Densities, excess volumes, isobaric expansivity, and isothermal compressibility of the (1-ethyl-3-methylimidazolium ethylsulfate + methanol) system at temperatures (283.15 to 333.15) K and pressures from (0.1 to 35) MPa

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Abstract

Densities of pure 1-ethyl-3-methylimidazolium ethylsulfate ionic liquid – [C2mim][EtSO4] and its mixtures with methanol have been measured with an accuracy of ±0.2 kg · m−3, over the temperature range (283.15 to 333.15) K and pressure range (0.1 to 35) MPa, using a vibrating tube densimeter. Excess volumes have been calculated directly from the experimental densities. The latter data have been correlated by the Tait equation with the temperature dependent parameters for the pure ionic liquid and by a van Laar-type equation, involving parameters dependent on temperature and pressure for the mixtures. The isobaric expansivity, isothermal compressibility, and related excess properties have been calculated. The exceptionally strong influence of pressure and temperature on these properties has been observed.

Introduction

This paper is a continuation of a systematic study on the volumetric properties of ionic liquids and ionic liquids mixed with organic liquids [1]. It has been inspired by the considerable interest in the unique properties of the ionic liquids. The origin of these interesting properties is not fully understood and new experimental data, such as reported here, could help in this regard.

The volumetric data on pure ionic liquids and on mixtures of ionic liquids with organic liquids, involving the density dependence on both temperature and pressure, are not numerous if one recalls a great number of synthesized ionic liquids and possible mixtures in which they can be involved. So far, 12 papers reporting such measurements for pure ionic liquids [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12] can be found in the literature and only two describing mixtures containing an ionic liquid [1], [13]. It was observed that densities of the pure ionic liquids are less dependent on pressure and temperature than typical organic liquids and therefore the observed isobaric expansivity and isothermal compressibility are considerably lower than usual [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Recently, we have noted that the excess volumes for the binary system (1,3-dimethylimidazolium methylsulfate ionic liquid + methanol) are exceptionally strongly influenced by temperature and pressure, and excess isobaric expansivity and excess isothermal compressibility have very high absolute values [1]. The same properties pertaining to the binary system (1-ethyl-3-methylimidazolium ethylsulfate + methanol) have been studied in this work.

Densities of pure [C2mim][EtSO4] at different temperatures and under normal pressure have been determined experimentally in a number of laboratories [14], [15], [16], [17], [18], [19], [20], [21]. They cover the temperature range (278.15 to 391.27) K. Recently, during the revision stage of this paper, densities of this ionic liquid as a function of temperature and pressure have been reported [12]. They were measured at T = (293 to 415) K and under (0.1 to 40) MPa. Densities or excess volumes for the mixtures containing 1-ethyl-3-methylimidazolium ethylsulfate have been measured under normal pressure for binary systems with methanol [22], ethanol [19], [20], 1-propanol [22], 2-propanol [22], and water [17], [20], [21], [23], [24]. The latter data were determined over a wide temperature range (278.15 to 348.15) K. The density data for one ternary system of ([C2mim][EtSO4] + ethanol + 2-ethoxy-2-methylpropane) have also been reported in the literature [19].

Section snippets

Materials

The 1-ethyl-3-methylimidazolium ethylsulfate (Solvent Innovation, mass fraction purity stated 0.997 and water content 1090 · 10−6) were dried and degassed under vacuum for 48 h at temperature about 350 K. As it was stated by the producer, the fluoride content was equal to 294.7 · 10−6 and no other halides were detected. Methanol (Aldrich, puriss >0.999) and was dried over 0.4 nm molecular sieves for several days. The water content stated by a producer did not exceed 500 · 10−6.

The water used in the

Density of pure 1-ethyl-3-methylimidazolium ethylsulfate

The density of pure [C2mim][EtSO4] was measured at temperatures T/K = (283.15, 293.15, 298.15, 303.15, 313.15, 323.15, and 333.15) and under pressures p/MPa = (0.1, 2.5, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, and 35.0) at each temperature; altogether 63 experimental data points were obtained. They are given in table 1. The comparison between our results and the literature data measured under normal pressure is shown in figure 2. The discrepancies between these densities are rather significant with the

Conclusions

The measured (p, ρ, T) properties of the pure 1-ethyl-3-methylimidazolium ethylsulfate and its mixtures with methanol confirm an existence of some striking features which can be attributed to the presence of the ionic liquid. A relatively strong temperature and pressure influence on the volumetric excess functions, viz. excess volumes, isothermal compressibility, and isobaric expansivity has been observed. These two latter properties show very high absolute values which, up to now have not been

Acknowledgement

This research has been supported by Polish Ministry of Education and Science within Joint Project of Polish-South African Scientific and Technological International Co-operation.

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