Freeze drying is the removal of ice or other frozen solvents from a material through the process of sublimation and the removal of bound water molecules through the process of desorption.
Lyophilization and freeze drying are terms that are used interchangeably depending on the industry and location where the drying is taking place. Controlled freeze drying keeps the product temperature low enough during the process to avoid changes in the dried product appearance and characteristics. It is an excellent method for preserving a wide variety of heat-sensitive materials such as proteins, microbes, pharmaceuticals, tissues & plasma.
Sublimation is when a solid (ice) changes directly to a vapor without first going through a liquid (water) phase. Thoroughly understanding the concept of sublimation is a key building block to gaining knowledge of freeze drying.
As shown below on the phase diagram for water, low pressures are required for sublimation to take place.
Sublimation is a phase change and heat energy must be added to the frozen product for it to occur.
Sublimation in the freeze drying process can be described simply as:
FREEZE - The product is completely frozen, usually in a vial, flask or tray.
VACUUM - The product is then placed under a deep vacuum, well below the triple point of water.
DRY – Heat energy is then added to the product causing the ice to sublime.
The steps required to lyophilize a product in a batch process can be summarized as follows:
Pretreatment / Formulation
Loading / Container (Bulk, Flask, Vials)
Freezing (Thermal Treatment) at atmospheric pressure
Primary Drying (Sublimation) under vacuum
Secondary Drying (Desorption) under vacuum
Backfill & Stoppering (for product in vials) under partial vacuum
Removal of Dried Product from Freeze Dryer
In addition to providing an extended shelf-life, successful freeze-drying should yield a product that has a short reconstitution time with acceptable potency levels. The process should be repeatable with well defined temperature, pressure and time parameters for each step. Visual and functional characteristics of the dried product are also important for many applications.
Successfully freeze dried productions
