• Energy Research
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AbstractThe data available in the literature for the molar excess Gibbs energies GE, azeotropes, molar excess enthalpies HE, activity coefficients γi∞, and partial molar excess enthalpies HiE,∞, at infinite dilution, and molar excess heat capacities CpE, of n‐alkan‐1‐ol (1) + n‐alkane (2) mixtures are examined on the basis of the DISQUAC group contribution model. Being available the interaction parameters for systems containing methanol or ethanol, we report the interchange coefficients from propanol to hexadecanol: Cah.1DISand Cah,1QUAC (1 = 1,2 or 3). For the dispersive coefficients: Cah,1DIS increase with the size of the n‐alkan‐1‐ol; Cah,3DIS decrease as far as propanol, and then increase regularly, an opposite behaviour is encountered for Cah,3DIS the quasichemical coefficients: Cah,1.DIS and Cah,3.DIS are constant, and Cah,3CUAC varies in a similar way to the maximum of the HE of the mixtures under study; from decanol, they are constant. The model describes consistently the molar excess functions for the systems investigated, even the CpE and, qualitatively, the temperature dependence of this magnitude. Partial molar excess quantities at infinite dilution are reasonably well represented. Larger differences are obtained for H1E,∞.

AbstractA flow microcalorimeter of the Picker design has been used to measure molar excess enthalpies at 298.15 K of the seven binary liquid mixtures 1‐chloronaphthalene + n‐hexane, + n‐heptane, + n‐octane, + n‐decane, + n‐dodecane. + n‐pentadecane, and + n‐hexadecane. Experiments were performed in the discontinuous mode, covering essentially the whole composition range. The overall imprecision of the measurements is characterized by standard deviations from Redlich‐Kister type smoothing equations of generally less than ± 1 per cent of the maximum value HEmax of the excess enthalpy (with respect to mole fraction). The most striking feature is that for 6 ± n ± 16 (n denotes the number of C‐atoms of the n‐alkane) HEmax decreases with increasing n, the correlation being approximately linear. – For the mixtures 1‐chloronaphthalene + n‐hexane, + n‐heptane, + n‐octane, + n‐dodecane, + n‐pentadecane, and + n‐hexadecane molar excess volumes VE at 298.15 K were obtained, as a function of mole fraction, from measurements of the density with a vibrating‐tube densimeter. The excess volumes are negative in all cases and become less negative with increasing chain length of the n‐alkane. At equimolar composition, for (1‐C10H7Cl + n‐C6H14) we find VE = ‐1.555±10−6 m3 mol−1, and for (1‐C10H7Cl + n‐C16H34), VE = ‐0.397±10−6 m3 mol−1. A Picker flow calorimeter was used to determine molar excess heat capacities at constant pressure CEp at 298.15 K for all mixtures except for 1‐C10H7Cl + n‐C10H22, and + n‐C16H34. The excess heat capacity is essentially zero for the mixture with n‐hexane, and increases with increasing chain length up to (1‐C10H7Cl + n‐C12H26); for (1‐C10H7Cl + n‐C15H32), CpE is somewhat smaller, thus indicating a trend inversion.

AbstractExcess heat capacities, CEp have been obtained through the concentration range at 25°C for five sets of systems of type An + B: hexafluorobenzene + 2,2,4‐trimethylpentanc and 2,2,4,4,6,8,8‐heptamethylnonane; hexafluorobenzene + cyclohexane (10° W) and dicyclohexyl (W); 1‐chloronaphthalene + 2,2‐dimethylbutane, 2,2,4‐trimethylpentane (W) and 2,2,4,4,6,8,8‐heptamethylncnane (W), 1‐chloronaphthalene + n‐hexadecane; 1‐chloronaphthalene + cyclohexane and dicyclohexyl (15°, W). For the systems indicated, CEp has a W‐shape, i.e., two minima separated by a maximum or two changes of sign of the curvature. The W‐shape does not occur for hexafluorobenzene + cyclohexane at 25° but appears at 10°. Temperature and molecular size act on CEp through the degree of solution non‐randomness as indicated by GE and the concentration‐concentration correlation function, Scc which is a good predictor for the W‐shape and of the concentration at which the maximum appears. The W‐shape corresponds to an Scc value greater than 0.7 and GE > 800 J mol−1, the temperature being within 100 K of the UCST.