José Carlos Cobos

Thermodynamics of mixtures with strongly negative deviations from Raoult's Law: Part 4. Application of the DISQUAC model to mixtures of 1-alkanols with primary or secondary linear amines. Comparison with Dortmund UNIFAC and ERAS results

Abstract Binary mixtures of 1-alkanols with primary or secondary linear amines have been characterized in the framework of DISQUAC. The interaction parameters for the corresponding OH/NH2 and OH/NH contacts are reported. DISQUAC represents fairly well the thermodynamic properties examined, which are critically evaluated: vapor–liquid equilibria (VLE), molar excess Gibbs energies (GE) and molar excess enthalpies (HE). For example, polyazeotropy of the methanol+diethylamine mixture is well reproduced. The methanol+ammonia system can be treated similarly to other 1-alkanols+primary amine systems (i.e., ammonia is assumed, as in a previous work, to be a primary amine without C atoms). The results are discussed in terms of effective dipole moments. The information derived from the concentration–concentration structure factors is briefly analyzed. DISQUAC provides better results than the Dortmund version of UNIFAC using the published geometrical and interaction parameters. Particularly, DISQUAC improves results on GE and for systems containing methanol. DISQUAC results on HE are also compared to those obtained from the ERAS model. For systems containing primary amines, parameters available in literature were used along calculations. In the case of methanol+diethylamine and 1-alkanols+dibutylamine mixtures, new ERAS parameters are reported in this work. The mean standard deviations for HE obtained using DISQUAC and ERAS, are 151 and 216 J mol-1, respectively. DISQUAC also improves results on GE, while ERAS describes properly the available excess volume (VE) data.

Application of the zeroth approximation of the DISQUAC model to cyclohexane + n-alkane mixtures using different combinatorial entropy terms

Abstract Literature data on molar excess functions, Gibbs energy GE, enthalpy HE, and heat capacity CpE, on activity coefficients γi∞, and partial molar excess enthalpies HiE,∞, 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 GE, lnγi∞ and SLE is also examined. HE, CPE or HiE,∞ 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 lnγ2∞ 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.

Thermodynamics of mixtures containing alkoxyethanols. Part XV. DISQUAC characterization of systems of alkoxyethanols with n-alkanes or cyclohexane

Binary mixtures of alkoxyethanols, CH3–(CH2)n–O–(CH2CH2O)mOH, and n-alkanes or cyclohexane are characterized in terms of DISQUAC. The corresponding dispersive (DIS) and quasichemical (QUAC) interchange coefficients, Ceh,lDIS/QUAC, for the (e,h) contacts (type e, –O–; type h, –OH) are given. In comparison with the values for 1-alkanol + monooxalkane systems, the proximity effects in CH3–(CH2)n–O–CH2–CH2–OH + n-alkane mixtures lead to an increase in the Ceh,lDIS and Ceh,lQUAC (l = 1,2) coefficients and to a decrease in Ceh,2DIS. For other hydroxyethers (3-methoxypropanol, 4-methoxybutanol), the Ceh,lQUAC (l = 1,2) coefficients approach those of 1-alkanol + monooxalkane mixtures with increasing separation between the –O– and OH– groups. However, the Ceh,2DIS coefficient is still lower than in alcoholic solutions, indicating that proximity effects in the framework of DISQUAC remain. DISQUAC yields a consistent description of the vapor–liquid equilibria, VLE, and of liquid–liquid equilibria, LLE. Good results are obtained for azeotropic data. The coordinates of the critical points are represented over a reasonable range of composition and temperature. Excess molar enthalpies HmE and the excess molar heat capacity at constant pressure, CpmE, are well reproduced. The typical large deviations for properties at infinite dilution, excess molar partial enthalpies, HmE,∞, and natural logarithms of activity coefficients, ln γi∞, of the associated compound are found. Thermodynamic properties of alkoxyethanol + alkane mixtures are determined by the self-association of the polar compound ia both inter- and intramolecular H-bonds, as well as by dipole–dipole interactions between alkoxyethanol molecules. These interactions are analyzed in terms of the effective dipole moments () and are more important than in 1-alkanol + alkane mixtures. The dipole–dipole interactions in systems with alkoxyethanols decrease along a homologous series, and are enhanced by the presence of two ether atoms. Intramolecular H-bonds are more relevant than the intermolecular H-bonds and become weakened with the separation between the –O– and –OH groups of the hydroxyethers.

Excess properties of mixtures of some n-alkoxyethanols with organic solvents: III. VE and CEp with butan-1-ol at 298.15 K

The excess molar volumes, VE, and the excess molar heat capacities, CEp are determined as a function of mole fraction, X, at atmospheric pressure and 298.15 K for 2-methoxyethanol (1), 2-ethoxyethanol (1), 2-butoxyethanol (1), 2-(2-methoxyethoxy)ethanol (1), 2-(2-ethoxyethoxy)ethanol (1), 2-(2-butoxyethoxy)ethanol (1) with butan-1-ol (2) mixtures. The VE values decrease in magnitude as the alkyl chain length of the n-alkoxyethanol increases for the two homologous series; they are positive except for the mixtures containing 2-butoxy-ethanol and 2-(2-butoxyethoxy)ethanol for which they are negative over the whole mole-fraction range. The CEp values are positive and relatively small for all the mixtures studied.

DISQUAC predictions of phase equilibria, molar and standard partial molar excess quantities for 1-alkanol+cyclohexane mixtures

Literature data for phase equilibria: vapor-liquid VLE, liquid-liquid LLE, and solid-liquid SLE; molar excess Gibbs energies GE, molar excess enthalpies HE; activity coefficients γi∞ and partial molar excess enthalpies HiE,o at infinite dilution for 1-alkanol (1)+cyclohexane (2) mixtures are examined by the DISQUAC group contribution model. For a more sensitive test of DISQUAC, the azeotropes, obtained from the reduction of the original isothermal VLE data, are also examined for systems characterized by hydroxyl, alkane and cyclohexane groups. The alkane/cyclohexane and alkane/hydroxyl interaction parameters have been estimated previously. The cyclohexane/hydroxyl interaction parameters are reported in this work. The first dispersive parameters increase regularly with the size of the alkanol; from 1-octadecanol they are constant; an opposite behavior is encountered for the third dispersive parameters, which are constant from 1-dodecanol. The second dispersive parameters decrease as far as 1-propanol and then increase regularly; from 1-octadecanol they are constant. The quasichemical parameters are equal to those for the alkane/hydroxyl interactions. Phase equilibria, the molar excess functions, and activity coefficients at infinite dilution are reasonably well reproduced. Poor results are found for HiE,o and DISQUAC predictions for HiE,o are strongly dependent on temperature.

Calorimetric and phase equilibrium data for linear carbonates + hydrocarbons or + CCl4 mixtures. Comparison with DISQUAC predictions

Abstract The disquac interaction parameters for the linear organic carbonate—alkane, carbonate—cyclohexane, carbonate—benzene or —toluene, and carbonate—CCl 4 contacts are revised on the basis of new experimental data on vapor—liquid equilibria for dimethyl or diethyl carbonate + n -alkane mixtures. The new parameters differ slightly from the previous ones. The main conclusions remain valid. The quasichemical interchange coefficients for carbonate—alkane or —cyclohexane contacts, and the purely dispersive interchange coefficients for carbonate—benzene or —toluene and carbonate—CCl 4 contacts, show a relatively weak steric effect. The model provides a fairly consistent description of low pressure fluid phase equilibria (vapor—liquid, liquid—liquid and solid—liquid) and related excess functions (Gibbs energy and enthalpy) using the same set of parameters.

Excess properties of mixtures of some n-alkoxyethanols with organic solvents I. HmE with di-n-butylether at 298.15 K

Abstract The excess molar volumes and excess molar heat capacities have been determined as functions of mole fraction x at atmospheric pressure and 298.15 K for six (an alkoxyethanol + di-n-butylether) mixtures. The alkoxyethanols were 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, and 2-(2-butoxyethoxy)ethanol. The VmEs decrease in magnitude as the alkyl chain length of the alkoxyethanol increases for the two homologous series. They are positive except for the mixtures containing 2-butoxyethanol and 2-(2-butoxyethoxy)ethanol. For these they are positives only at low mole fractions of alkoxyethanol. A parallel, almost linear, decrease is also observed for the Cp, mEs; they are strongly positive and smaller for the components with higher alkyl chain length.

Thermodynamics of mixtures with strongly negative deviations from Raoult’s law. Part 8. Excess molar volumes at 298.15 K for 1-alkanol + isomeric amine (C6H15N) systems ☆: Characterization in terms of the ERAS model

Excess molar volumes, VEm, at 25°C and atmospheric pressure, over the entire composition range for binary mixtures of methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol with-methylbutylamine are reported. They are calculated from densities measured with a vibrating-tube densimeter. All the excess volumes are large and negative over the entire composition range. This indicates strong interactions between unlike molecules, which are greatest for the system involving methanol, characterized by the most negative VEm. For the other solutions, VEm at equimolar composition, is approximately the same. The VEm curves vs. mole fraction are nearly symmetrical. The ERAS model is applied to 1-alkanol + N-methylbutylamine, and 1-alkanol + diethylamine systems. The ERAS parameters confirm that the strongest interactions between unlike molecules are encountered in solutions with methanol. The model consistently describes VEm and excess molar enthalpies HEm of the mixtures studied.

Characterization of the alkanol/alkanol contacts and prediction of excess functions of ternary systems of two n-alkan-1-ols and one n-alkane using DISQUAC

Abstract Gonzalez, J.A., Garcia de la Fuente, I., Cobos, J.C. and Casanova, C., 1992. Characterization of the alkanol/alkanol contacts and prediction of excess functions of ternary systems of two n-alkan-1-ols and one n-alkane using DISQUAC. Fluid Phase Equilibria, 78: 61-80. The data available in the literature on the molar excess Gibbs energies GE, molar excess enthalpies HE, and activity coefficients at infinite dilution γ∞i, for mixtures of two n-alkan-1-ols are examined on the basis of the DISQUAC group contribution model. Using the available interaction parameters for the hydroxyl/aliphatic contacts, the interchange coefficients for the hydroxyl/hydroxyl contacts CDISh1h2,l (l = 1, 2, 3)were fitted. One set of GE ternary data and 21 sets of HE ternary data for n-alkan-1-ol(1)+ n-alkan-1-ol(2) + n-alkane(3) systems are also investigated in the framework of this model. The relative standard deviations for the excess enthalpies are less than 0.1 for most of the mixtures.

An exact quasi-chemical equation for excess heat capacity with W-shaped concentration dependence

Abstract A reliable equation for the excess heat capacity C V E at constant volume is derived from Guggenheims 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.