(545g) Determining Recipes for Seeded Batch Crystallization for Many Chemical Systems with Optimal Control Theory and a Dimensionless Framework
AIChE Annual Meeting
2020 Virtual AIChE Annual Meeting
Modeling and Control of Crystallization
Tuesday, November 17, 2020 - 9:30am to 9:45am
The results suggest that seed properties have a greater effect on the nucleated mass and number of nuclei than the supersaturation trajectory. However, since product mean size depends strongly on seed mean size, there is a significant trade-off between objectives concerning nucleation and product mean size. The trade-off between nucleated number and nucleated volume is strong especially when nucleation rate is much more sensitive to supersaturation than growth rate as shown by plotting Pareto-optimal fronts. Objective values under constant growth trajectory are also evaluated since this control strategy can be implemented without prior knowledge of the kinetic parameters (Nagy, 2017). Results show that the difference in objective values is small when the nucleation rate is proportional to magma density or sensitivity of nucletion to crystal growth is small.
If the seed mean size is 50 microns and batch time is 1 hour, 22 of the 32 systems require 10% or lower seed loading to effectively inhibit nucleation (so that the nucleated mass is 1% of the seed-grown mass) after application of a constant growth trajectory. However, when the seed mean size is 200 microns, nucleation be suppressed with a seed loading less than 10 % in only four cases. Furthermore, increasing the batch time does not provide a significant benefit for most systems.
Though the kinetic models considered are relatively simple (size- and temperature-dependence of kinetic parameters as well as breakage and aggregation are neglected), this work provides understanding for optimal seeding and growth rate control policy for many chemical systems which can serve as a basis for understanding general trends and outliers in the synthesis of batch crystallization recipes.
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