Views: 452 Author: Site Editor Publish Time: 2024-10-03 Origin: Site
Yingtai: Analytical drying and factors affecting drying time
Resolution drying is also called secondary drying. At the end of primary drying, there remains a part of adsorbed water (physically adsorbed on the capillary wall and polar groups of the dried substance) and bound water (either bound on the crystal surface of the crystallized product or contained in the interior of the amorphous product), which are unfrozen, and can not be removed in the primary drying. When this water reaches a certain amount, it will provide conditions for the growth and propagation of microorganisms and certain chemical reactions, and some studies have shown that even the presence of a small amount of water can produce the same mobility and reactivity as an aqueous solution. Therefore, in order to improve the storage stability of the product and prolong the preservation period, it is necessary to remove the water. This is also the purpose of resolution drying. A drying is to remove the water in the form of ice crystals, so its temperature and pressure must be controlled in the product below the co-melting point, so as not to cause the ice crystals to melt. But adsorbed water and combined water adsorption energy is high, need to raise the product temperature to resolve out. At this time, even if the product temperature exceeds the co-melting point, will not melt, but should pay attention to not burn the product and does not cause the product due to overheating and denaturation of the limit, due to the difference in the temperature of the heat transfer, the general temperature of the shelves can be higher than the temperature of the material is slightly higher than the temperature of 2 ~ 5 ℃. In addition, in this stage in the freeze drying box must maintain a high degree of vacuum, so that the product inside and outside the formation of a large pressure difference between the water vapor, resolved out of the water vapor to have enough impetus to escape from the product. Due to adsorption; and combined with the role of water by the bonding force, its saturation vapor pressure is much lower than the saturation vapor pressure of free water, so the evaporation rate is also slower. After the second drying, the content of residual moisture in the product depends on the product type and requirements, generally between 1% and 5%.
Affect the analysis of drying time factors
01 product varieties: different products, drying different degrees of difficulty, the maximum allowable temperature is different. Maximum allowable temperature of the product, due to the higher temperature can be maintained, the analysis of drying time can be shortened accordingly.
02 product moisture content: the content of the product for low, drying time is longer. The residual moisture content of the product should be favorable to the long-term storage of the product, too high or too low are not suitable. Should be based on the test to determine.
03 the performance of the freeze dryer: in the resolution of the late stage can achieve a high degree of vacuum, condenser temperature is low, the shelves of the freeze dryer temperature difference is small, the resolution of the drying time can be relatively shorter.
04 whether to use pressure control method: if the pressure control method, can improve the heat transfer, so that the product to reach the maximum allowable temperature of the time to shorten the resolution of the drying time is also shortened, usually at this time to control the vacuum in the freeze-drying box for the vacuum degree of 20 ~ 30Pa.