The crystallization and its special case precipitation have to be looked at in their entirety. Due to the comparatively small enthalpy changes along with low temperatures at the solid/liquid phase change, the process treats the product and the required process energies rather sensitively. Nonetheless, for a better understanding of the process, the crystallization requires a higher experimental effort compared to other separation processes.
In distillation, the required physical properties are mostly recorded in databases or can be easily measured, and the columns can be reliably designed by means of thermodynamically sophisticated models. The crystallization however, is initially much more complex from an experimental point of view. It requires experimentally accessible information of the specific crystal growth velocities and the determination of the process limits.
What minimum or maximum temperatures are necessary at what time? How do secondary components affect the crystal growth and hence the achievable reactor duty? Moreover, the crytallization is influenced by several equipment figures: The design of the mixer/agitator is not trivial since a too high agitation can cause problems just like a too low agitation does. Heat exchangers have to be suitably designed as wall temperatures and local temperature gradients are not only relevant for the heat transfer. Last but not least, the choice of the used reactor and the startup and seeding stategy determine the success of the process. But if the process is once understood, the operator is sustainably rewarded with reproducable high product purities together with low energy and downstream costs.