After so many years of chemical industry, distillation, fractionation and rectification are still not clear?

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Original title: After so many years of chemical industry, distillation, fractionation and rectification are still not clear? It is well known that distillation is to separate the components contained in a liquid mixture by using the difference in volatility of the components in the liquid mixture to partially vaporize the liquid mixture and then partially condense the vapor. It is a unit operation of mass transfer separation. So what is distillation, what is fractionation, and what is rectification? Distillation The combined operation of heating a liquid to boiling, changing the liquid to a vapor, and then allowing the vapor to cool and recondense to a liquid is called distillation. 1. Simple distillation Under a certain pressure, the liquid mixture is heated in the distillation still. When it is heated to a certain temperature, the liquid begins to vaporize, and the generated steam is immediately drawn out and continues to be heated. The steam is continuously formed and drawn out, and it is condensed and cooled into liquid. The distillate with different composition ranges is introduced into different containers for storage. This operation is called simple distillation. Quality Control Principle of Simple Distillation Product Expand the full text When the average composition of the distillate or the composition of the retentate drops to a specified value (depending on the separation task), the distillation operation is stopped. In a batch operation, the distillate may be collected in sections to obtain distillates of different compositions (or components). Features: low processing capacity and low separation effect. Scope of application: only suitable for small rough separation or as a preliminary processing. 2. Equilibrium distillation If the mixture is heated to boiling, the vapor phase and the liquid phase are kept in close contact for a long time, and the two phases reach an equilibrium state, and finally the two phases are moved into the separator for separation, this operation is called equilibrium distillation. Operating Instructions for Equilibrium Distillation Continuous operation. The raw material liquid is continuously added, and the products at the top and bottom of the tower are continuously led out. Single stage. There is only one equilibrium in the knockout drum and only limited separation. Steady state. The temperature (t) in the separation tank remains unchanged, and the composition of overhead and bottom products (xA, yA) remains unchanged. Continuous operation. The raw material liquid is continuously added, and the products at the top and bottom of the tower are continuously led out. Single stage. There is only one equilibrium in the knockout drum and only limited separation. Steady state. The temperature (t) in the separation tank remains unchanged, and the composition of overhead and bottom products (xA,thin film distillation, yA) remains unchanged. Features: Only partial separation, can not meet the separation requirements of high purity Scope of application: only applicable to rough separation or preliminary processing. Pinch the head and tail, when steaming wine, only take the second change into the tin pot of cold water to cool the outflow of wine, the taste is the most mellow, called "Erguotou". 3. Oldest distillation equipment Kettle type distilling pot data map Kettle still is the oldest distillation equipment. Mainly comprises a preheater, a distilling pot and a snake-shaped condenser; The whole pot body is generally made of copper for four reasons: first, copper has good thermal conductivity; second, it has good acid resistance; third,jacketed glass reactor, it is used as a catalyst to promote the synthesis of aromatic substances; The insoluble copper salt formed by butyric acid, caproic acid and the like is precipitated, and the acidity of the distilled liquor is reduced. When distilling the mixed liquid with large difference in boiling point, the liquid with lower boiling point is distilled out first, the liquid with higher boiling point is distilled out later, and the non-volatile liquid is left in the distiller, so that the purpose of separation and purification can be achieved. It is obvious that distillation can separate volatile and less volatile substances, and also separate liquid mixtures with different boiling points. However, the boiling point of each component of the liquid mixture must be very different (at least above 30 ℃) in order to obtain a better separation effect. Difference between fractionation and distillation When distilling a mixture with a relatively close boiling point, the vapors of various substances will be distilled out at the same time, but the vapors with a lower boiling point are more, so it is difficult to achieve the purpose of separation and purification, so we have to resort to fractional distillation. Same: Distillation and fractionation are methods of separating liquid mixtures. There is no essential difference, and it is in this sense that fractionation is the application of the principle of distillation. Distillation and fractionation are based on the different boiling points of the components in the liquid mixture. By controlling the temperature and heating, some substances are vaporized, rotovap distillation ,decarboxylation after extraction, then condensed and liquefied and collected, while the other part remains in the original state in the original device. Distillation and fractionation are methods of separating liquid mixtures. There is no essential difference, and it is in this sense that fractionation is the application of the principle of distillation. Distillation and fractionation are based on the different boiling points of the components in the liquid mixture. By controlling the temperature and heating, some substances are vaporized, then condensed and liquefied and collected, while the other part remains in the original state in the original device. Difference: Distillation is carried out only once for vaporization and condensation, and the separated substances are generally pure, for example, distilled water is made from natural water, and absolute ethyl alcohol is obtained by distillation after adding quicklime to industrial alcohol; Fractionation requires continuous vaporization and condensation for many times, and the separated substances are still mixtures with different boiling point ranges. For example, after atmospheric and vacuum distillation of petroleum, multiple fractions with different boiling point ranges can be obtained. Distillation is carried out only once for vaporization and condensation, and the separated substances are generally pure, for example, distilled water is made from natural water, and absolute ethyl alcohol is obtained by distillation after adding quicklime to industrial alcohol; Fractionation requires continuous vaporization and condensation for many times, and the separated substances are still mixtures with different boiling point ranges. For example, after atmospheric and vacuum distillation of petroleum, multiple fractions with different boiling point ranges can be obtained. The biggest difference between distillation process and other distillation processes Based on the difference of volatilization ability of each component in the mixture, through the reflux of liquid phase and gas phase, the two phases of gas and liquid are in reverse multi-stage contact. Driven by heat energy and constrained by phase equilibrium, the volatile component (light component) is continuously transferred from the liquid phase to the gas phase, while the non-volatile component is transferred from the gas phase to the liquid phase, so that the mixture is continuously separated. This process is called distillation. The raw material liquid is continuously added into the rectifying tower. A portion of the liquid is continuously withdrawn from the reboiler as a bottom product (referred to as kettle bottoms). The overhead vapor enters the total (cold) condenser to be fully condensed, part of the condensate is pumped (or by gravity) back to the overhead as reflux liquid, and the rest is recovered as overhead product (called distillate). In this process, heat transfer and mass transfer are carried out at the same time, which belongs to mass transfer process control. In the rectifying section, during the rising process of the gas phase, the light component of the gas phase is continuously refined, the concentration is continuously increased in the gas phase, and the light component product is obtained at the top of the tower. In the tower, the concentration of the gas and liquid phases varies in a stepwise manner along the height of the tower. In the stripping section, in the descending process of the liquid phase, the light component is continuously stripped out, so that the heavy component is continuously concentrated in the liquid phase, and the product of the heavy component is obtained at the bottom of the tower. The biggest difference between distillation process and other distillation processes Liquid phase and gas phase reflux with high purity are provided at both ends of the tower at the same time, which provides the necessary conditions for mass transfer in the distillation process. High-purity reflux is provided, so that a certain mass transfer driving force can be always ensured when high-purity separation is realized for rectification under the condition of the same theoretical plate. Therefore, as long as there are enough theoretical plates and the reflux is large enough, it is possible to obtain high-purity light component products at the top of the tower and high-purity heavy component products at the bottom of the tower. Pay attention to our energy-saving internal reference public micro-signal: jnnc01 We insist on original depth or selected every article, welcome to pay attention and share. If you need to reprint, please be sure to indicate the source, and retain the words "energy-saving internal reference" and two-dimensional code. Also hope that through this platform to know more like-minded friends, communicate with each other, learn from each other, make progress together, and make a contribution to the cause of green environmental protection! (Disclaimer: This article comes from Chemical 707, only represents the author's views,50l rotovap, does not represent the position of this public number. If there are intellectual property disputes, contributions and cooperation matters, please contact) Return to Sohu to see more Responsible Editor:. toptiontech.com


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