Supersaturation control

Jones, H.P., Davey, R.J., Cox, B.G., 2005, Crystallization of a Salt of a Weak Organic Acid and Base Solubility Relations, Supersaturation Control and Polymorphic Behaviour, J. Phys. Chem. B, 109, 5273-5278. 

Solution crystallisers are usually classified according to the method by which supersaturation is achieved, that is by cooling, evaporation, vacuum, reaction and salting out. The term controlled denotes supersaturation control whilst classifying refers to classification of product size. 

Figure 9.5 Cascaded feedback-control scheme for supersaturation control. Reprinted with permission from Liotta (2004).47...

Gron, H. Borissova, A. Roberts, K.J. In-process ATR-FTIR spectroscopy for closed-loop supersaturation control of a batch crystallization producing monosodium glutamate crystals of defined size. Ind. Eng. Chem. Res. 2003, 42 (1), 198-206. 

Since the inherent growth rate of many organic compounds is relatively slow, addition times may be long in order to achieve supersaturation control within the metastable zone. Higher addition rates can result in nucleation and the creation of a bimodal distribution. Experimentation to determine acceptable addition rates can be evaluated by focused beam reflectance measurement (FBRM) and other in-sim, online methods (Chapter 2) or microscopic observation of the crystal slurry which could reveal the presence of fines. These issues are highhghted in the examples below. 

Nonoyama, N., K. Hanaki, and Y. Yabukt (2006). Constant supersaturation control of anti-solvent-addition batch crystaUization. Org. Process R D 10, 727-732. 

After the control of supersaturation, control of nuclei formation is the most important consideration in the design of crystallization equipment. If a constant number of crystals are maintained in the crystallizer, then a constant surface area for crystal growth will be available. This will result in good control of product size. 

HC1, H2SO4, or Ca +) and total protein concentration, but not on mixing conditions. Their conclusion was that primary particle growth is governed by supersaturation-controlled nucleation/growth phenomena. 

Many of these classes are self-explanatory, but some require definition. For example, the term controlled refers to supersaturation control. The term classifying refers to the production of a selected product size by classification in a fluidized bed of crystals. In a circulating-liquor crystallizer the crystals remain in the crystallization zone only the clear mother liquor is circulated, e.g., through a heat exchanger. In the circulating-magma crystallizer the crystals... 

Jeremiassen, F. and Svanoe, H. (1932) Supersaturation control attains close crystal sizing. Chemical and Metallurgical Engineering, 39, 594-596. 

Di Rrofio, G., Curcio, E., Ferraro, S., Stabile, C. and Drioli, E. 2009. Effect of supersaturation control and heterogeneous nucleation on porous membrane surfaces in the crystallization of 1-glutamic acid polymorphs. 9 2179-2186. 

Table 7-7. Typical crystallizers using flash evaporation for solution supersaturation classified by supersaturation control, nucleation control and crystal bed control. Representation according to Mannesmann Engineering AG, Messo-Chemietechnik.

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