Thermodynamic and Spectroscopic Studies of Levitated Microdroplets of Highly Supersaturated Solutions

该项目研究了在结晶之前必须形成的过饱和溶液的行为。溶液结晶是一种重要的分离工艺，广泛应用于各种工业中。本项目将采用电动悬浮溶液微滴测量电解质的过饱和水溶液（如氯化钾、硫酸铝钾和硫酸铵）和非电解质的水溶液和非水溶液（如甘氨酸、己二酸和琥珀酸）的溶剂活度。使用这种技术可以去除容器壁和溶液中的大部分灰尘和污垢，从而实现非常高的过饱和。这将允许在接近旋量的大范围内确定过饱和溶液的热力学性质。此外，拉曼光谱将用于检查亚临界分子团簇的形成和时间演化。将发展适当的热力学和光谱数据的理论处理，并用于计算成核诱导时间、团簇的尺寸分布和亚稳极限边界。由于过饱和溶液很难制备和保持稳定，因此研究过饱和溶液的热力学性质和团簇演化是相当困难的。悬浮微滴技术为制备高度过饱和溶液提供了一种独特的方法，可以用拉曼光谱对其进行检测。高度过饱和溶液的拉曼光谱可以提供成核前分子团簇在过饱和溶液中的时间演化的重要信息。此外，这些将是第一次研究非水溶液的过饱和溶液的热力学和光谱性质。该项目将为工业上重要系统的过饱和溶液的热力学特性提供额外的数据，从而允许利用热力学过饱和（基于活性而不是浓度的过饱和）对这些系统的成核和晶体生长进行建模。对于过饱和大于10%的情况，已经证明，基于浓度使用过饱和的误差是显著的，并且随着过饱和的增加而迅速增加。此外，这项工作将通过光谱测量提供亚临界团簇在成核之前形成的基本数据。使用适当的理论，这些数据将允许计算对结晶工业实践很重要的性能，并将有助于设计和开发结晶工艺。＊＊＊

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. ***