VLE Predictions

UNIFAC zation Property Prediction VLE prediction http //chemistry.berkeley.edu/... 

We have applied some of these principles to the extraction of 1-butene from a binary mixture of 1,3-butadiene/1-butene. Various mixtures of sc solvents (e.g., ethane, carbon dioxide, ethylene) are used in combination with a strongly polar solvent gas like ammonia. The physical properties of these components are shown in Table I. The experimental results were then compared with VLE predictions using a newly developed equation of state (18). The key feature of this equation is a new set of mixing rules based on statistical mechanical arguments. We have been able to demonstrate its agreement with a number of binary and ternary systems described in the literature, containing various hydrocarbon compounds, a number of selected polar compounds and a supercritical component. 

Consider an analysis of the same test data, but with an equilibrium curve based on a VLE prediction which gives higher relative volatilities (average of about 2,5) than the experimental data. With the calculated VLE, the McCabe-Thiele diagram (Fig, 7,125) requires only eight theoretical stages. 

Once the interaction energies were obtained, they were used to calculate the parameters in the UNIQUAC and Wilson models given by Eq. (24). To test the validity of the method, low-pressure vapor-liquid equilibrium (VLE) predictions were made for several binary aqueous systems. The calculations were done using the usual method assuming an ideal vapor phase (Sandler, 1999). Figures 7 and 8 show the low-pressure VLE diagrams for the binary aqueous mixtures of ethanol and acetone [see Sum and Sandler (1999a,b) for results for additional systems and values of the... 

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.)...

To demonstrate the differences between the WS and the HVO models, the results of VLE predictions for the 2-propanol and water binary system at 353 K with the parameters obtained from the DECHEMA tables at 303 K are shown in Eigure 4.3.9 in which the solid line is the prediction with the WS mixing rule and the dashed line describes the results of the HVO model. The significant advantage of the WS model over the HVO model in predictions is clearly visible in this figure. 

Figure 5.1.1. VLE prediction for the methanol and benzene binary system at 293 K by various methods. Circles represent experimental data, the solid line with crosses shows the UNIFAC predictions, and the smooth solid line denotes the results of the WS model. The large, medium, and short dashed lines are from the HVOS, HVO, and MHVl models, respectively the dotted line is from the MHV2 model and the dot-dash line reflects the results of the LCVM model. (Points are VLE data from the DECHEMA Chemistry Series, Gmehling and Onken 1977, Vol. 1, Pt, 2a, p. 220 the data file name on the accompanying disk for this system is MB20.DAT.)...

Figure 5.3.3. VLE predictions for the methane and n-decane binary system using the HVOS (solid lines) and LCVM (dashed lines) models. See text for details. (The points (O, for 377 K, and , at 542 K) are measured VLE data reported in DECHEMA Chemistry Data Series Knapp et al. 1982, p. 486 and 489. The data files for this system on the accompanying disk are C1C10377.DAT and C1C10542.DAT.)...

Example D.3.C Binary VLE Predictions Using the van der Waals One-Fluid Model... 

With this command the results above are appended to the file temp4.out opened earlier to save the results of previous VLE predictions at 373.15 K.)... 

D.6. Program WSUNF Binary VLE Predictions Using the Wong-Sandler Mixing Rule Combined with the UNIFAC Excess Free-Energy Model... 

Example D.6.A Use of the Wong-Sandler Mixing Rule and UNIFAC for Binary VLE Predictions Using an Existing Data File... 

D.7. Program HVUNF Binary VLE Predictions from the Huron-Vidal Mixing Rule (HVO) and Its Modifications (MHVI, MHV2, LCVM, and HVOS)... 

In the first part of this example, we compared VLE predictions for the acetone-benzene binary mixture at 25 C with experimental data entered from the keyboard. In the second part, shown below, we use the same model (HVOS) to predict isothermal VLE data at lOO C, this time using internally generated liquid... 

The thermodynamics community was rather slow to accept the early modified RK methods for VLE prediction. This writer, despite being an interested observer during the development of the RKJZ method, only became an enthusiast for the method after considerable applications experience. The reason for this early skepticism was the feeling that it was asking too much of the simple volume dependence of the RK equation to represent the fugacity functionality in both phases with sufficient accuracy. 

Equations (1.5-12)-(1.5-15) together constitute the most common formulation for predicting or correlating subcritical VLE at low to moderate pressures. When using the formulation for VLE predictions, one requites data or correlations for pure-component vapor pressures (e.g., Antoine equations), for the activity coefRcients (e.g., the UNIQUAC equation or the UNIFAC correlation), for the second virial coefficients (e.g., one of the correlations referent in Section 1.3-2), and for the molar volumes of the saturated liquid (e.g., the Rackett equation - for v ). The actual VLE calculations are iterative and require the use of a computer, details are given in the monograph by Ptausnitz et al. ... 

Figure 14.9 Comparison of VLE predictions from binary data ethanol(l) -benzene(2) - n-heptane(3) at 180 mm Hg. (a) vdW-711/UNIQUAC model (b) vdW-711/conventional mixing rules (Kalospiros et al, 1991).

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