A predictive model for self-, Maxwell-Stefan, and Fick diffusion coefficients of binary supercritical water mixtures

Self-, Maxwell-Stefan, and Fick diffusion coefficients of binary supercritical water mixtures (species 1: H₂O, species 2: H₂, CH₄, CO, O₂, CO₂) at 673-973 K and 250 atm were calculated by molecular dynamic simulations using mean-squared displacement, Onsager coefficient, and thermodynamic factor. The mole fraction of species 2 is from 1% to up to 30%. The results show that self- and Maxwell-Stefan diffusion coefficients are largely determined by temperature and mole fraction. Despite the small fluctuations, Fick diffusion coefficient can be treated as a constant at certain temperature of a binary mixture regardless of mole fraction. We developed a general predictive model for different types of diffusion coefficients of binary supercritical water mixtures. Shared modification factors for equations are defined in this model. Overall, the average deviation for our predictive model is 4.15%