Reactive Extraction in Kühni Column
Reactive Extraction of ZnSO4/D2EHPA/n-heptane in Kühni Column
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Summary
Liquid extraction is a complex and important separation technology, which is widely used in numerous industrial processes. It has been extensively studied for non-reactive chemical systems recommended by the European Federation of Chemical Engineering (EFCE) with single and swarm droplet experiment [1]. These experiments were carried in a test cell, a mini-, pilot- and industrial plant column in order to develop and verify a design methodology based on droplet population balances. That involved modeling of the multiphase flow using an empirical knowledge, used to express the hydrodynamics of droplet interactions (breakage and coalescence), droplet velocity, axial dispersion and mass transfer. However, several of these industrial processes rely on reactive extraction and due to a scarce data base still deficiencies exist. Therefore, the reactive EFCE test system (Zn and di(2-ethylhexyl) phosphoric acid) was used to bridge this gap using single and swarm droplet experiments [2].
The focus of this work was to study the influence of reactive mass transfer on droplet-droplet interactions and droplet size distribution, at steady state and transient conditions in a mini-plant Kühni extraction column (DN32). Prior to this single droplet experiments were performed to investigate the breakage probability in a lab scale column using one Kühni compartment with 6 blade stirrer. The results were compared to different breakage frequency models under different operating conditions and mother droplet sizes. Further drop swarm experiments were done in the mini-plant Kühni extraction column with 40 compartments. The outlet droplet distribution, holdup, pH and concentration profile (continuous and dispersed phase) along the column height is measured under different operating conditions (initial concentration, rotational speed, flow rate). This will improve the accuracy of the column layout during reactive extraction and also extended the foundation for development of new models and for further validation purposes.
Literature
[1] Misek, T. (1994), General hydrodynamic design basis for columns, In: Slater, M. J., Godfrey, J.C. (Eds.), Liquid–liquid Extraction Equipment, John Wiley & sons., Chichester.
[2] Bart, H.-J. and Slater, M. J. (2001), Standard Test system for Reactive Extraction – Zinc/D2EHPA, available online http://www.dechema.de/Extraktion/.
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