Influence of the molecular structure on the viscosity of some alkoxyethanols
Introduction
Our research concerning polyalkylene glycol polyalkyl ethers aims to create a complete database of experimental thermodynamic and transport properties for these fluids, which could be used to develop models able to accurately represent the behaviour with both temperature and pressure of the thermophysical properties of these interesting compounds. As a part of our studies on polyalkylene glycol polyalkyl ethers, the density and dynamic viscosity of several polyethylene glycol dimethyl ethers [1], [2], [3], [4], [5], [6] (diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether) are reported up to 60 and 100 MPa, respectively. Moreover, densities for several diethylene glycol monoalkyl ethers (diethylene glycol monomethyl ether and diethylene glycol monoethyl ether) up to 25 MPa, and the speed of sound of triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether up to 100 MPa have recently been published [7], [8]. The present work was undertaken with the aim to complete our database.
More precisely, the present work was undertaken with the aim to analyse the high-pressure viscosity behaviour of the three monoethylene glycol monoalkyl ethers also called alkoxyethanols obeying the formula CnH2n+1OCH2CH2OH: monoethylene glycol methyl ether (MEGME; n = 1), monoethylene glycol ethyl ether (MEGEE; n = 2) and monoethylene glycol iso-propyl ether (iso-MEGPE; n = 3) which have been actively studied for various applications. For example, the phase equilibrium behaviour of alkoxyethanols, such as monoethylene glycol ethyl ether, with CO2 is essential to process development in the food and cosmetic industries [9], [10]. In the last years, measurements of the viscosity of monoethylene glycol alkyl ethers under pressure have become important because of the use of these data in studying the reliability of these fluids as lubricants in refrigeration compressors and as absorbents for absorption systems. However, the database for transport properties of these compounds is scarce and available at very limited temperature and pressure conditions. Most measurements have been made at atmospheric pressure and at temperatures between 293.15 and 323.15 K. Thus, while there are abundant data for these compounds describing the temperature dependence of the viscosity at 0.1 MPa [11], [12], [13], [14], studies versus pressure are less frequent. With respect to other thermophysical properties, density values of these compounds have been studied by us [15].
To complete our experimental and theoretical studies of some physical properties of monoethylene glycol alkyl ethers, in this paper new viscosity data at temperatures from 293.15 to 353.15 K and at pressures up to 100 MPa are reported. These experimental values are used to test the correlation ability of the hard-sphere scheme and free-volume model.
Section snippets
Measurement techniques
At atmospheric pressure, the kinematic viscosities, ν, were measured with an Ubbelohde-type glass capillary tube viscometer with a Schott-Geräte automatic measuring unit (model AVS 350) in a thermostated bath, which regulates the temperature to within an accuracy of ±0.01 K. After multiplication by the density at atmospheric pressure, the dynamic viscosity, η, is obtained with a relative uncertainty lower than 1%. The calibration has been checked with certified calibrated Cannon oil.
A
Experimental results
The experimental dynamic viscosity values for MEGME, iso-MEGPE and MEGEE, at different pressures and temperatures are listed in Table 1. To our knowledge, there are no literature viscosities for these fluids at pressures different from atmospheric. Our experimental kinematic viscosity values for MEGME at atmospheric pressure agree with published measurements of Pal and Sharma [23], [24] at 298.15 and 308.15 K, with an average deviation of 1.3%, with the data of Muhuri and Hazra [25] at 298.15 K
Modified Andrade representation
The experimental data of viscosity on an isotherm, η(P), can be fitted for each isotherm to the following Tait-like equation:and on an isobar, η(T), can be fitted for isobar to the following Andrade's equation [31]:Both previous equations can be combined in order to fit the viscosity as a function of temperature and pressure. Then, we have proposed [2] the following equation:where η0(T) is the temperature
Conclusion
The dynamic viscosity of some monoethylene glycol alkyl ethers has been measured up to 100 MPa in the temperature range 293.15–353.15 K. The experimental uncertainty for the viscosity measurements is less than 2%, except at 0.1 MPa where the uncertainty is 1%. It follows from the discussion that some simple viscosity approaches with a strong physical and theoretical background (the hard-sphere scheme, the free-volume model) are able to model the viscosity of these compounds (MEGME, MEGEE and iso
Acknowledgements
This work was supported by Spanish Science and Technology Ministry (PPQ2001-3022), European Union (FEDER), Xunta de Galicia (PGIDIT03PXIC20609PN) and Spanish–French Joint Action (HF 2001-0101 and 04238PG).
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