Crystallization process systems / Кристаллизационные системы

Crystallization from solution is a core technology in major sectors of the chemical process and allied industries. Crystals are produced in varying sizes ranging from as small as a few tens of nanometers to several millimetres or more, both as discrete particles and as structured agglomerates. Well-established examples include bulk and fine chemicals and their intermediates, such as common salt, sodium carbonate, zeolite catalysts and absorbents, ceramic and polyester pre-cursors, detergents, fertilizers, foodstuffs, pharmaceuticals and pigments. Applications that are more recent include crystalline materials and substances for electronics devices, healthcare products, and a wide variety of speciality applications. Thus, the tonnage and variety of particulate crystal products worldwide is enormous, amounting to about half the output of the modern chemical industry. The economic value, social benefit and technical sophistication of crystal products and processes are ever increasing, particularly in the newer high added value sectors of global markets. This places yet greater demands on the knowledge, skill and ingenuity of the scientist and engineer to form novel materials of the required product characteristics and to devise viable process engineering schemes for their manufacture.

Particulate crystallization processes often require subsequent solid-liquid separation. Thus, the unit operation of crystallization is normally only part of a wider processing system. These systems should preferably be designed and optimized as a whole - problems detected in one part of the plant (poor filtration say) may in fact arise in another (inadequate crystallizer control). Attention to the latter rather than the former can result in a simpler, cheaper and more robust solution. Similarly, the scale of crystallizer operation can have a large effect on crystal product characteristics and hence their subsequent separation requirements. Previously a largely empirical art, the design of process systems for manufacturing particulate crystals has now begun to be put on a rational basis and the more complex precipitation processes whereby crystallization follows fast chemical reactions have been analysed more deeply. This progress has been aided by the growing power of the population balance and kinetic models, computational fluid dynamics, and mixing theory. This not only increases understanding of existing processes but also enhances the possibility of innovative product and process designs, and speedier times to market. Several large gaps in knowledge remain to be filled, however, thereby providing opportunities for further research. This perspective gives the reason for writing the book, and provides its theme.<...>