María J. P. Comuñas

High-Pressure Measurements of the Viscosity and Density of Two Polyethers and Two Dialkyl Carbonates

The viscosity and density of four pure liquid compounds (dimethyl carbonate, diethyl carbonate, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether) were measured at several temperatures between 283.15 and 353.15 K. The density measurements were performed up to 60 MPa with an uncertainty of 1×10−4g·cm−3. The viscosity at atmospheric pressure was measured with an Ubbelohde-type glass capillary tube viscometer with an uncertainty of ±1%. At pressures up to 100 MPa the viscosity was determined with a falling ball viscometer with an uncertainty of ±2%. The density (410 experimental values) and viscosity data (184 experimental values) were fitted to several correlation equations.

Relationship between viscosity coefficients and volumetric properties using a scaling concept for molecular and ionic liquids.

In this work, a scaling concept based on relaxation theories of the liquid state was combined with a relation previously proposed by the authors to provide a general framework describing the dependency of viscosity on pressure and temperature. Namely, the viscosity-pressure coefficient (partial differentialeta/partial differentialp)T was expressed in terms of a state-independent scaling exponent, gamma. This scaling factor was determined empirically from viscosity versus Tvgamma curves. New equations for the pressure- and temperature-viscosity coefficients were derived, which are of considerable technological interest when searching for appropriate lubricants for elastohydrodynamic lubrication. These relations can be applied over a broad range of thermodynamic conditions. The fluids considered in the present study are linear alkanes, pentaerythritol ester lubricants, polar liquids, associated fluids, and several ionic liquids, compounds selected to represent molecules of different sizes and with diverse intermolecular interactions. The values of the gamma exponent determined for the fluids analyzed in this work range from 1.45 for ethanol to 13 for n-hexane. In general, the pressure-viscosity derivative is well-reproduced with the values obtained for the scaling coefficient. Furthermore, the effects of volume and temperature on viscosity can be quantified from the ratio of the isochoric activation energy to the isobaric activation energy, Ev/Ep. The values of gamma and of the ratio Ev/Ep allow a classification of the compounds according to the effects of density and temperature on the behavior of the viscosity.

Density scaling of the transport properties of molecular and ionic liquids

Casalini and Roland [Phys. Rev. E 69, 062501 (2004); J. Non-Cryst. Solids 353, 3936 (2007)] and other authors have found that both the dielectric relaxation times and the viscosity, η, of liquids can be expressed solely as functions of the group (TV (γ)), where T is the temperature, V is the molar volume, and γ a state-independent scaling exponent. Here we report scaling exponents γ, for the viscosities of 46 compounds, including 11 ionic liquids. A generalization of this thermodynamic scaling to other transport properties, namely, the self-diffusion coefficients for ionic and molecular liquids and the electrical conductivity for ionic liquids is examined. Scaling exponents, γ, for the electrical conductivities of six ionic liquids for which viscosity data are available, are found to be quite close to those obtained from viscosities. Using the scaling exponents obtained from viscosities it was possible to correlate molar conductivity over broad ranges of temperature and pressure. However, application of the same procedures to the self-diffusion coefficients, D, of six ionic and 13 molecular liquids leads to superpositioning of poorer quality, as the scaling yields different exponents from those obtained with viscosities and, in the case of the ionic liquids, slightly different values for the anion and the cation. This situation can be improved by using the ratio (D∕T), consistent with the Stokes-Einstein relation, yielding γ values closer to those of viscosity.

pρT measurements of polyethylene glycol dimethylethers between 278.15 and 328.15 K at pressures to 12 MPa

In this paper we present a new experimental apparatus designed to measure pressure–density–temperature (pρT ) properties with a high-pressure vibrating tube densimeter. Data reliability has been verified by comparing our experimental results for methanol, n-heptane, toluene, and HFC-134a with literature data. In this work we also report new experimental densities from 278.15 to 328.15 K, and up to 12 MPa, of triethylene glycol dimethylether (TrEGDME) and tetraethylene glycol dimethylether (TEGDME). The isobaric thermal expansion coefficients, isothermal compressibility, and internal pressure have been calculated. The dependence of these properties on the length of polyethylene glycol dimethylether, CH3O–((CH2)2O)n–CH3, is analyzed.

Experimental excess volumes of organic carbonate+alkane systems. Estimation of the parameters of the Nitta–Chao model for this kind of binary mixture

Excess volumes at 298.15 K and atmospheric pressure of some organic carbonate+alkane binary systems have been measured using an Anton Paar 602 HP densimeter. For the first time, published data on excess enthalpies, excess volumes, excess Gibbs energies of the above-mentioned binary systems together with the vaporisation enthalpies and the molar volumes of the pure organic carbonates, were used to estimate the interaction parameters between the carbonate group O–CO–O and the methyl and methylene groups, CH3, CH2, respectively. The mean deviations between experimental and theoretical values were smaller than 6% for all the properties. We have also compared our results with those obtained by Garcia etal. with the Original, Tassios etal., Larsen etal. and Gmehling etal. versions of the UNIFAC model and with those obtained by Kehiaian etal. using the DISQUAC model.

PρTx measurements for HFC-134a + triethylene glycol dimethylether system

Experimental densities in the compressed liquid phase are reported for 1,1,1,2-tetrafluoroethane (HFC-134a), triethylene glycol dimethylether (TriEGDME) and six of their mixtures from 293.15 to 373.15 K and at pressures up to 60 MPa. From the experimental results, we have analysed the volumetric behaviour of HFC-134a+TriEGDME. In almost all the measurement range, the density of the refrigerant is greater than that of the polyether. Furthermore, above 333.15 K the densities of the mixtures display a crossover phenomenon with composition. The excess volumes are strongly negative and asymmetrical towards high refrigerant concentrations, becoming more negative when the temperature increases and the pressure decreases.

Reference Correlation of the Viscosity of Squalane from 273 to 373 K at 0.1 MPa

The paper presents a new reference correlation for the viscosity of squalane at 0.1 MPa. The correlation should be valuable as it is the first to cover a moderately high viscosity range, from 3 to 118 mPa s. It is based on new viscosity measurements carried out for this work, as well as other critically evaluated experimental viscosity data from the literature. The correlation is valid from 273 to 373 K at 0.1 MPa. The average absolute percentage deviation of the fit is 0.67, and the expanded uncertainty, with a coverage factor k = 2, is 1.5%.

Reference Correlations for the Density and Viscosity of Squalane from 273 to 473 K at Pressures to 200 MPa

This paper presents new reference correlations for both the density and viscosity of squalane at high pressure. These correlations are based on critically evaluated experimental data taken from the literature. In the case of the density, the correlation, based on the Tait equation, is valid from 273 to 473 K at pressures to 200 MPa. At 0.1 MPa, it has an average absolute deviation of 0.03%, a bias of −0.01%, and an expanded uncertainty (at the 95% confidence level) of 0.06%. Over the whole range of pressures, the density correlation has an average absolute deviation of 0.05%, a bias of −0.004%, and an expanded uncertainty (at the 95% confidence level) of 0.18%. In the case of the viscosity, two correlations are presented, one a function of density and temperature, based on the Assael-Dymond model, and the other a function of temperature and pressure, based on a modified Vogel-Fulcher-Tammann equation. The former is slightly superior to the latter at high temperatures (above 410 K), whereas the reverse is ...

Phase equilibria and pVT predictions for alkyl carbonate + n-alkane systems using equations of state

Abstract In this paper experimental data available in the literature on vapor–liquid equilibria, densities and excess molar volumes of dialkyl carbonate+ n -alkane mixtures on broad temperature and pressure ranges have been used in order to test four equations of state (EoS): Soave–Redlich–Kwong (SRK), Peng–Robinson (PR), Patel–Teja (PT) and Dohrn–Prausnitz (DP). For the pure components, when the critical parameters were not available in the literature, the group contribution method of Klincewicz and Reid was used to estimate the critical temperature and pressure. For dialkyl carbonate+ n -alkane mixtures we have determined the binary interaction parameter, k ij , using experimental vapor–liquid equilibria data and then with these parameters the pVTx values were predicted. The best correlations for VLE and predictions for the volumetric behavior were obtained with PR and PT equations.

Analysis of the molecular interactions of organic anhydride+alkane binary mixtures using the Nitta–Chao model

Abstract The Nitta–Chao EOS group-contribution model, based on cell theory, is used to study the interactions of the organic anhydride+n-alkane binary mixtures. A database of excess enthalpies, excess Gibbs energies and excess volumes for this kind of mixtures, together with molar volumes and vaporization enthalpies of pure organic anhydrides, were used to calculate the characteristic parameters of the Nitta–Chao group-contribution model. In order to enlarge the database, the excess molar volumes at 298.15 K for the binary mixtures of pentanoic and hexanoic acid anhydrides with an n-alkane are reported. An analysis of the interactions is presented with the estimation of the changes of the mean numbers of contacts between the different groups during the mixing process. The influence of the dispersive and non-dispersive interaction energy parameters on the excess volumes and excess enthalpies is also presented. The model consistently describes the experimental data of organic anhydride+n-alkane mixtures, i.e. the excess volumes increase when the anhydride chain length decreases and when alkane chain length increases. The symmetry of the VE(x) curves and the sign and magnitude of the excess volumes are strongly dependent on the lengths of the alkane and of the organic anhydride.