Study Water And Carbon Dioxide Systems By Molecular Simulation

An improved fully flexible fixed-point charges model for water has been developed to predict the vapor-liquid coexistence properties using the NVT-Gibbs ensemble Monte Carlo technique (GEMC) and the pressure in supercritical region. The average deviation between our simulation and experimental data for saturated liquid densities is 2.75% over temperature range of 314 to 609K. Comparing with experimental data for T_c, P_c andρ_c (P_c=220.064bar, T_c=647.096K, andρ_c=0.322g/cm³ for the experimental data), our calculated results (P_c=213bar, T_c=644.3K, andρ_c=0.325g/cm³ for our simulations) are acceptable and are better than those by the SPC-E and TIP4P models. The saturated pressure is calculated by evaluating the pressure of vapor from NPT-MD simulation at the coexistence vapor densities at the nominal temperature. The agreement of our simulated pressures of supercritical water at any density and temperature with the experimental values is excellent. The second virial coefficient and radial distribution function in ambient and supercritical conditions are also estimated. The radial distributions consist with experimental data very well.A folly flexible alterable -point charges model for carbon dioxide has been developed to predict the vapor-liquid coexistence properties using the NVT-Gibbs ensemble Monte Carlo technique (GEMC). The average deviation between our simulation and the literature experimental data for saturated liquid densities is 0.3%. Comparing with the experimental data for T_c, P_c andρ_c (P_c=7.3773MPa, T_c=304.13K, andρ_c=0.4676g/cm³ for the experimental data), our calculated results (P_c=7.39MPa, T_c=304.365 K, andρ_c=0.46673g/cm3 for our simulations) are good and are better than those by the EPM2 model. The agreement of our simulated saturated pressure and the pressures of supercritical water at any density and temperature with the experimental values are excellent. The radial distribution function in supercritical conditions is also estimated, which give that the carbon dioxide is a nonline molecule with the C=O bond length to be 1.17 A and the O=C=O bond angle to be 176.4°.The radial distributions consist with Car-Parrinello molecular-dynamics(CPMD) very well, but the EPM2 model shows large deviation.Finally, in this thesis phase coexistence properties of H₂O/CO₂ systems of interest for chemical industries were investigated using the NPT-Gibbs ensemble Monte Carlo (MC) simulations. Simulation results deviated from experimental data for the pressure-composition diagrams of the binary systems. And vapor density was compared to the density of pure CO₂.