(468a) Identifying Nucleation and Growth Kernels of Crystallization

Crystallization, a separation process, is simply attachment and detachment of molecules across time scales. Minor changes in the operating conditions have proven to change the outcome of crystallization and controlling the process of crystallization remains a challenge. Nucleation and crystal growth are the two processes of the crystallization and are modeled using the thermodynamic approaches. Mechanism of both processes is the same, but the time scales of the two processes are different. The challenge in modeling the process of crystallization is to derive nucleation rate of crystal structure and growth rates of energetically stable faces on the crystal. The theories used to find these rates rely on calculating interfacial free energies which is often difficult and lacks generality. With the help of a novel approach based molecular simulations, we were able to find the nucleation and growth rates. Once the rates are known, it is necessary to connect the operating conditions to outcome of crystallization. A set of operating conditions which lead to a specific outcome of crystallization will be called as kernel of crystallization. To effectively capture the time scales and the mechanism of crystallization without lack of generality, we propose the use of Population Balance Modeling (PBM). PBM finds the rate of change of internal coordinate and for crystallization, the internal coordinates are nucleation and growth rates. The rates obtained from different operating conditions can be connected to the outcomes of crystallization and hence PBM successfully finds the kernel of crystallization. Knowledge of these kernels can successfully control the process of crystallization and also shows potential to solve the problem of polymorphism.