| In recent years,dyestuff industry has been sustainably and rapidly developed in China and the output of dyestuff has steadily occupied the first place in the world,accounting for 60 % of the world’s total output.Thus China has become the main production countries and supply regions of dyestuff intermediate.However there are some serious problems in the process of dyestuff intermediate(A),such as large particle size,wide size distribution,etc.In this paper,crystallization thermodynamics,crystallization kinetics,crystallization process and different cooling methods including evaporation and wall cooling were studied systematically.By optimizing the crystallization process,the crystal products with small particles and uniform distribution were obtained.The solubility of A in water was determined using a gravimetric method.The solubility of A in water was correlated by empirical equation,and the result of fitness was good.The metastable zone of A in aqueous solution at 150 rpm and 0.5 K/min cooling rate was determined,which provided the basis for crystallization kinetics.The relationship between the boiling point of A aqueous solution with different concentrations and the vacuum degrees was measured.Batch dynamic method was used to investigate the crystallization kinetics of A,the results showed that the crystal growth rate was size-dependent and the ASL model was chosen to fit the experimental data.On the basis of the population balance equation and mass balance equation,the kinetics model of A cooling crystallization was established via the method of moment transformation.In addition,the correlation parameters of secondary nucleation and crystal growth rate equations were fitted by least square regression model parameters.Based on the study of the thermodynamics and kinetics of the crystallization,the experimental conditions of the crystallization process were optimized.The effects of vacuum degree and residence time on the crystallization process were investigated.And then,the optimal process conditions were obtained.This paper provided an useful reference for the crystallization process of A.On the basis of the above studies,the crystallization process characteristics of A under different cooling methods,evaporation and wall cooling were discussed.At the same initial concentration and cooling rate,the total chord counts and the chord length distribution as a function of time in the crystallization process were compared.These properties were analyzed in terms of crystallization dynamics. |
