The precipitation of crystalline substances from liquid (solution or melt) or gaseous raw materials is a unit operation that belongs to the process of heat and mass transfer. The process of crystallization from the melt is used for single crystal preparation, the process of crystallization from gas is used for vacuum coating, and the process of crystallization from solution is often encountered in chemical production. According to the characteristics of liquid-solid equilibrium, the crystallization operation can not only obtain solid solute from the solution, but also realize the separation of solute and impurities, so as to improve the purity of the product.
As early as 5,000 years ago, people began to use solar energy to evaporate seawater to make table salt. Crystallization has been developed as an economical and efficient operation for preparing pure solid products from impure solutions. Many chemical products can be prepared by crystallization. The obtained crystal products not only have a certain purity, but also have a beautiful appearance, which is convenient for packaging, transportation, storage and application.
Crystallization equipment is a commonly used operating unit in pharmaceutical and chemical processes, and is widely used in the production processes of almost all crystalline drugs. At present, the evaporative crystallization commonly used by enterprises mainly includes heat convection type and forced circulation type. The above two types of evaporative crystallizers are mostly forced external circulation evaporative crystallizers.
The principle of this evaporator is to heat the material solution in the external heater under the action of the pump, and evaporate it in the evaporator. After so many cycles, when the solution concentration exceeds the solubility at this temperature, the solute precipitates and crystallizes. In this state The solution in which crystals have appeared continues to be heated repeatedly under the action of the pump. The circulation process of evaporation, until a large number of crystals appear, the solution becomes a very thick suspension of crystals and cannot be circulated. Because many varieties of drugs are heat-sensitive, and the hardness of the crystals is high, the solution is very viscous after reaching saturation. , fluidity is greatly reduced, therefore, in the use of above-mentioned commonly used evaporators at present, the problems that occur are poor quality of pharmaceutical products, high evaporation temperature in the later stage, low effect of material liquid utilization, increased energy consumption, and final product yield. Low, and the equipment is worn out due to the erosion of a large number of crystals, and the service life is short, and the metal particles washed down pollute the drug, which increases the metal content of the drug and reduces the purity of the product.Compared with the traditional batch crystallizer, it has many significant advantages: good economy, low operating cost, and easy control of the operation process.
Due to the adoption of crystallization elimination and cleaning mother liquor overflow technology, the continuous crystallizer has the means to control the particle size distribution of the product and the density of the crystal slurry, so that the crystallization main particle size is stable, the amount of mother liquor is small, and the production intensity is high.