Feedback Control for the Size and Shape Evolution of Needle-like Crystals in Suspension. II. Cooling Crystallization Experiments

The experimental validation of a model-free path following control (PFC) scheme to manipulate the size and shape evolution of needle-like crystals in a seeded, growth-dominated batch cooling crystallization process is presented. To this aim, constant supersaturation control (CSC) and PFC experiments were performed on the needle -shaped compound beta L-glutamic acid. First, the feedback controllers were coupled with an online size and shape monitoring tool. Second, attainable regions for the average particle dimensions of two different seed populations were determined experimentally using the CSC strategy, which enabled selecting reasonable targets in the size and shape space for the PFC experiments. Then, PFC experiments were performed to guide the populations of seed crystals to certain targets within the attainable region exhibiting different average sizes and shapes. The PFC strategy was able to successfully and repeatedly complete this task, thereby operating in a model-free fashion in the sense of not requiring multidimensional crystal growth rate models. The experimental validation underlines the effectiveness and the robustness of this feedback control scheme for the considered process.