PEF-Crystallization 制药工程与设备基础　Pharmaceutical Equipment Fundamentals　教学课件　.pptVIP

Pharmaceutical Equipment Fundamentals Crystallization Crystallization Crystallization + solvent separation + washing + drying A key operation in the freeze-concentration of fruit juices; the desalination of sea water; the recovery of valuable materials (eg. metal salts from electroplating processes); the production of materials for the electronic industries; biotechnological operations such as the processing of proteins Crystallization Features Less energy requirements Enthalpies of crystallization Enthalpies of vaporization Operating at ambient temperature Low cost Simple equipment Easy to operate. Good selectivity: Only congeneric elements and ions can be arranged in crystal, most of the impurities remain in the solvent. Crystallization in Nature Geological time scale process examples include: Natural (mineral) crystal formation Stalactite/stalagmite, rings formation Usual time scale process examples include: Snow flakes formation Honey crystallization Process Nucleation is the step where the solute molecules dispersed in the solvent start to gather into clusters, on the nanometer scale (elevating solute concentration in a small region), that becomes stable under the current operating conditions. These stable clusters constitute the nuclei. Crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. Crystallization Process When the clusters are not stable, they redissolve. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by the operating conditions (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms arrange in a defined and periodic manner that defines the crystal structure Note that crystal structure is a special term that refers to the relative arrangement of the atoms, not the macroscopic properties of