Abstract: Industrial crystallizers have to be operated at the optimum supersaturation which is less than the metastable zone width to obtain a desired product quality, such as median article size,crystal size distribution, shape and purity. Due to the time-consuming experimental determination of metastable zone width, the theoretical calculation method was studied in this paper. According to the nuclear theory and the dynamics of crystal growth, a theory model based on the model of Mersmann’s was suggested for calculating the metastable zone width of organic system with high viscosity. Also, its computation program was suggested. Combining with the parameters of crystallization process of monomehypo pesticide, the metastable zone width of industrial crystallization process was calculated, and its result is close to the experimental value. This method could be as a model for choosing the supersaturation of industrial crystallization.

Key words: Industrial crystallization, Metastable zone width, Theoretical calculation