Fugacity ethane

To illustrate calculations for a binary system containing a supercritical, condensable component. Figure 12 shows isobaric equilibria for ethane-n-heptane. Using the virial equation for vapor-phase fugacity coefficients, and the UNIQUAC equation for liquid-phase activity coefficients, calculated results give an excellent representation of the data of Kay (1938). In this case,the total pressure is not large and therefore, the mixture is at all times remote from critical conditions. For this binary system, the particular method of calculation used here would not be successful at appreciably higher pressures. 

Figure 5.17 illustrates the effect on hydrate formation when ethane and propane are combined at constant temperature. Ethane acts as an inhibitor to sll formation due to competition of ethane with propane to occupy the large cages of sll. Propane also acts as an inhibitor to si formation when added to ethane+water. In this case, however, since propane cannot enter the si cavities, the fugacity of ethane is lowered as propane is added, destabilizing the si hydrate. Holder (1976) refers to this inhibiting capacity as the antifreeze effect. 

It should be noted that, while the expressions for the derivatives of the fugacity (activity) coefficients in ternary mixtures with respect to mole fractions (Eqs. (25) and (26)) employed to derive Eq. (42) are rigorous, Eq. (42) for the solubility also implies that lim o 2 i3 = 0. The latter approximation is probably not entirely accurate at very high pressures when the intermolecular interactions between the SC fluids become comparable to those in liquids. Indeed, the predicted solubilities of phenanthrene in the mixture of SC CO2 and SC ethane (Eig. 3) deviate somewhat from the experimental data [26] at high pressures. This deviation might have been caused also by the experimental solubilities of phenanthrene in SC ethane [26] employed in our calculations, which are quite different from other experimental data [27]. 

In the above model, the driving force is given by if - /eq). which is the difference between the fugacity of the dissolved gas and its three-phase equilibrium value. In Eq. (4a), is the intrinsic rate constant for the hydrate particle growth reaction and is the mass transfer coefficient around the particle. If the experiments are carried out under conditions such that heat and mass transfer resistances around the particle are eliminated, then k and K k. The intrinsic rate constants K, for methane, ethane, and carbon dioxide are reported in Table 3. 

Compute the fugacities of pure ethane and pure butane at 373.15 K and 1, 10, and 15 bar, assuming the virial equation of state can describe these gases at these conditions. 

Compute the fugacities of ethane and /i-butane in an equimolar mixture at 323.15 K at 1, 10, and 15 bar total pressure assuming that the Lewis-Randall rule is correct. 

Figure 6. Fugacity coefficients of pure liquid methane, ethane, propane, n-butane, and n-pentane at Tr = 0.4 (----------------------), this work (A), Chao tabulation and ( J), Kobayashi tabulation.

Figure 7. Fugacity coefficients of pure liquid methane, ethane, propane,...

Stu claims that when the temperature and absolute pressure of the effluent stream are 1000 K and 10.0 atm, respectively, the conversion of ethane is 95%. If one takes the standard states of these three materials as the pure gases at 298 K and unit fugacity, the following thermodynamic data are applicable for T in kelvin. 

Problem 7.7 Use the Pitzer correlation and the Lee-Weser (p tables to calculate the fugacity of ethane at the following states ... 

FIGURE 1.3-2 ConqxMhion dependence of fugacity coefficient of hydrogen sulfide in binaiy mixtures with ethane at 300 K. Curves labeled V are for superheated vapors at 15 bar, those labeled L are for subcooled liquids at 50 bar. All curves are computed ftxnn the Soave-Redlich-Kwong equation, with values of interaction parameter k,2 as shown. 

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. 

In this example, the SRK EOS was used to compute the fugacities of each species in each of the phases it estimates the VLE very well. We also see that the departures from ideality are in opposite directions for the two components Ethane has a slightly lower K value than we would estimate from Raoult s law, and M-heptane has a much higher one. Looking back at Figure 10.1 (which is not directly applicable here because it is only for 150°F), we see that at 800 psia the K value for ethane is just about equal to the Raoult s law value, while that for -heptane is 4 times the Raoult s law value. The K values in Table 10.2 show the same behavior. Table 10.3 shows some more of the details of the SRK calculation. We see the following ... 

Figure 11.3 Fugacity coefficients of napthalene in ethane at saturation. (Calculated from the solubility data of Johnston et al, 1982.)...

EXAMPLE 7.3 Determine the fugacity and the fugacity coefQcient of ethane at a pressure of 50 bar and a... 

Outline the calculations that you would do to produce the graph for the fugacity coefBcient of methane in a binary mixture of methane and ethane, as shown on the left side of Figure 7.3. Show the representative part of a MATLAB code that could be used to perform this calculation. Use mixing rules given by Equations (7.15), (7.17), and (7.18). 

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