Population balances for extraction column situations: an overview

The paper reviews the current literature on extraction column simulation when using droplet population modelling. Numerical methods are briefly discussed and background information to necessary kernels and correlations as well as parameter evaluation is presented. This comprises physical and chemically enhanced mass transfer, droplet movement and interactions in stirred columns. Furthermore, the benefits of CFD calculations to resolve local hydrodynamic details or ultra-fast simulation concepts for model-based forward control are covered. The hydrodynamics and mass transfer in liquid-liquid extraction columns (LLECs) involve a larger number of operating variables than vapour-liquid unit operations, which makes the scale-up of LLEC difficult and hence pilot-scale experiments are still inevitable. Bench-scale semi-continuous experiments give a firm basis to evaluate the droplet interactions. The droplet breakage can be easily correlated via power input or energy dissipation but the coalescence behaviour is more difficult to describe. An alternative is to obtain the coalescence parameters numerically in an optimisation procedure, as is to solve the so-called inverse population balance problem. In this paper, correlations are reviewed for a population balance model (PBM)-based LLEC simulation. Finally, two case studies for an RDC and Kühni extraction column provide in detail the methodology on how to handle a design case which in principle can be extended to other extraction apparatus.
The paper reviews the current literature on extraction column simulation when using droplet population modelling. Numerical methods are briefly discussed and background information to necessary kernels and correlations as well as parameter evaluation is presented. This comprises physical and chemically enhanced mass transfer, droplet movement and interactions in stirred columns. Furthermore, the benefits of CFD calculations to resolve local hydrodynamic details or ultra-fast simulation concepts for model-based forward control are covered. The hydrodynamics and mass transfer in liquid-liquid extraction columns (LLECs) involve a larger number of operating variables than vapour-liquid unit operations, which makes the scale-up of LLEC difficult and hence pilot-scale experiments are still inevitable. Bench-scale semi-continuous experiments give a firm basis to evaluate the droplet interactions. The droplet breakage can be easily correlated via power input or energy dissipation but the coalescence behaviour is more difficult to describe. An alternative is to obtain the coalescence parameters numerically in an optimisation procedure, as is to solve the so-called inverse population balance problem. In this paper, correlations are reviewed for a population balance model (PBM)-based LLEC simulation. Finally, two case studies for an RDC and Kühni extraction column provide in detail the methodology on how to handle a design case which in principle can be extended to other extraction apparatus.