Fugacity coefficient from generalized correlations

The fugacity coefficients in Equation (7.29) can be calculated from pressure-volume-temperature data for the mixture or from generalized correlations. It is frequently possible to assume ideal gas behavior so that 4>A = 1 for each component. Then Equation (7.29) becomes... 

According to equation 184, all fluids having the same value of CO have identical values of Z when compared at the same T and P. This principle of corresponding states is presumed vaHd for all T and P and therefore provides generalized correlations for properties derived from Z, ie, for residual properties and fugacity coefficients, which depend on T and P through Z and its derivatives. 

The fugacity coefficient 0 is generally calculated from an equation of state. However, many equations of state require a knowledge of the critical parameters of the solute, which may not always be available. Nevertheless, solubilities can be correlated, and sometimes extrapolated, using this approach. The addition of more solutes poses few problems from a thermodynamic viewpoint, as long as the appropriate solid-state fugacity is used in the calculations. This type of approach may also be used to study... 

The description of vapour-liquid equilibrium behaviour can be obtained from analytical equations and generalized correlations. The generalized conelations are generally for the equilibrium ratio, K, and the fugacity coefficients. 

The liquid-phase fugacity coefficient = /f/P may be calculated from a generalized correlation in terms of reduced temperature and pressure such as those of Lydersen et al.42 and Curl and Pitzer.15 Chao and Seader used a modified form of the Curl and Pitzer correlation. The correlation was modified by use of experimental data such that appropriate values of could be computed for the case where a component does not exist as a liquid and for the case of low temperatures. The following expression was proposed for the calculation of the fugacity coefficient for any component / in the liquid phase... 

A fugacity coefficient of 1 represents the case where attractive and repulsive forces balance and is usually indicative of an ideal gas. If (pi < 1, attractive forces dominate the system behavior, while 9 > 1 indicates that the repulsive forces are stronger. The fugacity and fugacity coefficient for pure species and for mixtures can be solved with available data from thermodynamic property tables, equations of state, or generalized correlations. In the case of mixtures, there are three levels of rigor from which to calculate the fugacity coefficient. 

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