What is the difference between evaporative crystallization and evaporative cooling crystallization?

- Mar 18, 2020-

Evaporation crystallization and evaporation cooling crystallization are almost the same meaning, which is to remove the solvent and make the solute supersaturated so as to separate from the solvent.
1. Evaporative crystallization is mainly used to extract solute from single solute aqueous solution, such as sodium chloride solution.
2. Evaporation crystallization is mainly used for the solute solubility, which is not affected by temperature, for example, a small amount of potassium chloride is contained in sodium chloride (but the water must be filtered if it cannot be evaporated).
3. Heating evaporation concentration crystallization is mainly used for purification of solute whose solubility is greatly affected by temperature. For example, a small amount of sodium chloride in potassium chloride is used for evaporation concentration crystallization to separate a solute with low solubility in multi solute solution.
Evaporated crystallization directly heats the evaporated solution in the evaporating dish until a large number of crystals (or crystalline film) appear, and then stops. Evaporate the remaining solvent with the waste heat of the evaporating dish.
For cooling crystallization, it is necessary to heat and condense to obtain hot saturated solution, then filter to remove insoluble impurities while hot, then cool and crystallize, filter, and other impurities may be contained in the obtained crystal. If further purification is required, recrystallization can be carried out.
The principle of cooling hot saturated solution and cooling crystallization is the same. It saturates the solution and precipitates solute by cooling. This method is generally used for solute whose solubility changes greatly with temperature. The only difference is that the starting point of cooling is different.
Evaporation solvent crystallization promotes the solution to be saturated and precipitates solute through the continuous reduction of solvent. This method is mainly used for solute whose solubility changes little with temperature.
Evaporation crystallization: the solubility remains unchanged, reducing solvent and solute precipitation.
Cooling heat saturation: with the decrease of temperature, solubility decreases and solute precipitates.