Freeze drying, also known as lyophilization, is a dehydration technique that removes water or other frozen solvents from a material through sublimation and desorption. In this process, the product is first completely frozen, typically in vials, flasks, or trays - then placed under a deep vacuum, well below the triple point of water. Heat energy is carefully added, causing the ice within the product to sublime directly into vapor without passing through the liquid phase. This phase change, known as sublimation, is essential to freeze drying and requires precise thermal control to ensure the quality of the final product.
● Freeze Drying Procedure (Discrete)
The material balances are based on the evaporation percentages of the components designated as volatile (solvent). These percentages can either be specified by the user or calculated by the program from the difference between the initial and the final LOD%.
A cooling duty is calculated to reduce the material temperature to the specified freezing point, during which a user-defined percentage of the solvent is assumed to freeze. This calculation incorporates the enthalpy of fusion, which may also be specified by the user. Following freezing, a heating duty is determined to raise the material temperature from the freezing point to the sublimation temperature, at which the frozen solvent is assumed to sublimate. The enthalpy of sublimation, likewise user-defined, is used in this calculation. Finally, the remaining material is heated to the designated exit temperature. If the amount of solvent sublimed is insufficient to achieve the target final LOD percentage, the program assumes that the residual solvent is evaporated at the exit temperature, and the associated energy demand is included in the overall energy balance.
In Design Mode, the program calculates the sublimation capacity (in kg per cycle) based on the percentage of components that sublimate. If the calculated sublimation capacity exceeds the maximum, the program assumes multiple units operating in parallel with a total sublimation capacity equal to the calculated. The total tray area is calculated based on the number of entities processed per cycle and the entity specific area.
In Rating Mode, the user specifies the number of parallel units, their tray area and their sublimation capacity. If the sublimation or the area occupied by the entities exceeds the specified one then the program warns the user.
The drying time is either specified by the user or calculated based on the sublimation rate (in mm/h).
The interface of this operation has the following tabs:
● Oper. Cond’s, see Discrete Freeze Drying: Oper. Conds Tab
● Utility Data, see Freeze Drying: Utilities Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab