INVESTIGATION OF A COOLING CRYSTALLIZATION OF AN ORGANIC COMPOUND BY COMBINING LABORATORY EXPERIMENTS, SIMULATION AND PLANT EXPERIMENTS

摘要

The typical steps in improving an industrial crystallization process are described. In the process that serves as an example a batch cooling crystallization in jacketed vessels is applied for the separation of two isomers. Towards the end of the batch water for drowning-out is added to increase the yield. Problems that have been encountered are extraordinarily long batch-times, inclusions of mother liquor in the crystals and caking of the final product. Measurements in the production plant and experiments in the laboratory were performed to reveal the weak points of the crystallization process. It could be shown that the long batch-times result from an ineffective cooling of the suspension due to short circuits in the cooling water flow pattern. The caking occurs because of a high amount of fines in the crystalline product. These fines are a result of nucleation bursts that occur near the cold spots at the vessel wall and during the addition of the water for the drowning-out. Furthermore a lot of small particles is produced by breakage and attrition during the downstream processing. A crystallization model was built up and used for the optimization of the industrial process. It could be shown that adding the water at the beginning of the batch would reduce the amount of fines and would thus avoid caking. Other proposals for the improvement of the process concern the optimization of seeding and the modification of the cooling trajectory in order to reach a better control of the supersaturation during the batch.