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: H-2, CH4, CO, O-2, 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% for all types of diffusion coefficients (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

By using molecular dynamic simulations, diffusion coefficients of binary supercritical water mixtures (species 1: H2O, species 2: H-2, CH4, CO, O-2, CO2) at high temperatures and pressures were calculated, showing that temperature and mole fraction play significant roles in determining self- and Maxwell-Stefan diffusion coefficients, while Fick diffusion coefficient can be considered constant at certain temperatures in binary mixtures. Overall, a general predictive model with shared modification factors for equations was developed.