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Molecular distillation technology and its applications

时间:2013-11-12 10:58
来源:网络
作者:网络
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内容介绍
Molecular distillation is carried out under high-vacuum distillation of non-equilibrium techniques (vacuum up 0.01Pa), gas diffusion is the main form of freedom of molecular motion using different materials to achieve different process Separation on Mixture. Surface due to evaporation and condensation surface separation distance less than or equal to the material mean free path of vapor molecules, so also known as short path distillation. As the molecular distillation process, separation of material components can be much lower than the boiling point temperature evaporation, and the various components of the heating process is very short, so molecular distillation has become a high boiling point and heat-sensitive material and an effective means of separation . Has been widely used in food, pharmaceutical, oil processing, petrochemical and other fields, for the enrichment or purification of low volatility, high molecular weight, high boiling point, high viscosity, heat-sensitive, biologically active materials.

1. The basic concepts of molecular distillation
Effective diameter of molecules: molecular during the collision process, two molecules of mass center of the shortest distance, which happened exclusion distance from the center of mass. Free path of molecular motion: refers to a molecule with other gas molecules between collisions between two molecules to go away. Mean free path of molecular motion: a certain external conditions, the different materials in the various elements of the free path varies. On a particular molecule, in a certain time interval is called the mean free path mean free path.

2 The basic principle of molecular distillation
Molecular distillation is based on the separation of different substances on the basis of different volatility, the operation is carried out below the material boiling point, when the condensation temperature and evaporation of surface material when the surface temperature differences can be carried out by molecular distillation. According to kinetic theory, the various elements to heat the liquid mixture will escape from the surface, different types of molecules, due to their effective diameter of different escaped after the straight line flight distance surface is not the same. Mean free path of light elements large, heavy molecules mean free path is small, if the light from the surface is less than the average molecular weight greater than the molecular free path and mean free path of Department to set a condensing surface, making light condensing surface molecules fall by condensation, and the molecular weight condensation surface due to reach back to the original surface, so that the mixture will be separated.

3. The basic process of molecular distillation
According to the basic theory of molecular distillation, distillation process can be divided into the following five steps: ① the formation of film material in the heated surface; ② molecules in liquid film free surface evaporation; ③ molecular condensate from the heating surface for the movement; ④ light elements in the condensation surface capture molecules return to re-film materials; ⑤ distillates and residue collection.

4. The characteristics of molecular distillation
Compared with the traditional ordinary distillation, molecular distillation has the following characteristics: (1) separation of materials based on substances of different volatility based on the material below the boiling point separation operation carried out under solvent extracted for use off the liquid solvent is Youxiao ; (2) ordinary distillation is the evaporation and condensation of the reversible process, liquid and gas phase can form dynamic equilibrium, and molecular distillation process, escape from the evaporating surface molecules directly from flying to the condensation surface, the middle is not with other molecules collision, in theory, did not return to face the possibility of evaporation, so molecular distillation is irreversible; (3) General distillation although it could be vacuum distillation, but is not very high vacuum, the material in the dissolved gases will lead to materials with bubbling , boiling phenomena, and molecular distillation is carried out under very low pressure of the free liquid surface evaporation, evaporation under non-boiling; (4) high vacuum molecular distillation operation. Molecular distillation is a short-range high-vacuum distillation, evaporation and condensation surface area is less than the distance between the mean free path of light elements, evaporation of the light elements are not collisions with other molecules, almost no pressure drop to achieve the condensation surface material is more conducive to separation; (5) Distillation temperature lower than ordinary distillation. Conventional distillation at the boiling point temperature, and molecular distillation to operate at very high vacuum, conventional distillation can not separate the thermal stability of substances with poor distillation; (6) material heating time is short. In the evaporation process, the mixed materials skinny, and was directed to promote, liquid and heating surface area almost equal to the liquid in the separator makes the stay a short time (typically a few seconds to tens of seconds), they avoid the heat long time and some components of the mixture caused decomposition or aggregation may be more suitable for some high boiling point, heat-sensitive and easy to carry out effective separation of oxide materials (7) the separation of a higher degree of molecular distillation. When two components were separated mixture to the relative volatility that the separation capacity. (8) molecular distillation using the molecular mean free path of different separation, fractionation process is the physical process, separation of operation does not use toxic organic solvent, pure and safe products available.

5. The factors affecting the speed of molecular distillation
Affect the speed of the main factors of molecular distillation is the temperature and vacuum distillation rate with increased temperature and vacuum degree rise, therefore, good thermal stability of the material, in a vacuum for some time, elevated temperature can accelerate the process of distillation.

6. Other factors affecting molecular distillation
The mixture of volatile substances: such as low boiling point components, dissolved air, moisture, in progress should be removed before the distiller, or cause violent boiling and affect product quality. ② mixture viscosity: viscosity affect the mean free path of molecular motion one of the factors, but also affect the film thickness and residence time one of the factors. ③ film thickness: the spread of the liquid evaporation rate is to control the speed of molecular factors, it should be thin liquid film thickness. ④ distillation temperature: should be based on the thermal stability of the separated material to choose a reasonable distillation temperature, while the internal hot and cold evaporator surface temperature difference should be enough, usually 70 ~ 100 ℃. ⑤ vacuum distillation system: molecular distillation must be carried out under high vacuum evaporation of elements to ensure free path is greater than equal to the average movement distance between hot and cold sides.

7. Molecular distillation applications in chemical industry
Molecular distillation can remove material in the light of molecular components in the polyurethane industry to remove toxic isocyanate monomer. In the natural flavors and fragrances industry, essential oils to deodorization, decolorization and purification, extraction in the preparation process to remove residual organic solvents, catalysts, and products and other impurities. In addition, also used in the petrochemical waste oil recycling, oil residue and its analogues isolated, purified surface active agent, manufacture of high viscosity lubricants.

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