Freeze dryer technology principle

Drying is one of the ways to keep the material from spoilage. There are many methods of drying, such as drying, boiling, drying, spray drying, and vacuum drying. However, these drying methods are carried out at temperatures above 0 ° C or higher. The product obtained by drying generally shrinks in size and hardens in texture. Some substances are oxidized, and most of the volatile components are lost. Some heat-sensitive substances such as proteins and vitamins are denatured. Microorganisms lose their vitality, and the dried substances are not easily dissolved in water. Therefore, the dried product has a large difference in properties compared with that before drying. The freeze-drying method is different from the above drying method, and the drying of the product is basically carried out at a temperature below 0 ° C, that is, in a state where the product is frozen, until the later stage, in order to further reduce the residual moisture content of the dried product, the product is allowed to be Raise to a temperature above 0 °C, but generally does not exceed 40 °C.

The freeze dryer is a material containing a large amount of water, which is previously cooled down to a solid, and then the water vapor is directly sublimated under vacuum. The substance itself remains in the ice shelf when it is frozen, so it has a constant volume after drying and is loose and porous. The ice or other solvent that freezes the product during sublimation absorbs heat. It causes the temperature of the product itself to decrease and slows down the sublimation speed. In order to increase the sublimation speed and shorten the drying time, the product must be properly heated. The entire drying is carried out at a lower temperature.

Freeze dryers have the following advantages:

(1) Freeze-drying is carried out at a low temperature, and thus is particularly suitable for many heat-sensitive substances. Such as protein, microorganisms and the like will not degenerate or lose biological vitality. Therefore, it is widely used in medicine.

(2) When drying at low temperature, some volatile components in the material are lost little, which is suitable for drying some chemical products, medicines and foods.

(3) During the freeze-drying process, the growth of microorganisms and the action of the enzyme cannot be performed, so that the original trait can be maintained.

(4) Since drying is carried out in a frozen state, the volume is almost constant, the original structure is maintained, and concentration does not occur.

(5) The material after drying is porous and spongy. After adding water, the solution dissolves quickly and completely, and the original trait is almost immediately restored.

(6) Since drying is carried out under vacuum, there is little oxygen, so some easily oxidizable substances are protected.

(7) Drying can exclude more than 95-99% of water, so that the dried product can be preserved for a long time without deterioration.

Therefore, freeze drying is currently widely used in the pharmaceutical industry, food industry, scientific research and other sectors.