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Study on metastable zone width and nucleation kinetics of ammonium sulfate crystallization process

Peng Siyao;Shi Yunhai;School of Chemical Engineering,East China University of Science and Technology;  
The metastable zone width(MSZW) is a vital parameter for the design of industrial crystallization processes of inorganic salts.In the industrial production process of ammonium sulfate,the crystallization conditions can be controlled in the metastable zone to prepare ammonium sulfate with high purity and large granularity.MSZW of ammonium sulfate has been determined in the temperature range at 313.15~343.15 K polythermal method.The notable factors,such as cooling rate,initial composition,stirring rate,solution volume and presence of seed particles,affecting MSZW of ammonium sulfate have been investigated.It was observed that the MSZW of ammonium sulfate had an obvious decrease with the increase of initial composition,stirring rate and the mass of seed particles,respectively.However,the MSZW became wider by enhancing the cooling rate and the diameter of particles.Besides,no obvious effect of working volume has been found on the MZSW.Based on solubility data,the dissolution enthalpy of ammonium sulfate was calculated by the van′t Hoff equation.The self-consistent N伥vltlike equation and three-dimensional nucleation theory were used to estimate the nucleation kinetics of ammonium sulfate from the experimental MSZW data.According to the estimation results,the critical nucleation parameters,including nucleation order m,nucleation constant K and solid-liquid interface energy γ were obtained.
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