Closed-loop control of crystal shape in cooling crystallization of l-glutamic acid

Recent simulation research has proved the principle that it is possible to exercise closed-loop control over the particle shape of the crystals produced from cooling crystallisation processes through tracking an optimum temperature or supersaturation profile which can be obtained through optimisation using a morphological population balance (M-PB) model. Here, attention is given to experimentally designing a closed-loop control system on a real crystallisation process to produce the desired shape for rod-like crystals. An optimization algorithm was applied to an M-PB model developed for l-glutamic acid crystallisation to find the optimal profiles of cooling temperature and supersaturation that lead to the desired shape of β-form rod-like product crystals. A closed-loop feedback control system was designed to control the solution temperature or concentration to track the optimum trajectory. On a 1-l crystalliser, it was demonstrated that crystals of different shape can be obtained using the developed closed-loop control methodology. Both supersaturation control and temperature control are compared with each other, and also with constant supersaturation strategy in performance in achieving the final product shape.

► Closed-loop control of the shape of a population of crystals grown from solution is demonstrated in a real crystallisation process.
► This is made possible by applying optimisation to a newly proposed morphological population balance model for crystallisation.