Effect of stirring speed on the nucleation kinetics of dipyrone crystallization in Pilot-Scale experiments

Crystallization is an important procedure in the production process of separation and purification. Precise control of nucleation kinetics is critical for industrial solution crystallization, particularly in the production of pharmaceuticals such as dipyrone, where product quality is paramount. This study systematically investigates the influence of stirring speed on the metastable zone width (MSZW) and nucleation behavior of dipyrone in a pilot-scale stirred tank. The modified Sangwal’s model is applied to establish a consistent inverse relationship between stirring speed and MSZW. Increasing the stirring speed from 30 rpm to 50 rpm reduces the average MSZW by 12.70%, with the most significant reduction of 15.83% observed at higher saturation temperatures. Higher stirring speeds facilitate the overcoming of nucleation barriers, suppressing supersaturation by 7.98% and 11.70% at saturation temperatures of 333.15 K and 343.15 K, respectively. Nucleation kinetics analysis reveals that the average critical nucleus size increases by 11.74% as the stirring speed rises from 30 rpm to 50 rpm. Conversely, the nucleation rate ( J ) decreases with increasing stirring speed, though the average J is reduced by only 1.72%. From a crystal size perspective, due to shear-induced breakage, the D 32 crystal size at 50 rpm decreases by 5.35% compared to 30 rpm. These findings provide practical guidelines for optimizing stirring-induced nucleation efficiency and crystal size.