(p, Vm, T) measurements of (cyclohexane + nonane) at temperatures from 298.15 K to 328.15 K and at pressures up to 40 MPa
Introduction
Research activities of our laboratory comprise, among others, the systematic measurement of volumetric properties of different groups of organic compounds. Our new project is devoted to the systematic study of liquid systems modelling liquid engine fuels. As the first step, (cyclohexane + alkane) at normal pressure and temperature 298.15 K were studied [1].
To our knowledge, there exist no volumetric data for the liquid phase of (cyclohexane + nonane) at elevated pressures. Therefore, we have measured densities and calculated isothermal compressibilities and excess volumes of the system. The apparatus based on a high-pressure vibrating-tube densimeter working in a static mode [2] and designed for measuring the (p, Vm, T) behaviour of pure liquids and liquid mixtures at elevated temperatures (283 K to 333 K) and moderately high pressures to 40 MPa was used for the measurements. The measurements were carried out at the temperatures 298.15 K, 308.15 K, 318.15 K, and 328.15 K and in the pressure range 0.1 MPa to 40 MPa. To have sufficiently accurate values of densities at the reference (atmospheric) pressure for fitting the high-pressure density data to the Tait equation, the temperature dependence of densities at atmospheric pressure was measured first with vibrating-tube densimeter DSA 5000. In addition, excess volumes and adiabatic compressibilities were calculated from the data.
The densities and excess volumes of the investigated liquids and their mixtures are required, for instance, for relating excess enthalpy and excess Gibbs free energy values. From a practical point of view, the data are useful for the design of mixing, storage, and process equipment. Last but not least, the data measured reflect interactions between the molecules of the mixtures studied and can serve for testing the theories of the liquid state.
Section snippets
Materials
The nonane used in the experiments was the product from Fluka, purum, g.c. mass fraction ⩾0.99. The cyclohexane was from Sigma–Aldrich, for HPLC, g.c. mass fraction purity ⩾0.997. Both the hydrocarbons were dried and stored over 0.4 nm molecular sieves. In order to check the purity of the substances, their density and refractive index values were determined at T = 298.15 K and compared with the literature data [3], [4], [5] with the agreement being, in general, good (table 1). The contents of the
Atmospheric pressure measurements
The results of the atmospheric pressure measurements are given in table 2. The measured densities are tabulated along with excess volumes and adiabatic compressibility. The values of excess volume were calculated from the mixtures densities, ρ, and the densities, ρi, and molar masses, Mi, of pure components i (i = 1, 2) using the relationwhere subscript 1 refers to cyclohexane and 2 to nonane and x stands for the mole fraction of cyclohexane. The
Acknowledgements
The authors acknowledge the partial support from the Grant Agency of the Czech Republic. The work has been carried out under Grant No. 104/06/0656.
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