Crystallization Research in the 1990s

Abstract

Crystallization from solution is an important separation and purification process in a wide variety of industries. These range from basic materials such as sucrose, sodium chloride and fertilizer chemicals to pharmaceuticals, catalysts and specialty chemicals. The major purpose of crystallization processes is the production of a pure product. In practice however, a number of additional product specifications are often made. They may include such properties as the crystal size distribution (or average size), bulk density, filterability, slurry viscosity, and dry solids flow properties. These properties depend on the crystal size distribution and crystal shape. The goal of crystallization research therefore, is to develop theories and techniques to allow control of purity, size distribution and shape of crystals.The past 30 years have seen great advances in our understanding of the fundamentals of crystallization and has resulted in improved crystallizer design and operation. A dominant theme during this period was the analysis and prediction of crystal size distributions in realistic industrial crystallizers. This led to the development and refinement of the population balance technique which has become a routine tool of the crystallization community. This area is best described in the book of Randolph and Larson (1) which has been an indispensable reference and guide through two editions.Another important development which altered our view of crystallization processes was the realization of the importance of secondary nucleation due to contact between crystals and the impeller and vessel. Secondary nucleation of this type has been shown (2-6) to often have a dominant role in determining crystallizer performance. Our understanding of crystal growth, nucleation, flu id mechanics and mixing have all greatly improved. A number of review Qz 1Q) have appeared in recent years which describe the advances in these and

Model identification and control of solution crystallization processes: a review

“…Attempts have been made to calculate the effect of impurities and different solvent mixtures on final crystal habit [121]. This area has been reviewed by Myerson [119]. His conclusions are that although there are not as yet reliable methods to predict habit or select solvents and habit modifiers without extensive trial-and-error experimentation, recent progress may make habit and purity control a realistic goal for the near future.…”