Liquid-Phase Properties from VLE Data

Although values for vapor-phase fugacity coefficient are easily calculated (Secs. 11.6 

the fugacity of species i (in both the hquid and vapor phases) is equal to the partial pressure of species i in the vapor phase. Its value increases from zero at infinite dilution (jc, = y, - 0) to Pj for pnre species i. This is illnstrated by the data of Table 12.1 for the methyl ethyl ketone(l)/toluene(2) system at 323.15 K (50°C). The first tlnee columns list a set of experimental P-x -y data and colunms 4 and 5 show  

The fugacities are plotted in Fig. 12.2 as solid fines. The straight dashed lines represent Eq. (11.80), the Lewis/Randall rale, wliich expresses the composition dependence of the constituent fugacities in an ideal solution  

Although derived from a particular set of data. Fig. 12.2 illustrates the general characteristics of the and vs. x relationships for a binary liquid solution at constant T. The equilibrium pressure P varies with composition, but its influence on /i and is negligible. Thus a plot at constant T and P would look the same, as indicated in Fig. 12.3 for species i (i = 1,2) in a binary solution at constant T and P. 

The lower dashed line in Fig. 12.3, representing the Lewis/Randall rule, is characteristic of ideal-solutionbehavior. It provides the simplest possible modelforthe compositiondependence of fi, representing a standard to which actual behavior may be compared. Indeed, the activity coefficient as defined by Eq. (11.87) formalizes this comparison  

---

Figure 114 Liquid-phase properties from VLE data for methyl ethyl ketone(l)/toluene(2) at 50°C.

Adidharma and Radosz provides an engineering form for such a copolymer SAFT approach. SAFT has successfully applied to correlate thermodynamic properties and phase behavior of pure liquid polymers and polymer solutions, including gas solubility and supercritical solutions by Radosz and coworkers Sadowski et al. applied SAFT to calculate solvent activities of polycarbonate solutions in various solvents and found that it may be necessary to refit the pure-component characteristic data of the polymer to some VLE-data of one binary polymer solution to calculate correct solvent activities, because otherwise demixing was calculated. GroB and Sadowski developed a Perturbed-Chain SAFT equation of state to improve for the chain behavior within the reference term to get better calculation results for the PVT - and VLE-behavior of polymer systems. McHugh and coworkers applied SAFT extensively to calculate the phase behavior of polymers in supercritical fluids, a comprehensive summary is given in the review by Kirby and McHugh. They also state that characteristic SAFT parameters for polymers from PVT-data lead to... 

---