(179a) Modeling of Interfacial Properties and Mass Transfer at Elevated Pressure

The phase behavior and interfacial properties of systems at elevated pressure are essential for key industrial processes in the context of energy transition, such as the storage of methane, CO₂ or hydrogen. The application of rigorous thermodynamic models allows for the determination of interfacial properties and the mass transfer in these systems and are required for the simulation of the respective scenarios.

This study investigates interfacial properties and mass transfer in binary mixtures of CO₂ with solvents of different polarity at sub- and supercritical conditions. The insights gained from this study are used as basis for developing a model framework to study fundamental interfacial phenomena in vapor-liquid and liquid-liquid systems. As model liquids, n-dodecane, n-butanol and water are chosen to represent applications in subsurface as well as environmental processes such as gas storage in aquifers and depleted hydrocarbon reservoirs. In particular, the accurate prediction of interfacial properties is imperative for modeling the interfacial mass transfer and to alleviate the experimental effort for process equipment design.

The corresponding binary phase equilibria are initially described using the PCP-SAFT equation of state [1,2]. The interfacial properties, particularly the interfacial tension and density profiles perpendicular to the interface, are modeled by combining PCP-SAFT with the density gradient theory (DGT) [3]. This also allows for the estimation of the enrichment of surface-active components at the interface, which can significantly influence the interfacial mass transfer [4]. To validate the model, it is compared with experimental data of the temperature-dependent interfacial tension, which is determined using the pendant drop method in a high-pressure measuring cell [5]. The interfacial mass transfer is then modeled by combining PCP-SAFT with the dynamic DGT [6], which considers the gradient of the chemical potential as driving force for diffusion. For that purpose, we extend our established model framework [4] from incompressible liquid-liquid systems to compressible vapor-liquid systems, whereby the change in density during the diffusion is explicitly accounted for by PCP-SAFT.

In this contribution, we present the modeling results for interfacial properties at equilibrium as well as the interfacial mass transfer. The predictivity of the model is evaluated based on our own experimental data for the interfacial tension for system pressures up to 30 MPa. Furthermore, we discuss the influence of the interfacial enrichment of surface-active components on the mass transfer, based on the dynamic DGT modeling results.

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[2] J. Gross, AIChE J. 51 (2005) 2556-2568.

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

[4] R. Nagl, T. Zeiner, P. Zimmermann, Chem. Eng. Process. - Process Intensif. 171 (2022) 108501.

[5] S. Knauer, M.R. Schenk, T. Köddermann, D. Reith, P. Jaeger, J. Chem. Eng. Data 62 (2017) 2234-2243

[6] E.B. Nauman, N.P. Balsara, Phase equilibria and the Landau-Ginzburg functional, Fluid Phase Equilib. 45 (1989) 229–250.