Transport property of hydrogen sulfide in amorphous polyethylene using grand canonical Monte Carlo and molecular dynamics simulations

Abstract

H2S corrosion poses a significant hurdle to safely transporting sulfur-containing natural gas through metal gathering pipes. Reinforced thermoplastic composite pipes have emerged as a solution, using the polyethylene inner lining layer that resists H2S corrosion. However, the permeation of H2S in the polyethylene may lead to the failure of reinforced thermoplastic composite pipes, resulting in natural gas leakage and environmental pollution. Therefore, it is crucial to investigate the gas transport properties of H2S in polyethylene materials to ensure the reliable functioning of gathering pipes. In this study, the dissolution behavior of H2S for pure H2S and H2S/CH4 mixture in amorphous PE is investigated using the grand canonical Monte Carlo method in conjunction with the NPT, with consideration given to the swelling effect. In addition, the diffusion characteristic is explored through the NVT on the amorphous PE adsorbing H2S. Subsequently, the permeability coefficient is calculated based on the obtained data. The findings reveal that with as the temperature increases, the solubility coefficient decreases, while both the diffusion and permeability coefficients increase. With increasing pressure, both the diffusion and permeability coefficients increase. Additionally, the above three coefficients all increase with increasing H2S mole fraction. The relationships between solubility, diffusion, and permeability coefficients & temperature all conform to the Arrhenius law. Finally, the diffusion mechanism of H2S in amorphous PE is revealed at the microscopic level as the “jumping” mechanism by tracking the diffusion pathway of H2S molecule.