The eutectic points of different products are different, and the temperature requirements of the freeze dryer are also different. Products with a low eutectic point require a low refrigeration temperature of the freeze dryer, and a correspondingly low temperature of the condenser (cold trap). During the freeze-drying process, the pre-freezing temperature of the freeze-dryer should be 5-10°C lower than the eutectic point of the product to ensure that the material is completely frozen. If the pre-freezing temperature is higher than the eutectic point, the moisture in the product cannot be completely frozen, so that the moisture cannot be completely sublimated in the form of ice, and local boiling and foaming are prone to occur during the drying process, resulting in shrinkage and loss of shape of the material. question.
The refrigeration temperature range and condensation temperature of the freeze dryer plate are roughly as follows:
1. Traditional cold storage type freeze dryer (low temperature cold storage + vacuum drying oven + boiler): there is no cooling on the plate layer, pre-freezing is carried out in the low temperature cold storage, the temperature control range of the vacuum drying oven: normal temperature ~ 120 ° C, the cooling temperature of the condenser is - Around 40°C. This freeze dryer is suitable for the production of some products that are relatively easy to freeze-dry, such as low-end solid fruits and vegetables.
2. Pharmaceutical freeze dryer: the cooling temperature of the plate is about -55°C~-60°C, the temperature control range of the plate is -60°C~80°C, and the cooling temperature of the condenser is about -75°C. It is suitable for freeze-drying of pharmaceutical products, cosmetics, raw materials, biological products, etc.
3. New food freeze dryer (shelf pre-cooling type): the cooling temperature of the plate layer is about -45 ° C ~ -50 ° C. C, the temperature control range of the plate layer is -50°C~80°C, and the cooling temperature of the condenser is about -65°C, which is suitable for freezing in the food industry such as solid fruits and vegetables, liquid products, heat-sensitive products, and products with high activity requirements Dry.
4. Other lyophilizers: The small bell-jar type laboratory lyophilizer has no refrigeration on the plate, and pre-freezing is generally carried out in a cold trap or a low-temperature refrigerator. The cooling temperature of the condenser can be -50°C~-80°C. The cooling temperature of the pilot type freeze dryer is -50°C, the temperature control range of the plate layer is -50°C~80°C, the cooling temperature of the condenser is -70°C, and some pilot type freeze dryers use liquid nitrogen to preheat frozen way.