EXPERIMENTAL STUDIES ON FLASH CRYSTALLIZATION

Abstract

Crystallization is an important process for the manufacture of many products. The main aim of crystallization process is to produce crystals with well defined chemical and physical properties, as well as a certain mean crystal size and narrow crystal size distribution (CSD). In the conventional crystallization processes it is very difficult to meet the above requirements because crystal size distribution is a complex function of nucleation and growth kinetics of crystals which are in turn influenced by many parameters for example degree of supersaturation, impurities, stirrer speed, temperature etc. Many applications require a mean particle size down to submicron range. But conventional crystallization techniques are in many cases not suitable to attain the required small particle sizes, so that a grinding process has to follow in additional. To avoid the disadvantage of conventional methods, flash crystallization process is proposed in this thesis work. Flash crystallization is a process in which solution at high temperature and pressure is sprayed into a relatively low pressure vessel with the help of nozzle. As a result of pressure difference flashing takes place and solvent partly evaporates from the droplets and causes the droplets to cool down. This leads to a highly supersaturated solution in the droplets and nucleation takes place within these droplets. Particles formed in the flash crystallizer are much smaller than the conventionally produced crystals to afford the agglomeration process. Agglomeration is a process in which finer particles are combined to give big particles of desired shape. Another advantage of flash crystallization process is the production of particles in micron range. Many applications require a mean particle size down to submicron range. It is well known in the literature that higher supersaturation causes the formation of much smaller particles. It is possible to attain high super saturation in the flash crystallizer. So flash crystallization process can be used to produce the fine particles.