Prediction of vapour-liquid equilibria

Estimation of activity coefficients from azeotropic data 

If a binary system forms an azeotrope, the activity coefficients can be calculated from a knowledge of the composition of the azeotrope and the azeotropic temperature. At the azeotropic point the composition of the liquid and vapour are the same, so from equation 8.31  

The values of the activity coefficients determined at the azeotropic composition can be used to calculate the coefficients in the Wilson equation (or any other of the three-suffix equations) and the equation used to estimate the activity coefficients at other compositions. Horsley (1973) gives an extensive collection of data on azeotropes. 

The constants in any of the activity coefficient equations can be readily calculated from experimental values of the activity coefficients at infinite dilution. For the Wilson equation  

Relatively simple experimental techniques, using ebulliometry and chromatography, are available for the determination of the activity coefficients at infinite dilution. The methods used are described by Null (1970) and Conder and Young (1979). 

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Tochigi, K., Minami, S., Kojima, K. Prediction of vapour-liquid equilibria with chemical reaction by analytical solutions of groups./. Chem. Eng. Jpn. 1977, 10, 349-354. 

Kojima, K. and Tochigi, K. (1979) Prediction of Vapour-Liquid Equilibria by the ASOG Method (Elsevier). 

However, it was Soave s modification [30] of the temperature dependence of the a parameter, which resulted in accurate vapour pressure predictions (especially above 1 bar) for light hydrocarbons, which led to cubic equations of state becoming important tools for the prediction of vapour-liquid equilibria at moderate and high pressures for non-polar fluids. 

Table 2 UNIFAC group interaction parameters for prediction of vapour-liquid equilibria at temperatures between 250 and 425 K 539...

Raal, J. D. Naidoo, P. Excess enthalpy measurements using a novel highly refined microflow calorimeter and the prediction of vapour-liquid equilibria from such data Fluid Phase EqmUb. 1990,57,147-160... 

M. S. Lind and L. M. Naphtali Prediction of vapour-liquid equilibria with the Benedict-Webb-... 

KIK 91] Knac I., FermeguaM., Rasmussen P., UNIFAC prediction of vapour-liquid equilibria in mixed solvent-salt systems . Chemical Engineering Science, vol. 46, no. 11, pp. 2775-2780, 1991. 

KOJ 79] Kojima K., Togichi K., Prediction of Vapour-Liquid Equilibria byASOG Method, Kodansha-Elsevier, New York, 1979. 

For vapours, use the equation of state selected for predicting the vapour-liquid equilibria. For liquids, use the same equation if it is suitable for estimating liquid density. 

Orbey and Sandler also showed the Wong-Sandler mixing rule with the Flory-Huggins model for the excess molar Gibbs function can be used to predict the (vapour + liquid) equilibria of ethane with low-molar mass polymers. With three parameters the mixture (ethene + tetracontane) has been correlated by the same approach. ... 

We conclude by noting that while it has been shown that crossover versions of classical equations of state, including SAFT-like equations, typically provide accurate predictions for vapour-liquid equilibria, pf/j "2,261 derivative properties " " of both pure fluids and their mixtures close to and far from the critical region, such methods have yet to be applied to the study of liquid-liquid equilibria with the SAFT approach. 

Soa ve-Redlich-Kwong (SRK) equation of state An equation of state widely used to predict the vapour-liquid equilibria of substances. It is a development of the Redlich-Kwong equation of state that correlated the vapour pressure of normal fluids ... 

Dutta, M. The effect of molecular sice on vapour-liquid equilibria. Indian Chem, Eng. 13 (1971) 29. Elshayal, J. M., and Lu. B. C.-Y. Prediction of vapor-liquid-equilibria by means of a modified Clausius equation of state. Canad. J. chem. Engng. 51 (1973) 76. 

Subject areas for the Series include solutions of electrolytes, liquid mixtures, chemical equilibria in solution, acid-base equilibria, vapour-liquid equilibria, liquid-liquid equilibria, solid-liquid equilibria, equilibria in analytical chemistry, dissolution of gases in liquids, dissolution and precipitation, solubility in cryogenic solvents, molten salt systems, solubility measurement techniques, solid solutions, reactions within the solid phase, ion transport reactions away from the interface (i.e. in homogeneous, bulk systems), liquid crystalline systems, solutions of macrocyclic compounds (including macrocyclic electrolytes), polymer systems, molecular dynamic simulations, structural chemistry of liquids and solutions, predictive techniques for properties of solutions, complex and multi-component solutions applications, of solution chemistry to materials and metallurgy (oxide solutions, alloys, mattes etc.), medical aspects of solubility, and environmental issues involving solution phenomena and homogeneous component phenomena. 

The work was continued by Wichterle et al. [83d] and resulted in a generalized method of calculating and predicting vapour-liquid equilibria at high pressures. 

Furter [91] has analyzed the state of the art from the point of view of employing the salt effect in industrial processes, especially in extractive distillation. In addition, he ha.s made up a list of references covering the years 1966 to 1977 [91 a]. Schubert et al. [92] investigated the effect of some metal chlorides and other salts on the isothermal = 60°C) phase equilibrium behaviour of the systems n-propanol-water, n-butanol-water and methanol-water. Using CH30H/H20/NaBr as an example, the method of predicting salt effects for vapour-liquid equilibria as developed by Schuberth has been extended to uusaturated solutions [92a]. 

Shibata S.K., Sandler S.L, Critical evaluation of equation of state mixing rules for the prediction of high-pressure vapour-liquid equilibria, Ind. Eng. Chem. Res. 1989, (28), 1893-1898... 

One drawback of the MF1V2 model is the inability of UNIFAC to predict (vapour + liquid) equilibria (VLB) and (liquid + liquid) equilibria (LLE) conditions using the same set of group-interaction parameters. In general, cubic equations of state do not provide precise predictions of the phase equilibria when the mixture is asymmetric in size that is attributed to the large differences in the pure-component co-volumes. The Carnahan -Starling equation for hard spheres is a more realistic model for the repulsive contribution than that proposed by van der Waals. Mansoori et al. proposed an equation for mixtures of hard spheres that has been found to correlate the phase behaviour of non-polar mixtures with large molecular size differences. 

Kirss, H. Kuus, M. Siimer, E. Kudryavtseva, L. Measurement, correlation and prediction of binary vapour-liquid equilibria and enthalpies of mixing for systems containing isomeric alkynes. Thermochim. Acta 1992, 195, 85-94. 

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