Modeling the Surface Tension and Interfacial Density Profiles (CH4+n-Alkane) Mixtures with the Gradient Theory + PC-SAFT EoS

The main aim of the present study is to overcome the limitations of the gradient theory for binary mixtures of (CH4+n-alkane). To achieve this aim, the gradient theory of the interface was combined with the perturbed chain statistical association fluid theory equation of state to model the Surface Tension (SF) of the (CH4+n-alkane) system. Two methods were applied to the surface tension calculations. The first method used the constant-value Influence Parameter (IP) while the second method used the Influence Parameter (IP) in terms of the densities of bulk liquid and vapor phases. For accurate prediction of surface tension, the phase equilibrium calculations were improved by fitting binary interaction (BI) parameters. The overall deviation of phase equilibrium calculations was 3.81%. To distinguish the predictive aspects of the model, the binary interaction parameters of the IP were set equal to zero. The results of the model proved that the predictions of both methods agree well with experimental surface tensions, especially for high pressures at which the values of surface tension are very low. The overall Average Absolute Deviations (AADs) were 5.76% and 6.00% for these two methods, respectively. This model is needless of temperature-dependent binary interaction and influence parameters which can be considered as overcoming the limitations of the previous studies.