Vacuum Freeze-Drying Rotary Vane Vacuum Pumps & Compressors

The lyophilization process takes place in 3 steps. The first step is freezing, where all of the water or solvent in a solution is frozen. When frozen slowly, the water forms large ice crystals, potentially growing too large and tearing molecular bonds in the sample or solute. This is detrimental, for example, when a laboratory protein sample of biological origin is torn apart, allowing for no further research or utilization of said protein after the lyophilization process. As such is the case, the freezing process is typically done as quickly as possible, forming small ice crystals within and around the load.

After the freezing step is the primary drying, or sublimation. The pressure of the chamber is very low. At this point, the ice is able to transition from solid straight to its gaseous phase due to the lack of atmospheric pressure allowing for a liquid phase. As the ice sublimes, it draws heat out of the sample, cooling it and slowing the drying process. To counter this effect, the lyophilization chamber is heated slightly, countering the cooling and raising the pressure at which the solvents sublimate. Most of the moisture content of the material is lost in this process.

The third step is desorption. When water is chemically attached to the sample via hydrogen bonds, the molecules do not freeze. The heat of the chamber is raised while sustaining the low pressure to loosen these bonds and cause the water molecules to detach from the sample. At this point, removing water needs to be done carefully. Removing this bonded water will inevitably leave voids in the solute; too many voids or too large voids will cause the solid to collapse due to its lack of structural integrity. This will ruin shelf life, taste, and smell in food products, as well as effect and shelf life in active pharmaceutical ingredients and biologically sourced laboratory samples such as DNA samples. Thus, the removal of water via desorption is carefully done and never removes 100% of the water molecules.

After the lyophilization process, the sample or product is ideally fit for longer shelf life, resistance against bacteria and mold, constant quality, and resistance to oxidation. For mass-production of frozen foods, preservation of vaccines, or production of super dry powders, lyophilization is a powerful tool that is able to provide control that leads to quality material.