In this paper, we report new PVTx measurements for water + toluene binary mixtures at 11 near-critical and supercritical isotherms T ) 623, 627, 629, 631, 633, 643, 645, 647, 649, 651, and 673 K and pressures up to 39 MPa at a fixed concentration of x ) 0.0287 mole fraction of toluene. Using these PVTx data together with data obtained earlier by other authors, we developed a crossover Helmholtz free-energy model (CREOS) for pure toluene and dilute aqueous toluene solutions in a wide range of the parameters of state around the vapor-liquid critical points. In the temperature range 593 K e T e 680 K and density range 100 kg‚m -3 e F e 500 kg‚m -3 , the CREOS reproduces the PVT data for pure toluene with an average absolute deviation (AAD) of about 0.5%, the C P data with an AAD of about 1%, and the sound velocity data with an AAD of about 2.6%. In water + toluene mixtures, the CREOS yields an adequate description of all available experimental data in the region bounded by 0.35F c (x) e F e 1.65F c (x) and 0.98T c (x) e T e 1.15T c (x) at x e 0.04 mole fraction of toluene. The possibility of extrapolating the CREOS model to lower temperatures, 0.93T c e T eT c , and higher densities and concentrations, up to F ) 2F c and x ) 0.12, is also discussed.

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We present new PVTx measurements for water (A) + pentane (B) mixtures at the critical temperature of water (T C = 647.05 K) in the pressure range 4 MPa to 41 MPa at x b = 0, 0.028, 0.042, 0.061, 0.088, 0.184, 0.391, 0.694, and 1.0. The measurements were performed with a constant-volume piezometer. The sample was confined to a 36.8 cm3 cylindrical cell of a corrosion-resistant steel alloy, provided with a steel ball for stirring. The cell was separated from the rest of the fill and pressure measurement system by a diaphragm-type null indicator. The temperature was measured by a 10 Ω platinum resistance thermometer. The uncertainty in the temperature measurement is less than ±5 mK. Pressure was measured by means of a dead-weight gauge with a precision of ±2 kPa. The composition was determined with an uncertainty of ±0.002 in mole fraction. The volume of the cell was corrected for temperature expansion and elastic deformation by means of the known expansion coefficients of the cell. Taking into account the errors of temperature, pressure, and concentration measurements, the total experimental uncertainty of density, δρ, was estimated to be less than ±0.5%. From the PVTx results, the excess, partial, and apparent molar volumes were determined. Analysis of the results for dilute water + pentane mixtures showed that partial molar volume of pentane (solute) and excess molar volume of the mixture near the critical point of pure water (solvent) exhibit the behavior predicted by theory. A nonclassical (scaled) asymptotic relation has been used for the analysis of the partial and molar volumes behavior along the critical isotherm−isobar.

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The P V T properties of pure ethanol were measured in the near-critical and supercritical regions. Measurements were made using a constant-volume piezometer immersed in a precision thermostat. The uncertainty of the density measurements was estimated to be 0.15%. The uncertainties of the temperature and pressure measurements were, respectively, 15 mK and 0.05%. Measurements were made along various near-critical isotherms between 373 and 673 K and at densities from 91.81 to 497.67 kg · m −3 . The pressure range was from 0.226 to 40.292 MPa. Using two-phase P V T results, the values of the saturated-liquid and -vapor densities and the vapor pressure for temperatures between 373.15 and 513.15 K were obtained by means of an analytical extrapolation technique. The measured P V T data and saturated properties for pure ethanol were compared with values calculated from a fundamental equation of state and correlations, and with experimental data reported by other authors. The values of the critical parameters (T C ,P C ,ρ C ) were derived from the measured values of saturated densities and vapor pressure near the critical point. The derived values of the saturated densities near the critical point for ethanol were interpreted in term of the "complete scaling" theory.