Crystallization of paracetamol from mixtures of ethanol and water in a planar oscillatory flow crystallizer: effect of the oscillation conditions on the crystal growth kinetics

Isothermal seeded desupersaturation experiments were performed in a planar oscillatory flow crystallizer (planar-OFC) to investigate the effect of the oscillation conditions on the crystal growth kinetics for the isothermal crystallization of paracetamol. An empirical power-law equation was used to describe the influence of supersaturation on the crystal growth rate. The crystal growth kinetic parameters were estimated by fitting a mass balance equation to the experimental desupersaturation data by nonlinear optimization. It was found that the oscillation conditions have a minor effect on the crystal growth kinetics, which suggests that surface integration is the rate-controlling step of crystal growth. The relatively high values of the growth rate order and activation energy obtained in this work also support this conclusion. Furthermore, a separate mass transfer analysis confirmed that diffusion limitations have little impact on the crystal growth rate. These results suggest that the crystal size distribution control cannot rely on the effect of the oscillation conditions on the crystal growth step alone but rather on their relative impact on the nucleation and crystal growth steps.