Density Functional Theory Investigation of the Sulfur-Iron Compound Formation Mechanism in Petrochemical Facilities.

In order to investigate the formation mechanism of hydrogen sulfide corrosion products in petroleum and petrochemical facilities, the interaction mechanism between iron oxides and H2S was studied by density functional theory (DFT). First, the adsorption of H2S on Fe2O3 clusters and Fe3O4 clusters was studied. The results indicated that H2S was more inclined to adsorb on the Fe site. After adsorption, the S-H bond changed from 1.356 to 1.360 Å in the gas phase, which was the main reason for the decomposition of H2S. On this basis, the reaction paths of Fe2O3 clusters and Fe3O4 clusters with H2S and the rate-determining steps of different reaction paths were calculated. The thermodynamic parameters and kinetic parameters of the rate-determining step of each path are analyzed. The results indicated that reaction path 1 of H2S and Fe2O3 clusters is the best reaction channel. The reaction will gradually form products such as S, H2O, and Fe2S2, which can release a total of 622.23 kJ/mol heat. The reaction path 2 of H2S and Fe3O4 clusters is the best reaction channel. The reaction will gradually form products such as S, H2O, and Fe3S2, which can release a total of 260.40 kJ/mol heat. Finally, the reaction paths of Fe2S2, Fe3S2, and S2 were further calculated, and it was observed that the products formed by hydrogen sulfide corrosion were easy to react with S2 to form sulfur-iron compounds with different iron-sulfur ratios. This is consistent with the corrosion products including FeS, FeS2, and Fe3S4 observed in the experiment. It lays a theoretical foundation for the subsequent study of the effect of associated elemental sulfur on the spontaneous combustion of sulfur-iron compounds.