Molecular Dynamics Simulation of the Three-Phase Equilibrium Line of CO(2) Hydrate with OPC Water Model.

The three-phase coexistence line of the CO(2) hydrate was determined using molecular dynamics (MD) simulations. By using the classical and modified Lorentz-Berthelot (LB) parameters, the simulations were carried out at 10 different pressures from 3 to 500 MPa. For the OPC water model, simulations with the classic and the modified LB parameters both showed negative deviations from the experimental values. For the TIP4P/Ice water model, good agreement with experimental equilibrium data can be achieved when the LB parameter is adjusted based on the solubility of CO(2) in water. Our results also show that the influence of the water model on the equilibrium prediction is much larger than the CO(2) model. Current simulations indicated that the H(2)O-H(2)O and H(2)O-CO(2) cross-interactions' parameters might contribute equally to the accurate prediction of T(3). According to our simulations, the prediction of T(3) values showed relatively higher accuracy while using the combination of TIP4P/Ice water and EPM2 CO(2) with modified LB parameter. Furthermore, varied χ values are recommended for accurate T(3) estimation over a wide pressure range. The knowledge obtained in this study will be helpful for further accurate MD simulation of the process of CO(2)/CH(4) replacement.