Continuous Tubular Slug-flow Crystallization Of Sodium Cyclamate

Slug flow refers to the two-phase of gas and liquid alternately flow in the pipeline by introducing gas into liquid.Stable hydrodynamic environment,enhanced process control and improved crystal quality can be achieved when slug flow is introduced into the crystallization process.Based on the crystallization thermodynamics and kinetics of sodium cyclamate,the slug-flow crystallization was investigated in this paper,The solubility data of sodium cyclamate in water,methanol and water-methanol solution were determined by static method after the solvent screening.Then the solubility data were correlated by the four models of Apelblat equation,Van’t Hoff equation,RK equation and new J-A equation.Also,the metastable zone of sodium cyclamate in water was determined by laser method.The effects of stirring rate and cooling rate on the width of metastable zone were also investigated.Besides,the solubility properties of sodium cyclamate in the solvents above were estimated based on the Van’t Hoff equation and solubility data.The crystallization kinetics data of sodium cyclamate in water were measured by batch dynamic method.The nucleation rate equation and crystal growth rate equation were fitted using moment transformation method on the basis of granularity-independent growth model.Meanwhile,the effects of temperature,supersaturation,suspension density,cooling rate and stirring rate on nucleation and crystal growth were investigated in detail.The technological conditions of slug-flow crystallization of sodium cyclamate were studied with the guidance of crystallization thermodynamics data and kinetics data.The effects of mixers,liquid/gas flow rate ratios,final temperature and pipe inner diameters on crystal quality were investigated when stable slug flow formed.Also,it was verified that the slug flow stability and liquid slug aspect ratio were important factors for crystal quality.At the same time,it was concluded that the phenomenon of crystal breakage could be effectively reduced and crystals with large size and intact shape could be prepared using the slug-flow crystallization.The study on slug-flow crystallization in this paper provided not only a basis for the industrial application but also a novel idea for the enhancement of crystallization controllability.