During crystallisation, crystals are formed from a liquid solution through cooling or evaporation. This process is used to extract valuable substances, e.g. in the manufacture of medicines or fertilisers.
The crystals formed have a regular structure. However, it is difficult to predict which crystal shape will leave the apparatus, known as the crystalliser, at the end of crystallisation.
Many process conditions influence the final crystal shape:
- Different crystal shapes can form depending on the solvent or the speed of cooling.
- The more the apparatus is stirred, the more crystals collide with each other, resulting in crystal breakage. As a result, the crystals become smaller and rounder, and the crystal size distribution becomes broader.
- The crystals also stick together, forming so-called agglomerates, which also changes the crystal shape.
- Crystallisation must be carried out for long enough to bind as many valuable molecules as possible in crystal form. But not too long, otherwise crystal breakage increases.
And the most difficult thing is that all these phenomena overlap in a crystalliser; although they have been well researched individually, they are rarely understood in detail when combined.
And why is the final particle shape so important in crystallisation?
The crystallisation broth leaving the crystalliser is not yet the final product. The broth must then be filtered, dried and formulated into its final state (tablet, powder, fertiliser pallet).
All these steps only work well if the crystal shape is correct.
A few examples:
- The more uniform the crystals are, the better they dissolve and are more easily utilised by the body.
- The compactability and compressibility of a crystal powder in tablet form is highly dependent on the particle shape.
- Uniform, large crystals are easier to filter than small ones.
- Good flow properties are important during filling: round particles flow well, while needle-shaped crystals tend to clump together.
In order to avoid unnecessary disruption to the production process, the particle shape and size at the outlet of the crystalliser is determined very precisely by sampling. If the parameters are not correct, the crystals are discarded or dissolved again – an expensive, time-consuming and not particularly resource-efficient process.
So why not measure these parameters during crystallisation and actively counteract them? That is exactly what we want to achieve with our technology!
Less waste
Fewer process disruptions
Higher product quality