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Crystallization Kinetics of Potassium Sulfate Produced by Stirred Crystallization

Yayuan Zheng

This paper discusses the crystallization kinetics of potassium sulfate in a stirred bed crystallizer through experimental investigation. Using classical nucleation theory, the homogeneous and heterogeneous nucleation mechanisms of potassium sulfate are studied. The induction time and critical nucleation parameters, including surface tension (γ), critical nucleation radius ( r *), critical nucleation free energy (Δ G *), and critical nucleation molecule number ( i *), are measured under different temperatures and supersaturation ratios. Experimental results show that as temperature and supersaturation ratio increase, induction time, critical nucleation free energy, critical nucleation radius, and critical molecule number decrease while nucleation rate increases. The crystal shape remains relatively unchanged with temperature and supersaturation ratio, but the average particle size increases with increasing supersaturation and temperature. Changes in measured nucleation parameters are consistent with classical nucleation theory. In addition, the kinetic equations of crystal nucleation and growth rate in a stirred crystallization system are fitted using population balance equations, and the results show that the growth rate increases with increasing supersaturation and stirring speed. In addition, the effects of the parameters in the nucleation rate equation suggest that suspension density has the greatest impact, followed by supersaturation ratio and stirring speed.