Study On Taurine Crystallization Process In The Presence Of Process Impurities

Taurine plays an important role in regulating biological physiological functions and is widely used in food additives,feed additives,drugs and other fields.However,during the taurine production using the ethylene oxide method,effect of two process impurities,sodium isethionate(SI)and(β-ethyl sulfonate)aminoethyl sulfonate(SA),on taurine crystallization was unknown.Therefore,systematic studies about effects of impurities on the crystallization thermodynamics,crystallization dynamics,crystallization process and product quality of taurine can provide theoretical basis for precise regulation of taurine crystallization process in industrial production,so as to preparing high-quality taurine crystal products.Effects of process impurities on the crystallization thermodynamics and nucleation behavior of taurine were systematically investigated.Process impurities increased the solubility slightly but widened the metastable zone significantly.The weak solubilization is due to the trade-off balance between salting-out effect and solubilization effect caused by similar structure.The fitting results of the nucleation kinetics model and the viscosity measurement results indicate that impurities inhibit the nucleation of taurine and widen the metastable zone through the comprehensive effect of solubilization,increase of solid-liquid interface energy and viscosity enhancement.The difference in the nucleation inhibition between SI and SA is due to their different change in solubility,solid-liquid interface energy,and solution viscosity.Effects of process impurities and operating parameters on the crystallization process and crystal morphology of taurine were investigated.The significant influencing factors of crystallization indicators including length diameter ratio and yield were obtained by analyzing the orthogonal experiment results.The single factor experimental results showed that the increase of SA concentration and cooling rate could lead to the increase of length diameter ratio,and the development of crystal morphology from columnar to spindle or even needle shaped;that lower cooling rate and crystallization temperature range could give molecular units enough time to orient on the crystal surface,and make crystal surface relatively smooth.These results indicate that the control of supersaturation is the key to regulate taurine crystallization behavior.Secondary nucleation-growth rates of taurine in metastable zone were measured.The results showed that the growth order decreased from 2.4 to 1.27 with the increase of crystallization temperature from 292.65 K to 322.95 K,which indicates that growth process of taurine is controlled by surface integration and diffusion process.Molecular simulation technology was used to predict crystal habit of taurine,and the simulation results were consistent with experimental results.The simulation results showed that morphological importance of(0 0 2)face with low polarity in water environment decreased,while morphological importance of(1 0 2)and(1 1-1)face which are easily bound by solvents increased and proportion of crystal surface area increased.In SA aqueous solution environment,the predominant growth orientation in the single Water environment,(1 1-1)face,area ratio was significantly reduced and the inferior growth face,(1 0-2)face,area ratio was significantly increased,which was the main reasons why taurine morphology changed from columnar to spindle/needle-like.Considering the results of thermodynamics,kinetics,viscosity and molecular simulation,the internal mechanism how SA and the supersaturation rate/level affected the taurine crystal morphology were clarified.