265185 Prediction of Interfacial Tensions Between Demixed Solvents

Tuesday, October 30, 2012: 4:20 PM
414 (Convention Center )
Tommy Grunert and Sabine Enders, Thermodynamics and Thermal Engineering, TU Berlin, Berlin, Germany

The interfacial tension between demixed fluids plays an important role in many applications ranching from extraction over extractive distillation to interfacial chemical reactions. All of these processes require mass transport over the formed interface in a ternary system. Selective enrichment of one component in the interface can have a large impact on the mass transport. Unfortunately, the concentration profile in the interface can not be obtained by experimental investigations. For this reason, a theoretical framework can be helpful for the design and optimization of these processes.

Interfacial properties can be handled using the density gradient theory[1], where the Helmholtz-energy of the inhomogeneous system is developed in a Taylor series. This theory was developed for the description of the interface established between a liquid and a vapor phase. At constant temperature and pressure the densities and the composition will be changed during this interface. If it is assumed that the equilibrium between two liquid phases (LLE) does not depend on pressure then only the concentration will be changed during the interface between demixed liquids. Using this approach for binary mixtures the density gradient theory can also applied for the description of the interface caused by the LLE[2]. In this situation the density gradients will be replaced by the concentration gradients and the Helmholtz-energy by the Gibbs- energy.

In the suggested contribution this theoretical framework of binary systems is extended to more relevant ternary systems. The two selected ternary systems (system 1: water + butan-1-ol + ethanol; system 2: water + acetone + toluene) show one demixing gap starting from one binary sub-system. The first step in the theoretical framework is the calculation of the corresponding LLE using the Koningsveld-Kleintjens[3] model. For these systems the final equation for the interfacial tension contains only one adjustable parameter. This parameter is fitted to the interfacial tension of the corresponding binary subsystem. The predicted interfacial tensions of the ternary system are compared with experimental data from the literature[4] and with own experimental data obtained by spinning drop measurements. Both systems differ in the enrichment behavior. Whereas ethanol will be enriched in the interface to a small amount, the enrichment of acetone is much more pronounced.

[1] J.W. Cahn, J.E. Hilliard, J. Chem. Phys. 28 (1958) 258-267.

[2] S. Enders, K. Quitzsch, Langmuir 14 (1998) 4606-4614.

[3] R. Koningsveld, L.A. Kleintjens, Macromolecules 4 (1971) 637-641.

[4] T. Misek, R. Berger: Standard Test Systems for Liquid Extraction, Rugby, England, 1985.

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See more of this Session: Fundamentals of Interfacial Phenomena III
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