Crystallizer supersaturation

It was shown in Chapter 3 that supersaturation, or concentration driving force, is essential for any crystallization. In a batch crystallizer supersaturation can be generated in several ways, either solely or in combination ... 

Crystallisation equipment can be classified by the method used to obtain supersaturation of the liquor, and also by the method used to suspend the growing crystals. Supersaturation is obtained by cooling or evaporation. There are four basic types of crystalliser these are described briefly below. 

An experiment was performed to examine the supposition that increases in supersaturation lead to greater impurity content in crystals. In a batch unseeded cooling crystallizer supersaturation is expected to be high at the point of nucleation, diminish rapidly after nucleation and then approach zero as the batch is... 

The process of crystallization or precipitation involves the nucleation and growth of crystals (particles) from a supersaturated solution and is often followed by the agglomeration of crystals. Supersaturation is the driving force for precipitation, which is defined by the difference between the real solute concentration c and equilibrium solute concentration c P,T) at given pressure and temperature. The strict definition of supersaturation is linked to the difference of chemical potential Ap ... 

The first factor to be considered for particle size reduction is the supersaturation profile. For very low concentrations of the nonvolatile solutes in antisolvent crystallization, supersaturation during the initial precipitation stage is characterized by the maximum attainable supersaturation, a. This... 

In cooling crystallization, supersaturation is obtained by undercooling the solution that is supersaturated by the evaporation of the solvent in evaporative crystallization. The relatively large average sizes of the end product can be obtained through both cooling and evaporative crystallization. 

In a batch crystallizer supersaturation can be achieved by cooling, evaporation of solvent, or both combined if Ac /AT) > 0. If orrly one component crystalUzes, the mass balance for this component is (suspension derrsity nij = p - [Pg.436]

The former case is usually associated with the use of evaporators for crystallization objectives. Crystal growth on the heat transfer surface competes with the process of crystal growth on the greater deposition area of the suspended crystals. Supersaturation with respect to the heat transfer surface which has e higher temperature than the bulk solution is lower for normal solubility salts and higher for inverse solubility salts. 

In diffraction experiments, the diffraction pattern is directly obtained from the crystallizing supersaturated solution, and when the contribution from the diffuse scattering due to the solvent is filtered out, the data allow a time-resolved study of crystal formation. Solution patterns can be compared with the pattern from dry powders, and the growth process can be monitored for example, a nice coincidence of solution and dry powder diffraction patterns was observed for benzamide and dibromoaniline [53]. Such techniques are widely used in nucleation and growth studies for inorganic materials [54]. 

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