An investigation of some H2S thermodynamical properties at the water interface under pressurised conditions through molecular dynamics

K Ofori and CM Phan and A Barifcani and S Iglauer, MOLECULAR PHYSICS (2021).

DOI: 10.1080/00268976.2021.2011972

Geo-sequestration of hydrogen sulphide in geological formations is a disposal method with potential economic benefits. The process is governed by among other things, variables such as the water-H2S interfacial tension, H2S absorption into water and H2S adsorption onto water. However, the influence of pressure on these parameters is poorly understood. This study investigates these parameters as functions of pressure and temperature via molecular dynamics (MD) simulations. Simulations were carried out for the isotherms 40, 70 and 120 degrees C and a pressure range of 0.45-15 MPa. A comparison was made against N-2-water systems to clarify the effects of adsorption on interfacial tension, gamma. The predicted water-H2S interfacial tension and phase densities below H2S saturation pressure matched experimental values well. The adsorption can be quantified via the interfacial thickness, delta, which correlated well with the H2S pressures. Above the H2S saturation pressure, the interfacial thickness remained constant, which indicated a saturation of H2S at the water surface. Further increment of pressure above saturation revealed a significant absorption of H2S. The molecular analysis indicated the main binding interaction is between O of water and H of H2S, instead of S and H of water due to the electronegativity of the water O atom.

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