B H yyB[13

Table 2 Visual test of consistency of activity coefficients for binary systems

1. log — evaluated at x1 = 0.25 should be approximately equal to log y2 evaluated at x1 = 0.75.

2. Let a be the value of log - evaluated at x1 = 0 and p be the value of log y2 evaluated at x1 = 1. log — evaluated at x1 = 0.5 should be approximately equal to 0.25p.

log y2 evaluated at x1 = 0.5 should be approximately equal to 0.25a.

3. If a is greater than or equal to p, then the value of log - evaluated at x1 = 0.5 should be less than or equal to the value of log y2

4. If a is less than p, then the value of log — evaluated at x1 = 0.5 should be greater than the value of log y2 evaluated at x1 = 0.5.

5. Both log yi versus xi curves show horizontal tangency as xi approaches unity and log yi approaches zero.

6. If there is a maximum (or minimum) on one of the log yi versus xcurves, there is a corresponding minimum (or maximum) on the other curve at the same x1.

7. If there is neither a maximum nor a minimum on the curves, both curves should be on the same side of the horizontal line that is representing log — = 0.

Figure 2 Visual consistency test of binary vapour-liquid equilibrium of (A) the acetone # benzene system at 318.15 K (Brown I and Smith F (1957) Liquid-vapor equilibrium VIII. The system acetone # benzene and acetone # carbon tetrachloride at 45°C. Australian Journal of Chemistry 10: 423-428), (B) the heptane # 3-pentanone system at 368.15 K (Geiseler G and Koehler H (1968) Thermodynamic behavior of the binary systems methyl ethyl ketoxime/n-heptane, diethyl ketone/n-heptane, and methyl ethyl ketoxime/diethyl ketone. Berichte, Bunsengesellschaftfuel Physikalische Chemie. 72: 697-706), (C) the toluene # n-octane system at 101.3 kPa. (Bromiley EC and Quiggle, D (1933) Vapor-liquid equilibria of hydrocarbon mixtures. Industrial and Engineering Chemistry 25: 1136-1138).

Figure 2 Visual consistency test of binary vapour-liquid equilibrium of (A) the acetone # benzene system at 318.15 K (Brown I and Smith F (1957) Liquid-vapor equilibrium VIII. The system acetone # benzene and acetone # carbon tetrachloride at 45°C. Australian Journal of Chemistry 10: 423-428), (B) the heptane # 3-pentanone system at 368.15 K (Geiseler G and Koehler H (1968) Thermodynamic behavior of the binary systems methyl ethyl ketoxime/n-heptane, diethyl ketone/n-heptane, and methyl ethyl ketoxime/diethyl ketone. Berichte, Bunsengesellschaftfuel Physikalische Chemie. 72: 697-706), (C) the toluene # n-octane system at 101.3 kPa. (Bromiley EC and Quiggle, D (1933) Vapor-liquid equilibria of hydrocarbon mixtures. Industrial and Engineering Chemistry 25: 1136-1138).

is used for the second virial coefficient of the mixture under consideration. When i O j, the cross second virial coefficient Bij represents the interaction between molecule i and molecule j. Z is the compressibility factor of the mixture. The (i values obtained from eqns [11] and [12] are practically identical. A generalized method proposed by Hayden and O'Connell in 1975 may be used for predicting the second virial coefficients for pure components and the cross second virial coefficients. For an ideal gas mixture, ( is unity.

Expressions are available for representing the dependence of yt on the composition of the solution. The activity coefficients are related to the excess Gibbs energy function by the equation

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