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Crystallisation and Particle Size Distribution Crystals, Made to Order: Quality Parameter in Crystallisation

Author / Editor: Sven Hanselmann, Dr. Bernd Nienhaus* / Manja Wühr

Potash, Sugar or APIs are commonly formed by crystallisation. In an optimised crystallisation system the particle size distribution can be narrowed and the impact on the crystals, e.g. breakage or the production of fines, will be reduced.

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Microscopy of Crystals
Microscopy of Crystals
(Source: Ekato)

Crystallisation is a unit operation in a vast range of applications and industries such as chemicals, API production, food manufacturing and precipitation of ores. Depending on the process requirements, cooling, evaporation or precipitation is selected to form crystals. Accordingly, the variation of applied machines is numerous. Loop-Crystallisers are often called Forced Circulation (FC) Crystallisers due to the fact that the solution is forced to flow by a pump while the crystallisation in layers is a static process. In agitated services there are two main mixing systems. Either an open system with a hydrofoil impeller or a draft tube is utilized.

For a proper design of a crystallizer it is important to know the relevant parameters for the application. There are three main routes to achieve supersaturation: cooling, evaporation and precipitation. For cooling and evaporation the goal is to create target particle sizes, mostly in the range of 100 μm up to >2000 μm.