Virtis and FTS Systems, SP Scientific brands, have authored a reference white paper for those with an interest in the basic principles of freeze drying.
Copies of 'Basic principles of freeze drying' are available in English, Chinese, French, German, Portuguese or Spanish and are downloadable from the SP Scientific website.
Freeze drying, also known as lyophilisation, is a process whereby a product is rendered chemically inactive by freezing and the ice is then removed by sublimination with the intent of being able to store the product at a higher temperature than the original freezing point, while retaining chemical inactivity.
Lyophilisation requires the development of a recipe or cycle based on the thermal and physical characteristics of the product, along with consideration of temperature and pressure relationships, phase changes and heat transfer.
A basic understanding of the theory behind freeze drying is said to be essential for any scientist to begin to design a working lyophilisation process.
This white paper provides an overview of all of the steps involved in freeze drying, including product freezing, primary drying (sublimation) and secondary drying (desorption).
Also introduced are the concepts of critical temperature (eutectic and glass transition), thermal treatment (annealing), vapour pressure of ice, product collapse, determination of completion of primary drying and cycle optimisation.
Common freeze-dryer equipment designs are reviewed, along with their typical components and sub-systems.
