixture. The material liquid is heated to partially vaporize, the volatile components are enriched in the vapor, and the involatile components are also enriched in the remaining liquid, which realizes the separation of the two components to a certain extent.

Qiaoyou Kai <>

The greater the difference in the volatile capacity of the two components, the greater the degree of enrichment described above. In industrial distillation equipment, the partially vaporized liquid phase is in direct contact with the partially condensed gas phase for vapor-liquid interphase mass transfer, and the result is that the refractory components in the gas phase are partially transferred to the liquid phase, and the volatile components in the liquid phase are partially transferred to the gas phase, that is, the partial vaporization of the liquid phase and the partial condensation of the vapor phase are realized at the same time.