溶液间歇结晶过程成核与生长阶段的定量识别

为定量识别溶液间歇结晶过程中的成核和生长阶段,基于晶粒数目和粒度的变化对粒度分布(CSD)的二阶和三阶矩量影响程度的不同,定义并关联了无因次变量K和K^*.添加晶种KNO₃-H₂O溶液结晶过程模拟计算的结果表明,K和K^*值均呈先降后升的变化趋势,成核时单调下降,生长过程中单调上升;且K与K^*值较接近.测定了KNO₃-H₂O溶液自发成核结晶过程中溶液浓度和透光率的变化,用K^*判据定量识别出成核阶段和生长阶段,并与晶体线性生长速率模型检验的结果相吻合.K值的计算依赖于CSD和结晶动力学参数,而K^*作为成核和生长阶段的模型判据,由实验测定的溶液浓度和透光率计算得到.

Quantitative Identification of Nucleation and Crystal Growth Stages in Batch Crystallization from Solution

For improving the precision of kinetic parameter estimation and further research of the mechanism, it was very important to identify nucleation and crystal growth stages quantitatively in the batch crystallization from solution. The dimensionless variables of K and K * were described based on the difference of crystal number and its size contributing to the second and third moments of crystal size distribution(CSD), respectively. For a typical seeded crystallization of potassium nitrate in water reported in the literature, the simulated results showed that both K and K * had a similar tendency and were also close during the crystallization process, and monotonously decreased in the nucleation stage and increased in the crystal growth stage. The solute concentration and transmittance were determined for an unseeded batch cooling crystallization of KNO 3 H 2O solution, and K * was applied to identify the nucleation and crystal growth stages. It was noted that the crystal growth stage obtained by K * agreed well with that by linear growth rate model. Compared with K simulated on the CSD and kinetic parameters, K * could be calculated directly from relevant on line information such as solute concentration and transmittance, and therefore should be much more convenient and feasible.