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In this article the optimal supersaturation for cooling and evaporation crystallization are presented. This information is based on a simplified model which describes the metastable zone width of activated nucleation. The model assumes that the nucleation step is very fast and the occurrence of the shower of nuclei which is used to define the metastable zone width is caused by the growth of activated nuclei. In future new sensors for the measurement of supersaturation will help to operate batch crystallizers at the optimal supersaturation during the entire batch time.

In this article the optimal supersaturation for cooling and evaporation crystallization are presented. This information is based on a simplified model which describes the metastable zone width of activated nucleation. The model assumes that the nucleation step is very fast and the occurrence of the shower of nuclei which is used to define the metastable zone width is caused by the growth of activated nuclei. In future new sensors for the measurement of supersaturation will help to operate batch crystallizers at the optimal supersaturation during the entire batch time.

Up to now supersaturation measurement can be generalized as using physical properties that show a dependence on concentration as measurands for supersaturation. Impurities, foreign particles or ions influence the metastable zone width as well as the kinetics of nucleation and crystal growth, but most of the existing measurement methods are not able to incorporate those disturbances in the measured supersaturation. Therefore, a supersaturation sensor considering the actual crystallization process itself has been developed. The idea of the new supersaturation sensor is to induce crystallization on the sensor surface by generating an additional supersaturation by cooling and to observe the time-dependent development of the incrustation. Assuming a constant cooling rate and constant properties of the sensor surface the starting time of the incrustation on the sensor surface depends only on the prevailing supersaturation in the process solution. Experimental results obtained for inorganic ( KNO 3) and organic (Adipicacid) crystallizing solutes proved the applicability of the new sensor.