Thermodynamic Properties of Binary Mixtures of Water and Room

Article pubs.acs.org/jced

Thermodynamic Properties of Binary Mixtures of Water and Room-Temperature Ionic Liquids: Vapor Pressures, Heat Capacities, Densities, and Viscosities of Water + 1-Ethyl-3-methylimidazolium Acetate and Water + Diethylmethylammonium Methane Sulfonate Christiane Römich,*,† Nina C. Merkel,† Alessandro Valbonesi,† Karlheinz Schaber,† Sven Sauer,‡ and Thomas J. S. Schubert‡ †

Institute for Technical Thermodynamics and Refrigeration, Karlsruhe Institute of Technology (KIT), Engler-Bunte-Ring 21, 76131 Karlsruhe, Germany ‡ IoLiTec Ionic Liquids Technologies GmbH, Salzstraße 184, 74076 Heilbronn, Germany ABSTRACT: Vapor−liquid equilibria (VLE), heat capacities, densities, and viscosities of mixtures of water and 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) and mixtures of water and diethylmethylammonium methane sulfonate ([DEMA][OMs]) were measured in the temperature range T = (293.15 to 353.15) K. VLE measurements were carried out by Fourier transform infrared (FTIR) spectroscopy in a dynamic cell, and the experimental VLE data were correlated to the nonrandom two-liquid (NRTL) model. Measurements of the heat capacity were conducted via differential scanning calorimetry (DSC). The density was measured with a pycnometer and the viscosity with a falling-sphere viscometer.

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INTRODUCTION Room-temperature ionic liquids (RTILs) are salts with a melting point below room temperature at atmospheric pressure. They consist of an organic cation and an inorganic or organic anion. The large number of possible combinations of anions and cations offers the adaption of physical and chemical properties in a wide range.1,2 This leads to a huge amount of applications in synthetic, analytical, and engineering processes and thus to an enormous increase of scientific investigations in the last years.3−6 To dimension the processes and survey the substitution of conventional organic solvents, experimental data and their correlation with existing models, such as the nonrandom two-liquid (NRTL) model, are necessary.7 In this paper we present the thermophysical properties, vapor− liquid equilibrium (VLE), specific heat capacity, density, and viscosity of two hygroscopic RTILs. 1-Ethyl-3-methylimidazolium acetate ([EMIM][OAc]) and diethylmethylammonium methane sulfonate ([DEMA][OMs]) are both fully miscible with water and possess a negligible vapor pressure. This makes them, for example, applicable in absorption cycles.8,9

rotary evaporator. The materials thus obtained were dried in vacuum at ca. 60 °C for 60 h with efficient stirring to afford the desired ionic liquids as clear colorless or yellow viscous oils. The following commercially available materials were used: 1-ethyl3-methylimidazolium methylcarbonate (BASF, pure, solution in methanol, w = 0.3); acidic acid (Sigma-Aldrich, Reagent Plus, > 99 %); diethylmethylamine (Acros, 98.0 %); methane sulfonic acid (Sigma-Aldrich, in water, w = 0.7) where w is the concentration of the substance in the solution in weight %. The purity of the ionic liquids was determined by ion chromatography using a Metrohm modular setup (709 IC pump, 732 IC detector, 733 IC separation center, 753 suppressor module, 762 IC interface, 812 valve unit), with an uncertainty of ± 10 ppm and found to be halide-free. The water content of the ionic liquids was determined by Karl Fischer titration (Metrohm, 795 KFT Titrino) with an uncertainty of ± 50 ppm, before each series of measurements and taken into account for the calculation of the composition of the respective binary mixtures. [EMIM][OAc] was prepared by adding dropwise acidic acid (840.0 g, 14.0 mol) under cooling to a methanolic solution (28.8 %) of 1-ethyl-3-methylimidazolium methylcarbonate (2.6 kg, 14.0 mol). [DEMA][OMs] was prepared by adding dropwise diethylmethylamine (470.72 g, 5.40 mol) under cooling to an

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EXPERIMENTAL SECTION Materials and Purities. [EMIM][OAc] and [DEMA][OMs] were prepared by mixing accurately measured equimolar amounts of the respective acid and base in methanolic or aqueous solution, with stirring followed by the removal of the methanol/ water under reduced pressure at elevated temperatures using a © XXXX American Chemical Society

Received: February 27, 2012 Accepted: June 20, 2012

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dx.doi.org/10.1021/je300132e | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Figure 1. Dynamic VLE measurement cell: TH, water thermostat; EC, equilibrium cell; D, demister; TC, thermocouple; TIC, temperature-control of the six different sections; PT, platinum resistance thermometer; CP, circulation pump; FTIR, Fourier transform infrared spectrometer.

Figure 2. Vapor-pressure versus mole fraction for water (1) + [EMIM][OAc] (2) at three temperatures. ■, at 303.15 K; ●, at 323.15 K; ▲, at 353.15 K; , calculated data, NRTL.

Figure 3. Vapor-pressure versus mole fraction for water (1) + [DEMA][OMs] (2) at three temperatures. ■, at 303.15 K; ●, at 323.15 K; ▲, at 353.15 K; , calculated data, NRTL.

aqueous solution (70.0 %) of methane sulfonic acid (727.91 g, 5.40 mol). Apparatus and Procedure. VLE measurements were conducted in a dynamic measurement apparatus shown in Figure 1. It consists of a glass flask with an internal volume of 0.5 L as the equilibrium cell, a circulation pump (KNF, N012 St.11E), and a Fourier transform infrared (FTIR) spectrometer (BOMEM Hartmann & Braun, model 9100). The equilibrium cell is equipped with a demister to prevent liquid droplets to get into the spectrometer. The liquid phase is heated by a water thermostat (Lauda, E200), and the temperature is measured by a platinum resistance thermometer (PT100 sensor) with an uncertainty of ± 0.01 K. The temperature of the whole apparatus, except the spectrometer itself and the feed line, is equal to the equilibrium temperature. The FTIR spectrometer and the feed line are held on a temperature of 110 °C ± 1 K to prevent condensation. The equilibrium cell is connected to the atmosphere to ensure atmospheric pressure during the

measurements. At worst, this causes a loss of 1.5·10−4 % of the water vapor which is circulating in the gas phase and thus can be neglected. The gas phase passes the demister, gets into the spectrometer, and is recirculated afterward into the equilibrium cell. This recirculation causes the mixing of the liquid phase, intensifies the heat and mass transfer, and accelerates the approach of the VLE. After reaching the temperature of measurement, the mixture was held at isothermal conditions for about (30 to 40) min. This time to reach the VLE is dependent on the substance and was evaluated for each mixture separately. The absorbance of the water vapor in the gas phase is measured by the FTIR spectrometer. After a baseline subtraction the area of the water peak at (2112.863 to 2117.2) cm−1 is calculated. For calibration this area was correlated to the water vapor pressure of pure water and a saturated solution of potassium acetate.10,11 Because of the varying atmospheric pressure, every measurement has to be standardized to a pressure of 105 Pa. Two equations were fitted to these calibration B



Article

Table 1. Experimental VLE Data for the System Water (1) + [EMIM][OAc] (2)a

a

Table 2. Experimental VLE Data for the System Water (1) + [DEMA][OMs] (2)a

T/K

x1

p/mbar

T/K

x1

p/mbar

T/K

x1

p/mbar

T/K

x1

p/mbar

293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15

0.687 0.745 0.782 0.818 0.855 0.886 0.933 0.957 1.000 0.612 0.655 0.686 0.745 0.782 0.818 0.855 0.885 0.933 0.957 1.000 0.495 0.553 0.612 0.655 0.686 0.745 0.782 0.817 0.855 0.885 0.933 0.956 1.000 0.494 0.553 0.612 0.654 0.686 0.745 0.781 0.817 0.854 0.884 0.932 0.956 1.000

1.40 3.60 5.41 7.82 11.32 13.95 19.30 21.05 23.18 1.83 3.05 3.90 8.22 10.92 14.75 19.86 24.94 36.32 40.86 44.43 1.45 2.71 4.70 8.67 8.71 14.85 18.89 25.44 37.12 47.10 64.35 71.78 77.86 3.52 5.33 8.19 12.77 15.73 25.05 34.27 47.32 63.57 79.83 105.59 116.02 126.69

333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15

0.494 0.553 0.611 0.654 0.686 0.744 0.781 0.816 0.853 0.883 0.931 0.955 1.000 0.494 0.553 0.611 0.653 0.685 0.743 0.780 0.815 0.852 0.882 0.930 0.954 1.000 0.494 0.552 0.611 0.653 0.684 0.742 0.778 0.814 0.851 0.881 0.929 0.952 1.000

6.45 9.55 14.71 22.05 26.41 45.75 59.26 78.14 103.64 127.52 166.52 182.77 199.28 10.90 16.11 23.24 37.74 47.01 75.58 94.62 122.92 161.62 197.12 255.91 283.28 305.97 17.80 25.06 38.59 63.95 76.87 117.52 147.00 189.97 245.64 298.54 386.79 429.49 463.22

293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15

0.352 0.415 0.483 0.540 0.584 0.614 0.644 0.674 0.720 0.843 0.907 0.937 1.000 0.279 0.352 0.415 0.483 0.540 0.584 0.614 0.644 0.674 0.720 0.843 0.907 0.936 1.000 0.203 0.279 0.352 0.414 0.483 0.540 0.583 0.614 0.644 0.674 0.720 0.842 0.906 0.936 1.000 0.203 0.279 0.351 0.414 0.483 0.540 0.583 0.614 0.643 0.673 0.719 0.842 0.906 0.936 1.000

1.66 1.86 2.97 3.59 3.99 4.78 5.15 5.95 7.54 14.30 19.26 21.92 23.18 1.91 3.22 3.79 5.37 6.83 7.77 9.18 10.47 11.92 14.41 25.15 34.32 39.53 44.43 1.73 3.65 5.47 6.85 9.74 12.11 13.76 15.73 17.95 20.43 24.57 46.93 61.52 69.52 77.86 3.33 6.28 9.26 11.84 15.86 19.42 22.37 25.56 31.14 36.71 46.07 79.95 101.88 112.50 126.69

333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15

0.203 0.278 0.351 0.414 0.482 0.539 0.582 0.613 0.642 0.672 0.718 0.841 0.905 0.935 1.000 0.202 0.278 0.351 0.413 0.481 0.538 0.582 0.612 0.641 0.671 0.717 0.840 0.903 0.934 1.000 0.202 0.278 0.350 0.412 0.480 0.537 0.580 0.610 0.640 0.670 0.716 0.838 0.902 0.932 1.000

6.03 11.57 14.70 18.91 25.32 32.25 39.10 45.56 54.05 62.39 76.31 127.93 161.72 178.88 199.28 9.88 16.75 22.47 30.82 43.55 54.14 64.28 73.25 87.57 99.20 117.59 199.43 252.17 277.05 305.97 17.77 24.71 36.64 50.00 68.45 84.31 103.84 119.01 135.07 152.34 184.75 305.56 384.94 419.58 463.22

Maximum uncertainties u are u(T) = 0.12 K.

measurements: a linear one at low water vapor pressures and a logarithmic equation at high water vapor pressures. With these resulting equations water vapor pressures below 1 mbar cannot be measured accurately. Water vapor pressures of the water + RTIL mixtures higher than this resolution limit can be determined with a mean uncertainty of ± 2.4 % and a maximum uncertainty of ± 8.8 %. The concentration of the mixtures was verified by volumetric Karl Fischer titration (Schott, TitroLine KF) with an uncertainty of ± 1 % of the measured mass fraction of water in the mixture.

a

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Maximum uncertainties u are u(T) = 0.15 K. dx.doi.org/10.1021/je300132e | J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

Table 3. Binary NRTL Parameters Fitted to Experimental VLE Data (Tables 1 and 2), with the Root-Mean-Square Deviation (RMSD) system

Δg12 / J·mol−1

Δg21/ J·mol−1

α12

rmsd

water (1) + [EMIM][OAc] (2) water (1) + [DEMA][OMs] (2)

28938 −1051.4

−25691 −5039.9

0.10243 0.70862

4.37 3.57

Table 5. Experimental Specific Isobaric Heat Capacity Data for the System Water (1) + [DEMA][OMs] (2)a

Table 4. Experimental Specific Isobaric Heat Capacity Data for the System Water (1) + [EMIM][OAc] (2)a

a

T/K

x1

cp/J·kg−1·K−1

T/K

x1

cp/J·kg−1·K−1

293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15

0.353 0.516 0.628 0.705 0.755 0.800 0.858 0.898 0.928 0.961 0.985 1.000 0.353 0.516 0.628 0.705 0.755 0.800 0.858 0.898 0.928 0.961 0.985 1.000 0.353 0.516 0.628 0.705 0.755 0.800 0.858 0.898 0.928 0.961 0.985 1.000 0.353 0.516 0.628 0.705 0.755 0.800 0.858 0.898 0.928 0.961 0.985 1.000

1940 2070 2170 2300 2420 2570 2830 3080 3330 3690 4020 4210 1970 2100 2210 2350 2470 2620 2880 3130 3380 3710 4020 4210 1990 2130 2250 2390 2520 2670 2930 3180 3410 3740 4030 4210 2020 2160 2290 2430 2560 2720 2980 3220 3450 3760 4040 4210

333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15

0.353 0.516 0.628 0.705 0.755 0.800 0.858 0.898 0.928 0.961 0.985 1.000 0.353 0.516 0.628 0.705 0.755 0.800 0.858 0.898 0.928 0.961 0.985 1.000 0.353 0.516 0.628 0.705 0.755 0.800 0.858 0.898 0.928 0.961 0.985 1.000 0.353 0.516 0.628 0.705 0.755 0.800 0.858 0.898 0.928 0.961 0.985 1.000

2050 2190 2330 2470 2610 2760 3020 3260 3480 3770 4040 4210 2070 2220 2360 2510 2640 2800 3060 3290 3500 3790 4050 4210 2100 2260 2400 2550 2680 2830 3090 3310 3520 3800 4060 4220 2140 2280 2430 2580 2710 2860 3110 3330 3540 3810 4060 4220

a

T/K

x1

cp/J·kg−1·K−1

T/K

x1

cp/J·kg−1·K−1

293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 293.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 303.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 313.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15 323.15

0.071 0.277 0.442 0.482 0.517 0.643 0.715 0.802 0.865 0.900 0.930 0.955 0.977 1.000 0.071 0.277 0.442 0.482 0.517 0.643 0.715 0.802 0.865 0.900 0.930 0.955 0.977 1.000 0.071 0.277 0.442 0.482 0.517 0.643 0.715 0.802 0.865 0.900 0.930 0.955 0.977 1.000 0.071 0.277 0.442 0.482 0.517 0.643 0.715 0.802 0.865 0.900 0.930 0.955 0.977 1.000

1890 1920 1980 2000 2020 2130 2240 2480 2720 2970 3230 3480 3850 4210 1900 1940 2000 2020 2050 2170 2280 2530 2770 3020 3270 3520 3860 4200 1920 1960 2020 2050 2080 2200 2320 2570 2810 3070 3310 3540 3870 4200 1940 1980 2040 2070 2100 2230 2350 2620 2860 3110 3350 3570 3880 4210

333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 343.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15 363.15

0.071 0.277 0.442 0.482 0.517 0.643 0.715 0.802 0.865 0.900 0.930 0.955 0.977 1.000 0.071 0.277 0.442 0.482 0.517 0.643 0.715 0.802 0.865 0.900 0.930 0.955 0.977 1.000 0.071 0.277 0.442 0.482 0.517 0.643 0.715 0.802 0.865 0.900 0.930 0.955 0.977 1.000 0.071 0.277 0.442 0.482 0.517 0.643 0.715 0.802 0.865 0.900 0.930 0.955 0.977 1.000

1950 2000 2070 2100 2130 2260 2390 2660 2900 3140 3380 3590 3900 4210 1970 2020 2090 2120 2160 2290 2420 2700 2940 3180 3410 3610 3910 4220 1990 2040 2120 2150 2180 2320 2450 2730 2970 3210 3430 3620 3920 4230 2000 2060 2140 2170 2210 2350 2480 2760 3000 3230 3450 3640 3920 4230


The heat capacity measurements were performed in a temperature range T = (293.15 to 353.15) K by using a

Maximum uncertainties u are u(T) = 0.16 K. D



Article

Table 6. Experimental Density Data for the System Water (1) + [EMIM][OAc] (2)a

a

T/K

x1

ρ/kg·m−3

SD(ρ)/kg·m−3

T/K

x1

ρ/kg·m−3

SD(ρ)/kg·m−3

293.15 293.15 293.15 293.15 293.15 313.15 313.15 313.15 313.15 313.15

0.347 0.517 0.578 0.627 0.705 0.347 0.517 0.578 0.627 0.705

1104.4 1107.2 1108.7 1108.5 1107.7 1092.2 1095.1 1097.3 1095.7 1094.9

0.000 0.070 0.070 0.778 0.070 0.141 0.353 0.070 0.212 0.141

333.15 333.15 333.15 333.15 333.15 353.15 353.15 353.15 353.15 353.15

0.347 0.517 0.578 0.627 0.705 0.347 0.517 0.578 0.627 0.705

1080.7 1083.0 1085.1 1083.1 1081.5 1068.5 1070.6 1073.1 1070.9 1069.5

0.070 0.212 0.353 0.141 0.000 0.353 0.353 0.353 0.495 0.566


Table 7. Experimental Density Data for the System Water (1) + [DEMA][OMs] (2)a

a

T/K

x1

ρ/kg·m−3

SD(ρ)/kg·m−3

T/K

x1

ρ/kg·m−3

SD(ρ)/kg·m−3

293.15 293.15 293.15 293.15 293.15 313.15 313.15 313.15 313.15 313.15

0.372 0.449 0.507 0.624 0.707 0.372 0.449 0.507 0.624 0.707

1134.9 1133.6 1133.0 1128.4 1122.2 1122.9 1120.5 1120.1 1115.4 1110.1

0.070 0.424 0.707 0.141 0.212 0.353 0.283 0.070 0.070 0.283

333.15 333.15 333.15 333.15 333.15 353.15 353.15 353.15 353.15 353.15

0.372 0.449 0.507 0.624 0.707 0.372 0.449 0.507 0.624 0.707

1109.7 1107.1 1106.7 1102.3 1096.4 1096.7 1094.2 1093.5 1089.5 1083.2

0.212 0.141 0.424 0.424 0.212 0.212 0.212 0.566 0.283 0.141


Table 8. Experimental Dynamic Viscosity Data for the System Water (1) + [EMIM][OAc] (2)a

a

T/K

x1

η/mPa·s

T/K

x1

η/mPa·s

293.15 293.15 293.15 293.15 293.15 313.15 313.15 313.15 313.15 313.15

0.347 0.517 0.578 0.627 0.705 0.347 0.517 0.578 0.627 0.705

93.67 59.39 51.08 42.81 32.69 35.21 24.45 21.41 18.22 13.96

333.15 333.15 333.15 333.15 333.15 353.15 353.15 353.15 353.15 353.15

0.347 0.517 0.578 0.627 0.705 0.347 0.517 0.578 0.627 0.705

16.92 12.27 11.00 9.39 7.36 9.51 7.19 6.46 5.63 4.38


glass-pycnometer with a capacity of V = 9.994 ± 0.004 mL. The samples were weighed using a microbalance (Mettler Toledo, PR 200 3DR) with an uncertainty of ± 10−6 kg. The temperature was measured with a mercury thermometer with an uncertainty of ± 0.5 K. The kinematic viscosities of the mixtures were measured with a Haake falling sphere viscometer (Thermo Electron GmbH, type C). Here the temperature was measured with a platinum resistance thermometer (PT100 sensor) with an uncertainty of ± 0.17 K. To reach thermal equilibrium the sample rested at isothermal conditions for 30 min before each measurement. The dynamic viscosities were calculated using the densities measured as described above.

Figure 4. Density versus mole fraction for ●, water (1) + [EMIM][OAc] (2) and ■, water (1) + [DEMA][OMs] (2) at T = 293.15 K.

differential scanning calorimeter (Setaram, Micro-DSC VII) with a calorimetric sensitivity of ± 0.4 μW. The water + RTIL mixtures were prepared by weighing precise quantities of each component using a microbalance (Mettler Toledo, AB265-S) with an uncertainty of ± 10−8 kg. The concentration of each sample was again verified by Karl Fischer titration. A sample was placed in the batch vessel, and the heat flow of both the sample and the empty reference vessel were measured and compared to a blank measurement of two empty vessels at the same conditions. The densities of the water + RTIL mixtures were measured in a temperature range T = (293.15 to 353.15) K by a calibrated

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RESULTS AND DISCUSSION The isothermal VLE measurements were conducted at T = (293.15 to 353.15) K in 10 K steps and at different E



Article

Table 9. Experimental Dynamic Viscosity Data for the System Water (1) + [DEMA][OMs] (2)a

a

T/K

x1

η/mPa·s

SD(η)/mPa·s

T/K

x1

η/mPa·s

SD(η)/mPa·s

293.15 293.15 293.15 293.15 293.15 313.15 313.15 313.15 313.15 313.15

0.372 0.449 0.507 0.624 0.707 0.372 0.449 0.507 0.624 0.707

65.26 49.94 41.92 27.93 20.00 27.27 21.55 18.69 13.36 10.09

0.433 0.130 0.261 0.341 0.114 0.114 0.000 0.132 0.000 0.057

333.15 333.15 333.15 333.15 333.15 353.15 353.15 353.15 353.15 353.15

0.372 0.449 0.507 0.624 0.707 0.372 0.449 0.507 0.624 0.707

13.95 11.37 9.98 7.34 5.72 8.20 6.83 6.08 4.58 3.60

0.115 0.000 0.000 0.000 0.018 0.000 0.021 0.012 0.010 0.010


concentration ranges a slightly positive deviation was observed. Nevertheless, an almost ideal behavior was examined for both mixtures over the whole concentration range. The density of water + [EMIM][OAc] and water + [DEMA][OMs] was measured with a combined measurement uncertainty of ± 0.06 % in a concentration range w = 0.05 to 0.2 and a temperature range of T = (293.15 to 353.15) K in 20 K steps at atmospheric pressure. Each experiment was repeated two times, and the results and the standard deviation (SD) are given in Tables 6 and 7. The measurement data show a decrease of density with increasing temperature. Figure 4 shows that in the case of water + [DEMA][OMs], the density decreases with increasing water concentration, but in the case of water + [EMIM][OAc] the density data show a maximum in the range of w = 0.1 to 0.15. Similar density behavior was observed in literature for aqueous acidic acid.13 The viscosity of water + [EMIM][OAc] and water + [DEMA][OMs] was also measured in a concentration range w = 0.05 to 0.2 and a temperature range of T = (293.15 to 353.15) K in 20 K steps at atmospheric pressure. The experiments were repeated four times at each concentration and temperature. The viscosity data and the standard deviations (SD) of the measurements are given in Tables 8 and 9. The data show, as expected, that the dynamic viscosity of both mixtures decrease with increasing water concentration and increasing temperature. The combined measurement uncertainty of the water + [DEMA][OMs] measurements was ± 3.9 %. It has to be mentioned that the Viton seals of the falling sphere viscometer are, especially at high temperatures, not resistant to [EMIM][OAc]. At water concentrations below w = 0.15 in the mixture water + [EMIM][OAc] and high temperatures (T > 40 °C), dark cords can be observed in the tube. As the fraction of impurities caused by the Viton seals is very low, the data viscosity of water + [EMIM][OAc] is given in Table 8. In this case it is not reasonable to refer to combined measurement uncertainties and standard deviations because the real deviation caused by the impurity may be higher. Nevertheless the measurements agree very well with measurements of Fendt et al. which were performed with a rotational viscometer at 25 °C.14

mole fractions of water (x1). The water vapor pressure data were measured with a mean uncertainty of ± 2.4 % and are listed in Tables 1 and 2. Though the spectra of water + [EMIM][OAc] showed another volatile component beside water in the gas phase, the peak of this component did not interfere with the water peak used to process the measurement. This gave us the possibility to evaluate the vapor pressure of water in the gas phase. The experimental data were correlated using the excess Gibbs free energy model NRTL.12 In this model the logarithmic activity coefficient of water γ1 is given as ⎛ exp( − 2α12τ21) ln γ1 = (1 − x1)2 ⎜τ21 2 ⎝ [x1 + (1 − x1)exp(−α12τ21)] + τij

⎞ ⎟ [(1 − x1) + x1 exp(−α12τ12)]2 ⎠ exp(− 2α12τ12)

(1)

with τ12 =

Δg12 RT

(2)

and

τ21 =

Δg21 RT

(3)

In eqs 2 and 3 R = (8.314) J·mol−1·K−1 is the molar gas constant. To calculate the NRTL parameters Δg12, Δg21, and α12, the following function was minimized: n

F=

∑ (ln γ1,cal − ln γ1,exp)2 i=1

(4)

The results of the correlation in comparison to the experimental results in Figures 2 and 3 show a good agreement with each other. The parameters of the NRTL equation are shown in Table 3. The specific heat capacities of the mixtures water + [EMIM][OAc] and water + [DEMA][OMs] were measured in the range of T = (293.15 to 363.15) K in 10 K steps and the results are shown in Tables 4 and 5. The maximum measurement uncertainty of this method is u(cp) = ± 15 J·kg−1· K−1. For water + [EMIM][OAc] a positive deviation from an ideal mixture was found over the whole concentration and temperature range. In the case of water + [DEMA][OMs] especially in low concentration ranges we observed a negative deviation from the behavior of an ideal mixture. In high

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CONCLUSION

In this work VLE data were measured for the mixtures water + [EMIM][OAc] and water + [DEMA][OMs] in the concentration range between pure water and pure RTIL and the temperature range T = (293.15 to 353.15) K by FTIR spectroscopy with a mean uncertainty of ± 2.4 %. The correlation of the data F



Article

(13) Perry, R. H.; Green, D. W. Perry’s Chemical Engineers’ Handbook, 7th ed.; McGraw-Hill: New York, 1997; pp 2−107. (14) Fendt, S.; Padmanabhan, S.; Blanch, H. W.; Prausnitz, J. W. Viscosities of Acetate or Chloride-Based Ionic Liquids and Some of Their Mixtures with Water or Other Common Solvents. J. Chem. Eng. Data 2011, 56 (1), 31−34.

with the NRTL model resulted in a good agreement between measured and correlated data. Furthermore, the specific heat capacity was measured in the whole concentration range between pure water and pure RTIL in the temperature range T = (293.15 to 363.15) K with an uncertainty of u(cp) = ± 15 J·kg−1·K−1. The density was measured in a concentration range of w = 0.5 to 0.2 at T = (293.15 to 353.15) K with a measurement uncertainty of ± 0.06 %. In case of water + [EMIM][OAc] a maximum was detected in the range of w = 0.1 to 0.15. The viscosity was also measured in this temperature range with a measurement uncertainty of ± 3.9 % in the case of water + [DEMA][OMs]. During the viscosity measurements of water + [EMIM][OAc] a decomposition of the Viton seals occurred. The influence of this decomposition on the measurements is estimated to be low but cannot be quantified yet.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: + 49 721 60842733. Fax: +49 721 60842335. E-mail: [email protected]. Funding

The authors thank the Deutsche Bundesstiftung Umwelt (DBU) for financial support. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Holbrey, J. D.; Seddon, K. R. Ionic Liquids. Clean Products Processes 1999, 1, 223−236. (2) Wasserscheid, P.; Stark, A. Handbook of Green Chemistry, Vol. 6: Ionic Liquids; Wiley-VCH-Verlag: Weinheim, Germany, 2010. (3) Constantinescu, D.; Schaber, K.; Agel, F.; Klingele, M. H.; Schubert, T. J. S. Viscosities, vapor pressures and excess enthalpies of choline lactate + water, choline glycolate + water and choline methanesulfonate + water systems. J. Chem. Eng. Data 2007, 52 (4), 1280−1285. (4) Jork, C.; Kristen, C.; Piaraccini, D.; Stark, A.; Chiappe, C.; Beste, Y. A.; Arlt, W. Tailor-made ionic liquids. J. Chem. Thermodyn. 2005, 37, 537−558. (5) Rogers, R. D.; Seddon, K. R. Ionic LiquidsSolvents of the future? Science 2003, 302, 792−793. (6) Brennecke, J. F.; Maginn, E. Ionic Liquids: Innovative Fluids for Chemical Processing. AIChE J. 2001, 47, 2384−2389. (7) Simoni, L. D.; Lin, Y.; Brennecke, J. F.; Stadtherr, M. A. Modeling Liquid-Liquid Equilibrium of Ionic Liquid Systems with NRTL, Electrolyte-NRTL, and UNIQUA. Ind. Eng. Chem. Eng. 2008, 47, 256−272. (8) Römich, Ch.; Merkel, N.; Schaber, K.; Schubert, T. J. S.; Koch, M. A Comparison Between Lithiumbromide−water and Ionic Liquid− Water as Working Solution for Refrigeration Cycles. Proceedings of the 23rd IIR International Congress of Refrigeration, 2011, Paper 287. (9) Wasserscheid, P.; Seiler, M. Leveraging Gigawatt Potentials by Smart Heat-Pump Technologies Using Ionic Liquids. ChemSusChem 2011, 4, 459−463. (10) Kleiber, M.; Joh, R. Stoffwerte und Zustandsgrößen: Stoffwerte von sonstigen chemische einheitlichen Flüssigkeiten und Gasen. In VDI Wärmeatlas, 10. Auflage; Springer Verlag: Berlin, Germany, 2006; pp Dca 1−Dca 46. (11) Wolf, H. Stoffwerte und Zustandsgrößen: Dampfdrücke über wässrigen Salzlösungen. In VDI Wärmeatlas, 10. Auflage; Springer Verlag: Berlin, Germany, 2006; pp Dca 1−Dca 12. (12) Renon, H.; Prausnitz, J. M. Local compositions in thermodynamic excess functions for liquid mixtures. AIChE J. 1968, 14, 135−144. G


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