Feedback Control for the Size and Shape Evolution of Needle-like Crystals in Suspension. IV. Modeling and Control of Dissolution

Several two-dimensional dissolution rate models for the needle-like compound beta L-glutamic acid (BLGA) in water are obtained by first conducting a series of lab-scale experiments and then applying the maximum likelihood parameter estimation technique within a population balance framework. Among these models, a reasonable choice consists of expressions for the dissolution rates along both particles dimensions that are linear in the driving force and yield a constant value of 12 for the ratio of the dissolution rate along the length of the needles to that along their width. The insights gained from this model are applied to discuss the potential of cyclic processes aimed at modifying the size and the shape of BLGA crystals. Furthermore, a model-free feedback control law with the goal to dissolve a given fraction of the overall solid volume initially suspended in a batch system is presented. This controller is tested in a simulation framework making use of the identified dissolution kinetics. It is also validated experimentally by using BLGA and another compound forming needle-like crystals, vanillin. The results demonstrate its effectiveness and its general applicability, making it suitable for the controlled operation of dissolution stages in cyclic size and shape modification processes.