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After quick-frozen raw materials are selected, rinsed, reshaped, put on disk, etc., they can enter the lyophilization stage. The first step of lyophilization must be quick freezing of the lyophilized material. The tray containing the material is placed in a lyophilizer for quick freezing (some lyophilizers do not have a quick-freeze function, and an additional freezer is required). The quick-freezing process has the following kinds:
Immersion method: The material is immersed in liquid nitrogen, liquid Freon, low temperature brine and other media for rapid freezing. This method freezes fastest.
Air-cooling method: The material is blown at low temperature and cold air to freeze the material to a certain temperature within a specified time.
Direct cooling method: The refrigerant or refrigerant is placed in the evaporative pipe to absorb the heat of the material for cooling purposes.
Vacuum refrigeration method: The use of vacuum to evaporate the moisture in the material to take away heat, cooling the material to achieve cooling purposes.
Regardless of the method used, materials should be guaranteed to freeze to a certain temperature within the specified time without substantial deformation.
In order to ensure that the ice in the material is insolubilized and vaporized (sublimation) and the vapors are continuously removed to ensure the normal sublimation, the degree of vacuum in the chamber must be lower than the saturated vapor pressure of ice at a certain temperature (below 610 pa).
The use of a cold trap is to trap water vapor and reduce the load of the vacuum pump. A properly designed cold trap will not cause the vacuum pump to fail, and the energy consumption is also low, but the design requirements for the refrigeration system and the cold trap are strict.
As ice continues to sublimate, the removal of vapors also removes the heat from the material, causing the material temperature (ice temperature) to continue to decrease, leading to a decrease in the saturated vapor pressure of the steam ice and a slower rate of sublimation. In order to maintain a certain rate of sublimation, it is necessary to constantly add heat to the material. Too little calorie supplement will reduce the rate of sublimation. Too much caloric supplement will cause the ice to melt, causing the material to collapse and freeze-dry.
Because the lyophilization process of the lyophilizer is complicated and the scope of working conditions is narrow, the quality of the lyophilized product will be reduced due to slight carelessness. Therefore, an automatic control system is required. The design of the lyophilization machine automatic control system requires simple operation, starting from the material into the button, quick-freeze vacuum sublimation drying one after the other, suggesting that the lyophilization is completed after the shutdown discharge. The relevant temperature and pressure control points should be carefully selected and reasonably controlled, and the associations of quick freezing, vacuum maintenance, and heating should be properly controlled, and the technological curves should be set for different materials.
Vacuum freeze-drying technology has been widely used in bioengineering, pharmaceutical industry, food industry, materials science and deep processing of agricultural and sideline products. Drug freeze-drying includes western medicine and traditional Chinese medicine. Western medicine freeze-drying has obtained certain development in China. Many large-scale pharmaceutical plants have freeze-drying equipment. In traditional Chinese medicine, it is currently limited to lyophilization of small amounts of Chinese medicinal materials such as ginseng, velvet, Chinese yam, and Cordyceps sinensis. A large number of proprietary Chinese medicines have not yet been lyophilized and have a large gap with foreign countries. In the field of biotechnology products, freeze-drying technology is mainly used for the production of serum, plasma, vaccines, enzymes, antibiotics, hormones and other drugs; biochemical examination of drugs, immunology and bacteriological examination of drugs; blood, bacteria, arteries, bones , skin, cornea, nerve tissue and various organs for long-term preservation.
Pre-freeze type and heating analysis of freeze dryer
Freeze dryer (freeze dryer) consists of refrigeration system, vacuum system, heating system, electrical instrumentation control system. The main components are drying ovens, condensers, refrigeration units, vacuum pumps, heating/cooling devices, etc. Freeze-Drying Abbreviated as lyophilization refers to the method of preserving water-containing substances by first freezing them into a solid state and then sublimating the water from the solids into a gaseous state to remove the water.