Influence of multi-phase phenomena on semibatch crystallization processes of aqueous solutions

摘要

Crystal properties, product quality and particle size are determined by the operatingconditions in the crystallization process. Thus, in order to obtain desired end-products,the crystallization process should be effectively controlled based on reliable kineticinformation, which can be provided by powerful analytical tools such as Ramanspectrometry and thermal analysis. The present research work studied variouscrystallization processes such as reactive crystallization, precipitation with anti-solventand evaporation crystallization. The goal of the work was to understand morecomprehensively the fundamentals, phenomena and utilizations of crystallization, andestablish proper methods to control particle size distribution, especially for three phasegas-liquid-solid crystallization systems.As a part of the solid-liquid equilibrium studies in this work, prediction of KCl solubilityin a MgCl2-KCl-H2O system was studied theoretically. Additionally, a solubilityprediction model by Pitzer thermodynamic model was investigated based on solubilitymeasurements of potassium dihydrogen phosphate with the presence of non-electronicorganic substances in aqueous solutions. The prediction model helps to extend literaturedata and offers an easy and economical way to choose solvent for anti-solventprecipitation.Using experimental and modern analytical methods, precipitation kinetics and masstransfer in reactive crystallization of magnesium carbonate hydrates with magnesiumhydroxide slurry and CO2 gas were systematically investigated. The obtained results gavedeeper insight into gas-liquid-solid interactions and the mechanisms of this heterogeneouscrystallization process. The research approach developed can provide theoreticalguidance and act as a useful reference to promote development of gas-liquid reactivecrystallization.Gas-liquid mass transfer of absorption in the presence of solid particles in a stirred tankwas investigated in order to gain understanding of how different-sized particles interactwith gas bubbles. Based on obtained volumetric mass transfer coefficient values, it wasfound that the influence of the presence of small particles on gas-liquid mass transfercannot be ignored since there are interactions between bubbles and particles. Raman spectrometry was successfully applied for liquid and solids analysis in semi-batchanti-solvent precipitation and evaporation crystallization. Real-time information such assupersaturation, formation of precipitates and identification of crystal polymorphs couldbe obtained by Raman spectrometry.The solubility prediction models, monitoring methods for precipitation and empiricalmodel for absorption developed in this study together with the methodologies used givesvaluable information for aspects of industrial crystallization. Furthermore, Ramananalysis was seen to be a potential controlling method for various crystallizationprocesses.