Atomistic molecular dynamics simulations of H 2O diffusivity in liquid and supercritical CO 2

Molecular dynamics simulations were employed for the calculation of diffusion coefficients of pure CO₂ and of H₂O in CO₂ over a wide range of temperatures (298.15 K < T < 523.15 K) and pressures (5.0 MPa < P < 100.0 MPa), that are of interest to CO₂ capture-and-sequestration processes. Various combinations of existing fixed-point-charge force-fields for H₂O (TIP4P/2005 and Exponential-6) and CO₂ (elementary physical model 2 [EPM2], transferable potentials for phase equilibria [TraPPE], and Exponential-6) were tested. All force-field combinations qualitatively reproduce the trends of the experimental data for infinitely diluted H₂O in CO₂; however, TIP4P/2005-EPM2, TIP4P/2005-TraPPE and Exponential-6-Exponential-6 were found to be the most consistent. Additionally, for H₂O compositions ranging from infinite dilution to, the Maxwell-Stefan diffusion coefficient is shown to have a weak non-linear composition dependence.