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Año 1997

- Gonzalez, JA; de la Fuente, IG; Cobos, JC; DISQUAC behaviour close to critical points application to methanol plus alkane mixtures; Ber Bunsen-Ges Phys Chem Chem Phys, 101 (2) 1997 219-227

Interactions present in binary mixtures
of methanol+alkanes have been previously characterized in terms of the
DISQUAC group contribution model. It was shown that DISQUAC is a
reliable tool to represent thermodynamic properties such as molar
excess functions: Gibbs energies, G^{E},
enthalpies, H^{E},
or heat
capacities at constant pressure, C_{P}^{E}. In this
work, we examine the
ability of the model to represent liquid-liquid equilibria, LLE, for
the whole series of methanol+n-alkanes
mixtures, as well as for
methanol+cyclohexane, +cycloheptane, or +cyclooctane. Up to now, we had
only considered LLE of those solutions involving n-hexane, n-heptane,
or cyclohexane.

Using the interaction parameters previously reported for methanol+n-alkanes mixtures, which are independent of the non-polar compound, DISQUAC predicts UCSTs (upper critical solutions temperatures) of the methanol+n-alkanes mixtures which are lower than the experimental values for those systems containing the longer n-alkanes. This is in contradiction with the critical exponents theory. The possibility of improving results by modifying only the third interchange coefficients is discussed. So, two groups of these parameters are given depending on n, hereafter the number of carbon atoms in the n-alkane (n less than or equal to 7; n greater than or equal to 8). The coordinates of the critical points are then fairly well represented. Nevertheless, the shape of the LLE curves (the experimental ones being much flatter than those calculated) is rather poorly described, mainly for mixtures containing the longer n-alkanes. The new interaction parameters are tested predicting vapor-liquid equilibria, VLE, at very high temperatures (up to 473.15 K) and at moderate pressures (up to 40 atm) of methanol+n-alkanes mixtures. It is noteworthy that DISQUAC correctly predicts the formation of azeotropes for systems with the lower n-alkanes, and the absence of azeotropes for mixtures with the longer n-alkanes (from n-nonane).

Properties of mixtures containing cycloalkanes are more difficult to represent because these compounds do not form an homologous series in terms of the c-CH_{2} groups. Nevertheless, it has been shown
that the
interaction parameters of 1-alkanols (methanol)+cyclohexane systems
can be applied to calculate H^{E}
Of mixtures with other
cycloalkanes. In
the case of LLE of methanol+cycloalkanes mixtures, different first
dispersive parameters are needed for each cycloalkane. The
quasichemical parameters are, as usually, independent of the n-alkane.
The LLE coexistence curves are better represented than in the case of
solutions including n-alkanes.

The possibility of modyfing the scaling temperature (equal to 298.15 K in DISQUAC) in order to improve LLE results is also briefly examined.

As usually, the experimental H^{E}
curves are much flatter than
the
calculated ones at temperatures close to the critical. Results for
methanol+n-propane, or +n-heptane are shown in order to
complete
information previously given.

Using the interaction parameters previously reported for methanol+n-alkanes mixtures, which are independent of the non-polar compound, DISQUAC predicts UCSTs (upper critical solutions temperatures) of the methanol+n-alkanes mixtures which are lower than the experimental values for those systems containing the longer n-alkanes. This is in contradiction with the critical exponents theory. The possibility of improving results by modifying only the third interchange coefficients is discussed. So, two groups of these parameters are given depending on n, hereafter the number of carbon atoms in the n-alkane (n less than or equal to 7; n greater than or equal to 8). The coordinates of the critical points are then fairly well represented. Nevertheless, the shape of the LLE curves (the experimental ones being much flatter than those calculated) is rather poorly described, mainly for mixtures containing the longer n-alkanes. The new interaction parameters are tested predicting vapor-liquid equilibria, VLE, at very high temperatures (up to 473.15 K) and at moderate pressures (up to 40 atm) of methanol+n-alkanes mixtures. It is noteworthy that DISQUAC correctly predicts the formation of azeotropes for systems with the lower n-alkanes, and the absence of azeotropes for mixtures with the longer n-alkanes (from n-nonane).

Properties of mixtures containing cycloalkanes are more difficult to represent because these compounds do not form an homologous series in terms of the c-CH

The possibility of modyfing the scaling temperature (equal to 298.15 K in DISQUAC) in order to improve LLE results is also briefly examined.

As usually, the experimental H

- Domanska, U; Gonzalez, JA; Solid-liquid equilibria for systems containing long-chain 1-alkanols. III. Experimental data for 1-tetradecanol, 1-hexadecanol, 1-octadecanol or 1-icosanol plus 1-butanol, 1-hexanol, 1-octanol or 1-decanol mixtures, characterization in terms of DISQUAC; Fluid Phase Equilibr, 129 (1-2) 1997 139-163

Solid-liquid equilibrium temperatures
for 1-tetradecanol, 1-hexadecanol, 1-octadecanol or 1-icosanol +
1-butanol, 1-hexanol, 1-octanol or 1-decanol systems have been measured
by a dynamic method from 275 K to the melting point of the long-chain
1-alkanol. An eutectic point was encountered for those mixtures
containing 1-decanol. However, first-order transitions between
different crystal forms (α, β,
γ) of the long-chain
1-alkanols were observed. It was noted that these solid-solid
transitions are very stable in alcohols unlike in hydrocarbons or other
solvents. The solubility of a given long-chain 1-alkanol is nearly the
same in all alcohols tested from 1-butanol to 1-decanol; Only below the
second phase transition point does the solubility change, increasing
with the molecular weight of the shorter alcohol.

The hydroxyl/hydroxyl interactions present in the investigated systems were characterized in terms of DISQUAC using dispersive interchange coefficients for such contacts. Calculations were developed taking into account the solid-solid transitions of the 1-alkanols. The mean relative standard deviations for the equilibrium temperatures are 0.006 for mixtures with an alcohol in the absence of 1-icosanol; and the experimental data are fairly well represented by ideal solubility curves. For mixtures including 1-icosanol, the mean relative standard deviations are 0.021, as the model cannot reproduce, using the proposed interaction parameters, their negative deviations from Raoult's law.

The hydroxyl/hydroxyl interactions present in the investigated systems were characterized in terms of DISQUAC using dispersive interchange coefficients for such contacts. Calculations were developed taking into account the solid-solid transitions of the 1-alkanols. The mean relative standard deviations for the equilibrium temperatures are 0.006 for mixtures with an alcohol in the absence of 1-icosanol; and the experimental data are fairly well represented by ideal solubility curves. For mixtures including 1-icosanol, the mean relative standard deviations are 0.021, as the model cannot reproduce, using the proposed interaction parameters, their negative deviations from Raoult's law.

- Serna, A; de la Fuente, IG; Gonzalez, JA; Cobos, JC; Excess molar volumes of 1-propanol plus n-polyethers at 298.15 K; Fluid Phase Equilibr, 133 (1-2) 1997 187-192

Excess molar volumes V_{m}^{E}
at 298.15 K
and atmospheric pressure for 1-propanol + 2,5-dioxahexane,
3,6-dioxaoctane, 2,5,8-trioxanonane, 3,6,9-trioxaundecane or
5,8,11-trioxapentadecane have been calculated from densities measured
with an Anton-Paar DMA 602 vibrating-tube densimeter. All the excess
molar volumes are negative over the whole mole-fraction range, nearly
symmetrical for mixtures with diethers and slightly skewed towards the
region of high mole fraction of 1-propanol for mixtures with triethers.
The value of V_{m}^{E}
decreases as the n-alkyl
chain
end length of the
diethers or the triethers increases. When the n-alkyl chain end of the
polyethers is the methyl group (-CH_{3}), V_{m}^{E}
is very small in absolute
value and similar for the diethers and triethers, whereas when the end
group is larger than the methyl group, the value of V_{m}^{E}
is more
negative for the diethers than for the triethers. These results,
together with previously published excess molar enthalpies, suggest the
formation of hydrogen bonds between the functional group -OH of the
1-alkanol and the -O-atoms of the polyethers.

- Cobos, JC; An exact quasi-chemical equation for excess heat capacity with W-shaped concentration dependence; Fluid Phase Equilibr, 133 (1-2) 1997 105-127

A reliable equation for the excess heat
capacity C_{V}^{E} at constant volume is
derived from
Guggenheim's
quasi-chemical lattice theory of liquid mixtures for the case of
equal-sized molecules, with the assumption that the interchange energy
depends on the temperature. Using suitable parameters, a W-shaped
concentration dependence for C_{V}^{E} is predicted.
The availability of
this exact quasi-chemical equation permits the study of the theoretical
dependence of C_{V}^{E} On temperature and
concentration, a comparison
with previous approximate results and better analysis of the molecular
meaning of the W-shapes found in the experimental excess heat
capacities C_{P}^{E} at constant pressure.
Moreover,
within this theory,
the long-wavelength limit of the Bhatia- Thornton
concentration-concentration partial structure factor S_{cc}(0)
is also
derived and its correlation with C_{V}^{E} or C_{P}^{E}
is discussed.

- Gonzalez, JA; de la Fuente, IG; Cobos, JC; Thermodynamics of mixtures containing linear monocarboxylic acids. II. Binary systems showing cross-association between components: DISQUAC characterization of linear monocarboxylic acid plus 1-alkanol, or plus linear monocarboxylic acid mixtures; Fluid Phase Equilibr, 135 (1) 1997 1-21

Binary mixtures containing compounds
which show cross-association between them are investigated in terms of
DISQUAC: namely, systems with two linear monocarboxylic acids, or with
one acid and one 1-alkanol. In the former, the interactions between the
COOH groups of the acids are represented by dispersive parameters only.
Binary systems involving two l-alkanols behave similarly. In the linear
monocarboxylic acids + 1-alkanol mixtures, the COOH/OH interactions are
represented by structure-dependent dispersive and quasichemical
parameters. It is shown that those solutions with methanol and ethanol
do not fit into the general scheme followed by the higher members of
each homologous series considered here. A similar behaviour is found
when mixtures containing methanol and benzene or CCl_{4} are
compared with
those involving higher alkanols in the frameworks of DISQUAC or of the
Barker's theory.

Vapor-liquid equilibria, VLE, and excess enthalpy, H^{E}, data
are
consistently described by DISQUAC. Discrepancies are analysed.

The UNIQUAC association model or an equation of state (Carnahan-Starling) with the association built in have been applied in the literature as pure correlation equations of the experimental data for acids + l-alkanols systems. Their results are compared with those reported in this work by DISQUAC.

Vapor-liquid equilibria, VLE, and excess enthalpy, H

The UNIQUAC association model or an equation of state (Carnahan-Starling) with the association built in have been applied in the literature as pure correlation equations of the experimental data for acids + l-alkanols systems. Their results are compared with those reported in this work by DISQUAC.

- Gonzalez, JA; de la Fuente, IG; Cobos, JC; Thermodynamics of mixtures with strongly negative deviation from Raoult's law. I. Application of the DISQUAC model to mixtures of alkan-1-ols and propanal or linear alkanones and trichloromethane; J Chem Soc-Faraday Trans, 93 (21) 1997 3773-3780

Thermodynamic properties: vapour-liquid
equilibria (VLE), molar excess Gibbs energies, H^{E}, molar
excess
enthalpies, H^{E}, or
the mole fraction structure factors, S_{ce}(O),
of
systems containing alkan-1-ols and propanal, or linear alkanones and
CHCl_{3}, i.e. strongly associated mixtures which show compound
formation,
are studied in the framework of the DISQUAC (dispersive quasichemical)
model. Interaction parameters for the contacts OH-CO (in propanal) and
Cl (in CHCl_{3})-CO (in alkanones) are reported. For
alkan-1-ol-propanal
systems, DISQUAC gives better results for VLE than other models
previously applied, such as lattice fluid (LF), lattice fluid
associated
solution (LFAS), extended real associated solution (ERAS), or the
universal quasichemical (UNIQUAC) association theory. For H^{E},
only the
latter improves results meaningfully but DISQUAC gives good agreement
for S_{cc}(0). It is shown that heterocoordination is an
esssential
characteristic of this class of systems. For linear alkanones with
CHCl_{3}, DISQUAC consistently describes G^{E} and H^{E}.
Only the symmetry
of the G^{E} curve Of
the propan-2-one-CHCl_{3}
mixtures is not entirely
satisfactory. The calculated S_{cc}(0) also shows that
heterocoordination
plays an important role in these mixtures. As a trend
heterocoordination seems to be represented by large and negative
enthalpic parameters for the selected contacts.

The ability of DISQUAC to predict VLE and H^{E} for the complex
ternary
systems propan-2-one-butan-2-one-CHCl_{3} and
methanol-propan-2-one-CHCl_{3}
is examined. Previously, the highly non-ideal mixture methanol-CHCl_{3}
was studied with the necessity for interaction parameters for the OH-CI
contact. DISQUAC accurately describes the VLE of this system, and
reproduces reasonably the S-shaped H^{E}.
S_{cc}(0)
shows that this system
is characterized by homocoordination. For the ternary mixtures
considered, DISQUAC yields good results for VLE at different
temperatures but H^{E}
values are only qualitative.

The ability of DISQUAC to predict VLE and H

- Gonzalez, JA; de la Fuente, IG; Cobos, JC; Thermodynamics
of
mixtures containing the CO and OH groups. III. DISQUAC predictions on
VLE
and H
^{E}for ternary mixtures containing 1-alkanols, n-alkanones, and one organic solvent; Can J Chem-Rev Can Chim, 75 (10) 1997 1424-1433

Thermodynamic properties: vapor-liquid
equilibria, VLE, or excess enthalpies, H^{E}, for a set of 21
ternary
mixtures of the type 1-alkanol + n-alkanone
+ organic solvent are
studied in the framework of the DISQUAC group contribution model. This
treatment is extended to the binaries involved. The DISQUAC analysis is
developed on the basis of binary interactions only, that is, ternary
interactions are neglected. Most of the interchange coefficients needed
are available in the literature. The average relative standard
deviations are 0.026 for pressure in the VLE (12 systems) and 0.098 in
the H^{E} (9
systems). The discrepancies observed are briefly
discussed.

- Gonzalez, JA; Thermodynamics of mixtures containing the CO and OH groups. I. Estimation of the DISQUAC interchange coefficients for 1-alkanol plus n-alkanone systems; Can J Chem-Rev Can Chim, 75 (10) 1997 1412-1423

1-Alkanol + n-alkanone mixtures are
treated in terms of the DISQUAC group contribution model, reporting the
interaction parameters for hydroxyl-carbonyl contacts. The
quasichemical interchange coefficients are independent of the compounds
in the mixture; the dispersive interchange coefficients depend on the
intramolecular environment of the hydroxyl and (or) carbonyl groups.
Mixtures of a given 1-alkanol with isomeric ketones are characterized
by the same first dispersive interaction parameter, which is constant
from 2-pentanone. This type of system, when including an alcohol up to
1-pentanol, needs different dispersive enthalpic parameters depending
on the symmetry of the ketone. In this case, such parameters are
constant from 2-pentanone or 3-pentanone. A detailed comparison is
presented between DISQUAC results and data available in the literature
on vapor-liquid equilibria, VLE (including azeotropic data), molar
Gibbs energies, G^{E},
molar excess enthalpies, H^{E},
solid-liquid
equilibria, SLE, natural logarithms of activity coefficients, In
γ_{i}^{∞}, and partial molar excess enthalpies at
infinite
dilution, H_{i}^{E,∞}.
For 54 systems, the mean
relative standard
deviation in pressure is 0.018; for 61 systems, this magnitude in the
case of the H^{E} is
0.059. It is noteworthy that the model
yields good
predictions over a very wide range of temperature for VLE and SLE. H^{E}
is also reasonably well represented at different temperatures. Larger
discrepancies are encountered, as usual, for partial molar quantities
at infinite dilution.

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