Vapor-liquid equilibrium benzene-toluene

Rgw 5.l Equilibrium and l/(y-.x) plots, Example 5,1, (a) Equi-atrium vapor-liquid compositions, benzene-toluene system, 14.7 psia, a = 2,90. 

Figure 9-98. Vapor-liquid equilibrium (data only), benzene-toluene. Diagram notes for this text by this author. Reproduced by permission of the American Institute of Chemical Engineers, Griswold, J., Anders, D., and Klein, V. A., Trans. AI.Ch.E. V. 39 (1943) p. 223 all rights reserved.

Griswold, J., D. Andres and V. A. Klein, Determination of High Pressure Vapor-Liquid Equilibria. The Vapor-Liquid Equilibrium of Benzene-Toluene," Trans. Amer. Inst. Chem. Engrs. 39, 223 (1943). 

Thus, by knowing aAB from vapor-liquid equilibrium and by specifying xA, A can be calculated. Figure 4.3a also shows a typical vapor-liquid equilibrium pair, where the mole fraction of benzene in the liquid phase is 0.4 and that in the vapor phase is 0.62. A diagonal line across the x-y diagram represents equal vapor and liquid compositions. The phase equilibrium behavior shows a curve above the diagonal line. This indicates that benzene has a higher concentration in the vapor phase than toluene, that is,... 

Figure 4.3 Vapor-liquid equilibrium for a binary mixture of benzene and toluene at a pressure of 1 atm. (From Smith R and Jobson M, 2000, Distillation, Encyclopedia of Separation Science, Academic Press reproduced by permission).

Assuming the relative volatility of a benzene-toluene mixture is 2.90, the vapor-liquid equilibrium compositions can be calculated as shown in Table 5.1. The resultant curve is plotted in Fig. 5.1a. 

Obtain (or plot from data) a phase diagram for the benzene/toluene system. Vapor-liquid equilibrium behavior of binary systems can be represented by a temperature-composition diagram at... 

FIG. 13-4 Isobaric vapor-liquid equilibrium curves for benzene-toluene. Brian, Staged Cascades in Chemical Processing, Frentice-Hall, Englewood Cliff , N.J., 1972.)... 

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... 

We conclude this discussion with one final reminder. The vapor-liquid equilibrium calculations we have shown in Section 6.4c are based on the ideal-solution assumption and the corresponding use of Raoult s law. Many commercially important systems involve nonideal solutions, or systems of immiscible or partially miscible liquids, for which Raoult s law is inapplicable and the Txy diagram looks nothing like the one shown for benzene and toluene. 

A spreadsheet that performs the required material and energy balances and vapor-liquid equilibrium calculations on this process unit is shown on the next page. In the test case, a 40 mole benzene-60 mole% toluene mixture is fed to the evaporator at 120°C and a pressure high enough to assure that the feed stream remains in the liquid state. The unit operates at 7 = lOO C and P = 800 mm Hg. 

A modified local composition (LC) expression is suggested, which accounts for the recent finding that the LC in an ideal binary mixture should be equal to the bulk composition only when the molar volumes of the two pure components are equal. However, the expressions available in the literature for the LCs in binary mixtures do not satisfy this requirement. Some LCs are examined including the popular LC-based NRTL model, to show how the above inconsistency can be eliminated. Further, the emphasis is on the modified NRTL model. The newly derived activity coefficient expressions have three adjustable parameters as the NRTL equations do, but contain, in addition, the ratio of the molar volumes of the pure components, a quantity that is usually available. The correlation capability of the modified activity coefficients was compared to the traditional NRTL equations for 42 vapor—liquid equilibrium data sets from two different kinds of binary mixtures (i) highly nonideal alcohol/water mixtures (33 sets), and (ii) mixtures formed of weakly interacting components, such as benzene, hexafiuorobenzene, toluene, and cyclohexane (9 sets). The new equations provided better performances in correlating the vapor pressure than the NRTL for 36 data sets, less well for 4 data sets, and equal performances for 2 data sets. Similar modifications can be applied to any phase equilibrium model based on the LC concept. 

Let us again consider the vapor-liquid equilibrium curve for benzene and toluene (Fig. 1-25). If one started with a mixture of 20 mole per cent benzene and 80 mole per cent toluene, the vapor in equilibrium with this mixture (upper curve) would have about 40 mole per cent benzene. This percentage corresponds to the composition of... 

Fig. 1 Isobaric vapor-liquid equilibrium of benzene and toluene at 1.01325 Bars.

A feed stream made up of 40% mole benzene and 60% mole toluene is to be separated into benzene-rich and toluene-rich products using a distillation column. The column has ten equilibrium stages including a partial condenser and a partial reboiler and is operated at 172 kPa. The feed stream, with a flow rate of 100 kmol/h, is at its bubble point at 172 kPa and is placed in the fourth stage from the top. It is required to determine the compositions of the two products at different reflux ratios. Vapor-liquid equilibrium data for the benzene-toluene system are provided in Table 5.1 at 172 kPa. 

Vapor-Liquid Equilibrium Data for the Benzene-Toluene Binary at 172 kPa... 

Example 18.1. A mixture of 50 mole percent benzene and 50 mole percent toluene is subjected to flash distillation at a separator pressure of 1 atm. The vapor-liquid equilibrium curve and boiling-point diagram are shown in Figs. 18.2 and 18.3. Plot the following quantities, all as functions of f, the fractional vaporization (n) the temperature in the separator, b) the composition of the liquid leaving the separator, and (c) the composition of the vapor leaving the separator. 

A mixture of benzene and toluene (50 1%) is fed to an evaporator at a rate of 100 kmol h , as shown in Figure Q2.20. The vapor effluent stream is 70 kmol h The uncertainty of each flow rate is 1%. The vapor-liquid equilibrium constant equals 1.78. Determine the fraction of benzene in the vapor phase and the uncertainty. The fraction of benzene in the vapour phase maybe calculated from the formula L.-D. Lafond... 

Consider binary mixtures of benzene(l) and toluene(2) in a closed system at vapor-liquid equilibrium. Bxpressions for pure-component vapor pressures are given in Appendix D. 

This linear relationship between the total pressure, P, and the mole fraction, x, of the most volatile species is a characteristic of Raoult s law, as shown in Figure 7.18a for the benzene-toluene mixture at 90°C. Note that the bubble-point curve (P-x) is linear between the vapor pressures of the pure species (at x, = 0, 1), and the dew-point curve (P-yJ lies below it. When the (x, yi) points are graphed at different pressures, the familiar vapor-liquid equilibrium curve is obtained, as shown in Figure 7.18b. Using McCabe-Thiele analysis, it is shown readily that for any feed composition, there are no limitations to the values of the mole fractions of the distillate and bottoms products from a distillation tower. 

Figure 5.15 Different types of vapor-liquid equilibrium diagrams for the following binary systems (1) benzene (1) -toluene (2) (2) methanol (l)-water (2) (3)...

Vapor-liquid equilibrium data of poly(methyl methacrylate) in benzene and toluene... 

Often the vapor-liquid equilibrium relations for a binary mixture of A and B are given as a boiling-point diagram shown in Fig. 11.1-1 for the system benzene (A)-toluene (B) at a total pressure of 101.32 kPa. The upper line is the saturated vapor line (the dew-point line) and the lower line is the saturated liquid line (the bubble-point line). The two-phase region is in the region between these two lines. 

Khurma, J. R. Muthu, O. Muiyal, S. Smith, B. D. Total-pressure vapor-liquid equilibrium data for binary systems of 1-chlorobutan withe pentane, benzene, and toluene J. Chem. Eng. Data 1983, 28, 93-99... 

Aizawa, K. Kato, M. Vapor-liquid equilibrium determination by total pressure measurements for three binary systems made of 1,2-dimethoxyethane with toluene, methylcyclohexane, or (trifluoromethyl)benzene 7. Chem. Eng. Data 1991,36, 159-161... 

Figure 3.3.6 Isobaric vapor liquid equilibrium of a toluene-benzene mixture at 1 bar (a) T versus x,y plot and (b) y versus x plot.

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