According to the three-phase diagram principle of water, whether it is liquid water or solid water, it has different saturated vapor pressures at different temperatures. If the solid water is below the vacuum of its saturated vapor pressure, the moisture is not It is directly sublimated by melting, and this principle is utilized in vacuum freeze-drying. Generally, in freeze-drying, the vacuum used is about 1/2-1/4 of the saturated vapor pressure at the corresponding temperature. The temperature of the water vapor condenser (cold trap) is lowered to below -40 ° C, so that the dehydrated water vapor is trapped and frozen and accumulated when passing through the cold trap, thereby avoiding a large amount of sublimated water entering the vacuum pump.
Why choose freeze drying? After the primary drying is completed, all the ice is raised. However, the combined water is still present in the product. In the secondary drying, the dry phase of the zui is firmly bonded to the water of the solid sample, which is called the absorption of water into water vapor. This process is called desorption. Desorption is a slow process because the absorbed water is at a lower pressure than the liquid water at the same temperature. Freeze-drying is accomplished at a similarly low vapor pressure across the sample and collector. If the sample leaves the system prematurely at the end of complete drying, it may degrade quickly and lose structural and biological properties. Conventional drying causes the material to shrink and destroy the cells, and the structure of the sample is not destroyed during the freeze drying process because the solid components are supported by the firm ice on its seat. When the ice sublimates, he leaves the pores in the dry remaining material. This preserves the biological and chemical structure of the product and the integrity of its activity. The condensable gas molecules are pumped out of the vacuum pump through the cold trap. The efficiency of the rise of the frozen sample depends on several factors. The difference in air pressure between the important frozen product and the collector. The effective freeze-drying of zui occurs when the sample is at a high temperature that it can withstand while still maintaining a frozen state, while the collector temperature and system vacuum are kept at a low value that can be achieved. The change in drying time depends on the eutectic temperature of the lyophilized material. For most biomaterials, this temperature is below 0 °C, and some even below -40 °C. High air pressure differences and temperature differences will result in effective drying. During the dehydration process, a certain amount of heat needs to be absorbed, so that the temperature of the material is lowered. When the externally added heat is equal to the sublimation heat absorption, the equilibrium state is reached, and the material is carried out at a certain sublimation rate. If no external heat is supplied, the material is The temperature will be reduced, so that the vapor pressure of the ice is excessively reduced and the sublimation rate is slowed down. For this reason, at the rate of controlling the drying, both the heat is supplied to the material and the solid material is prevented from being melted. The temperature of the plate is controlled to be no more than +60 ° C. The user can freeze and dry in the laboratory according to the required material rate. He has many different uses. He is indispensable in many biochemical and pharmaceutical applications. Obtaining biological materials that can be preserved for a long period of time, such as microbial culture, enzymes, blood and medicines, retains its inherent biological activity and structure in addition to long-term preservation stability.
Freeze drying can occur naturally, and in the natural case, this process is slow and unpredictable. Through the freeze-drying system, people have improved and subdivided many steps to speed up the process. To this end, lyophilization is used to prepare tissue samples for structural studies (such as electron microscopy studies), and freeze-drying is also used in chemical analysis to obtain dried samples or to concentrate samples to increase chemical sensitivity. Freeze-drying stabilizes the sample components without changing the chemical composition, making it an ideal analytical aid.
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