【 Weak current College 】 vacuum freeze-drying technology principle---Power By 【 China power house network 】

I. definition of vacuum freeze-drying and advantages:

Products by completely frozen, and in certain vacuum conditions make ice sublimation, so as to achieve the purpose of the low-temperature dehydration, this process is called lyophilization (Freeze-drying), hereinafter referred to as freeze-dried. Freeze-drying of solid substances due to the tiny ice crystals of sublimation and render a porous structure, and to maintain the original size of freezing time, plus water easily dissolved after the recovery, the products in the sublimation process temperature is maintained at a relatively low temperature conditions (generally below-250C), and therefore for those who do not heat-resistant material, such as enzymes, hormones and nucleic acids, blood and immune products etc, for drying is particularly appropriate. Drying results can emit 95 ~ 99% of moisture, conducive to the preservation of the products. Products of the drying process is carried out under vacuum conditions, it is difficult to oxidize. For biochemical drug chemistry, physics, biology of instability, freeze-dried has been proved to be a very effective tool. With biochemical substances and biological agents, freeze drying technology will increasingly shows its importance and superiority. II. medical freeze dryer's introduction to the structure and function:

Medical refrigeration dryer consists of refrigeration systems, vacuum systems, heating systems, electrical instruments control system. Main part is a drying Cabinet, condenser, refrigerating unit, vacuum heating/cooling devices. Products of freeze-dried is in the drying oven, oven Interior shelves made of stainless steel plate, with which the media conduit distribution, products for cooling or heating, drying oven equipped with a vacuum sensor later, it turned into a vacuum, the telecommunications number container door sealing around the mosaic has a rubber ring, near the front can be coated with vacuum grease guarantee box sealing. Condenser is best for winding cylindrical type, stainless steel cylinder outer circles have more than one group of air-conditioning coil, its working temperature is lower than the temperature of the oven, at up to-550C, from products out of the water vapor in the sublimation adequately condensation in contact with the cold pipe stainless steel cylindrical inner surface, thus ensuring the freeze-drying process smoothly, smooth cylindrical structure the biggest advantage is easy to clean, freeze dried finished, available heating will drop Frost layer. Rotary vacuum pump to the system vacuum, air intakes in mechanical pump installed a strip automatically electromagnetic vacuum valve, and Rotary pump for the same power control, when the pump, the solenoid valve closes automatically, while in the vacuum pump, vacuum system both protects and prevents vacuum pump return oil to the system. In the refrigeration system, 2 2 .2kW of semi-hermetic refrigeration parallel use of the wind out of high-pressure refrigerant condenser liquid (no fluoride refrigerant V55C), after drying filter and solenoid valve reaches the capillary, throttle back into the evaporator, condenser suction of the evaporator outlet pressure drops, the liquid refrigerant heat absorption environment and rapid boiling evaporation. Low pressure refrigerant gas is pumped back into the freezer, and then compressed into a high pressure gas, to complete a refrigeration cycle, heating/cooling plant cooling pipes to condenser pipes in cold as well as in the air condenser coil Ke to evaporation in the refrigeration system, they are two different refrigerant solenoid valve to supply. Heating system by electric heating tube, media (silicone), media, media box, such as the composition of a circular pipe, silicone oil as heating ducts, media pump to dry box shelf media carried out on products, to provide sublimation thermal heating, when frozen, the cooling pipes on the silicone oil is cooled by the media pump to ovenshelves Center Media catheter, on products for cooling and freezing. Electrical instrument control system for Electromechanical design, consists of a private industrial motor control, all the shelves the temperature, the temperature of the media temperature, products may be set to show on display that specific regulation control, please refer to the system specifications. Third, freeze-dried's basic principles and practice of freeze-dried products quality requirements is: biological activity and skin color uniform, form, structure and firm, dissolved speed, low residual moisture. To obtain high quality products, on the theory and freeze-drying process should have a more comprehensive understanding. Freeze-drying process including pre-freezing, sublimation and then dry frozen three stages. A reasonable surface effectively shorten the cycle of freeze-dried in industrial production has a significant economic value. (1) products frozen solution quick frozen (per minute cool down 10 ~ 50 ℃), grain remain visible under a microscope; rather slow freezing size (1 ° c/min), the formation of visible to the naked eye. Coarse grain in sublimation leave larger gaps, you can improve the efficiency of freeze-drying, fine grain in the gap left by sublimation is sufficiently low for the lower sublimation, quick frozen product particles and smooth, uniform appearance, surface area, porous structure, fast speed, the dissolution of the finished product cited wet correspondingly stronger. Drugs in freeze-drying machine pre-freezing in two ways: one is the simultaneous cooling and drying oven products; another is to wait until the oven shelves cooling to-40 ℃ or so, and then place the products, which is equivalent to slow freezing, the latter is between slow freezing cold and, therefore, between the often used to accommodate the freeze drying efficiency and product quality. The disadvantage of this method is the products into the tank, the water vapor in the air will quickly condense on the shelf, but in the early to board the sublimation heat up faster, due to the large area of sublimation will likely go beyond the normal load condenser. This phenomenon is particularly significant in the summer. Products frozen at rest. Experience has shown that undercooled phenomenon prone to make the product temperature has been reached the eutectic point. But the solute still does not, in order to overcome the cold, the temperature of frozen products should be lower than eutectic point following a range, and to maintain for a period of time pending the products completely frozen. (2) the sublimation of ice conditions and speed at a certain temperature is greater than the saturated vapour pressure of the water vapour partial pressure environment when you can begin the sublimation temperature than products; lower condenser suction of water vapour and capture, you are required to maintain lift. Gas molecules in two successive collisions between the distance is known as the mean free path, it is inversely proportional to the pressure. Under normal pressure, its value is small, the sublimation of the water molecules are easily and gas collisions and return to the steam source surface and, therefore, sublimation is diffuse. As pressure decreases 13.3Pa mean free path following, 105 times, enabling increased sublimation significantly faster, flyLeft out of the water molecules are rarely change their context, thus forming a directional flow of steam. Vacuum freeze-drying machine plays a pump the permanent gas to maintain required for low-voltage sublimation. 1g steam in atmospheric pressure as 1.25L in 13.3Pa has expanded to 10000 l, ordinary vacuum pump in unit time pump so much volume is not possible. Condenser actually formed a specialized collection of water vapour vacuum pump. Products and condensing temperatures usually-25 ° c and-50 ℃. Ice at a temperature of saturated vapor pressure respectively 63.3Pa and, consequently, in sublimation 1.1Pa and condensation between it produced a considerable pressure difference, if the system of Non-Condensable gas divider is negligible, it will make products out of steam distillation, to a certain flow directed to arrive at the condenser surface forming a frost. Ice sublimation heat about 2822J/g, if sublimation process does not supply heat, then reduce internal energy products only to compensate the sublimation heat until its temperature and temperature balanced condenser, sublimation is also stopped. In order to maintain the sublimation and condensation to the temperature difference, you must provide sufficient heat products. (3) the sublimation process in the warming of the first phase (a large number of sublimation phase), the product temperature to below its eutectic point of a range. So you want to control the temperature of the shelf, if products are part of the dry, but the temperature has exceeded its eutectic point and the melting phenomena occurring products, but at this point to melt the liquid, on ice saturating the solute yet saturated, and thus the rapid drying of solute will go in, the final concentration of dissolved into a zombie block, thin skin extremely bad, very bad dissolved speed, if the products of distillation in a large number of melting of late, due to the melting of the relatively small quantity of liquid, dry porous solid absorbed, causing the freeze drying of the defect after block, add water solubility dissolved when will still be able to find is slow. In a large number of sublimation process, although the shelves and products have great disparity of temperature, but because of plate temperature, temperature and vacuum condenser temperatures remain basically unchanged, and sublimation heat absorbing relatively stable, product temperature relatively constant. With products from top to bottom layer dry ice sublimation of resistance. Product temperature will rise slightly accordingly. Until visible is the presence of ice crystals. At this point, morethan 90% of the moisture has been removed. A large number of sublimation process to this end has been fundamental, in order to ensure that the whole case a large number of finished products, plate temperature sublimation still need to keep a stage before the second stage of warming. The remaining percentage of residual moisture, moisture that it and the free State of physical and chemical properties of water in different, residual moisture on include the chemical combination of water and water of physical medicine, such as the combination of crystal water of crystallization, protein through hydrogen bonding in water and solid surface or capillary absorption of water, etc. Due to the residual moisture from the bondage of gravitational, its saturated vapor pressure is reduced to varying degrees, thus drying rate decreased significantly. While improving product temperature for gasification of residual moisture, but if the temperature exceeds a certain limit, the biological activity may also be a sharp decline. Guarantee the safety of products of the highest drying temperature to determine by experiment. Usually we in the second phase plate temperature + 30 ℃, and remain constant. In this phase, the temperature rise due to plate, residual moisture less high and difficult to gasification, therefore products temperature to rise more rapidly. But as the product temperature and temperature accumulations, heat more slowly, you need the patience to wait for quite a long time, experience shows that the residual moisture drying time and large amounts of sublimation time almost equal and sometimes even exceeded. (4) lyophilized curve: the shelf temperature and product temperature changes over time can be recorded, freeze drying curve. Comparison of typical freeze-dried curve of the shelf warming is divided into two stages, in a large number of sublimation is shelf temperature low, according to the actual situation, can usually be controlled in the-10 to + 10. The second stage of the nature of the products will be appropriate to increase the temperature of the shelf, the law applicable to its relatively low melting point. If the performance of the products is not yet clear, machine performance is poor or inadequate stability in its work, with this method is also more secure. If products eutectic point higher system vacuum can maintain good, condenser cooling capacity sufficient, you can also use certain heating rate, the shelf temperature rise to allow maximum temperature, until the end of the freeze-drying, but also need to ensure that products in large quantities of sublimation temperature must not exceed the eutectic point. If products on thermal instability, the second phase plate temperature should not be too high. In order to improve the first stage of sublimation, La plate temperature a rise to products allow maximum temperature above; to be a large number of end stage basic sublimation, plate temperature dropped to allow the maximum temperature, the latter two ways while making a lot of sublimation speed some improvement, but its anti-jamming capability corresponding lower, vacuum and cooling capacity of sudden decreases or power outage may cause the product to melt. Reasonable and flexible command first, and still is by far the more common way.