Transferability of cross-interaction pair potentials: Vapor-liquid phase equilibria of n-alkane/nitrogen mixtures using the TAMie force field

The van der Waals contribution of force fields designed for calculating phase equilibria and thermodynamic properties are usually adjusted to experimental data of pure components. Using these force fields for mixtures by applying combining rules for the cross-wise interaction potentials does not always lead to satisfactory results. This study considers the cross-wise van der Waals energy parameters εαβ among individual pairs of (united-)atom groups as adjustable (but subsequently transferable) parameters. The cross-energy parameters are simultaneously adjusted to an experimental training set of several mixtures. An analytic equation of state, the Perturbed-Chain Polar Statistical Associating Fluid Theory (PCP-SAFT), is used for ensuring very swift convergence of the optimization procedure. As an example, we consider the phase equilibria of n-alkane/nitrogen mixtures. The cross-energy parameters (-CH3 to N and -CH2- to N) are adjusted to three mixtures as the training set. We explore the transferability of the so-obtained force field for varying temperatures and for mixtures that were not considered in the training set. Phase equilibria of nine n-alkane/nitrogen mixtures (each at various temperatures) are determined using Monte Carlo simulations in the grand canonical ensemble. Results for vapor-liquid equilibrium calculations show very good agreement with experimental data.