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- Tris(2-Ethylhexyl) trimellitate (TOTM) a potential reference fluid for high viscosity. Part II: Density measurements at temperatures from (293 to 373) K and pressures up to 68MPaPublication . Diogo, João C. F.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.In Part I of the present work we describe the viscosity measurements performed on tris(2-ethylhexyl) trimellitate or 1,2,4-benzenetricarboxylic acid, tris(2-ethylhexyl) ester (TOTM) up to 65MPa and at six temperatures from (303 to 373) K, using a new vibrating-wire instrument. The main aim is to contribute to the proposal of that liquid as a potential reference fluid for high viscosity, high pressure and high temperature. The present Part II is dedicated to report the density measurements of TOTM necessary, not only to compute the viscosity data presented in Part I, but also as complementary data for the mentioned proposal. The present density measurements were obtained using a vibrating U-tube densimeter, model DMA HP, using model DMA5000 as a reading unit, both instruments from Anton Paar GmbH. The measurements were performed along five isotherms from (293 to 373)K and at eleven different pressures up to 68MPa. As far as the authors are aware, the viscosity and density results are the first, above atmospheric pressure, to be published for TOTM. Due to TOTM’s high viscosity, its density data were corrected for the viscosity effect on the U-tube density measurements. This effect was estimated using two Newtonian viscosity standard liquids, 20 AW and 200 GW. The density data were correlated with temperature and pressure using a modified Tait equation. The expanded uncertainty of the present density results is estimated as 0.2% at a 95% confidence level. Those results were correlated with temperature and pressure by a modified Tait equation, with deviations within 0.25%. Furthermore, the isothermal compressibility, kT, and the isobaric thermal expansivity, ap, were obtained by derivation of the modified Tait equation used for correlating the density data. The corresponding uncertainties, at a 95% confidence level, are estimated to be less than 1.5% and 1.2%, respectively. No isobaric thermal expansivity and isothermal compressibility for TOTM were found in the literature.
- 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, João 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 (σ) 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 of liquid diethylene, triethylene and tetraethylene glycols at moderately high pressures using a vibrating wire instrumentPublication . Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.New viscosity measurements of compressed liquid diethylene glycol (DiEG), triethylene glycol (TriEG) and tetraethylene glycol (TeEG) have been performed using a vibrating wire instrument operated in the forced oscillation mode. The measurements have been carried out in a range of pressures up to 70 MPa and temperatures from (293 - 363) K, covering a total range of viscosities from (3.46 - 1.15 x 10^2) mPa,s. Complementary experimental density data were obtained for the same glycols using an Anton Paar vibrating U-tube densimeter. These measurements have been performed in a range of temperatures from about (283 - 363) K and at pressures up to about 70MPa. The viscosity results were correlated with density, using a modified hard-spheres scheme. The experimental density data were correlated, as a function of temperature and pressure, with a modified Tait-type equation. The expanded uncertainty of the present viscosity results at a 95% confidence level is estimated to be less than ±2.0% for viscosities up to 68 mPa s and less than ±2.6% for higher viscosities. The densities have an expanded uncertainty of ±0.2% at a 95% confidence level.
- Viscosity and density measurements on liquid n-tetradecane at moderately high pressuresPublication . Santos, Tânia V. M.; Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.The main aim of the work is to study the viscosity and density of compressed normal tetradecane in the region of pressures from saturation to 10 MPa, where the available literature data are scarce. New measurements of the viscosity of n-tetradecane (n-C-14) along eight isotherms in the range (283-358) K and at pressures up to 70 MPa, have been performed using the vibrating wire technique in the forced mode of operation. Density measurements have also been performed along nine isotherms in the temperature range from (283 to 373) K and pressures from (0.1 to 70) MPa. The vibrating wire viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square (rms) deviation of the data from the correlation is less than 0.32% and the maximum absolute relative deviation is less than 1.0%. The expanded uncertainty of the present viscosity data is estimated as +/- 1.5% at a 95% confidence level. 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. The isothermal compressibility and the isobaric thermal expansion were calculated by differentiation of the modified Tait equation. The uncertainties of isothermal compressibility and the isobaric thermal expansion are estimated to be less than +/- 1.7% and +/- 1.1%, respectively, at a 95% confidence level. The results are compared with the available literature data. (C) 2017 Elsevier B.V. All rights reserved.
- Tris(2-ethylhexyl) trimellitate (TOTM) a potential reference fluid for high viscosity. Part I: Viscosity measurements at temperatures from (303 to 373) K and pressures up to 65MPa, using a novel vibrating-wire instrumentPublication . Diogo, João C. F.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.The article reports viscosity measurements of compressed liquid tris(2-ethylhexyl) trimellitate or 1,2,4- Benzenetricarboxylic acid, tris(2-ethylhexyl) ester (TOTM) which is an important plasticizer in the polymer industry and has wide applications as a lubricant. Nevertheless, the main motivation for the present work is to propose TOTM as a plausible candidate for an industrial viscosity reference fluid for high viscosity, high pressure and high temperature. This kind of reference fluid is presently on demand by oil industries and the International Association for Transport Properties is developing efforts aiming to select appropriate candidates and to establish the corresponding reference data. The viscosity measurements were performed with a novel vibrating wire sensor. The new instrument was designed for operation at high pressures (up to 100MPa) and temperatures up to 373 K. The present measurements were obtained using the vibrating wire sensor in the forced oscillation or steady-state mode of operation. The viscosity measurements were carried out up to 65MPa and at six temperatures from (303 to 373) K. The viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square deviation of the data from the correlation is 0.53% and the maximum absolute relative deviation was less than 1.7%. The expanded uncertainty of the present viscosity results, at a 95% confidence level, is estimated to be less than 2% for viscosities up to 68mPa s, less than 2.6% for viscosities between (69 and 268) mPas and less than 3% for higher viscosities. The TOTM density data necessary to compute the viscosity results were measured using a vibrating Utube densimeter, model DMA HP and are described in part II of the present work. No literature data above atmospheric pressure could be found for the viscosity of TOTM. As a consequence, the present viscosity results could only be compared upon extrapolation of the vibrating wire data to 0.1 MPa. Independent viscosity measurements were performed, at atmospheric pressure, using an Ubbelohde capillary in order to compare with the vibrating wire results, extrapolated by means of the above mentioned correlation. The two data sets agree within 1%, which is commensurate with the mutual uncertainty of the experimental methods. Comparisons of the literature data obtained at atmospheric pressure with the present extrapolated vibrating-wire viscosity measurements have shown an agreement within 2% for temperatures up to 339K and within 3.3% for temperatures up to 368 K.
- Viscosity measurements of poly(ethyleneglycol) 400 [PEG 400] at temperatures from 293 K to 348 K and at pressures up to 50 MPa using the vibrating wire techniquePublication . Sequeira, Maria Carolina; Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.The article reports new measurements of the viscosity of Poly(ethyleneglycol) 400 [PEG 400] in the range (293–348) K and pressures up to 50 MPa. Complementary measurements of the density of the same sample of PEG 400 have been made covering the ranges of temperature and pressure, (293–353) K and (0.1–50) MPa, respectively. The viscosity measurements were performed using the vibrating wire technique in the forced mode of oscillation and the density measurements were carried out with an Anton Paar vibrating U-tube densimeter. The density raw data were corrected for viscosity effects. The overall uncertainty of the viscosity measurements is estimated to be less than ±2% for viscosities up to 68 mPa s and less than ±2.6% for higher viscosities. The densities have an estimated overall uncertainty of ±0.2%. The rheological behaviour of Poly(ethylene Glycol) 400 has also been studied, using a cone-plate Brookfield viscometer, in a temperature range between (293 and 333) K. The measurements were carried out at shear rates up to 20 s−1 and shear stresses up to 2.20 Pa and have evidenced Newtonian behaviour. The viscosity data obtained were correlated by means of a modified hard-sphere based correlation technique. The relative root mean square, rms, deviation of the experimental results from the correlation equations is 0.54%, and their bias is practically zero. The density data obtained were correlated using a Tait-type equation. As a complement of the present study, the surface tension of PEG 400 was measured by the pendant drop method. This study aims to be useful for viscosity measurements using capillary viscometers. As far as the authors are aware, the present viscosity measurements are the first results to be published for PEG 400 at pressures higher than atmospheric pressure.
- Viscosity of liquid diethylene, triethylene and tetraethylene glycols at moderately high pressures using a vibrating wire instrumentPublication . Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.New viscosity measurements of compressed liquid diethylene glycol (DiEG), triethylene glycol (TriEG) and tetraethylene glycol (TeEG) have been performed using a vibrating wire instrument operated in the forced oscillation mode. The measurements have been carried out in a range of pressures up to 70 MPa and temperatures from (293–363) K, covering a total range of viscosities from (3.46–1.15 × 102) mPa⋅s. Complementary experimental density data were obtained for the same glycols using an Anton Paar vibrating U-tube densimeter. These measurements have been performed in a range of temperatures from about (283–363) K and at pressures up to about 70 MPa. The viscosity results were correlated with density, using a modified hard-spheres scheme. The experimental density data were correlated, as a function of temperature and pressure, with a modified Tait-type equation. The expanded uncertainty of the present viscosity results at a 95% confidence level is estimated to be less than ±2.0% for viscosities up to 68 mPa s and less than ±2.6% for higher viscosities. The densities have an expanded uncertainty of ±0.2% at a 95% confidence level.
- Studying the PEG familyPublication . Sequeira, Maria Carolina; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.The main goal of this line of research is the realisation of experimental measurements of thermophysical properties of a homologous series of ethylene and polyethylene glycols [H(OCH2CH2)nOH], and the development of correlation methods, with an accuracy adequate for the applications. Ethylene glycols and poly (ethylene) glycols (PEG) are widely used in many industrial applications as green solvents and as components of important sustainable processes as they are considered environmentally acceptable compounds [1,2]. Liquid Poly(ethyleneglycols) [PEGs] are in general considered as green solvents. They are non-volatile; their toxicity is very low, such that they are being used as food additives [3]. PEGs have been found to be biodegradable by bacteria in soil or sewage, but the ability of bacteria to biodegrade PEG decreases with increasing molecular weight [3]. The study of this series of compounds is important in many respects, not only because it is aimed at the study of PEGs which have innumerable practical applications but also because this study can be useful to monitor the degree of polymerization in the production of PEGs, themselves. In the present work, the viscosity of three ethylene glycols, namely diethylene, triethylene and tetraethylene glycols [4] and PEG 400 were measured with high accuracy using the vibrating wire technique at moderately high pressures. Complementary experimental density, surface tension and rheological behavior were obtained for the same liquids. One of the aims of the work is to analyse the relation of the present results with those obtained before for CO2 saturated PEG400 mixtures
- Viscosity measurements of compressed ionic liquid EMIM OTfPublication . Sequeira, Maria Carolina; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.Ionic liquids have attracted considerable interest in recent years, as they can be used for multiple aims, namely, as antistatic agents, electrolytes, solvents, lubricants, and CO2 absorbents [1]. The use of ionic liquids in industrial processes require their thermophysical properties, in particular, the viscosity and the thermal conductivity. However, transport properties are scarce due to the difficulty of the measurements, particularly at pressures higher than the atmospheric pressure. Our group has developed a programme of measurements aiming at obtaining rigorous results for the viscosity of ionic liquids using the vibrating wire method. This technique, although very accurate for molecular, non-conducting liquids, could have some difficulties with ionic liquids due to their electrical conductivity [2]. As we were planning to use the vibrating wire method in the forced mode of oscillation, the method requires the acquisition of the frequency response of the wire in a range of frequencies containing the velocity resonance for the transverse oscillations of the wire. Therefore, it is important to verify if the ionic liquid sample is a good electrolytic conductor in the range of frequencies that matter for the measurement of viscosity. The problematic of measuring the viscosity of ionic liquids both in general and in particular, using the vibrating wire technique was studied [3]. Pardal et al. [4] have used 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIMOTf) mixed with water as the electrolyte to successfully reduce CO2 at high pressure. The objective of this work is to contribute with viscosity data in the pressure and temperature range of the work performed by those authors. Therefore, we present new ionic viscosity results for temperatures between 298 K and 347 K and pressures up to 50 MPa.