I. Advantages of Freeze Dryers
There are various drying methods, such as sun drying, boiling, baking, spray drying, and vacuum drying, but ordinary drying methods are usually carried out at temperatures above 0°C or higher. The resulting products generally suffer from volume reduction and hardening, with most volatile components lost, and some heat-sensitive substances denatured or deactivated, and some even oxidized. Therefore, the properties of the dried product differ significantly from those before drying.
Freeze drying is generally carried out below 0°C, i.e., in a frozen state. Only in the later stages, when reducing the residual moisture content, is the product raised to temperatures above 0°C, but generally not exceeding 40°C. Under vacuum conditions, when water vapor sublimates directly, the drug remains within the ice frame formed during freezing, creating a sponge-like, porous structure. Therefore, its volume remains almost unchanged after drying. Before reuse, it dissolves immediately upon the addition of water for injection.
Compared to conventional methods, freeze drying offers the following advantages:
1. Many heat-sensitive substances do not denature or become inactive.
2. During low-temperature drying, the loss of some volatile components in the substance is minimal.
3. Microbial growth and enzymatic activity are inhibited during freeze drying, thus preserving the original properties.
4. Because drying occurs in a frozen state, the volume remains almost unchanged, maintaining the original structure and preventing concentration.
5. Since the water in the material exists as ice crystals after pre-freezing, the inorganic salts originally dissolved in water are evenly distributed throughout the material. During sublimation, dissolved substances in water precipitate out, avoiding the surface hardening caused by inorganic salts carried by moisture migrating from the material's interior to the surface, which occurs in conventional drying methods.
6. The dried material is loose and porous, spongy in nature, and dissolves rapidly and completely upon adding water, almost immediately restoring its original properties.
7. Because drying is carried out under vacuum with very little oxygen, some easily oxidized substances are protected.
8. Drying can remove 95%–99% or more of the moisture, allowing the dried product to be stored for a long time without spoiling.
9. Because the material is in a frozen state at a very low temperature, the required heat source temperature is not high; heaters at room temperature or low temperatures are sufficient. If the freezing chamber and drying chamber are separate, the drying chamber does not require insulation, resulting in minimal heat loss and economical use of heat energy.
II. Disadvantages of Freeze Drying Machines The main disadvantage of vacuum freeze drying technology is its high cost. Because it requires vacuum and low temperature conditions, vacuum freeze dryers need to be equipped with a vacuum system and a low temperature system, which results in relatively high investment and operating costs.