Freeze-drying technology

Freeze-drying technology, one of the methods to keep the material from spoiling and deterioration, is to freeze the substance containing a lot of moisture in advance, and then sublimate the solid water directly under the condition of vacuum, and the substance itself remains in the ice shelf when freezing, so it does not change after drying. Solid water absorbs heat during sublimation, causing the temperature of the product itself to drop and slowing down the sublimation speed. In order to increase the sublimation speed and shorten the drying time, the product must be properly heated. The whole drying is carried out at a lower temperature.

Advantages A, freeze drying is carried out at low temperature, so it is particularly suitable for many heat-sensitive substances. Such as proteins, microorganisms and the like will not denature or lose biological vitality. Therefore, it is widely used in medicine. 2. When drying at low temperature, some volatile components in the substance are lost very little, which is suitable for some chemical products, medicines and food drying. 3. During the freeze-drying process, the growth of microorganisms and the role of enzymes cannot be carried out, so the original properties can be maintained. 4. Due to the drying in the frozen state, the volume is almost unchanged, the original structure is maintained, and the concentration phenomenon will not occur. 5. The dried substance dissolves quickly and completely after adding water, and almost immediately returns to the original properties. 6. Since the drying is carried out under vacuum, there is very little oxygen, so some easily oxidized substances are protected. 7. Drying can eliminate more than 95-99% of the water, so that the product can be stored for a long time without deterioration after drying. Therefore, freeze drying is widely used in the pharmaceutical industry, food industry, scientific research and other sectors. Application Freeze drying of products needs to be carried out in a certain device. This device is called a vacuum freeze dryer, referred to as a lyophilizer. The lyophilizer is divided into four main parts: refrigeration system, vacuum system, heating system, and control system. According to the structure, it consists of a lyophilized box or a drying box, a condenser or a water vapor condenser, a freezer, a vacuum pump and valves, and electrical control components. The lyophilized box is a high and low temperature box that can be cooled to about -40 ° C and heated to about + 50 ° C. It is also a closed container that can be pumped into a vacuum. It is the main part of the lyophilizer. The products that need to be lyophilized are placed on the layered metal plate layer in the box, frozen, and heated under vacuum to sublimate and dry the water in the product. The condenser is also a vacuum sealed container. There is a large surface area metal adsorption surface inside it. The temperature of the adsorption surface can be reduced to -40 ° C, and this low temperature can be maintained constantly. The function of the condenser is to freeze the water vapor sublimated by the products in the lyophilized box and adsorb it on the metal surface. The lyophilizer, condenser, vacuum pipe and valve, together with the vacuum pump, form the vacuum system of the lyophilizer. The vacuum system requires no air leakage. The vacuum pump is an important part of the vacuum system to establish a vacuum. The vacuum system is essential for the rapid sublimation and drying of the product. The refrigeration system consists of a freezer, a lyophilized box, and pipes inside the condenser. The freezer can be two sets independent of each other, or a set can be used together. The function of the freezer is to refrigerate the lyophilized box and the condenser to generate and maintain the low temperature required for their operation. It has two methods: direct refrigeration and indirect refrigeration. The heating system has different heating methods for different lyophilized dryers. Some use direct electric heating method; some use intermediate medium for heating, and a pump circulates the intermediate medium continuously. The function of the heating system is to heat the product in the lyophilized box so that the moisture in the product is continuously sublimated and meets the specified residual moisture requirements. The control system consists of various control switches, indicator adjustment instruments (see Figure 1) and some automatic devices, etc. It can be relatively simple or very complex. Generally, freeze-drying machines with a higher degree of automation have more complex control systems. The function of the control system is to manually or automatically control the freeze-drying machine, manipulate the normal operation of the machine, and freeze-dry out the required products. The freeze-drying procedure is as follows: before lyophilization, the products that need to be lyophilized are divided into suitable containers, usually glass bottles or ampoules, the filling amount should be uniform, and the evaporation surface should be as large and thin as possible; then put them into a metal plate that is suitable for the size of the lyophilized box. Before packing, the freeze-dried box is cooled down empty, and then the product is put into the freeze-dried box for pre-freezing. Before vacuuming, the condenser should be made to work in advance according to the cooling speed of the condenser freezer. When vacuuming, the condenser should reach a temperature of about -40 ° C. After the vacuum degree reaches a certain value (usually it should reach a vacuum degree above 100uHg), the product in the box can be heated. Generally, heating is carried out in two steps. The first step of heating does not make the temperature of the product exceed the temperature of the co-melting point. After the moisture in the product is basically dry, the second step of heating is carried out. At this time, the product can be quickly raised to the specified maximum temperature. Freeze-drying can be completed after the maximum temperature is maintained for several hours. It is related to the amount of the product in each bottle, the total amount, the shape and specification of the glass container, the type of product, the lyophilization curve and the performance of the machine. After lyophilization, dry and sterile air should be put into the drying oven, and then plug and seal as soon as possible to prevent the re-absorption of moisture in the air. In the lyophilization process, the temperature of the product and the plate layer, the temperature of the condenser and the vacuum degree are compared with the time to draw a curve, which is called the lyophilization curve. Generally, the temperature is the ordinate and the time is the abscissa. Freeze-drying different products use different lyophilization curves. When the same product uses different lyophilization curves, the quality of the product is also different, and the lyophilization curve is also related to the performance of the lyophilizer. Therefore, different products and different lyophilizers apply different lyophilization curves.