Batch crystallization of a photochemical: Modeling, control, and filtration

Model identification and control were studied for the seeded batch crystallization of an organic, industrial photochemical. The growth and nucleation kinetics are described by empirical power-law expressions in relative supersaturation, and an additional model describing crystal shape dynamics is proposed. The parameters in the kinetic models are estimated from on-line measurements of solute concentration and transmittance. Parameter uncertainty is assessed, and optimal experimental design techniques are used to construct experiments to diminish uncertainty. Given the identified model, optimal open-loop temperature schedules are designed to improve the filtration of final-time slurries. The profiles minimize the mass of nucleated crystal relative to seed crystal mass, subject to supersaturation and yield constraints. Filtration improvements are verified using constant pressure filtration tests to determine the flow resistance of the filter cake. The best control experiment gives a cake resistance 25% lower than the best identification experiment.