2PVDW model

S, Nonquadracic Combining Rules for the van der Waals One-Fluid Model (2PVDW Model)... 

The combinations of eqns. (3.3.4, 3.3.6, 3.3.8, and 3.5.5) will be referred to as the 2PVDW model. This model has been shown to provide a good correlation of VLE data of highly nonideal systems that previously could be correlated only with activity coefficient models. 

The correlation of data for the methane and pentane binary system is shown in Figure 4.2.1. In this case the van Laar excess Gibbs free-energy model has been used in the HVO model the two model parameters were fitted to VLE data on the 277 K isotherm, and the vapor-liquid equilibria at higher temperatures were predicted with the same temperature-independent parameters. The results are very good in this case and similar to those obtained with the IPVDW and 2PVDW models. 

For highly nonideal and polar mixtures of organic compounds, the IPVDW model is inadequate, and the various forms of the 2PVDW model have limitations as a correlative method and suffer from computational problems such as the dilution effect and the Michelsen-Kistenmacher syndrome mentioned in Section 3.5. Such models should only be used with caution as semipredictive methods, and they have little utility as... 

Figure 6.2.2. Excess enthalpy for the benzene and cyclohexane system at 293 K (dots) and at 393 K (triangles), Tlie lines denote correlations at 293 K and predictions at 393 K using various models. The solid line reflects predictions using the 2PVDW model, the dotted line represents the predictions using the van Laar activity coefficient mode , the short dashed lines signify predictions using the HVOS model, and the long dashed line denotes predictions made with the WS model. Data are from the DECHEMA Chemistry Series (Gmehling and Onken 1977, Vol. 3, Pt. 2, p. 992).

With this selection, the user can enter new VLE data from the keyboard, or use previously entered VLE data for correlation with IPVDW or 2PVDW models.)... 

This results in the selection of 2PVDW model for the VLE calculations. Next the message below will appear on the screen.)... 

Figure 3.5.1. VLE correlation of the n-pentane and ethanol binary system with the 2PVDW mixing rule and the PRSV equation of State. Solid lines are the results of correlation with k 2lk2i = 0.195/0,049 at 373 K, 0.2056/0.073 at 398 K, and 0.207/0.096 at 423 K, Short dashed lines are the results of VLE predictions widi k i/k2 = 0.200/0.073 at all temperatures, and the medium dashed lines are 1PVDW model cone-lations presented earlier in Figure 3,4,3. (Data are from Campbell et al., i 987 data files for this system on the accompanying disk are PE373.DAT, PE398.DAT and PE423.DAT.)...

Figure 3.5.3. VLB correlation of the 2-propanol and water binary system at 353 K with the 2PVDW mixing rule and the PRSV equation of state. Solid lines denote correlation results with 1 12/ 21 = 0.0953/0.0249. Dashed lines show IPVDW model correlations presented earlier in Figure 3.4.5. (Points are the data of Wu et ah, 1988 data file for this system on the accompanying disk is 2PW80.DAT.)...

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