Thermophysical Properties of the Binary Mixture of Water + Diethylmethylammonium Trifluoromethanesulfonate and the Ternary Mixture of Water + Diethylmethylammonium Trifluoromethanesulfonate + Diethylmethylammonium Methanesulfonate

Abstract

New working pairs of room-temperature ionic liquids (RTILs) and water offer an opportunity to replace the highly corrosive and partly immiscible working pair of lithium bromide (LiBr) and water in absorption cycles like the absorption chiller. To estimate the suitability of these working pairs, the knowledge of thermophysical properties is inevitable. Due to the lack of literature data the following properties of two RTIL−water mixtures will be presented in this paper. Vapor−liquid equilibria (VLE) of the binary mixture of water + diethylmethylammonium trifluoromethanesulfonate ([DEMA][OTf]) and the ternary mixture of water + [DEMA][OTf] + diethylmethylammonium methanesulfonate ([DEMA][OMs]) were measured in the temperature range T = (293.15 to 353.15) K. The VLE measurements were carried out by Fourier transform infrared (FTIR) spectroscopy in a dynamic cell. The experimental VLE data were fitted with the nonrandom two-liquid (NRTL) model. Heat capacities, densities, and viscosities of the binary mixtures water + [DEMA][OTf] and [DEMA][OTf] + [DEMA][OMs] were measured. The measurements of the heat capacity were conducted via differential scanning calorimetry (DSC) in the temperature range T = (293.15 to 363.15) K. The density was measured with a pycnometer and the viscosity with a falling sphere viscometer. The temperature range for both was T = (293.15 to 353.15) K. Diffusion coefficients of water in the RTILs were determined by pulsed field gradient-nuclear magnetic resonance spectroscopy (PFG-NMR) in the temperature range of T = (288 to 313) K. ■ INTRODUCTIONRoom-temperature ionic liquids (RTILs) are salts which are liquid at room temperature and atmospheric pressure. They are composed of an organic cation and an inorganic or organic anion. Due to the numerous possible combinations of anions and cations, physical and chemical properties can be adapted over a wide range. 1,2 The most preferable properties for industrial applications are a low melting point, a wide liquid range, a negligible vapor pressure, and nonflammability. 3 This leads to a large number of possible applications in synthetic, analytical, and engineering processes. Today RTILs are used for example as extraction agents in separation processes, and they are also suited to replace conventional organic solvents due to their negligible vapor pressure. 3,4 Other fields of application such as the use as lubricants, in electrochemistry, and in bioscience are also being considered. 5,6 This led to an enormous increase of scientific investigations over the past years. 1−18 Our group is investigating new working pairs for the absorption chiller to replace the highly corrosive and partly immiscible but still commonly used working pair LiBr and water. 7,8 The absorption chiller offers the opportunity for ambient cooling by the usage of waste heat or solar energy. A description of the process can be found in literature. 9 The temperature range of the solution cycle in the process is set by the cooling water temperature in the absorber (around 298 K) and...

Thermophysical Characterization of Two DyethylMethylAmmonium Ionic Liquids

“…Furthermore, the addition of water decreases the density of both ILs. These results are comparable with other bibliographic references [5][6][7]. In the case of speed of sound ( Figure 2), similar behaviors have been observed; that is, a decrease of this parameter with the temperature for all of the studied fluids, which is in good agreement with other previous works [1] Using Equation 2, the thermal expansion coefficient has been calculated and represented in and also decreases linearly with temperature.…”

Transport Properties, Local Coordination, and Thermal Stability of the Water/Diethylmethylammonium Methanesulfonate Binary System

“…This distinction is further supported by the infrared spectral profile of the O–H stretching modes (Figure 5), where the two main components assigned to different patterns in the hydrogen donor/acceptor scheme of water 55 display a concentration dependent relative contribution to the whole profile (see for instance the increase of the component at ∼3,450 cm −1 relatively to that at ∼3,530 cm −1 ). That water less easily evaporates at low concentrations is in qualitative agreement with the results presented by Merkel et al 28, 29 showing that the vapor pressure of water steadily decreases upon mixing with a PIL such as [DEMA][TfO] or [DEMA][OMs].…”

“…As recently demonstrated for imidazolium based ionic liquids, the effect of added water on self‐diffusion, conductivity, and local coordination can be thoroughly investigated combining vibrational with NMR spectroscopy 17, 27. It is also interesting that the partial pressure of water is reduced upon mixing with a PIL, making H 2 O/PIL mixtures suitable for other technological applications such as absorption cycles 28, 29.…”

Are Ionic Liquids Suitable as New Components in Working Mixtures for Absorption Heat Transformers?

“…Table 1 lists the most studied ILs in the literature and the thermophysical properties available. Alkylsulfate-and alkylphosphastebased ILs are well known, and their performance in working fluids {H 2 O + IL} was evaluated in different absorption cycles [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26].…”

“…The binary systems {H 2 O + dialkylimidazolium alkylphosphate}, 1-dimethylimidazolium dimethylphosphate, and 1-ethyl-3-methylimidazolium dimethylphosphate were extensively studied in numerous papers, where not only the data of vapor-liquid equilibria (VLE) but also density, viscosity, heat capacity, and excess enthalpy are available [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][27][28][29]. These data make it possible to simulate the performance of these binary mixtures as working fluids in the absorption refrigeration cycle [7-25, 27, 30].…”