Contact-sorption freeze-drying

Figure 12.2 Drying and sorption curves for contact-sorption freeze-drying for different thicknesses of the zeolite layer 1, 1 —10 mm 2, 2 —20 mm 3, 3 —30 mm.

Since the sublimation rate can be increased by a higher heating rate only to a certain extent, the rate of water vapor removal from the sublimation front becomes the key point in freeze drying. Adsorption of water vapor by sorbents placed inside a drying chamber or by direct contact of the sorbent and drying material (as a mixture) is one of the most promising methods in this area. Molecular sieves, zeolites, or ceramics can be recommended here because their sorption activity under rarefied conditions does not drop with temperature rise due to the heat of sorption. The use of particulate sorbents permits sublimation to take place in a fluidized state under atmospheric pressure [67,68]. 

The principle of contact-sorption drying on inert sorbents can also be applied under conditions of reduced pressure. Since the evaporation rate in freeze-... 

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