APPLICATION OF WOHL EQUATION TO TERNARY SYSTEM LIQUID-VAPOR EQUILIBRIA
Publication Date: 2012-Sep-17
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Page 01 of 34
APPLICATION OF THE WOHL EQUATION TO TERNARY LIQUID-VAPOR EQUILIBRIA
by S. B. Adler, L. Friend and R. L. Pigford
The use of the Wohl equation for activity coefficients is successfully tested for the most flonldeal ternary systems for which
experimental dati could be found. The three-suffix form possessing
seven constants is found to be successful in many cases. However,
because of the high degree of nonldealfty resulting from one or
more components being polar, the four-suffix form employing up
to ten constants was required for ten of the twenty-five ternaries
studied. Regardless of the form chosen all the constants but one,
c*, are derived from phase equilibrium data on the constituent
The ternary constant C* was found to be approximately zero.
In only two instances did its value not fall in the region of -i.0 to +l.O. Usln9 the binary constants C~}, predictions of vapor com- positions were made for each experimental ternary liquid composition,
temperature, and pressure. The results so obtained yielded average
absolute errors in predicted vapor mole fractions, without respect
to sign, as follows:
For 10 systems less than 0.01
" 17 " " :' 0.02 " 24 ' " " O. 03
an additional three sets the error ts still less than 0.05
Results were analyzed statistically for twenty-two of the systems determining mean values of the vapor mole fraction deviations and the confidence limits of the means.
The mass testin9 of the Wohl equation reported here far exceeds
the sum of aH work previously published tn the literature. It
appears that this equation provides a very 9cod way for expressing llquld nonldeallty for a wide range of types'of components.
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USE OF THE MARGULES-WOHL EQUATICN FOR REPRESENTING THE PHASE
~%~JILIBRIA OF LOW PRESSURE POLAR SYSTEMS
This paper .reports on the first part of a large scale program underway at the M. W. Kellogg Company for representing the phase equllibrla of any system whatever by a single approach. This will include ideal and nonideal liquids in the presence of an ideal or nonideal vapor. Components may be polar or nonpolar, hydrocarbons or nonhydrocarbons. Eventually it is hoped to include enthalpy as well as phase equilibrium in our single approach.
Initial work, reported herein, dealt with systems whose liquid phases were as nonldeal as could be found i~ the literature. One or more of the components in each mixture was polar. Only termary data are included. Pressures were atmospheric or below; the vapor phases were considered ideal.
Many equations have been proposed for describing the effect of liquid composition on phase equilibria at constant temperature and pressure. The Margules form of the Wohl equation was selected here.
It permits a simple framework for expanding results on three component systems to multlcomponent ones. It is an empirical expression and
we do not attach undue importance to its significance in terms of molecular interactions. Nevertheless, its constants, are not meani...