Transport and Equilibrium Properties of the CO ₂ + <i>n</i> -Butane Mixture Based on Molecular Simulation Data

A generalized molecular simulation-based framework for predicting thermodynamic equilibrium and transport properties of pure CO2, pure n-butane, and their binary mixture is presented. Fundamental Helmholtz energy equations of state are constructed on the basis of extensive molecular simulation data on residual Helmholtz energy derivatives, while ideal-gas contributions are taken from reference equations of state. The proposed simulation-based equations reproduce the underlying data well and can capture vapor–liquid and homogeneous equilibrium properties with good accuracy, except for n-butane. For the CO2 + n-butane mixture, the proposed equation of state reproduces homogeneous density data from experiments with an accuracy that is comparable to that of the GERG-2008 equation of state over most of the studied range of states, with larger deviations occurring only at high pressures and near the critical point. Shear viscosity and thermal conductivity are predicted with residual entropy scaling correlations coupled with the present simulation-based Helmholtz energy equation of state. All transport properties, including their zero-density limit contribution, required for residual entropy scaling parametrization, are sampled exclusively with molecular dynamics simulation. The present entropy scaling correlations reproduce the sampled transport properties of both pure fluids and the mixture, while also achieving shear viscosity accuracies comparable to other entropy scaling models that are based on experimental data. Pure CO2 and pure n-butane exhibit similar entropy scaling behavior, which propagates into the binary mixture. When compared to extensive experimental data sets for the pure fluids, these fully predictive correlations show deviations of about 12%, while maintaining physical consistency.