Chemistry Reference
In-Depth Information
this topic provides a wide variety of information concerning authors and the speciic
mixtures they studied.
It should be pointed out, however, that only a very small number of studies are
devoted to ternary mixtures of compounds miscible in the whole composition range,
where the KBIs have been calculated over the whole domain. Yet, ternary systems
are more challenging and appealing than binaries from the point of view of the
interpretation of the KBIs and the local composition in terms of the prevailing inter-
molecular interactions and the microscopic structure of the mixtures.
We believe there are at least two reasons that explain this omission. The main
one is the scarcity of the experimental thermodynamic data necessary for the KBI
calculation. In fact, it is generally time consuming and not trivial to experimentally
determine precise activity coefficient, γ, and
V
E
data in sufficient quantities to allow
a densely detailed coverage of the whole triangular domain, both for the three binary
sides and within the internal ternary area. Moreover, a high degree of accurate data,
especially of
G
E
or ln γ, is a must because the KBI calculation procedure requires
multiple differentiations of the functions representing the above properties. In addi-
tion, the absence of data cannot be circumvented by using group contribution models
to obtain
G
E
. These can provide useful predictions for engineering applications, but
there is no certainty that the accuracy is enough to warrant reliable values of the
required derivatives.
The other reason is the lengthy calculation procedure, which involves two dif-
ficult steps. The former is an accurate fitting of the experimental data for ln γ (or
G
E
) and for
V
E
by means of thermodynamically consistent equations. The latter is
the complexity and awkwardness of the mathematical procedure to derive the final
operative equations, which differ in their dependence on the type and analytical
form of the equations chosen for fitting
G
E
and
V
E
data. All this makes it desirable
to provide a software application, which taking as input the analytical forms and the
parameters of the fitting equations,
whichever
they are, is able to provide the KBIs
and related quantities, such as local composition and preferential solvation, at
any
given composition point in the triangular domain.
In previous papers (Matteoli and Lepori 1990, 1995), the results for six ternary
systems were presented. However, these results were limited to the calculation of
KBIs and preferential solvation coefficients at a small set of values for the ternary
composition ensemble. The same restriction is also found in papers by other authors
(see, for instance, Zielkiewicz 1995b; Ruckenstein and Shulgin 2001a; García et al.
2003; Aparicio et al. 2008). A representation of the KBIs and local composition in
such a way as to provide a full view in the whole triangular domain would be more
interesting and useful for understanding and discussing the structure of mixtures,
since their complete behavior would appear thereby allowing comparisons between
many different composition areas. This is the approach we have followed in this
chapter to report and discuss unpublished KBI results of three ternary mixtures of
compounds with different polarities and functional groups: ethanol (Et, 1) + tetra-
hydrofuran (THF, 2) + cyclohexane (cyH, 3) (system I), 2-methoxyethanol (MEt, 1)
+ THF + cyH (system II), trichloromethane (TCM, 1) + THF + cyH (system III).
They have in common two components, cyH, which can be considered practically
inert in this context, and THF, which is weakly polar and can participate in H-bond
