Solubility of Sulfur in Hydrogen Sulfide and Sour Gases

Abstract

Description of Problem In recent years the search for natural gas has yielded many reserves that contain high concentrations of hydrogen sulfide. Production of sour gas initially was on a limited scale but since has increased considerably as a result of price increases for fossil fuels. Substantial quantities of sulfur now are produced from the hydrogen sulfide in these natural gas sources. In several of these natural gas fieldse.g., in Canada and north Germany-gas production is hampered severely due to the presence of elemental sulfur dissolved in the gas. The gas-bearing deposits are interspersed with elemental sulfur, which is dissolved to a greater or lesser extent in the sour gas, the solubility being strongly dependent on the pressure, temperature, and composition of the gas. It is well-known that the solubility of sulfur increases with increasing pressure, temperature, and hydrogen sulfide content. As a result of the geothermal temperature profile, the gas stream cools as it rises up the production tubing and there is a drop in pressure due to frictional effects. Consequently, the solubility drops and sulfur is deposited when the solubility limit is exceeded. The gases desolved in the liquid sulfur- principally hydrogen sulfide and carbon dioxide- lead to a lowering of the freezing point. At temperatures between 393.15 and 373.15 K, the sulfur begins to solidify in the line, blocking the tubing and bringing gas production to a standstill. To prevent such blockages, suitable solvents are pumped into the well via an annular space surrounding the production tubing to dissolve the sulfur, which then is carried to the surface with the gas stream. A discussion of the technological problems involved in this process is beyond the scope of this paper. It would be of great value and solving the problem associated with the production of sour natural gas to have more data on, among other things, the solubility of sulfur in compressed sour gases of various compositions over a range of temperatures and pressures. There is little literature on the solubility of sulfur in different natural gases. Kennedy and Wieland reported the results of measurements on the methane/carbon-dioxide/hydrogen-sulfide/sulfur system at pressures up to 40 MPa and temperatures up to 394.15 K Roof examined the solubility of sulfur in hydrogen sulfide up to 30 MPa and 383.15 K, but his results differ considerably from those of Kennedy and Wieland. Swift has published data on the solubility of sulfur in hydrogen sulfide at pressures between 35 and 140 MPa and temperatures between 394.15 and 450.15 K. Using a gas saturation method, we now have measured the solubility of sulfur in pure hydrogen sulfide and in four synthetic sour gas mixtures composed of H2S, CO2, CH4, and N2 in the temperature range of 373.15 to 433.15 K and at pressures up to 60 MPa. Solubility of Solids and Liquids in Compressed Gases It is particularly important that gas-phase fugacity coefficients be employed when calculating the solubility of a solid or a high-boiling liquid in a compressed gas. In general, these fugacity coefficients must be determined experimentally. Corrections for the nonideality of the gas phase, as are employed at lower pressures, can lead to completely erroneous results here. A consideration of both systems-solid/liquid and liquid/liquid is presented in the following. P. 377＾