(50a) Simulation of Reactive Extraction Columns Based On Lab-Scale Experiments with Single Drops

Reactive extraction is not only used to refine noble metals or to enrich nuclear fuels but also to separate components of low concentration from a liquid phase. Due to superimposed reaction this is more efficient than by conventional solvent extraction. Compared to solvent extraction, the interactions in reactive extraction are more complex due to various reactions that may be taking place either in the bulk phases or at the interface parallel to physical mass transfer. For the reliable and efficient design of such processes, quantitative knowledge of mass transfer and reactions and their effect on the hydrodynamics in an extraction column is crucial.

A new method based on simulation with drop population balances and lab-scale single-drop experiments allows for understanding these effects in detail. The single-drop experiments are used to obtain system-specific parameters for models accounting for mass transfer and drop sedimentation. At AVT – Thermal Process Engineering, a drop population balance tool called ReDrop, originally developed and extensively verified for solvent extraction, has now been extended for reactive systems. Single-drop experiments with the standard test system for reactive extraction zinc + D2EHPA have been conducted. It was shown that, in contrast to physical extraction systems, for this test system, the interfacial reaction increases the drop’s sedimentation velocity. This is because D2EHPA, acting as a surface active agent that makes the interface rigid, is consequently removed from the surface by the interfacial reaction with zinc. As a consequence of this increased mobility of the interface, mass transfer is enhanced. To model this phenomena, existing mass-transfer models were extended and incorporated into ReDrop. Multi-component reactive equilibria were incorporated and G^E models were used to account for the non-idealities of both phases. For different operating conditions of a pulsed sieve-tray column, simulation results like Sauter mean diameter, hold-up and separation efficiency were then compared to data from pilot-plant experiments.

In the presentation, the results of the single-drop experiments for the reactive test system will be presented and discussed. It will be shown that accurate simulation of reactive extraction columns is possible employing single drop experiments and ReDrop.