(698b) Modeling of Interfacial Properties and Interfacial Mass Transfer in Liquid-Liquid Extraction Systems

The interfacial mass transfer is an essential factor for the design of separation processes in the chemical and pharmaceutical industry. To properly understand and predict the mass transfer in liquid-liquid extraction systems, the interfacial properties of the liquid phases have to be studied.

In this work the influence of the target component on interfacial properties and interfacial mass transport in ternary liquid-liquid extraction systems is analyzed. The mass transfer across a liquid-liquid interface is governed by the liquid-liquid equilibrium (LLE) and the interfacial tension, hence, both properties have to be studied. The well-documented system water + toluene + acetone is chosen as a reference system [1]. The target component, acetone, is then replaced by other molecules differing in size, polarity and structure. For this study, ethanol, tetrahydrofuran and acetonitrile are studied as other target components. Tie lines for the LLE of water + toluene + ethanol, water + toluene + tetrahydrofuran and water + toluene + acetonitrile are determined. The interfacial tension for the chosen tie lines is analyzed by the spinning drop method. Subsequently, mass transfer experiments are conducted in a Nitsch cell. Several experiments with different starting compositions are performed.

The experimental results are used to model the interfacial mass transfer applying the Density Gradient Theory (DGT) [2]. For that purpose, the DGT is coupled with the Koningsveld-Kleintjens (KK) model as a g^E-model [3]. The model parameters of the KK model are fitted to the LLE of the respective ternary system. Stationary DGT is applied to calculate the interfacial tension and interfacial concentration profile for different equilibrium compositions of the ternary mixtures. These calculations predict different enrichment of the target components at the interface. Based on the equilibrium calculations the time dependent concentration profile is modeled by instationary DGT. Furthermore, interfacial properties for quaternary systems containing two of the studied molecules as target components in a water + toluene system are predicted. For that purpose, the DGT and KK model are extended to describe quaternary systems [4].

The experimental results are compared with previously conducted mass transfer experiments with acetone as the target component [5]. Based on the predicted interfacial concentration profiles and experimental results for the interfacial mass transfer the influence of different target components can be discussed.

[1] Misek, T., Berger, R. and Schröter, J., Standard Test Systems for Liquid Extraction. Rugby: Institution of Chemical Engineers, 1985.

[2] Cahn, J.W. and Hilliard, J.E., “Free Energy of a Nonuniform System. I. Interfacial Free Energy”, Journal of Chemical Physics, vol. 28, pp. 258–267, 1958. doi:10.1002/9781118788295.ch4

[3] Koningsveld, R. and Kleintjens, L.A., “Liquid-Liquid Phase Separation in Multicomponent Polymer Systems. X. Concentration Dependence of the Pair-Interaction Parameter in the System Cyclohexane-Polystyrene”, Macromolecules, vol. 4, pp. 637–641, 1971. doi:10.1021/ma60023a026

[4] A. Kulaguin Chicaroux, T. Zeiner, Theoretical and experimental investigation of mass transfer in aqueous two-phase systems based on linear and branched polymers, Fluid Phase Equilib. 479 (2018) 106–113. doi:10.1016/j.fluid.2018.09.025.

[5] Kruber, K.F., Krapoth, M. and Zeiner, T., “Interfacial mass transfer in ternary liquid-liquid systems”, Fluid Phase Equilib., vol. 440, pp. 54–63, 2017. doi:10.1016/j.fluid.2017.02.013