An Air-Lift Crystallizer Can Suppress Secondary Nucleation at a Higher Supersaturation Compared to a Stirred Crystallizer

Secondary nucleation is suppressed in an air-lift crystallizer at levels of supersaturation where in a stirred crystallizer a clear contribution of secondary nucleation is visible. A comparison of batch crystallization of l-ascorbic acid in an air-lift crystallizer and in a stirred crystallizer is presented. The results demonstrate that at low supersaturation, secondary nucleation can be suppressed in both the air-lift crystallizer and the stirred crystallizer. At higher supersaturation, nucleation starts to dominate in the air-lift crystallizer. At an intermediate level of supersaturation, a clear contribution of secondary nucleation in the final product obtained from the stirred crystallizer is visible. However, experiments with similar conditions in the air-lift crystallizer show a significantly smaller contribution of secondary nucleation. The observed enlargement of the operating window in terms of supersaturation where secondary nucleation is suppressed in an air-lift crystallizer may have important practical consequences. Air-lift crystallizers can potentially operate with a higher crystal growth rate and the operating window for design and automated control can be extended.