Crystallization is a key unit operation in the fine chemical and pharmaceutical industries, many of which employ batch stirred vessels for crystallization. Although using stirred vessels for crystallization has advantages such as better mixing and faster cooling, one of the disadvantages is that due to the presence of mechanical parts in the vessel such as baffles, impeller etc., crystals break up while stirring and generate unwanted secondary nucleation. This process contributes to a wide crystal size distribution with a smaller than desired mean crystal size. For studying crystal breakage phenomenon, experimentalists choose to use nonsolvents for crystal breakage experiments to isolate breakage from simultaneously occurring phenomena such as Ostwald-ripening, aging and agglomeration. Although performing experiments in non-solvents eliminates other phenomena and helps isolate breakage, the results can not always be correlated to saturated solutions due to density and viscosity differences between the two conditions. In this research, the effects of Ostwald ripening, aging and agglomeration on the crystal size and shape distributions are quantitatively measured. Micro and macro scale experiments were performed in both non-solvents and saturated solutions and the results were compared to determine the effects. Both in situ focused beam reflectance method (FBRM) and off-line analyses were performed to characterize the crystal size distributions. Results from experiments show that there is significant difference between the breakage behavior of crystals in non-solvents and in saturated solutions, mplying significant impacts of Ostwald ripening, aging, agglomeration and dissolution in saturated solutions. Calculations using Zwietering correlation also show that the difference between the viscosities and densities in the two systems may also be a contributing factor to the difference in the breakage profiles. It was also found that growth rates of crystals can differ when they are subjected to stress and strain. In macroscale experiments, dissolution was found to have a significant impact on the crystal size distribution. Abrasion was found to be the dominating fracture mechanism for most systems. Extent of breakage and morphological changes were found to be dependent on stirring rates, suspension density, shape and hardness of crystals and the type of system.

Particle breakage can be significant in stirred vessels such as crystallizers. During crystallization, particle breakage can occur due to particle contact with other particles, the impeller, the suspension fluid, and/or the vessel. Such breakage produces fines and can cause filter plugging downstream. Although research has been conducted with respect to particle breakage, a comprehensive study is still needed to quantify the breakage occurring in stirred vessels. The overall goal of this research is to model the particle breakage occurring in a stirred vessel by analyzing the particle size and shape distributions that result from breakage. Breakage experiments are based on collision influences that affect the two dominant collisions types, crystal-to-crystal and crystal-to-impeller collisions. Results showed that the quantity of fines produced are affected by the solids concentration or magma density and suspension fluid utilized. Additionally, aqueous saturated solutions produced particle size distributions that differ from those obtained using a nonsolvent. Similar particle size distributions for two different materials (NaCl and KCl) are achieved in the same nonsolvent (acetonitrile) by adjusting the agitation rate using the Zwietering correlation to account for property differences; moreover, the same agitation rate adjustment produced similar distributions for KCl in acetone and acetonitrile which were both nonsolvents. However, modifications to the Zwietering correlation, such as changing the significance of the initial particle size, are proposed before this method of adjustment is deemed accurate. Number-based population modeling of particle breakage is achieved within 1-5% error for NaCl at each agitation rate investigated. Breakage modeling using a discretized population balance equation with Austin's equation for attrition and the power law form of the product function for fragmentation is a viable approach; however, more work is needed to increase the accuracy of this model.

Orientador: Jose Roberto Nunhez / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-10T17:37:46Z (GMT). No. of bitstreams: 1 Spogis_Nicolas_M.pdf: 4452795 bytes, checksum: 7a20afda92e9e3627bb4f46cbb630b88 (MD5) Previous issue date: 2002 / Resumo: Tanques de mistura são muito usados na indústria química, petroquímica, farmacêutica e alimentícia, onde a eficiência das operações de mistura freqüentemente tem um grande impacto no custo de produção e na qualidade do produto. O objetivo deste trabalho é determinar curvas para Número de Potência versus Número de Reynolds, para os impelidores mais comumente utilizados na indústria química, através da fluidodinâmica computacional. Os principais fluxos gerados pelos impelidores estudados serão determinados tanto para escoamentos laminares quanto turbulentos, calculando-se o bombeamento gerado e os padrões de circulação gerados no tanque. Através dos resultados numéricos gerados pelo modelo proposto, serão determinadas correlações empíricas para as curvas para Número de Potência versus Número de Reynolds, a fim de gerar uma ferramenta útil e prática para utilização em projetos de sistemas de agitação e ¿scale-up¿. O presente trabalho tem como objetivo mostrar que um projeto adequado de um sistema de mistura pode minimizar os gastos energéticos do equipamento e seu tempo de processamento, além de melhorar a uniformidade do processo, impedindo, ou minimizando, a formação de zonas mortas. A fluidodinâmica computacional mostrou que tem um grande potencial para melhorar sistemas de agitação, permitindo aos engenheiros simular o desempenho de sistemas alternativos, tentando emparelhar parâmetros de operação, projeto mecânico e manipulação das propriedades fluidas ou, então, otimizar sistemas reacionais já implantados na indústria / Abstract: Stirred vessels are widely used in chemical, petrochemical, pharmaceutical and food industries, where the mixing efficiency of the mixture frequently has a great impact in the product production cost and quality. The objective of this work is to build curves of Power Number versus Reynolds Number, for the most commonly used impellers in the chemical industry, through the use of CFD -computational fluid dynamics. The main flow generated by the studied impellers, the pumping number and the flow patterns in the tank will be determined. Through the numeric results generated by the proposed model, it is determined empiric correlations for Power Number versus Reynolds Number curve, in order to generate a useful and practical tool to be used in the design and scale-up of agitation systems. The present work aims to show that an optimized project of a mixture system can minimize the equipment power consumption and its processing time, improving uniformity for the whole process, minimizing the formation of dead zones. The computational fluid dynamics has proved to have a great potential to improve agitation systems, allowing the engineers to simulate alternative systems, trying to match operation parameters, equipment design and the fluids properties and also optimizing reactors that already implanted in the industry / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química