Determining diffusion coefficients of oxygen in supercritical water with molecular dynamics

The supercritical water oxidation is a significant way for the waste disposal. The diffusion of the oxygen in the water at the infinite dilution is simulated at 300 K and 1 atm, and 650 K, 673 K, 773 K, 873 K, 973 K, and 250 atm with the molecular dynamics software. The mean squared displacement method is used to calculate the diffusion coefficient. At 300 K, 1 atm, our calculation gives 0.20 ? 10?8 m2/s, which is very near to three empirical equations. When the condition is beyond the critical point, these empirical equations lost their accuracy, and only Kawasaki-Oppenheim equation can be compared to our calculation results. At supercritical conditions, we illustrate the diffusion coefficients with the Arrhenius equation and the activation energy is 22.54 kJ/mol.