Volumetric properties of mixtures of fluoroalcohols and water at high pressures

Densities of aqueous solutions of 2,2,2-trifluoroethanol, 2,2,3,3-tetranuoropropanol, and 2,2,3,3,3-pentanuoropropanol have been measured with a vibrating-tube densitometer. Measurements were performed at temperatures of 298 and 323 K and at pressures up to 80 MPa with an estimated uncertainty of ±0.2 %. Molar volumes obtained for these mixtures are correlated with pressure by the Tait equation within the experimental uncertainty. Excess molar volume, isothermal compressibility, and partial molar volume of these mixtures are determined in terms of this correlation equation and compared with those of the aqueous solutions of hydrocarbon alcohols. Composition dependence of partial molar volume is discussed in comparison with that of Raman spectroscopic data.     

Viscosity of mixtures of fluoroalcohols and water at high pressures

Viscosities of aqueous solutions of 2,2,2,-trifluoroethanol, 2,2,3,3-tetrafluoropropanol and 2,2,3,3,3-pentafluoropropanol have been measured with a falling-body viscometer. Measurements were performed at temperatures from 298 to 323 K and at pressures up to 80 MPa with an estimated uncertainty of ±2%. Viscosities obtained for these mixtures are represented by a simple empirical equation within the experimental uncertainty. The composition dependence of the viscosity is compared with that for mixtures of hydrocarbon alcohols and water.Paper dedicated to Professor Joseph Kestin.     

Volumetric behavior of pure alcohols and their water mixtures under high pressure

The specific volumes of C₁-C₄ alcohols and binary mixtures of water with methanol, ethanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol are presented as functions of temperature, pressure, and composition. The measurements were carried out using a modified Adams piezometer and a high-pressure burette method in a temperature range from 283.15 to 348.15 K at pressures up to 350 MPa. The uncertainties in the specific volume obtained are estimated to be less than 0.09%. The specific volumes of the pure alcohols and their mixtures with water are found to decrease monotonously with increasing pressure. The numerical P-V relations at each temperature and composition are correlated satisfactorily as a function of pressure by the Tait equation. Definite inflections appear on the isobars of isothermal compressibility or partial molar volume versus composition of alcohol + water mixtures.     

An Automated Vibrating-Tube Densimeter for Measurements of Small Density Differences in Dilute Aqueous Solutions

The core of the automated apparatus is a high-temperature high-pressure densimeter with a metal vibrating tube designed for accurate flow measurements of densities of liquids in the temperature range from 298 to 573 K and at pressures from 0.1 MPa up to 30 MPa. The densimeter is being employed for a study of dilute solutions of aqueous solutions of organic substances where the density difference {solution–water} is a primary experimental quantity. Consequently, partial molar volumes of solutes at infinite dilution in water are evaluated from the measured data. Two sampling sections are connected in series in the filling line of the densimeter. One of them is employed for manual filling of the measured sample into a sampling loop using a syringe. The other section allows fully automated measurement of up to 12 samples in one run. The recorded data are evaluated after the automated run is completed.     

Phase behavior of mixtures at very high pressures

The invention of the diamond anvil cell (DAC) has been an enormous stimulus to high-pressure research. This technique has only recently been used to investigate the behavior of binary systems, probably because of the extra experimental problems which arise in the study of mixtures. It will be shown that a variety of aspects of the behavior of the mixture can, nevertheless, be studied under extreme conditions. Although the first investigations were carried out only recently, some very interesting results have already been obtained. A variety of two-components systems has been studied, e.g., He-Kr, Ne-Xe, He-H₂, NH₃-H₂O, and N₂-He₂. Some of these results are discussed. Finally, a comparison is made between experimental results and theoretical calculations.Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Group Contributions for an Estimation of Partial Molar Volumes at Infinite Dilution for Aqueous Organic Solutes at Extended Ranges of Temperature and Pressure

Experimental data on the partial molar volume at infinite dilution in water for two groups of organic solutes (derivatives of benzene and aliphatic hydroxyl derivatives) measured using a vibrating-tube densimeter in the temperature and pressure ranges 298 to 573K and 0.1 to 30MPa are summarized. Smoothed values of partial molar volume as a function of temperature and pressure are employed for the evaluation of group and structural contributions. The contributions are used to estimate the partial molar volumes at infinite dilution in water for various solutes. The average deviation between partial molar volumes calculated from the contributions and the experimental data employed for the evaluation of the contributions is less than 1cm³mol^–1 in most cases. Predictions of partial molar volumes of solutes not included in the evaluation of the contributions are performed and results are compared with experimental data.     

Density and viscosity of linear perfluoropolyethers under high pressures

New experimental data on the density and viscosity of linear, unbranched perfluoropolyethers are presented at temperatures from 273 to 333 K and pressures up to 180 MPa. The measurements were carried out by a high-pressure burrette apparatus and a falling-cylinder viscometer. The uncertainties of the measurements are estimated to be less than 0.09% for the specific volume and 2.5% for the viscosity. The P-V data at each temperature are correlated satisfactorily by the Tait equation. The viscosity data are also analyzed and correlated with pressure or molar volume by several empirical and theoretical equations.     

Volumetric properties of 1-alkanols at temperatures in the range 298–348 K and pressures up to 40 MPa

Molar volumes, thermal expansion coefficients, and isothermal compressibilities of six higher 1-alkanols (1-hexanol, 1-octanol, 1-decanol, 1-dodecanol, 1-tetradecanol, and 1-hexadecanol) have been determined at temperatures from 298 to 348 K and pressures up to 40 MPa. The density measurements were performed using a vibrating densitometer with an uncertainty of ±0.06%. The relationship between the properties and the structures of these alkanols is discussed in terms of the carbon-chain lengths.     

Thermodynamic properties of R 22 + R 114 mixtures in the high-density region for temperatures from 310 to 370 K

The densities for mixtures of R 22 and R 114 have been measured with the variable-volume method using a metal bellows as a function of temperature and pressure. The results for three different compositions (75, 50, and 25 mol% R 22) cover the high-density region along seven isotherms between 310 and 370 K at 15 pressures from 1.0 to 10 MPa. Based on the present density measurements, the values of the excess molar volume, the volume expansion coefficient, and the isothermal compressibility have been calculated. The excess molar volumes for each mixture below 340 K are positive, whereas those above 350 K decrease with decreasing pressure and become negative at low pressures. The behavior of the volume expansion coefficient and the isothermal compressibility for the equimolar mixture are closer to that for R 114 than the average of those for both pure components.     

Thermal conductivity of aqueous solutions of NaCl and KCI at high pressures

This paper presents new experimental measurements of the thermal conductivity of aqueous solutions of NaCl and KCl at high pressures. The measurements were made with a parallel-plate apparatus. The temperatures covered the range from 293 to 473 K at pressures up to 100 MPa and concentrations from 0.025 to 0.25 mass fraction of NaCl and KCl. The measurements included 6 isobars at pressures from 0.1 to 100 MPa at intervals of 20 MPa, 10 isotherms at temperatures from 293 to 473 K at intervals of 20 K, and 6 isopleths at concentrations from 0.025 to 0.25 mass fraction of NaCl and KCl at intervals of 0.05. The precision of the measurements was ±1.6%. The thermal conductivity obtained for NaCl + H₂O and KCl + H₂O was compared with data of other authors, with satisfactory agreement. The viability of the technique was confirmed and the essential features of a high-precision instrument were established.     

PVTx Measurements and Partial Molar Volumes for Aqueous Li2SO4 Solutions at Temperatures from 297 to 573 K and at Pressures Up to 40 MPa

Densities of four aqueous Li₂SO₄ solutions (0.0944, 0.2798, 0.6115, 0.8850 molkg^–1) have been measured in the liquid phase with a constant-volume piezometer immersed in a precision liquid thermostat. Measurements were made for ten isotherms between 297 and 573 K. The range of pressure was from 3.9 to 40 MPa. The total uncertainty of density, pressure, temperature, and concentration measurements were estimated to be less than 0.06%, 0.05%, 10 mK, and 0.014%, respectively. The reliability and accuracy of the experimental method was confirmed with measurements on pure water for two isobars at 10 and 38 MPa. Experimental and calculated (IAPWS formulation) densities for pure water show excellent agreement within their experimental uncertainties (average absolute deviation within 0.02 to 0.05%). Saturated liquid densities were determined by extrapolating experimental P- data to the vapor pressure at fixed temperature and composition using an interpolating equation. Apparent and partial molar volumes were derived using measured densities for aqueous solutions and pure water. Derived apparent molar volumes were extrapolated to zero concentration to yield partial molar volumes of electrolyte (Li₂SO₄) at infinite dilution. The temperature, pressure, and concentration dependences of partial and apparent molar volumes were studied. A polynomial type of equation of state for specific volume was obtained as a function of temperature, pressure, and composition by a least-squares method using the experimental data. The average absolute deviation (AAD) between measured and calculated values from this polynomial equation for density was 0.02%. Measured values of solution density, and apparent and partial molar volumes were compared with data reported in the literature by other authors.     

Thermophysical properties of liquids at high pressures

Most of the thermophysical properties of fluids are greatly altered at high pressures, and the studies of these changes are of much scientific and technological importance. In this paper, the effects of temperature and pressure on the density, viscosity, and thermal conductivity of various liquids are described briefly, based on recent experimental results from the author's laboratory. The objectives of this investigation, methods of measurements, and some of the experimental results are reviewed, as well as the present aspects in this field. Several important problems to be interpreted are also pointed out from the present measurements.Presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.     

Isotope effect on the viscosity of benzene and cyclohexane mixtures under high pressures

Viscosities of binary mixtures of cyclohexane with protiobenzene, C₆H₆, or deuteriobenzene, C₆D₆, have been measured at 298 and 323 K and at pressures up to 50 MPa using a capillary viscometer. The viscosities of these mixtures obtained were represented by a empirical Tait-type equation within the experimental uncertainty of ±2%. The effect of the isotopic substitution on the viscosity has been discussed.     

Measurements of the thermal conductivity of aqueous LiBr solutions at pressures up to 40 MPa

This paper describes absolute measurements of the thermal conductivity of aqueous LiBr solutions in the concentration range 5 to 15m (molality), the temperature range 30 to 100°C, and the pressure range 0.1 to 40 MPa. The measurements have been performed with the aid of a transient hot-wire apparatus employing a thin tantalum wire coated with an anodic tantalum pentoxide insulation layer. In using the tantalum wire, a modification of the bridge circuit has been made to keep the electric potential of the wire always higher than the ground level in order to protect the insulation layer from breakdown. The experimental data, which have an estimated accuracy of ±0.5%, have been correlated in terms of the polynomials of concentration, temperature, and pressure for practical use. Also, it has been found that the pressure coefficient of the thermal conductivity decreases with increasing concentrations.     

Thermodynamic properties and excess volumes of 2,2,4-trimethylpentane + n-heptane mixtures from 298 to 338 K for pressures up to 400 MPa

(p, V, T) data for mixtures of 2,2,4-trimethylpentane (TMP) and heptane have been obtained in the form of volume ratios for four temperatures in the range 298.15 to 338.15 K for pressures up to 390 MPa. The data have been represented by the Tait equation of state for the purposes of interpolation and extrapolation. The atmospheric pressure densities of both pure components and their mixtures for three temperatures have been measured and used to determine the excess molar volumes. Isothermal compressibilities have been evaluated from the volumetric data.     

A vibrating tube flow densitometer for measurements with corrosive solutions at temperatures up to 723 K and pressures up to 40 MPa

A new version of a vibrating tube flow densitometer has been designed permitting measurements of density differences between two fluids in the temperature range from 298 to 723 K and at pressures up to 40 MPa. The instrument is equipped with a Pt/Rh20 vibrating tube (1.6-mm o.d.) and a Pt/Rh10 transporting tube (1.2-mm o.d.) permitting measurements with highly corrosive liquids. The period of oscillation of the tube is about 7.5 ms, with a typical stability better than 10⁻⁴% over about a 1-h period over the entire temperature interval. The calibration constantK at room temperature is about 530 kg·m⁻³·ms⁻², with a temperature coefficient of approximately −0.13kg·m⁻³·ms⁻²·K⁻¹, and is practically pressure independent. It can be determined by calibration with a reproducibility generally better than 0.1%. The instrument was tested with NaCl(aq) solutions in the temperature range from 373 to 690 K for density differences between sample and reference liquid ranging from 200 to 2 kg·m⁻³; the corresponding errors are believed to be below 0.3 and 5%, respectively. A highly automated temperature control maintains the temperature of the tube stable to within ±0.02 K.     

Thermodynamic behavior of supercritical fluid mixtures

The recent surge of interest in supercritical extraction has brought the unusual properties of supercritical mixtures into the focus of attention. We discuss some of the properties of binary mixtures in a range around the gas-liquid critical line from the point of view of supercritical solubility. The general thermodynamic relationships that govern the enhancement of supercritical solubility are readily derived by a mathematical method introduced by Ehrenfest. The enhancement is governed by a strong divergence centered at a critical end point. We give the classical and nonclassical power-law behavior of the solubility along the experimental paths of constant temperature or pressure. The factor multiplying the strong divergence contains the partial molar volume or enthalpy of the solute in the supercritical phase. These partials are quite anomalous, especially if the mole fraction of the solute is small. They diverge at the solvent's critical point. We cite experimental evidence of these divergences, especially the results of recent experiments in dilute near-critical salt solutions. The anomalies found in these salt solutions are common to all dilute near-critical mixtures with a nonvolatile second component. We show that on experimentally convenient paths the solubility in a binary liquid mixture near its consolute points is not strongly enhanced. Finally, we sketch a nonclassical model based on the decorated lattice gas that can be used to describe supercritical solubility enhancement at low solubility, with the pure solvent used as a reference.Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Densities of liquid R 114 at temperatures from 310 to 400 K and pressures up to 10 MPa

Density measurements for liquid R 114 (dichlorotetrafluoroethane) have been obtained with a variable-volume method. The results cover the high-density region from 1007 to 1462 kg·m^–3 along ten isotherms between 310 and 400 K at 16 pressures from 0.5 to 10.0 MPa. The experimental uncertainty in the density measurements was estimated to be no greater than 0.2%. Based on the present results the derivatives with respect to temperature and pressure were calculated, and numerical values of the volume expansion coefficient and of the isothermal compressibility are tabulated as a function of temperature and pressure.     

Vibrating-wire viscometers for liquids at high pressures

The design and operation of two independent vibrating-wire viscometers are described. The instruments are intended for operation in the liquid phase at pressures up to 300 MPa and have been designed specifically for this purpose using the detailed theory of the device. Extensive evidence is adduced to demonstrate that the operation of the viscometers is consistent with the theory. Although the instruments attain a precision in viscosity measurements of ±0.1%, when used in an absolute mode the accuracy that can be achieved is no better than ±3%. However, if the instrument is calibrated for two welldefined instrumental parameters, the uncertainty in the reported viscosity is improved to +0.5%. The results of measurements of the viscosity of normal heptane in the temperature range 303 to 348 K at pressures up to 250 MPa made with one of the viscometers are reported. The results are shown to be totally consistent with measurements reported earlier using the instrument designed for lower pressures.