Ind. Eng. Chem. Res. 2007, 46, 1421-1430
1421
Enthalpy and Solubility Data of H2S in Water at Conditions of Interest for Geological Sequestration Diana Koschel, Jean-Yves Coxam,* and Vladimir Majer Laboratoire de Thermodynamique des Solutions et des Polyme` res, UniVersite´ Blaise Pascal Clermont-Ferrand/ CNRS, 63177 Aubie` re, France
The dissolution of hydrogen sulfide in water was studied by measuring the heat of mixing ∆Hmix at conditions of interest for geologic storage of acid gases in deep aquifers. The measurements were performed with a new mixing unit equipped with a Hastelloy tubing, developed specifically for an isothermal differential heat flux calorimeter of Setaram. The heats of mixing were determined at target temperatures of 323, 353, and 393 K and pressures up to 31 MPa in the regions where the solution is unsaturated or saturated by H2S, that is, gaseous, liquid, or supercritical states. The concentration dependence of ∆Hmix allowed the simultaneous determination of the limiting enthalpy of solution ∆Hsol and the gas solubility limit. The agreement between our solubility results and the data from the direct phase equilibrium measurements reported in literature was good. Although no calorimetric data exist for verifying the correctness of ∆Hsol values, their internal consistency was tested by conversion to the low pressure enthalpies of hydration ∆Hhyd. These values agreed reasonably well with those derived from the temperature derivative of the Henry’s law constants calculated from representative correlations in the literature. The solubility and enthalpic data for aqueous H2S as a function of temperature and pressure were compared with analogous data for CO2 in water that we have published earlier. Introduction Hydrogen sulfide, H2S, is a gas encountered in biochemical processes and abundant in geological fluids, presenting, however, serious hazards when liberated in important quantities. It is a dangerous irritant and toxin and is harmful in elevated concentrations for living organisms. When penetrating the groundwaters, it makes them undrinkable, and when spreading in air, it forms a poisonous and explosive mist. Hydrogen sulfide is together with carbon dioxide a constituent of natural gas with concentrations achieving at certain sites several tens of percent. The separation of these gases from methane and other hydrocarbons is an important step in the treatment of a natural gas at the production site before transport. The usual practice was to produce sulfur from the captured H2S, but this is not actually an economically viable procedure. The petroleum industry therefore explores intensely the possibilities of geological storage in depleted oil and gas reservoirs, unminable coal beds, or in deep saline aquifers. It is namely this last option that offers high capacity of storage and is actively explored for sequestrating both carbon dioxide and hydrogen sulfide. The data on the solubility of these gases in aqueous systems under pressure and the heat effects during dissolution are therefore of direct interest for the development of these processes. It is expected that the temperatures typically encountered in deep aqueous reservoirs are up to 423 K and occasionally to 473 K, and the gas is introduced at high pressures that may reach up to 80 MPa. While the data on the solubility of carbon dioxide in water and also in salt solutions under pressure are relatively abundant, information on the solubility of hydrogen sulfide as a function of temperature and pressure is much more limited. Table 1 reports the primary literature sources concerning the system hydrogen sulfide-water over extended ranges of temperatures and pressures. The sources containing exclusively experimental * To whom correspondence should be addressed. E-mail:
[email protected]. Phone +33 4 73407190.
Table 1. Review of Literature Sources Presenting Solubility Data for Hydrogen Sulfide in Water as a Function of Temperature and Pressure T (K)
p (MPa)
no. of data pointsa
ref
273-363 278-333 273-298 310-444 303-316 433-603 323-443 273-323 273-293 283-453 273-303 310-590 303-653 310-589 298-368 303-373 298-593 313 298-338
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