The freeze drying process of a vacuum freeze dryer is basically carried out below 0°C, that is, the product is frozen, and the analytical drying generally does not exceed 60°C. Under vacuum conditions, when water vapor sublimates directly, the drug remains in the frozen ice shelf, forming a sponge-like loose porous structure, so its volume remains almost unchanged after drying. Before using it again, as long as injection water is added, it will dissolve immediately.
Using a vacuum freeze dryer for processing has the following advantages over conventional methods:
1. Many heat-sensitive substances will not be denatured or inactivated.
2. When drying at low temperatures, some volatile components in the substance are lost very little.
3. During the freeze-drying process, the growth of microorganisms and the action of enzymes cannot be carried out, so the original properties can be maintained.
4. Since the drying is carried out in a frozen state, the volume remains almost unchanged, the original structure is maintained, and no concentration occurs.
5. Since the water in the material exists in the form of ice crystals after pre-freezing, the inorganic salts dissolved in the water are evenly distributed in the material. During sublimation, the dissolved substances dissolved in the water are precipitated, avoiding the phenomenon of surface hardening caused by the inorganic salts carried by the internal water of the material migrating to the surface in the general drying method.
6. The dried material is loose and porous, sponge-like, and dissolves quickly and completely after adding water, and almost immediately restores its original properties.
7. Since the drying is carried out under vacuum and there is less oxygen, some easily oxidized substances are protected.
8. If the freezing chamber and the drying chamber are separated, the drying chamber does not need to be insulated, and there will not be a lot of heat loss, so the use of heat energy is very economical.
Different enterprises have different characteristics and require different types of vacuum freeze dryers. At present, there are many manufacturers producing vacuum freeze dryers. How to choose a vacuum freeze dryer that suits the actual needs of our company? We need to refer to the following factors:
The type of vacuum freeze dryer should be selected based on the comprehensive consideration of refrigerant, cooling capacity, environmental conditions and application occasions. Its main dimensions must be determined by thermodynamic calculation and heat transfer calculation.
Vacuum freeze dryer capacity: should be selected according to the production scale or experimental needs of the enterprise. Freezers are generally divided into three series: experimental series, pilot and small-scale production series, industrial production series, and each series has models of different sizes.
Series laboratory freeze dryers are mainly used for scientific research, and their freeze-drying capacity is very small. The freezing capacity of the condenser is less than 10 kg per batch, and the plate area of the freezer is less than 0.5 square meters. The freeze drying box of some laboratory freeze dryers is bell-shaped or manifold-shaped.
Users should decide which model of vacuum freeze dryer to choose according to their own output, and some data can be determined by calculation. For example, if each batch of 200 kg (L) of liquid products needs to be freeze-dried, a freeze dryer with a condenser ice volume of not less than 200 kg (L) should be selected first. Then calculate the loading area of the freeze drying box, which is related to the loading method of the product. The area used by the tray method and the bottle method is not necessarily the same. The plate loading method makes full use of the area of the plate layer, while the bottle loading method requires a larger plate layer area because the gap between the bottles is not fully utilized.
