The pure water phase equilibrium is calculated over a wide
temperature range using the Gibbs ensemble
Monte Carlo method with simple two-body molecular models. The
Ewald summation method is used to
account for the long-range Coulombic interactions. Coexisting
liquid and vapor densities and vapor pressure
at different temperatures are calculated explicitly. A new
expression is developed for the direct calculation
of pressure suitable for systems where the Ewald method is used.
To improve agreement with experimental
data, a simple scaling procedure is proposed that allows
reparametrization of the molecular models without
the need for additional calculations. Critical constants, second
virial coefficient, and heat of vaporization are
calculated from the different models. Finally, water structure is
examined at low and high temperature. In
all cases, comparison with experimental data is shown.
Monte Carlo simulations were used to calculate water−methane and water−ethane phase equilibria over a
wide range of temperatures and pressures. Simulations were performed from room temperature up to near
the critical temperature of water and from subatmospheric pressure to 3000 bar. The Henry's law constants
of the hydrocarbons in water were calculated from Widom test particle insertions. The Gibbs ensemble
Monte Carlo method was used for simulation of the water-rich and hydrocarbon-rich phases at higher pressures.
Two recently proposed pairwise additive intermolecular potentials that describe accurately the pure component
phase equilibria were used in the calculations. Equations of state for 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 simulation-based predictions of the mutual
solubilities are accurate within a factor of 2, which is comparable with the accuracy of the best equations of
state.
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