Optimal Control of Crystal Shapes in Batch Crystallization Experiments by Growth-Dissolution Cycles

The control of the evolution of the crystal size and shape distribution (CSSD) during crystallization processes is an important task in crystallization, as the final CSSD decisively influences the physical and solid state properties of crystalline material. This work utilizes sequential growth and dissolution cycles, which turn out to result in an essentially enlarged region of attainable crystal sizes and shapes. Using potassium dihydrogen phosphate as a model substance, such a cyclic crystallization process is realized in a hatch scale and in a novel, fully automated, and controlled manner. TO this end, a novel observer setup is presented; which is based on video microscopy, and facilitates the real-time monitoring of the evolution of the crystal size and shape distribution. Given this information, optimal strategies for the control of supersaturation profiles as well CSSD are experimentally successfully implemented, proving a reliable and high-precision generic control scheme for crystal shape manipulation. The proposed theoretical and experimental research results are expected to be of use in targeted crystal size and shape manipulation in chemical and pharmaceutical industries.