Crystallization is one of the essential downstream steps of the manufacturing of chemical and pharmaceutical compounds when it comes to separation, purification, and final product formation. Although it has been years since it is widely applied in the aforementioned industries, it is known as one of the complex processes where continuous optimization is increasingly necessary. Insufficient understanding of crystallization phenomena and their interactions from one side, and demanding requirements for product specifications in such industries from the other side, form the basis of challenges within this unit operation... ... Read more

In this research, a process model has been developed for an airlift and compared with that of a draft tube stirred crystallizer to clarify the crystallization kinetics in this novel type of crystallizer. Recently it has been shown that although secondary nucleation is strongly suppressed in this crystallizer, it is not completely absent and further development and scale up requires a more quantitative prediction of the kinetics in this type of crystallizer. A number of growth and nucleation models were examined in a parameter estimation study in which a dataset of a number of seeded batch experiments has been used to estimate the kinetics in both an airlift and a draft tube stirred crystallizer. It is shown that a kinetic model, consisting of a two-step growth model and two additive nucleation mechanisms, i.e. an attrition based and a surface nucleation mechanism, gives an excellent and statistically acceptable description of all studied experiments with one parameter set each for both type of crystallizers. The main difference in the two types of crystallizers being that the attrition terms by crystal-impeller and crystal–crystal collisions in the airlift crystallizer can be completely neglected. ... Read more

A hollow fiber membrane module was assessed for its potential in assisting crystallization processes. The membrane module was characterized in the sweeping gas membrane distillation configuration considering various solution and sweeping gas flow rates, temperatures and solution concentrations. A model, coupling mass and heat transfer, was developed to predict the membrane flux. The effect of the process conditions on the membrane flux was experimentally determined and the results were used to validate the model. Feed temperature and air flow rate were found to have a significant effect on the membrane flux. Having found the optimal process conditions for membrane distillation process, batch seeded crystallization experiment were performed to confirm the potential of membrane distillation in the generation of adequate rate and level of supersaturation. Since the desired supersaturation level could be maintained in the crystallizer while seeds were growing, it is confirmed that membrane distillation can be an efficient alternative to conventional supersaturation generation processes. Finally, comparing the modelling results with experiments confirms the acceptable accuracy and predictability capability of the developed model. ... Read more