Effect of process impurities on crystallization thermodynamics and nucleation kinetics of taurine

Abstract

Solubility and metastable zone width (MSZW) are the basis for purifying products by crystallization. The effects of two process impurities, sodium isethionate (SI) and sodium N‐(β‐ethyl sulfonic acid) aminoethyl sulfonate (SA), on taurine solubility and MSZW in water under different conditions were studied. Solubility and MSZW were measured by laser transmission method. The results show that the process impurities can increase solubility slightly but increase MSZW significantly. The weak solubilization might be due to the antagonism of salting‐out effect and structural similarity between taurine and impurities. Combining the viscosities and parameters calculated by nucleation models, the reason for the different effects of the two impurities on MSZW was studied. The fitting and experiment results show that the solid–liquid interfacial energy γeff was increased by 9.1% and the viscosity by 5.4% at 303.15 K in the presence of SI (0.12 mol per kilo H2O). Meanwhile, γeff was increased by 90.4% and the viscosity by 10.5% with SA added (0.12 mol per kilo H2O). Changes in thermodynamic factors (solubility, γeff) and kinetic factors (viscosity) caused by impurities contribute to the extension of MSZW. This study expands the understanding of the role of process impurities in taurine crystallization.