VAPOR-LIQUID-EQUILIBRIA OF THE TERNARY MIXTURE CH4+C2H6+CO2 FROM MOLECULAR SIMULATION

The NpT + test-particle method for the calculation of vapor-liquid equ ilibria by molecular simulations is extended to ternary mixtures. It i s applied to the system methane + ethane + carbon dioxide, for which a ll binary molecular interaction models are available from previous wor k. Methane is described as one-center Lennard-Jones fluid, ethane as t wo-center Lennard-Jones flui, and carbon dioxie as two-center Lennard- Jones plus point quadrupole fluid. The unlike interactions are treated in the same way as the binary mixtures, using two parameters for each binary interaction. No ternary parameters are introduced. Vapor-liqui d phase equilibria are calculated for the ternary mixture at the follo wing temperature-pressure pairs: 233.15 K-2 MPa; 250.5 K-2 MPa; and 25 0.5 K-3.04 MPa. Comparison of the simulation data with experimental an d equation-of-state results shows excellent agreement. Bubble and dew densities are also reported.