Determination of the solubility, diffusion coefficient and hydrate stability of hydrogen sulfide in water and brine

The dissolution and diffusion process of hydrogen sulfide (H₂S) in aqueous solutions are critical in the formation of many metal deposits and the stability of H₂S hydrate also play an important role in natural gas exploitation and transportation due to the tendency of H₂S to form hydrate at low temperature and high pressure, which can lead to pipeline blockage. In this study, the solubility and diffusion coefficient of H₂S in water and brine as well as the stable conditions of H₂S hydrates have been determined using fused silica capillary cell, high pressure optical cell, high pressure reactor, and Raman spectrometers.The details are as follows: (1) H₂S solubility data in water were obtained at temperatures up to 573 K and pressures up to 100 MPa. These new data extend the predictable range of previous models. (2) The diffusion coefficients of H₂S in water at 0.1–2 MPa and 273.1–373.1 K and in four brine solutions (0.62, 1, 2, and 3 mol•kg⁻¹ NaCl) at 1 MPa and 273.1–373.1 K were determined. The results showed that the diffusion coefficient increased with the temperature and was inhibited by salinity. (3) The stability of H₂S hydrate in water and brine including NaCl, KCl, MgCl₂, NH₄Cl, Na₂SO₄ and K₂SO₄ at the temperature range from 273.4 to 298.8 K, pressure ranging from 1.13 to 21.90 bar, and salinity from 3.4-20.0 wt.% were investigated. The results showed that the inhibitory effect of six electrolytes on H₂S hydrate formation is in the order of MgCl₂ > NH₄Cl > NaCl > KCl > Na₂SO₄ = K₂SO₄.