Phase equilibrium and interfacial properties of water + methane mixtures

This work aims to use the density gradient theory (DGT) for one alkane-water mixture, namely the methane + water system, combined with the perturbed chain statistical associating fluid theory (PC-SAFT) in order to model phase behavior and interfacial properties, simultaneously. A new combining rule taking into account the temperature as well the composition dependency for the dispersion energy parameter is suggested. Applying this new combining rule leads to very good agreement between the modeled and the experimental solubility of water in methane as well as the solubility of methane in water. The solubility minimum of methane in water as function of temperature could be captured. The calculation of the surface tension was possible also in accordance to the experimental data, if a binary, temperature-independent influence parameter is used. Other calculated interfacial properties, which can not be measured, are in agreement with molecular simulation data and with theoretical results based on the density gradient theory in combination with the SAFT-VR-Mie approach.