Crystallisation / chemical precipitation
Crystallisation is a fundamental separation process in chemical engineering. It is used for the purification, concentration and recovery of valuable substances after chemical synthesis.
Crystallisation occurs when solutions are supersaturated, melts are supercooled or solvents evaporate. In all cases, the equilibrium between the dissolved and solid phases is deliberately shifted, resulting in ordered solid structures, known as crystallises.
If the solubility of a target substance is reduced by the addition of a precipitating agent, this is referred to as precipitation crystallisation or chemical precipitation. This method enables rapid separation of the solid with controllable particle size and is particularly suitable for substances with high thermal sensitivity.
In industrial practice, crystallisation and precipitation processes often take place in batch operation in a reaction vessel. This is where amixon® process equipment (VMT and AMT) comes into play. amixon® equipment provides
- a large specific heat transfer surface
- low-gradient mixing and
- homogeneous temperature control.
The homogeneous mixing of the suspension ensures controlled crystal growth.
Most synthesis reactions take place in the liquid phase, as heat transfer and mass transfer are significantly more efficient here than in dry dispersions. Once the reaction is complete, the reaction mixture is specifically brought to crystallisation or precipitation – by cooling, evaporation or addition of a solvent mixture.
The particle size, crystal morphology and filter properties of the end product are significantly influenced by:
- the cooling rate,
- the stirring intensity,
- the residence time in the crystalliser,
- and the chemical composition of the solution.
Crystallisation and precipitation are indispensable in many branches of industry – for example, in the manufacture of active pharmaceutical ingredients, pesticides, plastic additives, pigments and dyes.
Precise process control in the reaction mixer enables reproducible product quality and scalable process transfer from laboratory scale to production. amixon® process equipment homogenises liquid substances regardless of their viscosity just as efficiently as powdery or crystalline solids. This high mixing quality is the key factor for reproducible syntheses with maximum yield.