Solubility evolution of elemental sulfur in natural gas with a varying H₂S content

The solubility variations of elemental sulfur are of great importance in the prevention of sulfur deposition during the development of high-sulfur gas formations. It has been observed that the solubility varies with H₂S content, which is the main solvent of elemental sulfur in natural gas. Moreover, the addition of small amounts of CH₄ and/or CO₂ in H₂S leads to a dramatic solubility reduction of which the mechanism remains unclear. Using a modified direct coexistence method, molecular dynamics simulations are conducted to uncover the molecular mechanism of the solubility reduction. The observed solubility variations with H₂S content are reproduced, and the solubility reduction is interpreted by the antisolvent effect of CH₄ and CO₂. While the H₂S content varies in a wide range in the known high-sulfur gas formation, our simulations provide useful information for controlling the sulfur deposition in gas development.

Molecular dynamics simulations are carried out using the LAMMPS package. The initial models are constructed with the Packmol software. The Ballone and Jones’ potential is used for S₈, the Galliero’s potential for H₂S and CO₂, and the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field for CH₄. The time step is set to 1 fs, and the molecular trajectories of additional 2 ns after equilibrium are collected for analysis.