Industrial crystallization in practice: from process to product

Abstract

Scope of the book Crystallization refers to the phase transformation of a compound from a fluid or an amorphous solid state to a crystalline solid state. However, a crystallization process is not just a separation process; it is also a production process and a purification technique, as well as a branch of particle technology. It thus encompasses key areas of chemical and process engineering (Davey and Garside, 2000). Crystallization is an extremely old unit operation, but is still used to produce highly specified speciality chemicals, and pharmaceuticals. In fact, there are few branches of the chemical and process industries that do not, at some stage, employ crystallization or precipitation for production or separation purposes (Mullin, 2003). Crystalline products include bulk chemicals such as sodium chloride and sucrose, fertilizer chemicals such as ammonium nitrate, potassium chloride, ammonium phosphates and urea; valuable products such as pharmaceuticals, platinum group metal salts and organic fine chemicals; products from the new and rapidly expanding field of engineered nanoparticles and crystals for the electronics industry, as well as biotechnology products such as protein crystals. Although crystallization is an increasingly important industrial process, one that is governed by thermodynamics of phase separation, mass and heat transfer, fluid flow and reaction kinetics, it is not usually explicitly covered in any of the existing core chemical engineering material. A large percentage of final or intermediate industrial products consist of a product of a crystallization process, i.e. tiny crystals or particles that have to conform to product specifications with respect to crystal size and shape, crystal size distribution, degree of agglomeration and uptake of either liquid or solid impurities. These product properties relate to the selected type of crystallization process as well as to the specific crystallization mode and type of hardware used for production. Crystallization is therefore much more than just a simple separation process. Unfortunately, the technology to design, operate and optimize crystallization processes is usually covered only very briefly as part of a broader overview on separations or particle technology, such as the chapter on Crystallization and Precipitation by Mullin in Ullmann's Encyclopaedia of Industrial Chemistry (Mullin, 2003) or other, similar, volumes (Richardson et al ., 2002 and Ruthven, 1997).