Ethane-water system

Figure 6. Experimental and predicted vapor and liquid phase compositions for the ethane-water system at 220°F ((——) P-R prediction ("AJ (21) (O) (23))...

Figure 5.13 Pressure vs. temperature diagram for ethane + water system. 1000...

Structural transitions (si and sll) have been experimentally determined in the methane + ethane + water system via Raman, NMR, and diffraction between... 

Figure 5.16 is the pseudo-binary pressure versus excess water composition diagram for the methane + ethane + water system at a temperature of 277.6 K. In the diagram, pure ethane and pure methane both form si hydrates in the presence of water at pressures of 8.2 and 40.6 bar, respectively. Note that between the compositions of 0.74 and 0.994 mole fraction methane, sll hydrates form at the incipient formation pressure. Similar to the methane + propane + water system, only a small amount of ethane added to pure methane will form sll hydrates. 

Figure 5.16 Pseudo-P-x diagram for methane + ethane + water system at 277.6 K.

G. Bouchard, A. Pagliara, P.-A. Carmpt, et al. Theoretical and experimental exploration of the lipophilicity of zwitterionic dmgs in 1,2-dichloro-ethane/water system. Pharm. Res., 19, 1150-9 (2002)... 

The ethane-water system forms two immiscible liquid phases over most of the composition range. At O C in the water-rich liquid (i.e., the liquid that is almost pure water), if we take the standard-state fugacities to be Raoult s law type (0.09 psia for water and 23 atm for ethane), then the activity coefficients are practically independent of composition and are equal to 1.0 for water and 550 for ethane. Based on these data, estimate the mol fraction of ethane in the water-rich phase for pressures high enough that two liquid phases are present. 

The interaction parameters for binary systems containing water with methane, ethane, propane, n-butane, n-pentane, n-hexane, n-octane, and benzene have been determined using data from the literature. The phase behavior of the paraffin - water systems can be represented very well using the modified procedure. However, the aromatic - water system can not be correlated satisfactorily. Possibly a differetn type of mixing rule will be required for the aromatic - water systems, although this has not as yet been explored. 

Ethane - Hater System. The data used for the determination of the interaction parameters for the ethane - water binary are those of Culberson and McKetta (21), Culberson et al. (22)... 

Propane - Water System. The interaction parameters for the propane - water system were obtained over a temperature range from 42°F to 310°F using exclusively the data of Kobayashi and Katz (24). This is because among the available literature on the phase behavior of this binary system, their data appear to give the most extensive information. A constant interaction parameter was obtained for the propane-rich phases at all temperatures. The magnitude of the temperature - dependent interaction parameter for this binary was less than that for the ethane - water binary at the same temperature. Azarnoosh and McKetta (25) also presented experimental data for the solubility of propane in water over about the same temperature range as that of Kobayashi and Katz but at pressures up to 500 psia only. However, a different set of temperature - dependent parameters... 

Three-Phase Loci. Figure 11 shows the three-phase loci for the alkane - water systems. No experimental three-phase data were available in the literature for the ethane - water binary. 

Fig. 2. RPT regions for a methane-ethane-propane system on 298-K water.

Jafvert, C.T. and Wolfe, N.L. Degradation of selected halogenated ethanes in anoxic sediment-water systems. Environ. Toxicol C/je/n,.6(ll) 827-837. 1987. 

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. 

Of the possible binary combinations of methane, ethane, and propane, the methane + propane + water system (Figure 5.15) is the simplest. 

Figure 5.17 shows a predicted pressure versus excess water composition plot for the ethane+propane+water system at 274 K. At 0.0 mol fraction ethane (propane+ water) sll form at approximately 2 bar, and at 1.0 mol fraction ethane (ethane + water) si form at approximately 5 bar. At the intermediate composition of 0.78 mole fraction ethane, a quadruple point (Aq-sI-sII-V) exists in which both incipient hydrate structures are in equilibrium with vapor and aqueous phase. This point will be referred to as the structural transition composition the composition at which the incipient hydrate formation structure changes from sll to si at a given temperature. 

Figure 5.17 Pseudo-P-x diagram for ethane + propane + water system at 274 K.

As the temperature is increased to 277.6 K the pressure versus composition diagram for the ethane + propane + water system changes drastically as shown in Figure 5.18 Between 0.0 and 0.6 mole fraction of ethane, the incipient hydrate structure is sll hydrate. However, if the pressure is increased to approximately 11.45 bar, between 0.3 and 0.6 mol fraction ethane, sll is predicted to dissociate to form an Aq-V-Lhc region. 

Figure 5.20 is a pseudo-ternary phase diagram for the methane + ethane + propane + water system at a temperature and pressure of 277.6 K and 10.13 bar,... 

The methane+ethane+propane+water system is the simplest approximation of a natural gas mixture. As shown in Figure 5.20, the phase equilibria of such a simple mixture is quite complicated at pressures above incipient hydrate formation conditions. One of the most interesting phenomenon is the coexistence of si and sll hydrates which occurs in the interior of some pseudo-ternary phase diagrams. 

The phase boundary lines for supercritical ethane at 250 and 350 bar are shown in Figure 2. The surfactant was found to be only slightly soluble in ethane below 200 bar at 37 C, so that the ternary phase behavior was studied at higher pressures where the AOT/ethane binary system is a single phase. As pressure is increased, more water is solubilized in the micelle core and larger micelles can exist in the supercritical fluid continuous phase. The maximum amount of water solubilized in the supercritical ethane-reverse micelle phase is relatively low, reaching a W value of 4 at 350 bar. 

Johnston et al. l also examined the solvatochromic shift of pyridine N-oxide in an ethane/CjEj (C = 10-13 E = 5) water-in-oil microemuision, also in equilibrium with a lower liquid phase. Contrary to the behavior exhibited by the AOT system, the nonionic microemulsions display a polar environment at low pressures, which becomes progressively less polar as pressure increases. At a pressure of only 50 bar, they reported that the probe s environment resembles that observed in bulk hexane. Added water increases the polarity somewhat, yet a cosurfactant (octanol) is required to produce an environment similar to that in bulk water. The polarity of the ethane/ water/surfactant/cosurfactant system remains essentially constant as pressure increases up to 350 bar. 

Equilibrium with Aqueous Phases. The formation and properties of reverse micelle and microemulsion phases in equilibrium with a second predominantly water continuous phase is of practical interest for extraction processes. Figure 7 compares apparent hydrodynamic diameters observed in the ethane/AOT/water system at 37 C for values of 1, 3 and 16. In single phase systems at W - 1 (a) and 3 (b) the apparent hydrodynamic diameter decreases with increased pressure due to decreased micelle-micelle interactions as the solvent power increases. In contrast for a system with an overall W - 16 (c), where a second aqueous phase exists, hydrodynamic diameter increases continuously with pressure. 

---