Design of Median Crystal Diameter Using Gassing Crystallization and Different Process Concepts

The reproducibility of product properties of normal batch cooling crystallizations is often insufficient. For a reliable design of product properties like the median diameter, it is essential to control the nucleation process. An innovative technology to induce nucleation during cooling crystallization is gassing. Therefore, quantification of the influence of gassing and process parameters is important. For this purpose, Design of Experiment approaches were used, investigating a linear cooling profile with constant cooling duration and quadratic cooling profiles with varied cooling duration. Succinic acid/water was used as the model system. The supersaturation where gassing is started was identified as most important design parameter using linear cooling profiles. Using quadratic cooling profiles, the median diameter can be mainly designed by adjusting the cooling duration. By the choice of the cooling profile and gassing supersaturation, it is possible to control the median diameter in a range between 300 and 750 μm. The results show also that independent from the cooling profile, gassing crystallization has an enlarging effect on the median diameter of product crystals. This effect can be used to reduce batch time for crystallization processes