Modeling and Control of Crystallization Kinetics

Crystallization kinetics is monitored from batch crystallization as a route in a phase space mapped out by the crystal mass and the total chord count. We achieve monitoring of chord count by using the Focused-beam reflectance measurement (FBRM) which works by shining a ray of light on the suspended crystals and measuring the count by the number of rays reflected back. Another instrument used to monitor crystallization is the attenuated total reflectance Fourier transform inferred (ATR-FTIR). This is typically used to monitor the solution composition and, along with temperature measurement, the supersaturation of the solution. We also use ATR-FTIR to deduce the total crystal mass via a mass balance. Manual crystallization control can be achieved by intuitively understanding the kinetics through observing the dynamics of previous crystallization runs. Through manipulation of temperature, the supersaturation of the solution is affected which in turn sets the crystallization angle. We observed that the route to reach a set target point was different between the manual manipulation and a common crystallization technique, Direct Nucleation Control. After a couple of successful attempts, we were able to develop a feedback control through understanding the crystallization dynamics. The control model proved to be more energy efficient and hits the target on the mass-count visual relatively in the same amount of time as Direct Nucleation Control. This manual control is important in testing the idea that we can understand the crystallization dynamics through the mass-count visual and establish control through learning; similar to learning how to drive.