Crystallization
Crystallization is one of the important chemical solid-liquid separation techniques. In this process mass transfer of the solute, from a homogenous single phase solution, produces a pure solid crystalline phase.
Crystallization is based on the principles of solubility – the solutes tend to be more soluble in hot liquid solvents than they are in cold liquids. When a saturated hot solution is allowed to cool down the solute is no longer soluble in the solvent. This makes the solute forms crystals of the pure compound. Since the impurities get naturally excluded from the growing crystals, the pure solid crystals can be separated from the dissolved impurities through filtration process.
Crystallization from solution is a 3-step process
Crystal growth
growth of the nuclei to larger size; under specific heat transfer conditions
Supersaturation
formation of supersaturated solution
Nucleation
formation of the crystal nuclei
In ACME manufactured crystallizers, provisions are included so that the vessel may be heated with steam addition to the shell or cooling solution circulated through the jacket so as to control the temperature
The most critical factor in this process is to maintain a balance between low supersaturation and proper mixing for the fast reaction, while avoiding shear damage to the crystals.
Nucleation is a function of the mixing technique, and the following impacts play an important role
Crystallization has been practiced longer than any other form of crystallization in both atmospheric tanks, which are either static or agitated, as well as in vacuum or pressure vessels. Batch crystallizer is a jacketed closed tank with top-mounted agitator and feed connections.