Solubility of Sulfur in Hydrogen Sulfide and in Carbon Disulfide at Elevated Temperature and Pressure

Abstract

Abstract The solubility of sulfur in hydrogen sulfide has been determined by an absolute method at 21 combinations of pressure and temperature within the range of 1,020 to 4,520 psia and 110 deg. to 230 deg. F. respectively. Results, which appear to be consistent within about 2 percent, show the solubility to increase with pressure along an isotherm but to pass through maxima along isobars. Where direct comparison can be made, our values differ drastically from published results at lower pressures and are in serious disagreement at higher pressures. The solubility of sulfur in carbon disulfide is reported for pressures from 1,020 to 5,020 psia at 150 deg. F. No published data were found for direct comparison. Both the solubility of sulfur and the density of saturated solutions decrease with increasing pressure at this temperature. Introduction Difficulties in production arise when a fluid containing a high content of hydrogen sulfide occurs in a reservoir in which elemental sulfur is present Changes in pressure and temperature present Changes in pressure and temperature can cause deposition of dissolved sulfur from hydrogen sulfide-rich fluids in both the formation and the production tubing. The first step in a study of this problem is to determine the solubility of sulfur in pure hydrogen sulfide under conditions of interest in production. This report presents results of one such study. Values published in the literature generally appear to be grossly in error. In some approaches to repairing the damage caused by sulfur plugging of formation and tubing, carbon disulfide is used as a solvent. Experiments were run at a typical temperature of 150 deg. F and elevated pressure to obtain basic data on the solubility of sulfur in carbon disulfide. SOLUBILITY OF SULFUR IN HYDROGEN SULFIDE EQUIPMENT AND MATERIALS Except for the items described, the equipment used in this study was of the type commonly found in a high-pressure laboratory. A schematic sketch of the equipment is show in Fig. 1. The equilibrium vessel was a thin-walled Teflon bag machined from solid bar stock to the shape indicated in Fig. 1. The bag, of a design suggested by R. H. Arntson, Shell Development Co., was approximately 2.25 in. OD and 5.9 in. long, with a wall thickness of 0.045 in. A split ring around the upper flange pulled the tapered neck of the bag snugly onto the projecting cone of the pressure vessel to seal against the mercury surrounding the bag. Two-way Valve B was used to shut off the pressure vessel from the crossline between Valves pressure vessel from the crossline between Valves A and C. Valve B was designed to have minimal dead volume below the Teflon washer packing. Sulfur was caught for weighing in a special glass trap, also shown in Fig. 1. This vessel was made of 35-mm OD pyrex Tubing and was about 7.5 in. in length. Each end terminated in precision-ground 0.25-in. tubing to accept Swagelok fittings. Each chamber included a coarse glass frit at its downstream end and was loosely filled with glass wool. Pressure was measured on a Heise gauge, which had been calibrated against an Aminco dead-weight gauge. Uncertainties in pressure should seldom exceed 5 psia. The pressure differential across the wall of the Teflon bag fell within this uncertainty in pressure. Temperature in the pressure vessel was measured by a tubular iron-constantan thermocouple inserted into a small hole in the bottom of the vessel. Emf of the couple was measured on a Rubicon potentiometer. The thermocouple had been calibrated potentiometer. The thermocouple had been calibrated against a platinum resistance thermometer. Uncertainties in temperature probably were not greater than 1 deg. F. A Thermotrol was used to control the temperature of the air thermostat. Both the precipitated sulfur and the carbon disulfide were Baker's Analyzed grade. SPEJ P. 272