Molecular models for phase equilibria of alkanes with air components and combustion products I. Alkane mixtures with nitrogen, CO2 and water

The paper is the first of a series of two articles on molecular models for alkanes with air components and combustion products. This article reports simulations of the vapor-liquid equilibrium phase diagram for mixtures of linear hydrocarbons with nitrogen, carbon dioxide and water. We consider four alkanes: methane, propane, octane and dodecane as characteristic components of natural gas, liquefied natural gas, gasoline and kerosene. Combustion products are presented with common computationally inexpensive molecular models: three-center models for N2 and CO2, TIP4P-2005 model for water, and united-atom forcefield for alkanes. The parameters for nitrogen, CO2 and water oxygen interactions with CH2 and CH3 groups are calculated with Lorentz-Berthelot mixing rules with an adjustable coefficient for the energy parameter ε, a single temperature-independent coefficient for each non-alkane component. We obtained very reasonable agreement with the experimental data for most alkane-nitrogen and alkane-carbon dioxide binary mixtures and discuss in detail the capability of the models with unified adjustable parameters. For dodecane-water system, reasonable agreement between calculated solubility of water in dodecane and experimental data was obtained; the model however is unable to represent the near-critical and high pressure phase boundaries.