The Hydrogen Sulfide-Water System

The same two interaction parameters (ka, kd) were found to be adequate to correlate the VLE. LLE and VLLE data of the H2S-H20 system. Each data set was used separately to estimate the parameters by implicit least squares (LS). 

Parameter Values Standard Deviation Database Objective Function 

Note L is the light liquid phase and L2 the heavy. Source Englezos et al. (1998). 

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Table 14.6 Parameter Estimates for the Hydrogen Sulfide-Water System...

VLE data and calculated phase diagram for the hydrogen sulfide-water system [reprinted from Industrial Engineering Chemistiy Research with permission from the American Chemical SocietyJ. 

Selleck, F.T., L.T. Carmichael, and B.H. Sage. 1952. Phase behavior in the hydrogen sulfide-water system. Ind. Eng. Chem. 44 2219-2226. 

FIGURE 1.7-2 VLE for the hydrogen sulfide-water system at 171 °C. Circles are data. Curves are computed via the Soave-Redlich-Kwong equation with c,j = 0.08 and 12 = 0.163 (Evelein et al. ). 

The solubility of hydrogen sulfide in water at moderate pressures has been detomined by Wright and Maass (1932) and the behavior of the hydrogen sulfide-water system evaluated in more detail by Selleck et al. (1952) up to a pressure of 5,000 psig. Fortunately, the data from both of these investigations indicate that Henry s law holds reasonably well for the system at conditions which would normally be encountered in gas-purification operations. Equilibrium gas and liquid compositions can readily be calculated fiom Henry s law coefficients such as diose presented in Table 6-10. 

Data for the hydrogen sulfide-water and the methane-n-hexane binary systems were considered. The first is a type III system in the binary phase diagram classification scheme of van Konynenburg and Scott. Experimental data from Selleck et al. (1952) were used. Carroll and Mather (1989a b) presented a new interpretation of these data and also new three phase data. In this work, only those VLE data from Selleck et al. (1952) that are consistent with the new data were used. Data for the methane-n-hexane system are available from Poston and McKetta (1966) and Lin et al. (1977). This is a type V system. 

Hydrogen Sulfide - Water System. The data of Selleck et al. 

Until recently the ability to predict the vapor-liquid equilibrium of electrolyte systems was limited and only empirical or approximate methods using experimental data, such as that by Van Krevelen (7) for the ammonia-hydrogen sulfide-water system, were used to design sour water strippers. Recently several advances in the prediction and correlation of thermodynamic properties of electrolyte systems have been published by Pitzer (5), Meissner (4), and Bromley ). Edwards, Newman, and Prausnitz (2) established a similar framework for weak electrolyte systems. 

A large amount of comprehensive physical data on the potassium carbonate-potassium bicarbonate-carbon dioxide-water and potassium carbonate-potassium bicarbonatepotassi-um bisulfide-carbon dioxide-hydrogen sulfide-water systems is available in literature (Benson et al., 1954 Benson et al., 1936 Tosh et al., 1959 Tosh et al., 1960 Allied Chemical Coip., 1961 Bocard and Mayland, 1962). Some typical data are given below however, fm complete information, the reader is referred to the original sources. 

The potassium carbonate-potassium bicarbonate-potassium bisulfide-carbon dioxide-hydrogen sulfide-water system has been studied extensively by Tosh et al. (1960) and Field et al. (1960) of the U.S. Bureau of Mines. It was found that it is necessary that the gas to be treated contain some carbon dioxide in addition to hydrogen sulfide for successfiil use of this system in a gas treating operation. 

A more serious threat to the materials compatibility of CNG fuel systems is condensed water vapor. Water can cause steel and cast iron to rust and aluminum to corrode. Any corrosion of components that must withstand high pressures is a concern, since corrosion stress cracking can occur which can result in failure of the component with disastrous results. The presence of water greatly accelerates the corrosion properties of the hydrogen sulfide that might be found in the natural gas. For these reasons it has been recommended that the way to control corrosion in CNG systems is to remove sufficient water vapor to prevent it from condensing in the system under static conditions [3.13]. Natural gas dryers have been developed to help reach this goal. 

Figure 4.2b shows the equivalent of Figure 4.2a to be slightly more complex for systems such as ethane + water, propane + water, isobutane + water, or water with the two common noncombustibles, carbon dioxide or hydrogen sulfide. These systems have a three-phase (Lw-V-Lhc) line at the upper right in the diagram. This line is very similar to the vapor pressure ( V-Lhc) line of the pure hydrocarbon, because the presence of the almost pure water phase adds a very low vapor pressure (a few mmHg at ambient conditions) to the system. 

The study of Selleck et al. (1952) is considered the benchmark investigation of the system hydrogen sulfide + water. They published tables of smoothed data, which are commonly quoted in the literature. However, these tables are based on relatively few and scattered experimental data points. A discussion of their data was presented in the next appendix. 

The reactions, leading to the formation of disperse systems by oxidation are very common in nature. The reason for this ubiquity can easily be understood during the raise of volcanic melts and of the gases, fluid phases, groundwaters that separate from them, the mobile phases are transferred from zones of reduction located deep in the crust to zones of oxidation that are located near the surface. A good example that illustrates such a process is the formation of sulfur sols by reaction between the hydrogen sulfide dissolved in hydrothermal waters and oxidizers (sulfur dioxide or oxygen) ... 

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