Characterization of Coalescence in Extraction Equipment Based on Lab-Scale Experiments

Design of an extraction apparatus is significantly influenced by the coalescence behavior of a given material system. At the same time, quantifying coalescence of a systemin anextraction columnis tedious, as pilot-plant experiments have to be performed. These tests have to be carried out for each systemindividually, as coalescence is strongly influenced by traces of impurities. On the other hand, coalescence behavior for designing mixer–settler processes can be quantified in simple discontinuous lab-scale settling tests. 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 for quantifying coalescence were applied and compared. In order to transfer the results obtained in lab-scale experiments to model extraction columns, models available in the literature were tested and significantly modified. The new method allows separating the coalescence behavior in extraction columns into two factors: On the one hand, hydrodynamic effects determining, for example, the frequency of drop collisions and collision intensity have to be considered which depend on the geometry of a specific column and on the operating conditions, which 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 only with a simple lab-scale settling experiment, which characterizes the approach of two drops and their individual coalescence process. The results of simulations for extraction columns based on this model approach compare very well with experimental data. 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 lab-scale experiment