Estimation Methods for Each Phase Separately, Not Based on Raoults Law

2 Estimation Methods for Each Phase Separately, Not Based on Raoult s Law 

To see how it works we rewrite the general equation for equilibrium between vapor and liquid (Eq. 8.3) as 

In Raoult s law-type formulations, we normally take = / ,-, (the L-R rule, and ideal solution of nonideal gases), but Chao and Seader retained and computed it from the Redlich and Kwong (RK) EOS, as described in detail in the next section and in Appendix F. For the liquid they departed radically from Raoult s law by replacing pt with ( ))i)pure liquid r-P. Substituting this value in Equation 10.2 produces 

They calculated y,-, by a slightly modified version of Equation 9.24, based on Scatchard and Hildebrand s regular solution theory, and found ( i)pure liquid t by a Pitzer-type equation 

This method and its modifications will not be discussed further here because it has largely been supplanted by the methods discussed next. However, its approach was an important step toward the development of those methods, by showing a logical way to separate the liquid-phase behavior from the vapor-pressure (Raoult s law) data, and instead use an empirical equation for the liquid-phase fugacities. 

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