(153f) Modelling of Phase and Interfacial Behavior of Ternary Mixtures
Karlsruhe Institute of Technology, Institute of Technical Thermodynamics and Refrigeration Engineering, Engler-Bunte-Ring 21, D-76131 Karlsruhe, Germany.
Key words: vapor-liquid equilibria, oil recovery, density gradient theory, interfacial tension, density profiles, PCP-SAFT-EOS
My stay at the TU Delft in the group of Applied Thermodynamics in 1996 inspired me to study interfacial phenomena. The reason for this situation was the well-known paper by Cornelisse, Peters and de Swaan Arons  dealing with the application of the density gradient theory in combination with the Peng-Robinson Equation of state (PR-model). In this paper, is written â??However, in the previous section it was concluded, that the scaling behavior of gradient theory with the PR model did not agree with the experiments. Although from the gradient theory interfacial tension calculations have been illustrated by examples for pure the carbon dioxide and carbon dioxide/butane system, the conclusions are believed to be generally applicable. This was assumed, because the error in the results is probably caused by the PR model. In any event, the results presented here demonstrate that accurate predictions will at least require an equation of state with proper scaling behavior in the critical region.â??
In the last twenty years, I studied phase- and interfacial properties related to different phase equilibria (liquid-liquid  or liquid-vapor ), different binary  and ternary mixtures  and the application of different equations of state (SAFT , PCP-SAFT [6,7], lattice cluster theory , Sanchez-Lacombe ).
The interfacial properties play an important role in the field of oil recovery and in separation technology, especially for extraction. In this contribution the phase equilibria and the involved interfacial properties for binary and ternary mixture representing the situation for oil recovery will discussed, where the focus is the dependence of interfacial properties, like interfacial tension and relative enrichment in the interface, on pressure. Additionally, the impact of sulphur containing components, like H2O and SO2, on the interfacial tension will be discussed . For the investigation of this effect, thermodynamic modelling is very important, because no experimental data are available in the public literature. The following ternary mixtures: CO2+H2S+CH4, CO2+H2S+C7H16, CO2+SO2+CH4, CO2+SO2+C7H16 were investigated over a large pressure and temperature range. It turns out that the presence of the sulfur containing molecules leads to a decrease of the interfacial tension in comparison to the corresponding binary system  at the same temperature and pressure. At low pressures, CO2 as well as H2S will enriched at the interface in the CO2+H2S+C7H16 mixture, where the enrichment effect of CO2 is more pronounced.
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