Quantitative Beschreibung von Koaleszenzvorgängen in Extraktionskolonnen

摘要

A significant aspect of designing an extraction apparatus is determining the coalescence behavior of a given material system. As coalescence is strongly influenced by traces of impurities, tests have to be carried out with the same system, which is used for the later extraction process. Different measurement methods for determining the coalescence behavior of a system are described in the literature. The coalescence behavior for designing mixer-settler processes can be quantified in simple discontinuous lab-scale settling tests. At the same time, quantifying coalescence of a system in an extraction column is tedious as pilot-plant experiments have to be performed. Therefore, it was the objective of this work to develop a method to characterize the coalescence behavior in extraction columns with minimal effort. For this purpose, different measurement techniques discussed in the literature for quantifying coalescence were applied and compared. It was shown that the discontinuous settling test, which can be performed with comparatively low effort, can also be applied for characterizing coalescence in extraction columns. For transferring the results of the settling tests to extraction columns, model approaches, which are given in the literature, were improved. By applying these models, the coalescence behavior in extraction columns is separated into two factors: On the one hand, hydrodynamic effects determining e.g. frequency of drop collisions and collision intensity have to be modeled. The hydrodynamic effects depend on the geometry of a specific column and on the operating conditions and have to be characterized only once for each column type. On the other hand, coalescence behavior of a specific material system has to be quantified. The influence of the material system on the coalescence is characterized by the settling experiments. Thus, this new approach allows a universal characterization of coalescence for all common extraction equipment, namely mixer-settlers as well as columns, where the system specific coalescence is characterized in a simple and fast lab-scale experiment.