The Solubility of Solid Hydrogen Sulfide in Methane

Hydrogen sulfide, H2S, is one of the most common contaminants of natural gas and can pose a variety of problems to the operation of liquefied natural gas (LNG) plants including the potential to freeze-out and block the main cryogenic heat exchanger. There are, however, very few data available that can be used to estimate the conditions under which solid H2S formation can occur in LNG plants. Here, we detail the construction of a new, liquid nitrogen-cooled, high-pressure synthetic visual apparatus to address this data gap at LNG-relevant conditions. New solid–fluid equilibrium (SFE) measurements of binary mixtures of H2S + CH4 at temperatures from 112 to 168 K with pressures of up to 4.8 MPa are reported. Together with critically assessed literature data, the new measurements were then used to develop a thermodynamic model for the solubility of solid H2S in CH4 implemented in the freely available software package ThermoFAST. The new model, which performs nearly an order of magnitude better than the default one, can represent almost all the SFE data within their reported uncertainty, with an AADT of 0.3 K. In addition to improving the thermodynamic description of this binary system, these outcomes improve the ability of LNG plant designers and operators to assess and avoid the risk of H2S freeze-out.