Self-diffusion coefficients of the binary (H₂O + CO₂) mixture at high temperatures and pressures

An extensive study of the self-diffusion coefficients in the (H₂O + CO₂) mixture was carried out using atomistic molecular dynamics simulations. The conditions studied cover a wide range of temperatures (323.15 K ≤ T ≤ 1023.15 K) and pressures (200 MPa ≤ P ≤ 1000 MPa), of interest for geological and carbon sequestration applications. A combination of simple but accurate point charge force fields was employed, specifically the TIP4P/2005 for H₂O and EPM2 for CO₂. The simulations were found to be in good agreement with available experimental data at these high temperature and pressure conditions, but extend at conditions for which experiments have not been previously reported. The results were correlated with a generalized form of the Speedy-Angel (1976) relationship. The new phenomenological correlation is a function of pressure and temperature and is shown to reproduce all values to excellent accuracy. Thus, it can be used reliably for engineering calculations.