Have you mastered the process of freeze drying?

　　Freeze drying, also known as sublimation drying, is a drying method that freezes the material below the freezing point of water and places it in a high vacuum (10 ~ 40Pa) container to heat the moisture in the material directly from the solid ice to water vapor by heating .
　　Freeze drying production process
　　Due to the complicated lyophilization process of biological products and pharmaceuticals, in order to ensure the quality and energy saving of lyophilized products, it is necessary to strictly control the pre-freezing temperature and sublimation heat absorption during the production process, so that each stage of the lyophilization process follows the pre-established process jobs.
　　Maintain pre-freezing temperature
　　In the vacuum freeze-drying process, it is necessary to pre-freeze the dried medicines, and then in a vacuum state, the moisture is directly changed from ice to gas to dry the medicines. During the entire sublimation stage, the medicine must be kept in a frozen state, otherwise a product with good properties cannot be obtained. In the stage of drug pre-freezing, the pre-freezing temperature should be strictly controlled (usually a few degrees lower than the eutectic point of the drug). If the pre-freezing temperature is not low enough, the medicine may not be completely frozen, and it will expand and foam during vacuum sublimation; if the pre-freezing temperature is too low, not only will it increase unnecessary energy consumption, but for some biological drugs, it will reduce its Survival rate after lyophilization.
　　Focus on sublimation endothermic
　　Dry sublimation stage, the material needs to absorb heat (per gram of ice fully sublimed into water vapor to absorb about 2.8 kilojoules of heat). If the medicine is not heated or the heat is insufficient, the moisture of the medicine itself will be absorbed when the water sublimates and the temperature of the medicine will be reduced, resulting in a reduction in the vapor pressure of the medicine, which will cause a reduction in the rate of sublimation and the entire drying time will be extended. Productivity decreases; if the drug is heated too much, the sublimation rate of the drug will increase, but after offsetting the heat absorbed by the sublimation of the drug, the excess heat will cause the temperature of the frozen drug to rise, causing the drug to partially or even melt. , Causing the shrinkage and foaming of the medicine, the entire drying will fail.
　　Automatic control
　　In order to obtain good lyophilized medicines, according to the performance of each lyophilizer and the characteristics of the drugs, a lyophilization curve should be drawn up on the basis of tests, and then the machine should be controlled to make each stage of the lyophilization process The temperature change is in accordance with the freeze-drying curve established in advance. Vacuum freeze-drying production process control can use the computer to control the production system to work according to the preset freeze-drying curve. For example, the computer's control of the freeze-drying process of streptomycin sulfate can be divided into two stages: the first stage, at a temperature below the melting point, the water is sublimated from the frozen material, about 98% ~ 99% of the water Both were removed at this time. In the second stage, the temperature of the material is gradually increased to or slightly higher than room temperature, and the moisture can be reduced to less than 0.5% through this stage. The pre-freezing temperature in this process is about -40 ℃, and the time is about two hours. During the sublimation stage of freeze-dried drugs, the material temperature is about -30 ℃ ~ -35 ℃, and the absolute pressure is about 4 ~ 7 Pa. The final drying temperature of streptomycin can be raised to 40 ℃, the total drying time is about 18 hours. The use of computer automated control system helps to ensure that the drugs meet the quality requirements.