Yingtai Freeze-Drying Knowledge: Key Parameters in Freeze-Drying Process -- Eutectic Point

Yingtai Freeze-Drying Knowledge: Key Parameters in Freeze-Drying Process -- Eutectic Point

It is crucial to understand that during the freeze-drying process, the sample temperature is maintained through the vacuum level in the chamber (not the cold trap! The cold trap's role is to capture the moisture sublimated from the sample in the freeze-drying chamber). Therefore, appropriately setting the vacuum level is extremely important as it directly impacts the effectiveness and efficiency of freeze-drying. 

One key parameter in the freeze-drying process is the eutectic point.

What is the Eutectic Point?

The eutectic point is the temperature at which the components of a mixed solution all reach their freezing points and begin to form a fixed crystal lattice structure.

What is the Significance of the Eutectic Point in Freeze-Drying?

1. Indicates Pre-Freezing Temperature: To ensure that the material is completely frozen, setting the pre-freezing temperature is critical. If the pre-freezing temperature is too low, it will not only extend the freezing time but also increase production costs. Conversely, if the pre-freezing temperature is higher than the eutectic point, the moisture in the material may not freeze completely, leading to local boiling and bubbling during the drying process, which can cause material shrinkage and deformation, and other quality issues. Additionally, dissolved solutes in the unfrozen moisture cannot desorb locally during drying and may migrate to the surface of the material, potentially resulting in surface hardening of the freeze-dried product. Therefore, to ensure complete freezing of the moisture in the material, the pre-freezing temperature should be set 10-15°C below the eutectic point of the material.

2. Basis for Setting the Vacuum Level in the Drying Process: A critical condition for freeze-drying is maintaining the sample temperature 10-15°C below the eutectic point to ensure that the sample does not melt and to preserve the micro-porous structure and physical and chemical properties intact. For example, if a product’s eutectic point is -25°C, considering safety, energy loss, and other factors, the pre-freezing temperature might be chosen as -35°C or lower. Correspondingly, based on the saturation vapor pressure and temperature table, the vacuum level during the sublimation drying phase can be set at 0.22 mbar or lower.

3. Monitoring Sample Status: Maintaining the solid state of the sample during freeze-drying is crucial; otherwise, it could lead to structural collapse or shrinkage, affecting appearance or activity. Based on the characteristic of decreased electrical resistance with melting, Yingtai has developed a eutectic point detection system to monitor changes in sample electrical resistance during freeze-drying, thus ensuring the quality of the freeze-dried product.