Thermodynamic and Spectroscopic Studies of Levitated Microdroplets of Highly Supersaturated Solutions

点击翻译按钮获取中文摘要

ABSTRACT CTS-9625178 Allan Myerson The project examines the behavior of supersaturated solutions which must be formed prior to crystallization. Crystallization from solution is an important separation process which is used in a wide variety of industries. In this project, the solvent activity of supersaturated aqueous solutions of electrolytes (such as potassium chloride, potassium aluminum sulfate and ammonium sulfate) and aqueous and non aqueous solutions of non-electrolytes (such as glycine, adipic acid and succine acid) will be measured employing electrodynamically levitated solution microdroplets. The use of this technique removes the container walls and most dust and dirt from the solution so that very high supersaturation can be achieved. This will allow determination of the thermodynamic properties of supersaturated solutions over a wide range approaching the spinodal. In addition, Raman spectroscopy will be used to examine the formation and time evolution of subcritical molecular clusters. Appropriate theoretical treatments of the thermodynamic and spectroscopic date will be developed and used to calculate the nucleation induction time, size distribution of clusters and metastable limit boundaries. The study of the thermodynamics properties and cluster evolution in supersaturated solutions is quite difficult because these solutions are hard to prepare and keep stable. The technique of levitated microdroplets provides a unique method to prepare highly supersaturated solutions which can be examined employing Raman spectroscopy. Raman spectra of highly supersaturated solutions should yield important information on the time evolution of molecular clusters in supersaturated solutions prior to nucleation. In addition, these will be the first studies of thermodynamic and spectroscopic properties of supersaturated solutions of non-aqueous solutions. This project will supply additional data on the thermodynamic properties of supersaturated solutions of industrially important systems thus allowing modeling of the nucleation and crystal growth of these systems making use of the thermodynamic supersaturation (supersaturation based on activity instead of concentration). For cases in which the supersaturation is above 10%, it has been shown that the error in using supersaturated based on concentration is significant and increases rapidly with increasing supersaturation. In addition the work will supply fundamental data on the formation of subcritical clusters prior to nucleation through spectroscopic measurements. Using appropriate theory, this data will allow calculation of properties which are important to the industrial practice of crystallization and will aid in the design and development of crystallization processes. ***