The basic components of a freeze-drying system are:
- Vacuum drying chamber
- Vacuum pump for evacuating air from the drying chamber (gas pump) and regulating the drying vacuum with a pressure control valve
- Ice condenser with temperatures from –55 °C to –105 °C (depending on the type of system) for resublimating the water vapor from the drying chamber (Vapor pump)
Extensive accessories can be added to the basic components, such as:
- Heated or unheated storage areas for drying in trays
- Shelves with closures for drying in bottles.
- Rubber valves for connecting round-bottom flasks, wide-mouth bottles, etc.
- Manifold for connecting round-bottom flasks, wide-mouth bottles, etc.
- Controller for operation and observation of process parameters
For both lab systems and commercial production freeze-drying systems, a distinction is made between single and dual chamber systems. The principle is presented here at the laboratory scale:
As shown in Figure 3.2, in the single chamber system, freezing and subsequent drying of the product are performed in the ice condenser chamber. The sample is frozen due to the low temperature of the ice condenser (–55 °C or –105 °C). The interior can be chilled down to about –20 °C or –40 °C. A significant improvement in cold transfer from the ice condenser to the sample can be achieved with the use of a fan during the freezing phase in a lab system. For larger freeze-dryers, shelves that can be chilled are used for freezing. The moderate energy input to the frozen sample required for primary drying is provided via the heated shelf on which the product sits. The closure device shown in Figure 3.2 can close vials once drying is completed under vacuum or inert gas, so that the freeze-dried sample is then additionally vacuum-sealed to some degree.
The arrangement of shelves under an acrylic glass receiver outside of the ice condenser, as shown in Figure 3.3, is referred to as the dual-chamber principle. Its advantage is its substantially larger product capacity, even when using the same basic system. By closing off the product chamber from the ice condenser chamber (see the intermediate valve in the sketch), a pressure rise test can also be used to determine when drying is complete. The disadvantage is additional handling of samples, which must be pre-frozen externally, for example in a freezer or a deep-freeze unit. Once they are transferred to the freeze-dryer and the acrylic chamber is in place, the actual primary drying is then started. All Christ lab systems with shelf temperature control capability can be run under the single or dual chamber principle, as desired.
Find more information about fundamentals, process management, and applications of freeze-drying here.