N. Vannhu et al., ON THE THERMODYNAMICS OF ETHANOL PLUS HEXANE AT ELEVATED-TEMPERATURESAND PRESSURES, Fluid phase equilibria, 145(2), 1998, pp. 269-285
A recent experimental investigation of the system ethanol + hexane for
elevated temperatures and pressures is thermodynamically evaluated an
d then compared to an activity coefficient model as well as to equatio
n of state models. The thermodynamic evaluation starts from total vapo
r pressures and proceeds via the Gibbs-Duhem differential equation to
calculate vapor-liquid-equilibria and Gibbs energies. The way via the
Gibbs-Duhem equation is preferred because it does not involve possible
artefacts of a peculiar parametric model. For evaluation of the vapor
-liquid-equilibria at temperatures not far from the critical curve we
used reasonable estimates of the non-idealities of the vapor phase up
to order( p/RT)(2), The resulting excess Gibbs energy is compared to a
I-alkanol + alkane model developed previously for lower temperatures,
with very satisfying agreement. It proved to be very difficult to ass
ign equation of state models to this system which work satisfactorily
for the phase equilibria from low temperatures up to the critical curv
e and which give good values for the excess volumes as well. Two compr
omises were discussed: The first on the basis of the Trebble-Bishnoi e
quation of state, with good volumetric properties, but relatively poor
values for the phase equilibria; the second on the basis of the Peng-
Robinson equation of state (using the modification by Stryjek and Vera
) plus a Wong-Sandler mixing rule. Here the values of the phase equili
bria are quite reasonable, but the volumetric properties are not. Othe
r attempts tried a density correction to the Peng-Robinson equation of
state according to Mathias et al. but the results were inferior wheth
er using conventional mixing rules or a Wong-Sandler prescription. (C)
1998 Published by Elsevier Science B.V, All rights reserved.