MOLECULAR SIMULATION OF PHASE-EQUILIBRIA FOR WATER-METHANE AND WATER-ETHANE MIXTURES

Monte Carlo simulations were used to calculate water-methane and water -ethane phase equilibria over a wide range of temperatures and pressur es. Simulations were performed from room temperature up to near the cr itical temperature of water and from subatmospheric pressure to 3000 b ar. The Henry's law constants of the hydrocarbons in water were calcul ated from Widom test particle insertions. The Gibbs ensemble Monte Car lo method was used for simulation of the water-rich and hydrocarbon-ri ch phases at higher pressures. Two recently proposed pairwise additive intermolecular potentials that describe: accurately the pure componen t phase equilibria were used in the calculations. Equations of state f or associating fluids were also used to predict the phase behavior. In all cases, calculations were compared with experimental data. For the highly nonideal hydrogen bonding mixtures studied here, molecular sim ulation-based predictions of the mutual solubilities are accurate with in a factor of 2, which is comparable with the accuracy of the best eq uations of state.