M. Diaz Peña

Isothermal compressibilities of n-1-alcohols from methanol to 1-dodecanol at 298.15, 308.15, 318.15, and 333.15 K

Abstract Isothermal compressibility for twelve n -1-alcohols, from methanol to 1-dodecanol, have been determined at 298.15, 308.15, 318.15, and 333.15 K. Except for methanol, and perhaps ethanol, the compressibility decreases regularly with chain length.

Isothermal compressibilities of n-alkanes and benzene

Abstract The isothermal compressibilities of benzene and of 16 n -alkanes, from n -hexane to n -hexadecane, have been measured at zero pressure and 298.15, 308.15, 318.15, and 333.15 K.

Speed of sound in pure liquids by a pulse-echo-overlap method

An ultrasonic apparatus for the measurement of the speed of sound in pure liquids is described. To test its performance the speed of sound in several liquids at 298.15 K was measured and the results were compared with literature values. Isentropic compressibilities ks were also calculated from the experimental results and for the n-alkanes the variation with the chain number of atoms was studied.

Combination rules for intermolecular potential parameters. I. Rules based on approximations for the long‐range dispersion energy

Combination rules for intermolecular potential parameters based on different approximations for the long‐range dispersion energy are derived and applied to the Lennard‐Jones (12–6) and Kihara potential functions. The resulting group of rules is given by the expressions σ12 = <σ≳j, and e12 = <eσ6γ≳i/‖<σ≳6j<γ≳k ‖, where the i,j, and k subscripts may adopt the values a, g, or h indicating the type of mean (arithmetic, geometric, or harmonic, respectively) to be taken for the magnitude within the brackets. Expressions for γ depend on the approximation chosen for the van der Waals coefficient c6. This group of rules includes most of those previously proposed and others which are new. Experimental values of the interaction virial coefficient and unlike‐pair potential parameters obtained from viscosity data are used to test the validity of the rules. Six related rules are shown to be satisfactory for both potential functions and for accurate correlation of virial and viscosity data as well.

Combination rules for intermolecular potential parameters. II. Rules based on approximations for the long‐range dispersion energy and an atomic distortion model for the repulsive interactions.

Combination rules for intermolecular potential parameters based on the identification of the attractive term of the potential function with different expressions for the long‐range dispersion energy and the introduction of an improved model for the combination of repulsive potentials are derived and applied to the Lennard‐Jones (12–6) and Kihara potentials. The ability of the rules to predict interaction virial coefficients and unlike‐pair potential parameters obtained from viscosity data is examined. Results are compared to those obtained in similar tests in part I of this study. Combination rules based on the London dispersion formula and an assumption of a geometric mean rule for the distances at which the repulsive forces are in equilibrium are shown to have advantages over previously proposed rules for the two potential functions assumed.

Regression of vapor-liquid equilibrium data based on application of the maximum-likelihood principle

Abstract Rubio, R.G., Renuncio, J.A.R. and Diaz Pena, M., 1983. Regressin of vapor-liquid equilibrium data based on application of the maximum-likelihood principle. Fluid Phase Equilibria, 12: 217-234. A method first proposed by Anderson et al. (1978) has been applied to evaluate the excess Gibbs energy from vapor-liquid equilibrium (VLE) data. This method, which is based on the maximum-likelihood principle, is shown to be more accurate and to provide more information than classical methods based on the least-squares principle. The influences of experimental errors, the number of data points, and the vapor pressures of the pure components on the fitting are studied using reliable experimental data obtained for several systems. The selection of the set of variables to be considered ((p, T, x, y), (p, T, x) or (p, T, y)) and the criteria for choosing the equation which best fits the excess Gibbs energy are also discussed.

Excess enthalpies at 298.15 K of binary mixtures of cyclohexane with n-alkanes

Abstract Molar excess enthalpies for binary mixtures of cyclohexane + n -hexane, + n -octane, + n -decane, + n -undecane, + n -hexadecane, and n -heptadecane, were measured at 298.15 K. All these mixings were endothermic. The Redlich-Kister equation was used to correlate these mixtures H E with composition.

Isothermal compressibility of benzene + n-hexane, + n-heptane, + n-octane, and + n-decane at 298.15, 308.15, 318.15, and 333.15 K

Abstract The isothermal compressibilities have been determined at 298.15, 308.15, 318.15, and 333.15 K for benzene + n-hexane, + n-heptane, + n-octane, and + n-decane. For benzene + n-hexane the “excess” function −V −1 ( ∂V E ∂p ) T is negative but it is positive for the other mixtures. The absolute value of −V −1 ( ∂V E ∂p ) T increases with temperature for all mixtures and shows a maximum at a mole fraction about 0.6 of C6H6.

Excess gibbs energy and excess volume of (cyclohexane+2-propanone) and of (cyclohexane+2-butanone)

Abstract Isothermal vapour-liquid equilibria for cyclohexane + 2-propanone and +2-butanone were obtained at 323.15 K. The results were found to be consistent. Excess molar volumes were obtained at 298.15 and 303.15 K for (cyclohexane + 2-propanone) and at 298.15, 303.15 and 323.15 K for (cyclohexane + 2-butanone). The experimental results showed that both mixtures deviate positively from ideality.

Excess Gibbs energies of (benzene + n-pentadecane) at 298.15 and 323.15 K

Vapour pressures for (benzene + n-pentadecane) at 298.15 and 323.15 K are reported. A new degassing method is described which makes the reproduction of vapour-pressure measurements possible. Liquid-phase values of GmE have been determined from vapour pressures. Analysis using the maximum-likelihood principle enables the evaluation of the variances of the calculated parameters, and the selection, between two or more fits, of the one providing a better representation of the results.