How to choose the correct laboratory vacuum freeze dryer

I. Preface

Freeze-drying is a method in which an aqueous substance is preliminarily frozen into a solid state, and then the water therein is sublimated from a solid state into a gaseous state under vacuum to remove the water and preserve the substance. The articles obtained by the drying method have the original chemical and biological properties, are easy to be preserved for a long time, can be restored to the form before lyophilization after adding water, and can maintain their original biochemical characteristics, which is a high-quality drying. method. The main uses of modern freeze-drying technology are: freeze-drying storage of in vitro biological tissues; freeze-drying preservation of live bacteria; lyophilization of Chinese herbal medicines, western medicines, biological drugs and blood products; freezing of convenience foods, health foods, functional foods Dry storage and transportation; lyophilization preparation of nano ceramic materials and various metal micropowder materials. Therefore, freeze-drying technology has been widely used in the fields of chemicals, food, materials, medicine, and biological products. Vacuum freeze dryer (referred to as freeze dryer) is a device for realizing freeze-drying technology. It is a complex structure machine involving refrigeration, vacuum, thermal, mechanical, fluid, electrical control and pressure vessels. know how. Therefore, users often encounter many problems when purchasing freeze-drying equipment. The author stands at the user's point of view and mainly introduces the selection technology of some experimental series freeze dryers.

Second, the classification of experimental series freeze dryer

The performance index of the experimental series freeze dryer is small volume, light weight, multi-function, stable performance, high accuracy of the test system, preferably a multi-purpose machine, which can adapt to the freeze-drying experiment of various materials. The main division methods of the experimental series of freeze dryers are:

1, from the structure

l Bell-type freeze-drying machine: The freeze-drying chamber and the cold trap are separate upper and lower structures, and the freeze-drying chamber has no pre-freezing function. This type of lyophilizer requires manual operation when it is transferred to the drying process after the material has been pre-frozen. Most of the experimental freeze dryers are bell-type, which has a simple structure and low cost. Most of the freeze-drying chambers use a transparent plexiglass cover to facilitate the observation of the lyophilization of the material.

l In-situ freeze-drying machine: the freeze-drying chamber and the cold trap are two independent chambers. The shelf in the freeze-drying chamber has a cooling function. After the material is placed in the freeze-drying chamber, the material is pre-freezing and drying without manual. operating. This type of freeze dryer has a complicated manufacturing process and high manufacturing cost, but the in-situ freeze dryer is the development direction of the freeze dryer, and is an ideal choice for lyophilization process, especially suitable for medicine, biological products and other special products. Freeze-dried.

a, common type b, multi-manifold type c, gland type

2, from the functional points

Ordinary shelf type: The material is bulk in the material tray and is suitable for lyophilization of food, Chinese herbal medicine and powder materials.

With gland type: suitable for the drying of the bottled material of Xilin. When lyophilizing, prepare the material in the vial as needed, float the cap and freeze-dry it. After drying, operate the gland mechanism to compress the cap. It can avoid secondary pollution, re-adsorb moisture, and is easy to store for a long time.

Multi-manifold type: The flask is attached to the outside of the drying chamber, and the material frozen on the inner wall of the bottle is dried. At this time, the flask is connected as a container to the manifold outside the drying box, and the material in the flask is heated at room temperature, and the mixture is heated. The tube switch device can be removed or loaded at any time as needed without stopping the machine.

With pre-freezing function type: material pre-freezing process, cold trap as pre-freezing chamber pre-freezing material, in the drying process, the cold trap is a water trap, capturing the moisture overflowing the material. The lyophilizer with pre-freezing function, the pre-freezing and drying of the materials in the freeze-drying process are all completed on the lyophilizer, and the lyophilizer has high use efficiency, which saves the cost of the low-temperature refrigerator.

Third, several parameters should be paid attention to when purchasing the freeze dryer

1, freeze-dried area

The number in the lyophilizer model represents the lyophilization area of ​​the lyophilizer of this model. For example, the lyophilized area of ​​the LGJ-18C lyophilizer is 0.18 m2. The user should calculate the lyophilizer for the lyophilized area according to his own needs. For example, for each batch of products that require lyophilization of 1.8 kg (liter) of liquid, and loading the material with a material tray, each loaded with 10 mm thick, the load area of ​​the lyophilized layer can be calculated:

A (area, m2) = V (volume, m ³ ) / H (height, m) = 0.0018 m ³ /0.01 m = 0.18 m ²

A lyophilizer with a lamellar load area of ​​0.18 m2 is required.

2, cold trap temperature

The cold trap is a device for capturing moisture in the freeze-drying process. Theoretically, the lower the temperature of the cold trap, the stronger the water trapping ability of the cold trap, but the lower the temperature of the cold trap, the higher the requirements for refrigeration, the higher the machine cost and the running cost. The cold trap temperature of the experimental series freeze dryer mainly has several grades of about -45 °C, -60 °C, and -80 °C. Freeze-drying at -45 °C for some freeze-dried products, freeze-drying machine with a cold trap temperature of -60 °C for lyophilization of most products, freeze-drying at -80 °C Suitable for lyophilization of some special products. The effect of cold trap temperature on water-trapping capacity shows that the temperature of the cold trap drops from -35 °C to -55 °C, and the water-trapping capacity is obviously improved. The cold trap temperature is lower than -55 °C, and the water trapping capacity of the cold trap is not significantly improved. Therefore, in the absence of special needs, the choice of cold trap temperature -60 ° C is the ideal choice. The cold trap temperature of the LGJ-10D freeze dryer in the four-ring freeze dryer is ≤-55 °C, and the freeze dryer temperature of the LGJ-18 series and LGJ-25 series is ≤-60 °C, and the refrigerant is mixed with mixed refrigerant. The technology, in the case of the same refrigeration unit, has a low cooling temperature, a large cooling capacity, a high operational stability, and a low failure rate. The four-ring lyophilizer also includes the LGJ-10 freeze dryer with cold trap temperature ≤ -45 ° C, suitable for lyophilization of some freeze-dried products. The cold trap temperature of LGJ-50C freeze dryer is ≤-80 °C, which is especially suitable for lyophilization of medicines and special products.

3, cooling rate

The cooling rate reflects the cooling capacity of the refrigeration system. Under no-load conditions, the temperature of the cold trap should reach the minimum temperature specified in the index within one hour. For example, a lyophilizer with a cold trap temperature ≤ -60 ° C, the machine starts from the time of opening the refrigeration, and the cold trap temperature reaches -60 ° C for no more than 1 hour.

4, the ultimate vacuum

The ultimate vacuum reflects the leakage of the freeze dryer and the pumping efficiency of the vacuum pump. The degree of vacuum of the freeze-drying box, the past view that the higher the degree of vacuum, the better, the current view that the degree of vacuum should be within a reasonable range. The degree of vacuum is too high, which is not conducive to heat transfer, but the drying speed is reduced, but the vacuum limit of the freeze-drying box should reach 15Pa or more.

5, vacuum time

The emptying speed of the freeze-drying box should be pumped from atmospheric pressure to 15Pa within half an hour.

6, the layer temperature uniformity and flatness:

The uniformity and flatness of the lamellar temperature have a great influence on the uniformity of product quality. The better the temperature uniformity and the flatness, the better the uniformity of the quality of the freeze-dried product. The lyophilizer shelf temperature control has a heater type and an intermediate fluid type, and the freeze-drying machine shelf with the intermediate fluid control plate layer has uniform temperature uniformity and flatness, and the lyophilizer layer is a hollow sandwich structure, the slab layer The cooling and heating are achieved by circulating the intermediate fluid in the fluid channel inside the ply, so the temperature of the ply is uniform. The LGJ-50C freeze dryer in the four-ring freeze dryer uses the technology of the intermediate fluid in the shelf. The shelf temperature control of the bell-type lyophilizer is basically a heater, and the temperature uniformity of the plate layer is slightly poor. However, in general, the temperature difference of the lyophilizer for medical use should be controlled at ±1.5 °C, the temperature difference within the plate is ±1 °C, and the food freeze dryer can be appropriately relaxed.

7, control system

The type and function of the control system of the freeze dryer are different. For the freeze dryer of the experimental series, it is mainly applied to the lyophilization process of the material and a small amount of trial production. Therefore, the control system should display the parameters of the freeze-drying process in real time and record automatically; set, modify and effectively execute the freeze-drying process program; have a communication interface to facilitate data collection and storage.