Development of SAFT-based heteronuclear fused coarse-grained models of short alkanes and their mixtures with carbon dioxide and nitrogen.

Coarse-grained models for short n-alkanes were developed that capture the vapor-liquid equilibria of both their pure components and their mixtures with carbon dioxide (CO2) and nitrogen (N2) over a wide range of temperatures and pressures. We utilized an equation of state, namely Statistical Associating Fluid Theory (SAFT), in which chain models were composed of fused segments interacting via the Mie potential, parameterized according to group contribution principles. The molecular parameters predicted by SAFT were used as initial guesses to determine the necessary adjustments to make these models suitable for molecular simulations, helping to reduce the complexity of the optimization problem, and adjustments were made by expanding our methodology [Chremos et al., J. Phys. Chem. B 129, 3443 (2025)] developed on homonuclear diatomic molecules to heteronuclear chain models. We performed Wang-Landau transition-matrix Monte Carlo simulations in the grand canonical ensemble, ranging from methane up to n-hexane, and evaluated the phase behavior. The mixtures of short n-alkanes with CO2 and N2 were also investigated with the Gibbs ensemble at constant pressure. In addition, we also developed SAFT-γ Mie parameters for N2 mixtures with n-alkanes. The performance of our coarse-grained models was further evaluated in ternary mixtures. Overall, we found excellent agreement over a wide range of temperatures and pressures in pure components and mixtures. Our findings establish the foundations for a group contribution framework for thermodynamically consistent coarse-grained models.