Study of Batch Crystallization and Determination of an Alternative Temperature-time Profile by On-line Turbidity Analysis : Application to Glycine Crystallization

Abstract On-line information is valuable for the supervision of crystal size and crystal size distribution (CSD) in batch-cooling crystallizers. A spectral turbidimetric method was used to measure crystal size on-line during the cooling crystallization of glycine in water. In order to control CSD and crystal size several temperature–time profiles can be used in batch-cooling processes. The kinetic parameters of nucleation and crystal growth were first studied and used to calculate the convex optimal temperature–time profile. A comparison of simulated and real turbidities allowed to display secondary nucleation and to devise a new alternating cycle of temperature (ACT) obtained from turbidimetry. The results achieved while comparing the CSDs obtained by three different profiles (convex, linear and alternative) on glycine-seeded batch crystallization showed that the alternative temperature–time profile improves the final mean particle size and CSD. It allowed to reduce the coefficient of variation from 32 to 12%. The final product size is largely regular, 95% of crystals having a size between 1.0 and 1.6 mm. Moreover, fine particle concentration was less than 3%. Furthermore, an analogy between experimental and estimated turbidity time evolution showed that crystal growth prevails over the nucleation process throughout crystallization.

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