1. The form and composition of the material
According to the form of lyophilized material, it is usually divided into solid and liquid. The shape of the solid and the concentration of the liquid have a greater influence on the freeze-drying rate.
2. Pre-freezing rate
The size of crystals formed during freezing largely affects the rate of drying and the rate of product dissolution after drying. The process of quick freezing and slow freezing has the following differences: the ice crystals produced by quick freezing are smaller, and the ice crystals produced by slow freezing are larger. Large ice crystals are conducive to sublimation, and small ice crystals are not conducive to sublimation. Freezing results in a low sublimation rate and a fast desorption rate; slow freezing results in a fast sublimation rate and a slow resolution rate.
3. Loading
When the material is lyophilized, the ratio of the surface area and the thickness of the material after being packed into the container, that is, lyophilization is related to the amount of the material. The small surface area and thickness are conducive to sublimation of moisture, easy to freeze-dry and ideal quality. When drying, the wet weight load on the tray per unit area is the factor that determines the drying time. In general, the thickness of the material accumulation is thin, the faster the heat and mass transfer speed, the shorter the drying time. However, if the thickness of the material is thin, less material is dried per batch per freeze-dried area, which is detrimental to the high freeze-dried area per unit and the output per unit time.
4. Pressure in the drying room
The pressure inside the drying chamber affects the rate of heat and mass transfer. In terms of mass transfer, the lower the pressure, the better, and for heat transfer, the higher the pressure, the better. The size of the mass transfer rate is mainly determined by the temperature and pressure of the sublimation interface and the surface of the drying layer. To increase the escape rate of water vapor in the drying layer, 1 is to increase the temperature of the sublimation interface and make the interface water vapor pressure; second is T High vacuum in the drying chamber reduces the vapor pressure on the surface of the drying layer.
5. Heat transfer method
According to the traditional classification, it can be divided into: conduction, convection, heat radiation and medium heating (microwave heating). Since the process of sublimation and drying involves the transfer of heat and mass (water vapor), the heat transfer method used to transfer heat locally to the material has a greater impact on the drying rate.