Vapor-liquid equilibrium data ethanol/water

Use the simulator databank BIPs for NRTL to calculate the vapor-liquid equilibrium for ethanol/water at 1 atm. Compare the results for BIPs set to zero. Regress e5q)erimental VLE data ri21 to determine NRTL BIPs. 

Table I. Isobaric Vapor—Liquid Equilibrium Data for the Potassium Bromide—Ethanol—Water System at x = 0.206 0.001 (760 5 Torr)...

Vapor-liquid equilibrium data for the ethanol/water system (subscripts 1 and 2, respectively) at 70°C (158°F, 343 K) are given in the three left columns of Table 3.1. Check to see if the data are thermodynamically consistent. 

As an example, consider the distillation of an ethanol-water mixture at 101.3 kPa (1 atm). The initial charge is 100 mol of liqnid containing 18 mol % ethanol, and the mixture must be reduced to a maximum ethanol concentration in the still of 6 mol %. By using equilibrium data interpolated from Gmehling and Onken [Vapor-Liquid Equilibrium Data Collection, DECHEMA Chemistry Data Sen, vol. 1, Part 1, Frankfnrt (1977)], we get the following ... 

Figure 2. Vapor-liquid equilibrium data at atmospheric pressure for the boiling ethanol-water system containing potassium acetate at saturation and at various constant concentrations...

The Non-Random, Two Liquid Equation was used in an attempt to develop a method for predicting isobaric vapor-liquid equilibrium data for multicomponent systems of water and simple alcohols—i.e., ethanol, 1-propanol, 2-methyl-l-propanol (2-butanol), and 3-methyl-l-butanol (isoamyl alcohol). Methods were developed to obtain binary equilibrium data indirectly from boiling point measurements. The binary data were used in the Non-Random, Two Liquid Equation to predict vapor-liquid equilibrium data for the ternary mixtures, water-ethanol-l-propanol, water-ethanol-2-methyl-1-propanol, and water-ethanol-3-methyl-l-butanol. Equilibrium data for these systems are reported. 

Table V. Vapor-Liquid Equilibrium Data at 760 mm Hg Water (1)—Ethanol (2)-1-Propanol (3)...

Ternary System. The values of all binary parameters used in predicting the ternary data are shown in Table IV. The predicted values of the vapor-liquid equilibrium data—i.e.9 the boiling point, and the composition of the vapor phase, y, for given values of the liquid composition, x, are presented in Tables V, VI, and VII. Also shown are the measured boiling points for the given values of the liquid composition. The RMSD value between the predicted and measured boiling points for the systems water-ethanol-l-propanol, water-ethanol-2-methyl-l-propanol, and water-ethanol-2-methyl-l-butanol are 0.23°C, 0.69°C, and 2.14°C. It seems therefore that since the NRTL equation successfully predicts temperature, the predicted values of y can be accepted confidently. 

Isobaric vapor-liquid equilibrium data at atmospheric pressure are reported for the four systems of the present investigation in Tables I-VI. Salt concentrations are reported as mole fraction salt in the solution, while mixed-solvent compositions are given on a salt-free basis. A single fixed-liquid composition was used for potassium iodide and sodium acetate potassium acetate used three—all chosen from the region of ethanol-water composition where relative volatility is highest. In the... 

Table I. Isobaric Vapor-Liquid Equilibrium Data for the Potassium Iodide—Ethanol—Water System at x — 0.309 (758 d= 3 torr)...

Axial flow pumps, 134, 136, 140 applicafion range, 150 Azeotrope separation, 387,388,420-426 Azeotropic distillation, 420-426 acetonitrile/water separation, 422 commercial examples, 421-424 design method, 424 ethanol/water/benzene process, 424 n-heptane/toluene/MEK process, 424 vapor-liquid equilibrium data, 421, 423, 425,426... 

Figure 4.3. (a) Thermodynamic factor for the system ethanol-water at 40°C obtained from different activity coefficient models. Parameters from Gmehling and Onken (1977ff Vol. I/la p. 133). (h) Thermodynamic factor for the system ethanol-water at 50°C obtained using the NRTL equation using parameters fitted to isothermal vapor-liquid equilibrium data. Parameters from Gmehling and Onken... 

It should be noted that the Maxwell-Stefan D calculated from Eq. 4.1.5 can be quite sensitive to the model used to compute T, an observation first made by Dullien (1971). One of the reasons for this sensitivity is that E involves the first derivative of the activity coefficient with respect to composition. Activity coefficient model parameters are fitted to vapor-liquid equilibrium (VLE) data (see, e.g., Prausnitz et al., 1980 Gmehling and Onken, 1977). Several models may provide estimates of In % that give equally good fits of the vapor-liquid equilibrium data but that does not mean that the first derivatives of In % (and, hence, E) will be all that close. To illustrate this fact we have calculated the thermodynamic factor, E, for the system ethanol-water with several different models of In %. The results are shown in Figure 4.3 a). The interaction parameters used in these calculations were fitted to one set of VLE data as identified in the figure caption. Similar illustrations for other systems are provided by Taylor and Kooijman (1991). 

Table II compares predictions of Kes for the benzene-hexane-water-ethanol system with the experimental clata of El-Zoobi (13). The Wilson constant for the benzene-hexane pair for these calculations was taken from the compilation of Holmes and Van Winkle (14) derived from vapor liquid equilibrium data. The agreement of the prediction with experiment is satisfactory.

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