A Study On The Cooling Crystallization Process Of Acephate

Acephate is an important organophosphorus insecticide. It would probably be the most appropriate substitute of O,S-dimethylphoramidothioate for its higher medical effect, lower toxicity and biological degradability, and would be extensively used in the near future. There are some problems in the manufacture process of acephate products in China, such as the low purity and yield. Therefore, a study on the cooling crystallization process of acephate was carried out systematically.The solubility of acephate in dichloromethane, ethyl acetate, acetone and 2-propanol were measured using a laser-monitoring observation under the atmospheric pressure. The solubility data were correlated by Apelblat model with a satisfied precision. The metastable zone was also measured by the laser method and the effects of temperature and cooling rate on the metastable zone width were investigated experimentally. In addition, the induction period of the supersaturation dichloromethane solution of acephate was measured, through which the intersurface tension between the crystal and the solution was calculated.The cooling crystallization kinetics of acephate in dichloromethane solution was experimentally measured by the batch dynamic method. The moment transform method and the size-independent model were chosen to deal with the kinetic data, and the model equations of the nucleation rate and the crystal growth rate of acephate were finally obtained through the least square multivariate linear regression. The effects of the operational parameters such as supersaturation, the suspension density and the stir speed on the nucleation rate and the crystal growth rate were analyzed by these model equations.On the basis of thermodynamic and kinetic studies, the cooling crystallization process of acephate was optimized experimentally. Aimed at solving the problems existing in the manufacture process of acephate, the effect of operational parameters, such as concentration, final temperature, cooling rate, agitation speed, seeding, on the product quality was studied. The optimum operational conditions of the cooling crystallization process of acephate were finally obtained. In addition, the effects of dichloromethane, ethyl acetate, acetone and 2-propanol on the crystal habit and crystallographic form of acephate were investigated experimentally.