Unveiling the effect of H2S concentration in CH4 hydrate formation and growth: A molecular dynamics study

Abstract

We used molecular dynamics method to simulate the formation and growth of CH4 hydrates with different concentrations of H2S. At the large scale of simulation time, 10000 ns, it is unlikely to form hydrates at 10 MPa and 260 K if there are only CH4 and water; and if there was a small proportion of H2S in the gas, hydrates would easily form. When the molar concentration of H2S in the gas is 1 %, the formed hydrate is unstable and will eventually disintegrate, leaving the box in a two-phase state of gaseous and liquid. In contrast, at molar concentrations of 5 % or higher of H2S, hydrate formation is accelerated, and the hydrate will grow continuously. However, it is not structure I type as expected. These views are supported by the changes in F3 and F4 order parameters, numbers of different cage types, and the number of water molecules belonging to different states. Moreover, since the formation of hydrates is an energy reduction process, we can easily develop inhibitors targeted at hydrates in actual production and gas transportation. According to IGMH analysis, only van der Waals interactions occur between gas molecules inside the cages and the water cage.