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    Freeze Dryer Basics

    A freeze dryer, also known as a vacuum freeze dryer machine, is a technique that involves pre-freezing water-containing items and then sublimating the water in a vacuum state to obtain dried products. The freeze-dried items are easy to store for a long time, have good rehydration properties, and maintain their original biochemical characteristics. They are widely used in the fields of medical and pharmaceutical manufacturing, biological products, the food industry, traditional Chinese medicine health products, and new materials.

    Vacuum freeze dryer

    What is a freeze dryer?

    A freeze dryer, also known as a lyophilizer, is a kind of drying equipment that freezes food raw materials under low-temperature conditions, then uses the sublimation principle in a high-vacuum environment to remove the water from the frozen raw materials without melting through the ice, and directly sublimating from solid ice to steam, so as to achieve freeze-drying. Freeze-dried products are sponge-like, do not shrink, have excellent rehydration properties, and contain very little moisture. After packaging, freeze-dried products can be stored and transported at room temperature for long periods of time. Because vacuum freeze-drying has unparalleled advantages compared to other drying methods, this technology has become increasingly popular since its inception, and its applications in medicine, biological products, and food have become more and more widespread. Biological products such as serum, bacterial strains, and traditional Chinese and Western medicines often contain biologically active substances, and vacuum freeze-drying technology provides an effective solution for preserving their biological activity. 

    Freeze dryer component systems 

    1. Control system: Consists of a programmable program controller, a touch screen, peripheral relays, sensors, and other components.
    2. Refrigeration system: Consists of a refrigeration compressor and auxiliary facilities to provide a cooling source for drying chambers and cold traps. (In the refrigeration system, in addition to the displayed high and low-pressure gauges, a pressure controller is also installed. When the high-pressure pressure is too high, the high-voltage relay acts and the compressor stops working.)
    3. Circulation system: Freeze-drying and heating rely on the transfer of substances caused by temperature differences. The cooling and heating of the shelves are achieved through the heat transfer of thermal oil. To ensure the continuous circulation of thermal oil throughout the system, a shielded circulation pump is installed in the pipeline.
    4. Vacuum system: Consists of the drying chamber, cold trap, vacuum valves, vacuum pump, vacuum pipes, vacuum measuring gauge, and other components. The vacuum pump provides strong suction power, promoting the sublimation of moisture in the drying chamber under vacuum conditions. Additionally, the system creates a pressure difference between the cold trap and the drying chamber, which captures the moisture after sublimation.
    5. Hydraulic system: Mainly used to press the bottle plug into the bottleneck at the end of the drying process. 

    Freeze dryer process

    1. Preparation of products (pre-treatment): such as drug cultivation, sterilization, sub-packaging, bottle washing, half-stoppering, etc., selection of food raw materials, cleaning, cutting, enzyme deactivation, sub-packaging, etc.
    2. Freezing of products (pre-freezing): the free water in the sample is solidified by pre-freezing so that irreversible changes such as bubbling, concentration, shrinkage, and solute movement will not occur during vacuum drying.
    3. Primary Drying (Sublimation): Freeze-dried products are dehydrated by vacuum sublimation, in which ice crystals are directly sublimated into water vapor and evaporated from the material, making the product dry. Drying in this stage starts from the surface of the material and gradually moves inward, and the residual pores left after ice crystal sublimation become channels for the water vapor to escape. When all ice crystals are removed, the primary drying is completed.
    4. Secondary Drying (Adsorption): After the primary drying is completed, there is still some water absorbed on the capillary wall and polar groups of the dried material that was not frozen. To extend the shelf life and storage stability of the product, these water molecules must be removed, which is the purpose of secondary drying. The temperature of the product during desorption drying should be high enough but kept below the disintegration temperature.
    5. Sealed packaging: The dried product should generally be sealed in a vacuum or under inert gas to facilitate storage.

    Advantages of freeze-drying technology

    1. Freeze drying is a low-temperature drying process that does not cause protein denaturation but can make microorganisms and other biological entities lose their viability. It is particularly suitable for drying and preserving biological active products, biochemistry products, genetic engineering products, and blood products that have poor heat stability.
    2. Due to the low-temperature drying process, volatile components and heat-sensitive nutrients and aromatic compounds in the material are lost very little, making it an excellent drying method for chemical products, pharmaceuticals, and food.
    3. In the low-temperature drying process, the growth of microorganisms and the action of enzymes are almost impossible to carry out, so the original properties of the substance can be best preserved.
    4. The volume and shape of the material remain basically unchanged after drying, and the material appears spongy with no shrinkage. When rehydrated, the material has a large contact surface with water and can quickly return to its original shape.
    5. As the drying is usually carried out under a vacuum, there is very little oxygen, which protects easily oxidized substances.
    6. Freeze-drying technology can remove 95% to 99.5% of the water in the material, resulting in a long shelf life for the product.

    Application areas of freeze dryers

    1. Biological products and drugs: preservation of antibiotics, antitoxins, diagnostic agents, and vaccines.
    2. High-grade nutritional supplements and traditional Chinese medicine: royal jelly, honey, pollen, herbal preparations, and so on.
    3. Microorganisms and algae: long-term preservation of various bacteria, yeasts, enzymes, protozoa, microalgae, and so on.
    4. Preparation of ultrafine micronized powders: preparation of ultrafine micronized powders such as Al2O3, ZrO2, TiO2, YBa2Cu3O7-δ, Ba2Ti9O20. 
    5. Drying of food: drying of coffee, tea, meat, fish, eggs, seaweed, fruits, vegetables, seasonings, tofu, instant food, etc.
    6. Biological specimens and tissues: preparation of various animal and plant specimens, drying and preservation of peripheral tissues such as skin, bones, aorta, and heart valves for xenotransplantation or homotransplantation.
    7. Other applications: catalysts in the chemical industry can be improved 5-20 times in catalytic efficiency after freeze-drying. Freezing and drying of plant leaves and soil can be used to study the effects of soil, fertilizers, climate on plant growth, and the role of factors. Freeze-drying can also be used to dry damp wooden artifacts, water-damaged books, and manuscripts while maintaining their original state to the greatest extent possible. 

    ATO industrial automation offers freeze dryers in ordinary type, gland type, and multi-manifold type. All types are freestanding, with desktop and vertical designs, and a variety of capacities and power options. It is ideal for drying, baking, and heating materials. 


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