Principal Miembros Historia Investigación Laboratorio Publicaciones Proyectos Enlaces

Año 1995

- Gonzalez, JA; de la Fuente, I; Cobos, JC; Casanova C; Ait-Kaci, A; Application of the zeroth approximation of the DISQUAC model to cyclohexane plus n-alkane mixtures using different combinatorial entropy terms; Fluid Phase Equilibr, 112 (1) 1995 63-87

Literature data on molar excess
functions, Gibbs energy G^{E},
enthalpy H^{E}, and heat capacity C_{P}^{E},
on activity coefficients γ_{i}^{∞}, and partial molar
excess enthalpies H_{i}^{E,∞},
at infinite dilution and on solid-liquid equilibria, SLE, of the
cyclohexane + n-alkane
mixtures are examined on the basis of the zeroth approximation of the
DISQUAC group contribution model.

The model provides a quite satisfactory description of the thermodynamic properties for the mixtures under study, although the symmetry of the calculated excess functions differs from the experimental one for systems containing long-chain n-alkanes. This may be due to the so-called Patterson effect.

The influence of different combinatorial entropy terms (Flory-Huggins, Stavermann-Guggenheim or Kikic equations) on the prediction of thermodynamic properties such as G^{E},
ln γ_{i}^{∞} and SLE is also examined. H^{E},
C_{P}^{E} or H_{i}^{E,∞} are
represented by an interactional term only.

The results calculated using the Flory-Huggins term are slightly better than those obtained applying the Stavermann-Guggenheim equation. Results based on the Kikic expression are poorer than those given by Flory-Huggins, particularly at high concentration of cyclohexane in systems containing the longer n-alkanes. So, the Kikic equation leads to poorer results for ln γ_{2}^{∞} for these systems.

SLE predictions are determined mainly by the physical constants of the pure compounds. So, essentially they do not depend on the combinatorial term used. A comparison between the zeroth approximation of DISQUAC and the modified UNIFAC model (Lyngby version) is also presented. Such comparison shows that both methods lead to similar results; although the latter gives poorer predictions on the temperature dependence of the excess functions than the former. On the other hand, the number of interaction parameters needed in modified UNIFAC is larger than when the zeroth approximation of DISQUAC is applied and, more important, they change with the number of carbon atoms of the n-alkane in a rather erratic way for the first members of the series. This makes the predictive task of UNIFAC more difficult.

The model provides a quite satisfactory description of the thermodynamic properties for the mixtures under study, although the symmetry of the calculated excess functions differs from the experimental one for systems containing long-chain n-alkanes. This may be due to the so-called Patterson effect.

The influence of different combinatorial entropy terms (Flory-Huggins, Stavermann-Guggenheim or Kikic equations) on the prediction of thermodynamic properties such as G

The results calculated using the Flory-Huggins term are slightly better than those obtained applying the Stavermann-Guggenheim equation. Results based on the Kikic expression are poorer than those given by Flory-Huggins, particularly at high concentration of cyclohexane in systems containing the longer n-alkanes. So, the Kikic equation leads to poorer results for ln γ

SLE predictions are determined mainly by the physical constants of the pure compounds. So, essentially they do not depend on the combinatorial term used. A comparison between the zeroth approximation of DISQUAC and the modified UNIFAC model (Lyngby version) is also presented. Such comparison shows that both methods lead to similar results; although the latter gives poorer predictions on the temperature dependence of the excess functions than the former. On the other hand, the number of interaction parameters needed in modified UNIFAC is larger than when the zeroth approximation of DISQUAC is applied and, more important, they change with the number of carbon atoms of the n-alkane in a rather erratic way for the first members of the series. This makes the predictive task of UNIFAC more difficult.

- Serna, A; de la Fuente, IG; Gonzalez, JA; Cobos, JC; Casanova, C; Excess molar volumes of 1-alcohol plus aliphatic monoethers at 298.15 K; Fluid Phase Equilibr, 110 (1-2) 1995 361-367

Excess molar volumes V^{E} at 298.15 K and
atmospheric pressure for 1-propanol and 1-hexanol + butyl methyl ether,
+ dipropyl ether or + dibutyl ether have been calculated from densities
measured with a vibrating-tube densimeter. The V^{E} are negative over the
whole mole-fraction range and nearly symmetrical for all the systems
investigated. For each monoether, the V^{E}
decreases as the chain length of the 1-alcohol increases. For each
1-alcohol, the V^{E}
increases as the chain length of the symmetrical di-n-alkyl ethers increases. Moreover,
for the butyl methyl ether (an asymmetrical monoether), the V^{E} is more positive than
of the immediately higher symmetrical dipropyl ether. These results,
together with previously published excess molar enthalpies H^{E}, suggest the
formation of hydrogen bonds between the functional group (-OH) of the
1-alcohol and the (-O-) atoms of the monoethers.

- de la Fuente, IG; Gonzalez, JA; Cobos, JC; Casanova, C;
Thermodynamics of binary-mixtures containing organic carbonates. X.
Excess molar volumes of diethyl carbonate with hydrocarbons or
tetrachloromethane at 25 ºC; J
Solut Chem, 24 (8) 1995
827-835

The excess molar volumes V_{m}^{E} at
atmospheric pressure and at 25 ºC for binary mixtures of diethyl
carbonate with n-heptane, n-decane, n-tetradecane,
2,2,4-trimethylpentane, cyclohexane, benzene, toluene, or
tetrachloromethane have been obtained over the whole mole-fraction
range from densities measured with a vibrating-tube densimeter. The V_{m}^{E} are
positive for all the systems investigated, except for the mixture with
toluene which is negative. The results for V_{m}^{E} together
with data previously published on. excess molar enthalpies H_{m}^{E} and
excess molar Gibbs energies G_{m}^{E}
suggest interactions between carbonate and hydrocarbons which are
stronger with aromatic than, with aliphatic hydrocarbons.

- Barbes, B; Garcia, I; Gonzalez, JA; Cobos, JC; Casanova, C;
Excess properties of mixtures of some n-alkoxyethanols
with organic-solvents. VII. V
^{E}with toluene at 298.15 K; Thermochim Acta, 257 1995 103-110

The excess molar volume at 298.15 K and
atmospheric pressure for three (alkoxyethanol + toluene) mixtures have
been determined over the whole mole fraction range from densities
measured with a vibrating-tube densimeter. The alkoxyethanols were
2-methoxyethanol, 2-ethoxyethanol and 2-butoxyethanol. The three excess
volumes curves have a maximum in the toluene rich region and those with
2-ethoxyethanol and 2-butoxyethanol are sigmoidal. The excess molar
volumes increase as the alkyl chain length of the alkoxyethanol
decreases.

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