Crystallization from a Supercritical Solution CSS

The interest in CSS comes from a number of attractive features the possibility of tuning the crystal size distribution [1], of producing large crystals [13], and of purifying solid materials from impurities [14]. In this respect, we quote also a patent by Shlichta [15]. 

A batch CSS experiment can be carried out in a simple apparatus, essentially a stirred pressure-resistant vessel. First, the supercritical solution is prepared by loading into it the proper amounts of SCF and HC. Then, the stirrer is switched off, and the temperature and/or pressure of the solution are varied according to the policy adopted for the process, until the crystals are formed. 

Operating temperatures can be close to ambient, if a suitable SCF (such as CO2) is used the pressure value will be that needed to get the required concentration of the supercritical solution. 

Various crystal morphologies and sizes can be obtained by changing the main operating variables, such as the concentration of the starting solution and the T or p gradients applied. 

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