Loose songyuan huaxing parsing freeze-drying precool rate

Generally speaking, the freeze-drying theory books will mention that the greater the cooling rate, the greater the degree of supercooling and supersaturation of the solution, the smaller the grain size of the critical crystal, the faster the nucleation rate, the easier to form more small particles. Fine grain. Therefore, after sublimation of ice crystals, the pore size formed in the material is small and the drying rate is low, but the rehydration after drying is good. On the contrary, the slow freezing causes the formation of large-grained ice crystals. The size of the water escape channel formed after sublimation of the ice crystals is larger. , It is helpful to improve the drying rate, but the dry rehydration is poor.
Of course, there is nothing wrong with this, but don’t forget that this theory was obtained under the premise of even heating, but the lyophilization conditions provided by our company’s pharmaceutical lyophilizers are not so ideal, so-called fast freezing and slow freezing. It's not a matter of how quickly the heat-conducting oil cools down. Relatively speaking, I am still more in favor of the formulation of a forum comrade. He divided the quick-freezing and slow-freezing into the following categories: 1. The plate temperature dropped faster, and the plate temperature was much lower than the product temperature. The bottom of the product was first frozen and crystallized, but the upper liquid was still hot, so it was not instantaneous. Crystallization, crystallization will grow slowly, you get a slow-frozen effect. 2. The temperature of the board is reduced slowly. The difference between the board temperature and the product temperature is not large. Therefore, the product uniformly cools down and forms an overcooling. When the energy is accumulated enough, the crystal is instantaneously completely crystallized, and the quick freezing effect is obtained. 3, the plate temperature is very slow, and at a suitable temperature lower than the eutectic point to maintain (or slowly cooling), the product will form a small degree of subcooling, a small amount of crystal first appeared in the liquid, these crystallization phenomenon in the condition of further cooling Continue slowly, so that you get a larger crystal, which is the real slow-frozen. 4. The product is immersed in an ultra-low temperature environment (such as liquid nitrogen) and the whole crystal is instantly crystallized to form a very fine crystal (or in an amorphous state), which is a real quick-freeze. For the several phenomena mentioned by this comrade-in-arms, most of them have been observed during the experiment. Therefore, I still prefer this method of division.
What's more, in most cases, bottle freeze-drying methods are used in the company, and the uneven heating of the bottles is even more pronounced. According to the research on the pre-freezing process of the shelf of bottled products, the higher the initial temperature of the sample, the greater the temperature gradient in the upper and lower parts of the feed liquid and the slower the growth rate of ice crystals. If the cooling rate is slower, the ice crystals formed by the solution are coarser, and the ice interface advances slowly from bottom to top. The solute migration time in the solution is sufficient, and the accumulation of solute on the surface of the solution is relatively dense. As a result, the upper surface solute tends to have more solute and higher density, while the lower layer has lower density and loose structure. This delamination phenomenon is most evident in poorly framed products, or the bottom is shrivelled, or the mid-discontinuity layer, or the top protrusion, or the top of a layer of hard shell, and so on.
In order to bottle delamination phenomenon, in practice, it is advocated to use a three-step method, that is, the sample is first cooled from room temperature to the initial freezing temperature of the sample; then stop the cooling process, so that the temperature within the sample is automatically balanced, eliminating the temperature gradient; Finally cool down quickly. Since the temperature of the upper and lower parts of the sample is close to the crystallization temperature, the temperature gradient of the sample during the freezing process will be relatively small, and the ice crystal growth speed will be accelerated. In this way, the pre-freezing rate is increased, and the problem of solute gathering in the upper layer is solved. However, not all varieties have achieved significant results after using the three-step method.

If you want to engage in the above research, it is very important to choose the type of lyophilizer. The general experimental type and electric heating series cannot be realized in real sense. The most basic one is to choose the silicone oil series freeze dryer, and the silicone oil of Songyuan Huaxing Company. F series, with the slope control function of the freeze-drying process, the real significance of achieving controllable temperature rate.