Correlation for self-diffusion coefficients of H₂, CH₄, CO, O₂ and CO₂ in supercritical water from molecular dynamics simulation

Molecular dynamics simulations were employed for the calculation of self-diffusion coefficients of H₂, CH₄, CO, O₂ and CO₂ in supercritical water over a wide range of temperature (673–973 K) and pressure (250–280 atm). Based on our results, H₂ always diffuses the fastest while CO₂ diffuses the slowest, and self-diffusion coefficients of CH₄, CO and O₂ are between H₂ and CO₂. Temperature, density and viscosity of supercritical water are the main factors determining self-diffusion coefficient. Self-diffusion coefficient has an Arrhenius behavior in a certain temperature range. The term Dρ is independent of temperature and ln(Dη/T) has a linear relation with temperature. A new empirical equation is proposed as [Figure presented] to predict self-diffusion coefficient in supercritical water. The influence of the solute gas and solution supercritical water is divided into A₀ and F_scw, respectively. A₀ and exponential indexes of a, b, c are fitted from our calculation results. For all 75 data points, the average relative error between the results from simulation and this equation is only 4.40%.