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- Viscosity measurements of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM OTf) at high pressures using the vibrating wire techniquePublication . Sequeira, Maria Carolina; Avelino, Helena Maria Da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, J.M.N.A.The goal of the present work is to contribute to the characterization of ionic liquids by measuring their viscosity at high pressures. As 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM OTf) has been used as a solvent in CO2 capture processes, the temperature and pressure ranges of the measurements cover the intervals used in those processes. Measurements of the viscosity of EMIM OTf along five isotherms in the range (298-358) K and at pressures up to 50 MPa, have been performed using the vibrating wire technique in the forced mode of operation. As far as the authors are aware, these are the first measurements of this ionic liquid at pressures higher than 0.1 MPa, to be published. The viscosity results were correlated with the molar volume, using a modified hard-spheres model. The root mean square (sigma) deviation of the data from the correlation is less than 0.5% The expanded uncertainty of the present viscosity data is estimated as +/- 2.0% at a 95% confidence level. As a complement, the pressure-viscosity coefficient has been calculated within the temperature range of the present results. Previous studies of the influence of the electric conductivity of ionic liquids, including EMIM OTf, in the vibrating wire method, have been taken into account for the present work. Complementary measurements of the density have been performed along seven isotherms in the temperature range from (298-363) K and pressures from (0.1-70) MPa. The density measurements were carried out with an Anton Paar vibrating U-tube densimeter and the raw data were corrected for viscosity effects. The density results were correlated with the temperature and pressure using a modified Tait equation. The expanded uncertainty of the present density data is estimated as +/- 0.2% at a 95% confidence level.
- Viscosity and density measurements on liquid n-heptadecane at high pressuresPublication . Sequeira, Maria Carolina; Avelino, Helena Maria Da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, JoãoThis article reports novel measurements of the viscosity, eta, of liquid n-heptadecane at pressures up to 70 MPa, along six isotherms between 303 and 358 K. The experiments were carried out using a vibrating wire viscometer operated in the forced mode. The 303 and 313 K isotherms have a restricted range of pressures to avoid eventual solidification. The present measurements have an uncertainty less than U(eta) = 0.015.eta with a confidence level of 0.95. Complementary measurements of the density, rho, were performed with the same ranges of temperature and pressure, using a DMA HP Anton Paar U-tube densimeter, with a DMA 5000 instrument as a reading unit. The overall maximum uncertainty is U(rho) = 0.002.rho with a confidence level of 0.95. The article provides a correlation of the viscosity of compressed liquid n-heptadecane with the molar volume, constructed by means of a scheme based on a modified hard-sphere theory, which describes the experimental data within ca. 1%. A program is provided in the Supporting Information to promptly perform interpolation of the viscosity as a function of temperature and pressure. The isothermal compressibility and the isobaric thermal expansivity were calculated from the density. Viscosity-pressure coefficients have also been determined from the viscosity.
- Viscosity and density measurements of poly(ethyleneglycol) 200 and poly(ethyleneglycol) 600 at high pressuresPublication . Sequeira, Maria Carolina; Avelino, Helena Maria Da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, JoãoNew measurements for the viscosity and density of poly(ethyleneglycol) 200 [PEG 200] and of poly(ethyleneglycol) 600 [PEG 600], at pressures up to 50 MPa, are presented. The temperature range of the measurements performed for PEG 200 was from 293 to 348 K and for PEG 600 was from 303 to 348 K. A vibrating wire viscometer operated in the steady-state mode was used to carry out the measurements with an estimated overall uncertainty less than U(eta) = 0.02 center dot eta, for viscosities up to 68 mPa s, and less than U(eta) = 0.026 center dot eta, for higher viscosities with a confidence level of 0.95 (k = 2). Complementary density measurements for both PEGs were performed in the same ranges of temperature and pressure as for the viscosity measurements, using an Anton Paar HP vibrating tube densimeter, with an estimated overall uncertainty of about U(eta) = 0.002 center dot rho with a confidence level of 0.95 (k = 2). Moreover, pressure-viscosity coefficients were obtained for both PEGs. A method based on a dense hard-sphere fluid theory was used to correlate the viscosity data with the density, for both PEGs, with a deviation of the experimental results less than 1%. A modified Tait equation was used to correlate the density results with temperature and pressure.