I. García de la Fuente

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 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.

Excess molar volumes of diethyl carbonate with hydrocarbons or tetrachloromethane at 25°C

The excess molar volumes VmE at atmospheric pressure and at 25°C 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 VmE are positive for all the systems investigated, except for the mixture with toluene which is negative. The results for VmE together with data previously published on excess molar enthalpies HmE and excess molar Gibbs energies GmE, suggest interactions between carbonate and hydrocarbons which are stronger with aromatic than with aliphatic hydrocarbons.

Proximity effects and cyclization in oxaalkanes + CCl4 mixtures disquac characterization of the Cl-O interactions. Comparison with Dortmund UNIFAC results

Abstract Thermodynamic properties, vapor–liquid equilibria (VLE), molar excess Gibbs energies (GE), molar excess enthalpies (HE) and natural logarithms of activity coefficients at infinite dilution (ln γi∞) or partial molar excess enthalpies at infinite dilution (HiE,∞) of mixtures of oxaalkanes, linear or cyclic monoethers, diethers or acetals, and CCl4 are studied in the framework of DISQUAC. The oxygen/CCl4 contacts are characterized by dispersive (DIS) and quasichemical (QUAC) interaction parameters, which are reported. Contacts of the type (polar group)/CCl4 are usually characterized by DIS parameters only. The effects of proximity and cyclization on the interchange coefficients are examined. In comparison with systems of oxaalkanes and n-alkanes, some differences exist; e.g., linear monoethers and diethers+CCl4 mixtures are represented by different interaction parameters due to proximity effects of oxygen atoms (i.e., –O–C–C–O–) in diethers. In solutions with cyclic molecules, ring strain seems to be now more important. DISQUAC results are compared with those obtained using the Dortmund version of UNIFAC. From this comparison, it is concluded that it is necessary to distinguish at least between monoethers, diethers and acetals when treating mixtures with oxaalkanes and that each cyclic molecule should be characterized by its own set of interaction parameters.

Thermodynamics of organic mixtures containing amines - III: Molar Excess Volumes at 298.15 K for Tripropylamine +n‐Alkane Systems ‐ Application of the Flory Theory to N,N,N‐Trialkylamine + n‐Alkane Mixtures

Molar excess volumes at 298.15 K and atomospheric pressure for tripropylamine + n-hexane, + n-octane, + n-decane, + n-dodecane or + n hexadecane systems determined from densities measured with an Anton-Paar DMA 602 vibrating-tube densimeter are reported. N,N,N-trialkylamine + n-alkane systems have been studied using the Flory theory. Better results on excess enthalpies are obtained when the difference in size between the mixture components is large. The dependence of the excess volume at equimolar composition with the length of the n-alkane is correctly described. The simultaneous analysis of the experimental excess volumes and of the excess enthalpies reveal that free volume effects are important in systems formed by triethylamine or tripropylamine and longer alkanes, as well as in those involving tripropylamine or tributylamine and the shorter alkanes. The Patterson effect is present in the studied mixtures. The more globular amines, triethylamine, tripropylamine or tributylamine are order breakers of the longer alkanes. The amines of very large size, e.g., tridodecylamine, show an ordered structure.

Thermodynamics of branched alcohols. I. Extension of DISQUAC to tert-alcohols-n-alkanes or tert-alcohols-cyclohexane mixtures

Abstract DISQUAC interchange coefficients for the contacts tertiary OH-aliphatic and tertiary OHcyclohexane are reported. The quasichemical parameters are independent of the alkane; the first and third quasichemical parameters are common for the alkanols investigated, whereas the second depends on the position of the OH group. Therefore, two ensembles of alcohols are distinguished: 2-methyl-2-alkanols and 3-methyl-3-alkanols. Tert-butanol behaves differently owing to its high melting point. Dispersive parameters change with the alcohol. This behaviour is compared with that observed for other contacts. Vapor-liquid equilibria and excess functions, even the excess heat capacity, are well represented by the model. In contrast, partial molar excess quantities at infinite dilution are poorly described.

Excess molar volumes of 1-alcohol + aliphatic monoethers at 298.15 K

Abstract 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 with a vibrating-tube densimeter. The V E are negative over the whole mole-fraction range and nearly have been calculated from densities measured 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.

Excess molar volumes of 1-propanol + n-polyethers at 298.15 K

Abstract 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.

Estimation of DISQUAC interchange energy parameters for linear secondary alcohols + n-alkanes or + cyclohexane mixtures

Abstract The data available in the literature on vapor-liquid equilibria (VLE), molar excess Gibbs energies ( G E ), molar enthalpies ( H E ), molar excess heat capacities ( C p E ), activity coefficients ( γ i ∞ ) and partial molar excess enthalpies ( H i E,∞ ) at infinite dilution of linear secondary alkohols (1) + n -alkanes (2) or + cyclohexane (2) systems are examined on the basis of the DISQUAC group contribution model. The components in the mixtures are characterized by three types of groups of surfaces: hydroxyl (OH group); aliphatic (CH 3 , CH 2 and CH groups); and cyclohexane (c-CH 2 group). The purely dispersive parameters of the aliphatic/cyclohexane contacts are available in the literature. The parameters for the secondary OH/aliphatic and secondary OH/cyclohexane interactions are reported in this work. The quasi-chemical parameters are independent of the alkane. The first and third parameters are common for the alkanols investigated. The second quasi-chemical parameter depends on the position of the OH group. So, on the basis of available data, two groups of alcohols are distinguished: 2-alkanols and 3-alkanols. The dispersive parameters change with the alcohol. The model describes consistently the phase equilibria and molar excess functions. Dependence on temperature of C p E is well represented, except at very low temperatures. The absolute mean deviation for 1n γ i ∞ is about 6.6%. For i = 1, the deviation is 9.2%; for i = 2, it is 3.9%. DISQUAC cannot represent H i E,∞ , i.e. the calculated H E curves vs. x 1 , the mole fraction, are not as steep as the experimental ones at very high dilution of the alcohol. This may be considered the major limitation of the model. So, in terms of DISQUAC, the investigated mixtures behave similarly to 1-alkanol (1) + alkane (2) systems.

Solid-liquid equilibria using DISQUAC: Prediction for 1-alkanol + n-alkane systems

Abstract Gonzalez, J.A., Garcia de la Fuente, I., Cobos, J.C., Casanova, C. and Domanska, U., 1994. Solid-liquid equilibria using DISQUAC. Prediction for 1-alkanol + n -alkane systems. Fluid Phase Equilibria , 94: 167-179. Using the available interaction parameters for the hydroxyl/aliphatic contacts, the ability of the DISQUAC group contribution model to predict the solid-liquid equilibrium (SLE) is investigated. Twenty-eight sets of available data in the literature on solid-liquid equilibria for 1-alkanol(1) + n -alkane(2) systems are examined, neglecting transitions or miscibility in the solid phase. The mixtures studied contain 1-alkanols from ethanol to 1-eicosanol and n -alkanes from n -heptane to n -hexacosane. The relative standard deviations for the solid-liquid equilibrium temperatures are less than 0.02 K for all the mixtures investigated. The SLE curves are usually well represented by the model, even at low temperatures.