The key difference between lyophilization and sublimation is that lyophilization is the removal of water from a product by freezing it, followed by subliming a solid state to a vapor state, whereas sublimation is the conversion of a solid directly into a vapor state without passing through a liquid state.
Lyophilization and sublimation are processes that are related to each other because sublimation occurs as the second step of the lyophilization process.
CONTENTS
1. Overview and Key Difference
2. What is Lyophilization
3. What is Sublimation
4. Lyophilization vs Sublimation
5. Summary – Lyophilization vs Sublimation
What is Lyophilization?
Lyophilization is the process of removing water from a product after freezing it and placing it under a vacuum, which allows the ice to change directly from a solid state to a vapor state. Therefore, this process involves sublimation as a part of it. This method is very important in preserving perishable materials. It is also helpful in extending shelf life or making the material more convenient for transportation. Moreover, lyophilization works by freezing the material, reducing the pressure, and increasing heat, which allows the product to undergo sublimation.
Further, lyophilization is carried out at a temperature and pressure that is below the triple point. This enables sublimation. This entire process is performed at a low temperature and pressure using a vacuum system, making it suitable for drying thermolabile compounds.
The major objectives of performing a lyophilization process include preserving the biological activity of a product, reducing the product weight to lower the cost of transportation, extending the shelf life or the stability, drying the thermolabile materials, eliminating the need for refrigeration, etc.
Process of Lyophilization
There are four major steps of lyophilization: freezing stage, primary drying stage, secondary drying stage, and packaging stage.
During the freezing stage, the product is cooled to a temperature below its eutectic temperature, and this decreases the shelf temperature to about -50 degrees Celsius. Freons are used as refrigerants, and we can observe the formation of ice crystals. In the primary drying step, sublimation occurs, and heat is introduced from the shelf to the product. This heat treatment is performed under graded control using electrical-resistant coils. The temperature at this stage is below the triple point of water. This step easily removes up to 98-99% moisture.
Secondary drying step involves raising the temperature to 50-60 degrees Celsius, and the bound water is removed in this stage. However, the rate of drying in this stage is low, where it takes 10 – 20 hours. Then the product is ready for the packaging step. Here, the vacuum is replaced by filtered dry air or nitrogen. This establishes atmospheric pressure. Then the ampoules are sealed using either tip sealing or pull sealing methods.
What is Sublimation?
Sublimation is the process of changing the state of matter directly from a solid to a gas without going through a liquid phase. Generally, when we heat up a solid to its melting point, it will change its phase to a liquid. When the liquid is further heated up to its boiling point, it will change state to a gas. This is not the case with sublimation. Sublimation is the process of directly changing the state from solid to gas.
We can observe this process only under special situations in special materials. Pure naphthalene is such a subliming material. Another substance that sublimes is solid carbon dioxide, which is also known as dry ice. Iodine crystals, ice, and snow behave as subliming materials under some conditions. The misty gas evolving from an ice cube is subliming ice.
What is the Difference Between Lyophilization and Sublimation?
Lyophilization and sublimation are two related processes, as sublimation takes place as a part of the lyophilization process. The key difference between lyophilization and sublimation is that lyophilization is the removal of water from a product by freezing it, followed by subliming the solid state to a vapor state, whereas sublimation is the conversion of a solid directly into a vapor state without passing through a liquid state.
The below infographic presents the differences between lyophilization and sublimation in tabular form for side by side comparison.
Summary – Lyophilization vs Sublimation
The key difference between lyophilization and sublimation is that lyophilization is the removal of water from a product by freezing it, followed by subliming the solid state to the vapor state, whereas sublimation is the conversion of a solid directly into a vapor state without passing through a liquid state.
Reference:
1. “Lyophilization.”SlideShare.
Image Courtesy:
1. “Lyophilization of Pharmaceuticals in Vial” By Integrity Bio – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Dry Ice Sublimation 1” By Christopher from Salem, OR, USA – Fun with Dry Ice 1Uploaded by Diaa_abdelmoneim (CC BY-SA 2.0) via Commons Wikimedia