Crystallization from Solutions Containing Multiple Conformers. 1. Modeling of Crystal Growth and Supersaturation

A mechanistic model for supersaturation and crystal growth during batch crystallization of organic solids from solutions containing multiple conformers is presented. The model is based on the approach of the right conformer (RC) which assumes that only one conformer participates in the surface integration step. The model is concerned with systems characterized by slow crystal growth and low supersaturation, a behavior favored when the RC is the minority species in solution. Crystal growth is assumed to occur via a step advance mechanism with a variable step advance velocity (VSAV). Model derivation indicated that when the approach of the RC applies, crystal growth is inversely proportional to crystal size. Lastly, model simulations predicted an exponential increase of maximum relative supersaturation with linear antisolvent addition rate. The simulation also allowed estimation of maximum addition rate below which secondary nucleation is minimized.