GROWTH KINETICS OF POTASSIUM CHLORIDE IN WATER-ETHANOL SYSTEMS

摘要

Growth and dissolution kinetics of potassium chloride in ethanol-water solutions were obtained in a pilot-scale fluidized bed crystallizer. The experiments were carried out for different contents of ethanol in the solution. The influence of the organic solvent upon the width of the secondary nucleation zone and the morphologic characteristics of the crystalline product was also assessed. Experimental results obtained in water-ethanol systems were compared to data from pure aqueous solutions and showed that, under the same driving force, the growth and dissolution rates of KCl decrease as the concentration of the organic co-solvent increases. Both rates were found to be first order with respect to the thermodynamic driving force, independently of the content of ethanol. It was also inferred from the experimental results that the growth of KCl crystals in aqueous ethanolic solutions is mainly controlled by a surface mechanism characterised by a continuous deposition of solute. Additionally, the experimental data showed that the width of the secondary metastable zone of potassium chloride solutions increases directly with the ethanol content in the solvent.