Investigation of H₂S Diffusion in Transcritical and Supercritical Water: A Molecular Dynamics Simulation Study

In supercritical water (SCW) gasification technologies, H₂S is one of the important intermediate products. Studying the self-diffusion coefficient of H₂S in subcritical water and SCW can help us better understand the mass transfer characteristics. In this work, we used the molecular dynamics method to simulate the diffusion behavior of H₂S in the H₂S-H₂O system and calculated the self-diffusion coefficient of H₂S under different conditions (pressure: 235-280 atm, H₂S molar concentration: 1-5%, temperature: 600-1173 K). The result shows that the molar concentration and pressure of H₂S have little effect on its self-diffusion coefficient, but temperature and water density have a greater effect on it. In addition, the self-diffusion activation energy of the supercritical region of H₂S is only 32.58% of the subcritical region. Finally, we fitted new parameters of the empirical equation to predict the self-diffusion coefficient of H₂S in the H₂S-H₂O system, whose mean relative error in the supercritical region is 3.05%.