Gas Hydrates of Hydrogen Sulfide-Methane Mixtures

Abstract

Experimental data are presented for hydrate formation conditions for mixtures of hydrogen sulfide and methane. Vapor-solid equilibrium constants for hydrogen sulfide are also presented. Equilibrium constants, defined here as the ratio of the mole fraction of hydrogen sulfide in the vapor phase (dry basis) to the mole fraction of hydrogen sulfide in the solid phase (dry basis), were calculated using the vapor-solid equilibrium constants for methane presented in an earlier paper. The conditions at which a natural gas will form gas hydrates with water may be computed from its composition, when hydrogen sulfide is present in addition to carbon dioxide and the paraffin hydrocarbons.IntroductionMany gases are known to form solid hydrates in the presence of liquid water at temperatures above 32°F. This hydrate formation is of importance to the natural gas industry inasmuch as most of the constituents found in natural gases will form hydrates. The attention of the industry was called to hydrates by Hammerschmidt in 1934. A number of papers have been written giving the temperatures and pressures at which these hydrates will form and a bibliography on the subject has been compiled. Deaton and Frost report work for various pure gases and for some natural gases. Katz and co-workers have reported data for various gases at high pressure. They developed a method of predicting conditions for hydrate formation from equilibrium constants and from gas gravity. The effects of anti-freeze agents on the formation of hydrogen sulfide hydrate were reported by Bond and Nelson. The hydrogen sulfide-water system, including hydrate, has been the subject of recent investigation by Sage and co-workers.Mixtures of hydrates behave as solid solutions and an equilibrium exists between the vapor phase and the solid phase that appears to be comparable to the equilibrium between vapor and liquid phases. By means of the vapor-solid equilibrium constants which have been published for methane, ethane, propane, isobutane, and carbon dioxide it is possible to determine the temperature and pressure at which hydrates will form for a specific gas mixture when water is present.