R. Malhotra

The Tait equation: 100 years on

The “Tait equation,” which is now widely used to fit liquid density data over wide pressure ranges, is a modification of the original equation of Tait, published 100 years ago, to fit his results on the compressibility of fresh water and seawater at different pressures. The range of applicability of these different equations is discussed and it is concluded that their simplicity and accuracy in reproducing high pressure density data for dense gases, liquids, solids, and liquid mixtures will ensure their continued use.

Temperature and density dependence of the selfdiffusion coefficients of liquid n-octane and toluene

Selfdiffusion coefficients determined by the NMR spin-echo technique are reported for n-octane (-25–75°C, 0·1–361 MPa) and toluene (-50–50°C, 0·1–369 MPa). In the case of toluene, these are supplemented at 25°C by 14C radiotracer diaphragm cell measurements. The results for each substance are correlated with high pressure viscosity data. Those for toluene overlap the range of applicability of the rough hard sphere model, and this model is used to compare the transport properties of toluene with those of benzene and mesitylene.

Thermodynamic and transport properties of 1,2-dichloroethane

Abstract(p, V, T) data for dichloroethane (DCE) have been obtained at 278.15, 288.15, 298.15, 313.15, 323.15, and 338.15 K for pressures either slightly below the freezing pressure or up to a maximum of 280 M Pa, together with densities at 0.1 MPa. A high-pressure self-centering falling-body viscometer method has been used to measure shear viscosities at 278.15, 288.15, 298.15, 313.15, and 323.15 K for pressures either slightly below the freezing pressure or up to a maximum of 330 MPa. Self-diffusion coefficients for DCE are reported at 278.15, 288.15, 298.15, and 313.15 K for maximum pressures up to 300 MPa. Isothermal compressibilities, isobaric expansivities, and internal pressures have been evaluated from the volumetric data. The shear viscosities and self-diffusion coefficients have been interpreted in terms of a modified rough hard-spheres theory. The anomalous behavior observed for p-V-T, shear viscosities, and self diffusion at higher temperatures and pressures is suspected to be the result of temperature and pressure altering the population ratio of the two molecular conformers, trans and gauche.

Volume ratios {V(p)/V(0.1 MPa)} for n-heptane at temperatures from 278 K to 338 K for pressures up to 400 MPa

A bellows volumometer has been used to obtain volume ratios relative to 0.1 MPa for n -heptane at (278.15, 288.15, 298.15, 313.15, 323.15 and 338.15) K for pressures up to 400 MPa. A version of the Tait equation of state enables accurate extrapolation of the results to 198 K and to 363 K. Prediction of volume ratios with reasonable accuracy up to 423 K is possible if parameters of the critical point are included in the Tait equation. The isothermal compressibilities, isobaric expansivities, “internal pressures”, and changes in isobaric specific heat capacity, have been evaluated from the results.

Thermodynamic properties of propanone (acetone) at temperatures from 278 K to 323 K and pressures up to 400 MPa

A recently calibrated bellows volumometer(1) has been used to obtain volume relative to 0.1 MPa for acetone at the temperatures (278.15, 288.15, 298.15, 313.15, and 323.15)K for pressures up to 400 MPa. A well established version of the Tait equation(1) should enable accurate extrapolation of the results to temperatures approaching the normal melting temperature. Prediction of volume ratios, for temperatures beyond the maximum experimental temperature, is possible with reasonable accuracy if critical properties are included in the Tait equation. The effects of pressure on isothermal compressibility, thermal expansivity, internal pressure, and isobaric specific heat capacity have been evaluated from the results.

Thermodynamic Properties of 2,2,4-Trimethylpentane

Abstractp, V, T data for 2,2,4-trimethylpentane (TMP) have been obtained in the form of volume ratios for six temperatures in the range 278.15 to 338.15 K for pressures up to 280 MPa. Isothermal compressibilities, isobaric expansivities, and internal pressures have been evaluated from the volumetric data. There are strong indications that the combination of the present results with literature data at 348 and 373 K enable accurate extrapolations in the liquid range up to 473 K, and possibly to as low as 170 K, for pressures up to 980 MPa; use of only the present results with the requirement that the B coefficient of the Tait equation should become equal to the negative of the critical pressure at the critical temperature provides interpolations and extrapolations of comparable accuracy. It is suggested that 2,2,4-trimethylpentane is a suitable secondary reference material (because of its large liquid range at atmospheric pressure and the similarity of its volumetric properties to a wide range of fluids) for calibration of measuring cells used for determining volumes of fluids under pressure.

Thermodynamic properties of 2,2,2-trifluoroethanol

Abstract(p, V, T) data for 2,2,2-trifiuoroethanol (TFE) have been obtained in the form of volume ratios for six temperatures in the range 278.15 to 338.15 K for pressures up to 280 MPa. Isothermal compressibilities, isobaric expansivities, and internal pressures have been evaluated from the volumetric data. The compressibilities and internal pressures indicate that the behavior of TFE is closer to that of methanol than of ethanol for most of the pressure range. The use of only the present volumetric results together with the requirement that the B coefficient of the Tait equation should become equal to the negative of the critical pressure at the critical temperature provides interpolations and extrapolations up to 413 K of comparable accuracy.

An automated volumometer: Thermodynamic properties of 1,1-dichloro-2,2,2-trifluoroethane (R123) for temperatures of 278.15 to 338.15 K and pressures of 0.1 to 380 MPa

An automated bellows volumometer is described which is capable of obtaining p-V-T data in the form of volume ratios for pressures up to 380 MPa. Volume ratios for 1,1-dichloro-2,2,2-trifluoroethane (R123) have been measured for six temperatures in the range of 278.15 to 338.15 K in the liquid phase. The accuracy of the volume ratios is estimated to be ±0.05 to 0.1% for the experimental temperatures up to 298.15 K and better than ±0.15% for temperatures above the normal boiling point of R123 (300.15 K). They agree with the literature data (which do not extend beyond 4 MPa) within the experimental uncertainty of those results. Isothermal compressibilities, isobaric expansivities, internal pressures, and isobaric molar heat capacities have been evaluated from the volumetric data. The pressure dependence of isobaric molar heat capacities obtained from the data generally agree with the pressure dependence of experimentally measured literature values within the latters accuracy of ±0.4%.

Thermodynamic properties of butan-2-one at temperatures from 278 K to 338 K and pressures from 0.1 MPa to 280 MPa; predictions for higher ketones

A bellows volumometer has been used to obtain volume ratios relative to 0.1 MPa for butan-2-one at the temperatures (278.15, 288.15, 298.15, 313.15, 323.15, and 338.15) K for pressures up to 280 MPa. These have been used to evaluate the effects of pressure on isothermal compressibility, isobaric expansivity, internal pressure, and molar isobaric heat capacity. Combining the parameters B of the Tait equation for butan-2-one and propanone and expressing them as functions of reduced temperature has enabled prediction of volumetric properties for pentan-2-one, pentan-3-one, and hexan-2-one usually within experimental error.

Intradiffusion and viscosity measurements in acidified iron(III) chloride solutions at 25°C

Intradiffusion of species in acidified (using eithe hydrochloric or perchloric acid) iron(III) chloride solutions has been studied using labeled iron(III), chloride and water. Comparison with data for iron(III) perchlorate has enabled the influence of complexed species upon the diffusion to be ascertained. The chloro-iron species formed have larger diffusion coefficients than the free iron(III) ion as would be expected from their lower net charge. Simple diffusion models have been employed to enable estimates of the diffusion of the complexed species and of the free chloride diffusion coefficients to be obtained. These are discussed in relation to literature data for similar systems. In addition esitmates of the effective hydration of the iron(III) species in solutions have been obtained from the diffusion data. These are discussed in relation to two other trivalent metal salt systems, chromium chloride and lanthanum chloride; the overall hydration of the three cations is virtually identical.