Research On Dicyandiamide Purification Process By Cooling Crystallization

Dicyandiamide (DCD)’s production in Ningxia accounted for about80%of the country, it is an important processing product of calcium carbide and widely used in the production of pesticides, pharmaceutical, fertilizer, electronics, adhesive, the agent which dealing with environmental protection and so on. Especially, DCD used in the electronics industry CCL production, high purity products are required. Therefore, the development of preparation technology of the high purity DCD and equipment has important practical significance. This paper measured the thermodynamic data of DCD by the crystallization method and investigated the crystallization kinetics, the crystallization process conditions on the DCD quality.First, the solubility of DCD in methanol and different methanol-water mixed solvent under different temperature was measured. Solubility data were between0.0085-0.0297and0.0031-0.0396. These data were correlated with the modified Apelblat, Van’t Hoff, λh equation, the simulation results are satisfactory. Simultaneously, the super solubility of DCD in methanol and different methanol-water mixed solvent was measured, and determined the metastable zone width of DCD in different solvent. The data were between0.25-4.78℃、1.68-6.38℃、0.94-5.4℃.Then investigated the DCD crystal dynamics, obtain kinetic nucleation rate equation. The effect of saturation temperature, cooling rate, stirring rate and the amount of seed on DCD crystal products of calcium content, yield, the average particle size and crystal morphology. The calcium content of DCD is20.22μg/g, decalcification was88.90%, yield80.87%, mean particle diameter of945.93μm, which reached a standard electronic grade DCD products under the optimized conditions of temperature under saturated solution50℃, the cooling rate of0.2K·min-1, stirring rate of200r·min-1, the amount of seed added7.5%. The results of this research provide a theoretical basis for the establishment and optimization of the cooling crystallization process of DCD and the basic data for the further study and industrial production.