Ionic Conductivities of Binary Mixtures Containing Pyridinium-Based

May 9, 2013 - Figure 7. Walden plot for methanol mixtures at T = 303.15 K: □ ... viscosity and ionic conductivity was studied using the Walden diagr...
0 downloads 0 Views 603KB Size
Download PDF
Article pubs.acs.org/jced

Ionic Conductivities of Binary Mixtures Containing Pyridinium-Based Ionic Liquids and Alkanols Mónica García-Mardones, Henrry M. Osorio, Carlos Lafuente, and Ignacio Gascón* Departamento de Química Física, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain ABSTRACT: In this study, we have determined ionic conductivities of six binary systems composed of an ionic liquid (1-butylpyridinium tetrafluoroborate, 1-butyl-3methylpyridinium tetrafluoroborate, or 1-butyl-4methylpyridinium tetrafluoroborate) and a short chain alkanol (methanol or ethanol) at four temperatures, T = (293.15, 303.15, 313.15, and 323.15) K. The ionic conductivity data have been correlated using both an empirical equation and the Vogel−Tamman−Fulcher equation. We also have compared the behavior of different mixtures, paying special attention to the influence of methyl group in the pyridine ring and the effect of both alkanols in the mixtures. Ionic conductivities of all the mixtures are bigger than those of the pure components and present a maximum at small mole fractions of the ionic liquid. Moreover, conductivity values are bigger for the binary mixtures containing methanol instead or ethanol. Finally, the relationship between viscosity and ionic conductivity from Waldeńs rule has provided a measurement of the ionicity of the mixtures.

■

INTRODUCTION Ionic conductivity of ionic liquids (ILs) is a property of critical importance for the development of electrochemical applications of these compounds.1−5 The study of this transport property gives a measure of the size, shape and mobility of the charge carriers that are present in the IL.2 Moreover, the comparison of different conductivities of ILs can be used in theoretical studies for a better understanding of the factors that govern the behavior of ILs, such as ionic aggregation.2,6−8 A great downside for the development of electrochemical devices based on ILs is their high viscosity. The higher is the viscosity on an ionic liquid, the lower is the mobility of its ions and, consequently, its conductivity. On the other hand, ionic liquids that show less aggregation possess more charge carriers available and the ionic conductivity is bigger.9 Another common feature of ILs is that their ionic conductivities are not too high due to the existence of strong interactions inside the fluid.2 To increase the conductivity of the IL, which is required for many industrial applications, it is necessary to blend these compounds with other organic solvents, to reduce the viscosity, and augment their ionic conductivity.10 However, the experimental measurements of the ionic conductivity of liquid mixtures containing ILs are scarce in the literature. Zarrougui et al.11 presented a study of volumetric and transport properties of N-butylN-methylpyrrolidinium bis trifluoromethanesulfonyl imide with methanol in the temperature range 253.15 K to 318.15 K. Toumi et al.12 studied the ionic conductivity as a function of temperature for the liquid mixture triethylamine plus KCl aqueous solution. Zhang et al.13 measured the ionic conductivity of solutions of pyridinium based ionic liquids with methanol, ethanol, acetonitrile, and propylene carbonate. The mixtures were investigated in the temperature range 283.15 to 313.15 K. The aim of this work was to study the influence of the methylene (−CH2−) group and the organic solvent in the ionic conductivity measurements. Rilo et al.10 © XXXX American Chemical Society

measured the viscosity and ionic conductivity of binary mixtures of 1-alkyl-3methylimidazolium tetrafluoroborate (CnMIM-BF4, n = 2, 4, 6, and 8) with ethanol at the temperatures T = (288, 298, 308 and 318) K. Moreover, they calculated viscosity deviations and molar conductivity from experimental data. Finally, CanongiaLopes et al.14 focused on binary mixtures composed of 1-butyl3methylimidazolium bis(trifluoromethanesulfonyl)imide with six different polarity, size, and isomerism solvents: acetonitrile, dichloromethane, methanol, 1-butanol, t-butanol, and water. These authors presented polarity, viscosity, and conductivity measurements for all the systems. Also, they obtained the relationship between viscosity and ionic conductivity through Walden plot curves. In this contribution, we report ionic conductivities of the binary systems containing an IL: 1-butylpyridinium tetrafluoroborate ([bpy][BF4]), 1-butyl-3methylpyridinium tetrafluoroborate ([b3mpy][BF4]), or 1-butyl-4methylpyridinium tetrafluoroborate ([b4mpy][BF4])) and one organic solvent (methanol or ethanol). These systems were studied at the temperatures T = (293.15, 303.15, 313.15 and 323.15) K over the whole range of composition at atmospheric pressure. The [bpy][BF4] + ethanol system presented miscibility problems at T = 293.15 K, therefore it has not been possible to measure conductivities in these conditions. Temperature dependence of experimental Table 1. Water Content in the Studied ILs ionic liquids

water content/ppm

[bpy][BF4] [b3mpy][BF4] [b4mpy][BF4]

470 60 260

Received: December 14, 2012 Accepted: April 25, 2013

A

dx.doi.org/10.1021/je301347v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 2. Experimental Ionic Conductivities, κ, for Pyridinium Ionic Liquid + Alkanol at Several Temperatures x1

κ/mS·cm−1

x1

κ/mS·cm−1

x1

κ/mS·cm−1

x1

1-Butylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 293.15 K 0.0432 28.7 0.1773 37.8 0.5618 11.98 0.0485 29.8 0.2273 34.7 0.6317 8.94 0.0698 32.1 0.2401 34.3 0.6980 7.40 0.0901 34.5 0.2966 31.4 0.8355 4.06 0.1091 37.1 0.3803 23.7 0.8790 3.21 0.1252 37.5 0.4277 20.7 0.9279 2.70 0.1420 38.2 0.4808 17.54 1.0000 1.807 0.1629 37.9 1-Butylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 303.15 K 0.0432 33.7 0.1773 45.7 0.5618 17.19 0.0485 35.1 0.2273 43.0 0.6317 13.54 0.0698 38.2 0.2401 42.6 0.6980 10.68 0.0901 41.7 0.2966 39.9 0.8355 6.47 0.1091 43.9 0.3803 30.5 0.8790 5.14 0.1252 45.4 0.4277 27.1 0.9279 4.46 0.1420 46.1 0.4808 22.9 1.0000 3.21 0.1629 45.9 1-Butylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 313.15 K 0.0432 39.1 0.1773 53.8 0.5618 22.2 0.0485 39.5 0.2273 51.6 0.6317 18.12 0.0698 44.5 0.2401 51.3 0.6980 14.47 0.0901 48.9 0.2966 48.1 0.8355 9.66 0.1091 51.4 0.3803 37.2 0.8790 7.76 0.1252 53.5 0.4277 33.9 0.9279 6.84 0.1420 54.5 0.4808 28.9 1.0000 5.19 0.1629 54.9 1-Butylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 323.15 K 0.0432 42.8 0.1773 61.2 0.5618 27.7 0.0485 46.2 0.2273 60.1 0.6317 23.5 0.0698 51.1 0.2401 59.4 0.6980 18.92 0.0901 54.6 0.2966 55.9 0.8355 13.86 0.1091 58.1 0.3803 45.1 0.8790 11.19 0.1252 60.6 0.4277 40.8 0.9279 9.76 0.1420 61.2 0.4808 34.9 1.0000 7.85 0.1629 61.9 1-Butylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 303.15 K 0.0353 7.85 0.1033 16.8 0.3929 21.7 0.0417 8.63 0.1165 17.97 0.4464 19.56 0.0455 10.60 0.1291 18.57 0.5095 16.59 0.0461 10.36 0.1597 21.6 0.6170 11.95 0.0551 11.47 0.1656 22.8 0.7008 8.84 0.0564 12.38 0.2093 23.8 0.8158 5.66 0.0634 14.39 0.2237 24.4 0.8973 4.36 0.0735 14.30 0.2751 24.6 1.0000 3.21 0.0840 15.56 1-Butylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 313.15 K 0.0353 10.24 0.1033 22.4 0.3929 27.0 0.0417 11.80 0.1165 23.9 0.4464 25.0 0.0455 12.68 0.1291 25.1 0.5095 22.0 0.0461 12.91 0.1597 27.4 0.6170 17.66 0.0551 14.75 0.1656 27.7 0.7008 14.26 0.0564 15.01 0.2093 29.5 0.8158 10.32 0.0634 16.37 0.2237 29.6 0.8973 8.21 0.0735 18.21 0.2751 29.7 1.0000 5.19 0.0840 19.83 1-Butylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 323.15 K 0.0353 13.16 0.1033 25.6 0.3929 32.0 0.0417 13.76 0.1165 27.0 0.4464 28.6 0.0455 15.42 0.1291 29.2 0.5095 25.6 0.0461 15.40 0.1597 30.1 0.6170 21.7 0.0551 17.20 0.1656 32.3 0.7008 17.10 0.0564 18.30 0.2093 34.1 0.8158 12.83

κ/mS·cm−1

x1

κ/mS·cm−1

x1

κ/mS·cm−1

1-Butylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 323.15 K 0.0634 22.2 0.2237 34.3 0.8973 10.42 0.0735 21.2 0.2751 34.5 1.0000 7.85 0.0840 23.1 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 293.15 K 0.0337 22.9 0.1734 33.1 0.5198 13.05 0.0438 24.5 0.2236 31.1 0.6100 9.44 0.0479 26.6 0.2696 27.8 0.7290 4.72 0.0567 29.0 0.3345 24.3 0.8344 2.80 0.0699 31.7 0.3780 21.9 0.9177 1.905 0.1142 33.3 0.4258 17.61 1.0000 1.549 0.1504 33.7 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 303.15 K 0.0337 27.1 0.1734 40.1 0.5198 18.17 0.0438 28.9 0.2236 38.0 0.6100 13.22 0.0479 31.2 0.2696 34.4 0.7290 6.86 0.0567 34.1 0.3345 30.8 0.8344 4.13 0.0699 38.5 0.3780 28.0 0.9177 3.11 0.1142 39.8 0.4258 23.1 1.0000 2.81 0.1504 40.6 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 313.15 K 0.0337 31.1 0.1734 47.4 0.5198 23.0 0.0438 33.4 0.2236 45.5 0.6100 17.82 0.0479 36.0 0.2696 41.5 0.7290 10.42 0.0567 39.6 0.3345 37.7 0.8344 6.72 0.0699 44.9 0.3780 34.5 0.9177 5.23 0.1142 46.6 0.4258 29.5 1.0000 4.61 0.1504 47.4 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 323.15 K 0.0337 35.0 0.1734 55.2 0.5198 28.7 0.0438 38.0 0.2236 53.4 0.6100 22.7 0.0479 40.9 0.2696 48.9 0.7290 15.83 0.0567 45.3 0.3345 44.9 0.8344 10.52 0.0699 51.0 0.3780 41.1 0.9177 8.17 0.1142 53.8 0.4258 35.9 1.0000 7.04 0.1504 55.0 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 293.15 K 0.0613 7.87 0.2393 15.20 0.5281 9.34 0.0737 8.88 0.2811 15.05 0.5747 8.23 0.0915 10.16 0.3174 14.12 0.6938 5.10 0.1113 11.43 0.3652 13.25 0.7799 3.70 0.1366 12.43 0.4385 11.90 0.9102 2.15 0.1670 13.97 0.4652 10.89 1.0000 1.549 0.1985 14.71 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 303.15 K 0.0613 10.17 0.2393 19.69 0.5281 12.76 0.0737 11.41 0.2811 19.64 0.5747 11.69 0.0915 13.12 0.3174 18.53 0.6938 7.70 0.1113 14.78 0.3652 17.58 0.7799 5.60 0.1366 16.34 0.4385 16.07 0.9102 3.60 0.1670 18.13 0.4652 14.86 1.0000 2.81 0.1985 19.20 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 313.15 K 0.0613 12.60 0.2393 24.0 0.5281 16.81 0.0737 14.20 0.2811 24.0 0.5747 15.65 0.0915 16.29 0.3174 23.1 0.6938 11.52 0.1113 18.44 0.3652 22.4 0.7799 8.91 0.1366 20.4 0.4385 21.1 0.9102 5.90 0.1670 22.2 0.4652 19.23 1.0000 4.61 0.1985 23.6 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 323.15 K 0.0613 15.29 0.2393 28.9 0.5281 22.1 0.0737 17.16 0.2811 28.9 0.5747 20.4 B

dx.doi.org/10.1021/je301347v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 2. continued x1

κ/mS·cm−1

x1

κ/mS·cm−1

x1

κ/mS·cm−1

x1

1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 323.15 K 0.0915 19.61 0.3174 28.5 0.6938 16.28 0.1113 21.9 0.3652 27.6 0.7799 13.34 0.1366 24.3 0.4385 25.4 0.9102 9.03 0.1670 26.8 0.4652 24.5 1.0000 7.04 0.1985 28.1 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 293.15 K 0.0426 28.1 0.1256 37.6 0.4593 21.8 0.0499 29.9 0.1425 37.8 0.5657 14.21 0.0584 31.8 0.2197 34.7 0.6744 9.93 0.0716 33.8 0.2475 33.1 0.7908 5.65 0.0898 35.8 0.3050 31.3 0.8788 3.41 0.1093 37.2 0.3465 28.1 1.0000 1.318 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 303.15 K 0.0426 32.5 0.1256 45.2 0.4593 26.8 0.0499 34.6 0.1425 45.6 0.5657 19.28 0.0584 37.1 0.2197 43.8 0.6744 12.82 0.0716 39.9 0.2475 42.2 0.7908 7.61 0.0898 42.5 0.3050 38.4 0.8788 4.87 0.1093 44.3 0.3465 35.3 1.0000 2.54 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 313.15 K 0.0426 35.5 0.1256 52.0 0.4593 33.0 0.0499 39.3 0.1425 52.7 0.5657 24.7 0.0584 41.7 0.2197 51.5 0.6744 17.1 0.0716 45.6 0.2475 50.0 0.7908 11.19 0.0898 48.2 0.3050 46.1 0.8788 7.80 0.1093 50.8 0.3465 42.7 1.0000 4.39 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Methanol (2) at T = 323.15 K 0.0426 40.9 0.1256 58.2 0.4593 38.3 0.0499 43.7 0.1425 59.2 0.5657 28.5 0.0584 46.5 0.2197 58.5 0.6744 19.91 0.0716 50.2 0.2475 57.0 0.7908 12.87 0.0898 54.0 0.3050 52.7 0.8788 9.25 0.1093 56.7 0.3465 49.0 1.0000 6.87 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Ethanol (2) at T = 293.15 K 0.0448 6.96 0.1551 15.00 0.4126 13.99 0.0521 7.91 0.1602 15.13 0.5649 11.01 a

κ/mS·cm−1

1-Butyl-4methylpyridinium 0.0608 8.93 0.0701 9.91 0.0843 11.47 0.1046 12.94 0.1232 13.91 0.1347 14.38 1-Butyl-4methylpyridinium 0.0448 8.77 0.0521 10.07 0.0608 11.46 0.0701 12.77 0.0843 14.72 0.1046 16.48 0.1232 18.01 0.1347 18.59 1-Butyl-4methylpyridinium 0.0448 10.12 0.0521 12.24 0.0608 14.19 0.0701 15.84 0.0843 18.20 0.1046 20.79 0.1232 22.56 0.1347 23.31 1-Butyl-4methylpyridinium 0.0448 10.96 0.0521 13.01 0.0608 15.47 0.0701 17.60 0.0843 19.50 0.1046 24.1 0.1232 26.4 0.1347 27.6

x1

κ/mS·cm−1

Tetrafluoroborate (1) + 0.2251 15.87 0.2470 15.87 0.3371 15.20 0.3512 14.96 0.3799 14.53 0.3856 14.44 Tetrafluoroborate (1) + 0.1551 19.54 0.1602 19.72 0.2251 20.88 0.2470 20.94 0.3371 20.18 0.3512 19.96 0.3799 19.45 0.3856 19.35 Tetrafluoroborate (1) + 0.1551 24.66 0.1602 24.91 0.2251 26.65 0.2470 26.80 0.3371 26.12 0.3512 25.89 0.3799 25.24 0.3856 25.19 Tetrafluoroborate (1) + 0.1551 29.2 0.1602 29.6 0.2251 32.2 0.2470 32.6 0.3371 32.2 0.3512 32.2 0.3799 31.7 0.3856 31.6

x1

κ/mS·cm−1

Ethanol (2) at T = 293.15 K 0.6798 8.51 0.7941 6.01 0.9258 3.05 0.9963 1.543 1.0000 1.318 Ethanol (2) at T = 303.15 K 0.4126 18.79 0.5649 13.71 0.6798 10.18 0.7941 6.96 0.9258 3.80 0.9963 2.42 1.0000 2.54 Ethanol (2) at T = 313.15 K 0.4126 24.56 0.5649 20.07 0.6798 16.12 0.7941 12.00 0.9258 7.17 0.9963 4.59 1.0000 4.39 Ethanol (2) at T = 323.15 K 0.4126 31.0 0.5649 26.3 0.6798 21.6 0.7941 16.84 0.9258 10.63 0.9963 7.40 1.0000 6.87

Standard uncertainties u are u(T) = 0.01 K, u (x1) = 0.0001, and the combined expanded uncertainty Uc is Uc (κ) = 2 % with 0.95 level of confidence (k ≈ 2).

conductivities has been fitted by means of an empirical equation and the Vogel−Tamman−Fulcher equation. In previous contributions we have reported conductivities of the three pure ILs6 and densities and viscosities of the six binary systems.15−17 In this work, we have used correlated absolute viscosity together with ionic conductivity data to classify the behavior of the mixtures making use of the Walden plot.

Glass vials closed with screw caps were used to prevent solvent evaporation; moreover, conductivities were always measured immediately after the mixture was prepared and vigorously stirred. Ionic conductivities, κ, were measured using a CRISON conductimeter, model GLP31. A closed cell was used in our measurements to avoid the liquid sample exposure to air. All the measurements were repeated at least three times, and the conductivity values were averaged. The estimated uncertainty of conductivity measurements is ± 2 %, according to manufacturer specifications and previous studies performed in our laboratory. The temperature of the samples was kept constant within ± 0.01 K by means of a Lauda E-200 thermostat and it was measured with a thermometer F250 from Automatic Systems Laboratories. The equipment was calibrated with different KCl aqueous solutions provided by CRISON.

■

EXPERIMENTAL SECTION The ionic liquids 1-butylpyridinium tetrafluoroborate, 1-butyl3methylpyridinium tetrafluoroborate, and 1-butyl-4methylpyridinium tetrafluoroborate with purities > 0.99 in mass were provided by IoLiTec. The alkanols used were methanol and ethanol obtained from Aldrich with purities > 0.998 and > 0.995 in mass, respectively. Since impurities can affect conductivity measurements, ILs were additionally purified before their study following a procedure previously described.6 The water content of the samples, as shown in Table 1, was less than 500 ppm as determined using the Karl Fischer method by means of an automatic CRISON titrator, model KF 1S-2B. All the mixtures were prepared by mass, making use of a Sartorius semimicro balance CP225-D (precision ± 1·10−5 g).

■

RESULTS AND DISCUSSION Experimental ionic conductivities for the six binary systems studied are given in Table 2. To describe the relationship between ionic conductivity and composition of the mixtures we have used the following empirical equation, which is a classical polynomial equation C

dx.doi.org/10.1021/je301347v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 3. Parameters and Standard Deviations of the Fitting to Equation 1 A/mS·cm−1

T/K 293.15 303.15 313.15 323.15

14.499 11.128 12.951 16.677

303.15 313.15 323.15

1.150 −0.959 1.639

293.15 303.15 313.15 323.15

4.194 7.339 10.365 14.832

293.15 303.15 313.15 323.15

−0.647 0.828 −0.844 −1.180

293.15 303.15 313.15 323.15

5.788 8.054 10.756 14.653

293.15 303.15 313.15 323.15

−4.683 −2.030 −8.765 −11.171

B/mS·cm−1

C/mS·cm−1

D/mS·cm−1

1-Butylpyridinium Tetrafluoroborate (1) + Methanol (2) 593.79 −1311.82 728.9 869.26 −1783.27 945.6 967.86 −1923.10 1000 1000 −1936.27 996.4 1-Butylpyridinium Tetrafluoroborate (1) + Ethanol (2) 232.73 −474.56 250.9 377.71 −603.26 254.4 386.34 −631.22 278.2 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Methanol (2) 905.23 −1883.37 1000 971.62 −1943.59 1000 1000 −1940.79 982.4 1000 −1886.20 943.2 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Ethanol (2) 176.86 −341.05 171.4 228.27 −424.11 207.7 286.69 −484.71 219.0 357.71 −529.82 209.5 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Methanol (2) 1000 −1886.21 872.50 1000 −1875.05 897.56 1000 −1828.65 865.37 993.95 −1853.12 901.91 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Ethanol (2) 346.99 −394.21 68.57 309.67 −474.60 181.78 554.82 −565.36 69.30 612.50 −553.46 24.70

E

σ (κ)/mS·cm−1

6.982 8.638 7.993 7.115

0.84 0.21 1.06 1.31

1.541 4.037 3.368

0.90 0.13 0.82

13.548 11.858 10.127 8.552

0.64 0.92 1.12 1.34

2.704 2.785 3.331 4.115

0.23 0.26 0.30 0.23

14.138 10.746 8.812 7.361

0.49 0.14 0.32 0.02

10.739 5.154 10.288 9.218

0.08 0.34 0.06 0.30

Table 4. Parameters and Standard Deviations of the Vogel−Tamman−Fulcher Equation κ∞0/mS·cm−1

κ∞1/mS·cm−1

κ∞2/mS·cm−1

κ∞3/mS·cm−1

B0/K

B1/K

B2/K

B3/K

T00/K

T01/K

T02/K

T03/K

74.3 121.9 212.0 −1.8 151.3 231.2 −6.9 181.9 185.3 31.1 259.4 205.2

24.4 55.7 228.3 −9.4 20.4 264.0

1-Butylpyridinium Tetrafluoroborate (1) + Methanol (2) −3905.7 3255.5 −12.5 209.9 86.2 −37.4 1-Butylpyridinium Tetrafluoroborate (1) + Ethanol (2) 2418.1 −3668.5 1285.0 1250.1 −1330.6 12.2 −417.5 694.6 −241.9 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Methanol (2) 6144.6 −14788.2 11475.9 2246.0 −4901.1 3470.2 −377.5 1005.2 −654.8 1-Butyl-3methylpyridinium Tetrafluoroborate (1) + Ethanol (2) 1990.4 −4491.8 5531.9 305.8 157.3 148.6 −161.3 294.0 −158.6 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Methanol (2) 1783.6 351.9 −70.3

1700.7 −3319.5 1741.4 623.8 −416.9 −6.4 −120.8 71.1 60.9 1-Butyl-4methylpyridinium Tetrafluoroborate (1) + Ethanol (2) 658.5 775.6 6145.5 529.7 2283.2 −1824.6 −261.9 28.3 147.6 D

σ(κ)/mS cm−1

0.54

0.84

0.61

0.22

0.39

0.34

dx.doi.org/10.1021/je301347v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Figure 1. Ionic conductivities, κ, for 1-butylpyridinium tetrafluoroborate (1) + methanol (2) as a function of ionic liquid mole fraction, x1: ■, T = 293.15 K; □, T = 303.15 K; ●, T = 313.15 K; ○, T = 323.15 K; ―, eq 1.

Figure 3. Ionic conductivities, κ, for 1-butyl-3methylpyridinium tetrafluoroborate (1) + methanol (2) as a function of ionic liquid mole fraction, x1: ■, T = 293.15 K; □, T = 303.15 K; ●, T = 313.15 K; ○, T = 323.15 K; ―, eq 1.

Figure 2. Ionic conductivities, κ, for 1-butylpyridinium tetrafluoroborate (1) + ethanol (2) as a function of ionic liquid mole fraction, x1: ■, T = 293.15 K; □, T = 303.15 K; ●, T = 313.15 K; ○, T = 323.15 K; ―, eq 1.

Figure 4. Ionic conductivities, κ, for 1-butyl-3methylpyridinium tetrafluoroborate (1) + ethanol (2) as a function of ionic liquid mole fraction, x1: ■, T = 293.15 K; □, T = 303.15 K; ●, T = 313.15 K; ○, T = 323.15 K; ―, eq 1.

including an extra adjustable parameter in the quotient to reproduce the asymmetric shape of the experimental curves: κ=

A + Bx1 + Cx12 + Dx13 1 + Ex1

The conductivity data can also be correlated with temperature and composition fitted by means of the Vogel− Tamman−Fulcher (VTF) equation:18−20

(1)

where A, B, C, D, and E are adjustable parameters at a given temperature and x1 is the mole fraction of the IL in the mixture. These parameters together with standard deviations of the fittings are given in Table 3.

⎛ ⎞ B κ = κ∞ exp⎜ ⎟ ⎝ (T − T0) ⎠ E

(2)

dx.doi.org/10.1021/je301347v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

where the parameters κ∞, B, and T0 depend on the mixture composition by means of the following expressions:

κ∞ =

∑ κ∞ ix1i i=0

B=

∑ Bi x1i i=0

T0 =

∑ T0ix1i i=0

(3)

(4)

(5)

Adjustable VTF parameters and standard deviations of the fittings for the six binary systems are given in Table 4. Standard deviations obtained in the fitting with both the VTF equation and empirical eq 1 are similar and can be considered satisfactory. Before starting the discussion of experimental results, it is important to underline that the conductivity of ILs depends on the strong interactions between ions and also on the mobility and the number of charge carriers. In binary mixtures, logically, it is also influenced by the characteristics of the solvent used. Ionic conductivities of the mixtures are graphically represented in Figures 1 to 6 together with the fitted values given by eq 1. As

Figure 6. Ionic conductivities, κ, for 1-butyl-4methylpyridinium tetrafluoroborate (1) + ethanol (2) as a function of ionic liquid mole fraction, x1: ■, T = 293.15 K; □, T = 303.15 K; ●, T = 313.15 K; ○, T = 323.15 K; ―, eq 1.

when more solvent is added. It has been pointed out that in mixtures with low ionic liquid concentration the number of charge carriers is smaller since aggregation becomes the dominant effect in this region.13,14,21 Finally, it should be underlined that the values of the maximum ionic conductivity depend on the solvent,15 methanol mixtures show the highest ionic conductivity values and these points are shifted toward the small mole fractions of the ionic liquid. Maximum values appear at mole fractions of the IL (x1) around 0.14 and 0.25 for mixtures containing methanol or ethanol, respectively. The ionic conductivity sequence for the mixtures containing the same alkanol is [bpy][BF4] > [b4mpy][BF4] > [b3mpy][BF4]. As results show, ionic conductivity is related to the size of the cation. In this sense, the larger is the cation size, the smaller is the ionic conductivity.7,8 For this reason, if we compare systems containing the same alkanol, the mixture with [bpy][BF4] shows higher ionic conductivities than mixtures containing [b4mpy][BF4] or [b3mpy][BF4], due to the absence of methyl group in the pyridine ring of [bpy][BF4]. On the other hand, differences between the two isomers containing one methyl group are scarce: pure [b3mpy][BF4] presents a slightly bigger conductivity than [b4mpy][BF4],6 however, viscosity deviations for the mixtures containing an alkanol and [b4mpy][BF4] are more negative than the mixtures formed by the same alkanol and [b3mpy][BF4].15 This more marked viscosity decrease produces that ionic conductivities are slightly bigger in the systems containing [b4mpy][BF4]. Comparing mixtures containing the same IL, it can be noticed that the ionic conductivity decreases with the extension of the alkanol. Thus, the larger values correspond to methanol systems. Taking into account the viscosity of the mixtures15 it can be concluded that methanol decreases more efficiently than ethanol the viscosity of the ILs because it weakens more the electrostatic interactions between ions. Viscosity reduction leads to an increment of conductivity. Additionally, there exists another reason to justify this behavior, since solvation with

Figure 5. Ionic conductivities, κ, for 1-butyl-4methylpyridinium tetrafluoroborate (1) + methanol (2) as a function of ionic liquid mole fraction, x1: ■, T = 293.15 K; □, T = 303.15 K; ●, T = 313.15 K; ○, T = 323.15 K; ―, eq 1.

these plots show, the ionic conductivity increases when the temperature rises in all the systems, because temperature produces an increment of the mobility of the ions.11,13 It is also remarkable that ionic conductivities of the mixtures are higher than pure compounds values.11,14 All the experimental curves have the same shape and can be divided in two parts which are separated by the maximum of the graph: at high ionic liquid concentrations, ionic conductivities are small because the viscosity of the mixture is too large, when small quantities of the organic solvent are added, the viscosity decreases and the mobility of charge carriers rises, consequently ionic conductivity continuously increases until it reaches its maximum. From this point, ionic conductivity decreases F

dx.doi.org/10.1021/je301347v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

ideal line corresponds to a 0.01 M KCl aqueous solution which is fully dissociated and its ions have the same mobility. Binary mixtures below the line are poor ionic liquids, whereas mixtures over the line are good ionic liquids. Using correlated absolute viscosities, previously reported for these systems,15 together with ionic conductivities given here, we have obtained the Walden plot for all the binary systems at T = 303.15 K. As it can be observed in Figures 7 and 8 all the mixtures analyzed are located below the ideal line, thus they are subionic (poor) ionic liquids.6 This classification was proposed by Angell et al.24 and is mainly qualitative, because there exist relevant differences between a diluted electrolyte solution and an ionic liquid solution. The addition of an organic solvent significantly changes the shape of the curves, which are close to the ideal line for high alkanol concentrations. This effect is most noticeable in the mixtures containing ethanol, since it is less polar than methanol.14 Comparing ILs mixed with the same alkanol, differences between them are scarce, especially when the fluidity increases. In this part of the graph, the curves overlap, indicating that the effect of the methyl group in the pyridine ring is not relevant.

methanol reduces ionic aggregation; resulting in an increment of the charge carriers mobility.2 Other similar conclusions have been found with different ionic liquids solutions.10,13,14,22 The ionic conductivity and viscosity have been related through the Waldeńs rule23 using the well-known equation: Λ·η = constant

(6)

This rule is obtained from the Stokes−Einstein equation and the Nerst−Einstein equation6 and is mainly applied to solutions, even though it can be applied to pure ionic liquids.6 Depending on the Walden plot position, different categories have been defined for the binary systems. The position of the

■

CONCLUSIONS The ionic conductivity of the binary mixtures formed by one of the following pyridinium ionic liquids: 1-butylpyridinium tetrafluoroborate, 1-butyl-3methylpyridinium tetrafluoroborate, or 1-butyl-4methylpyridinium tetrafluoroborate with two short chain alkanols (methanol or ethanol) were measured at four temperatures, T = (293.15, 303.15, 313.15, and 323.15) K. The objective of our study was to determine the modification of this property when an organic solvent is added to the ionic liquid. Our results have shown that ionic conductivity presents a maximum as a function of composition. The higher values for these maxima have been found in the systems containing methanol. These results have been discussed in terms of the methyl group effect. Finally, the relationship between viscosity and ionic conductivity was studied using the Walden diagrams; pure ionic liquids, and their binary mixtures with methanol or ethanol, are founded below the KCl ideal line.

Figure 7. Walden plot for methanol mixtures at T = 303.15 K: ■, [bpy][BF4]; □, [b3mpy][BF4]; ●, [b4mpy][BF4].

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +34976761200. Fax: +34976761202. E-mail:igascon@ unizar.es. Funding

We are grateful for financial assistance from Gobierno de Aragón and Fondo Social Europeo 2007−2013 (EU). Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Brennecke, J.; Maginn, E. Ionic liquids: Innovative Fluids for Chemical Processing. AIChE J. 2001, 47, 2384−2389. (2) Wasserscheid, P.; Welton, T. Ionic Liquids in Synthesis, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2003. (3) Vila, J.; Gines, P.; Pico, J. M.; Franjo, C.; Jimenez, E.; Varela, L. M.; Cabeza, O. Temperature Dependence of the Electrical Conductivity in EMIM-Based Ionic LiquidsEvidence of Vogel− Tamman−Fulcher Behavior. Fluid Phase Equilib. 2006, 242, 141−146. (4) Tokuda, H.; Hayamizu, K.; Ishii, K.; Abu Bin Hasan Susan, M.; Watanabe, M. Physicochemical Properties and Structures of Room Temperature Ionic Liquids. 1. Variation of Anionic Species. J. Phys. Chem. B 2004, 108, 16593−16600.

Figure 8. Walden plot for ethanol mixtures at T = 303.15 K: ■, [bpy][BF4]; □, [b3mpy][BF4]; ●, [b4mpy][BF4]. G

dx.doi.org/10.1021/je301347v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

(5) Quinn, B. M.; Ding, Z. F.; Moulton, R.; Bard, A. J. Novel Electrochemical Studies of Ionic Liquids. Langmuir 2002, 18, 1734− 1742. (6) Bandres, I.; Montano, D. F.; Gascon, I.; Cea, P.; Lafuente, C. Study of the Conductivity Behavior of Pyridinium-Based Ionic Liquids. Electrochim. Acta 2010, 55, 2252−2257. (7) Vila, J.; Varela, L. M.; Cabeza, O. Cation and Anion Size Influence in the Temperature Dependence of the Electrical Conductivity in Nine Imidazolium Based Ionic Liquids. Electrochim. Acta 2007, 52, 7413−7417. (8) Leys, J.; Wubbenhorst, M.; Menon, C. P.; Rajesh, R.; Thoen, J.; Glorieux, C.; Nockemann, P.; Thijs, B.; Binnemans, K.; Longuemart, S. Temperature Dependence of the Electrical Conductivity of Imidazolium Ionic Liquids. J. Chem. Phys. 2008, 128, 064509. (9) Freemantle, M. An Introduction to Ionic Liquids; RSC Pub.: Cambridge, UK, 2010. (10) Rilo, E.; Vila, J.; Garcia, M.; Varela, L. M.; Cabeza, O. Viscosity and Electrical Conductivity of Binary Mixtures of CnMIM-BF4 with Ethanol at 288 K, 298 K, 308 K, and 318 K. J. Chem. Eng. Data 2010, 55, 5156−5163. (11) Zarrougui, R.; Dhahbi, M.; Lemordant, D. Volumetric and Transport Properties of N-Butyl-N-methylpyrrolidinium Bis(trifluoromethanesulfonyl)imide−Methanol Binary Mixtures. Ionics 2011, 17, 343−352. (12) Toumi, A.; Hafaiedh, N.; Bouanz, M. Electrical Conductivity Investigation of Diluted Potassium Chloride Solutions in Binary Mixture Triethylamine−Water Near Its Consolute Point. Fluid Phase Equilib. 2011, 305, 185−191. (13) Zhang, Q.; Sun, S.; Pitula, S.; Liu, Q.; Welz-Biermann, U.; Zhang, J. Electrical Conductivity of Solutions of Ionic Liquids with Methanol, Ethanol, Acetonitrile, and Popylene Carbonate. J. Chem. Eng. Data 2011, 56, 4659−4664. (14) Canongia Lopes, J. N.; Gomes, M. F. C.; Husson, P.; Padua, A. A. H.; Rebelo, L. P. N.; Sarraute, S.; Tariq, M. Polarity, Viscosity, and Ionic Conductivity of Liquid Mixtures Containing [C(4)C(1)im][Ntf(2)] and a Molecular Component. J. Phys. Chem. B 2011, 115, 6088−6099. (15) Garcia-Mardones, M.; Gascon, I.; Lopez, M. C.; Royo, F. M.; Lafuente, C. Viscosimetric Study of Binary Mixtures Containing Pyridinium-Based Ionic Liquids and Alkanols. J. Chem. Eng. Data 2012, 57, 3549−3556. (16) Garcia-Mardones, M.; Barros, A.; Bandres, I.; Artigas, H.; Lafuente, C. Thermodynamic Properties of Binary Mixtures Combining Two Pyridinium-Based Ionic Liquids and Two Alkanols. J. Chem. Thermodyn. 2012, 51, 17−24. (17) Garcia-Mardones, M.; Perez-Gregorio, V.; Guerrero, H.; Bandres, I.; Lafuente, C. Thermodynamic Study of Binary Mixtures Containing 1-butylpyridinium tetrafluoroborate and methanol or ethanol. J. Chem. Thermodyn. 2010, 42, 1500−1505. (18) Vogel, H. Das Temperatur-abhängigkeitsgesetz der Viskosität von Flüssigkeiten. Phys. Z. 1921, 22, 645−646. (19) Fulcher, G. S. Analysis of Recent Measurements of the Viscosity of Glasses. Am. Ceram. Soc. J. 1925, 8, 339−355. (20) Tammann, G.; Hesse, W. Die Abhängigkeit der Viscosität von der Temperatur bei Unterkühlten Flüssigkeiten. Z. Anorg. Allg. Chem. 1926, 156, 245−257. (21) Wang, J.; Wang, H.; Zhang, S.; Zhang, H.; Zhao, Y. Conductivities, Volumes, Fluorescence, and Aggregation Behavior of Ionic Liquids [C(4)mim][BF4] and [C(n)mim]Br (n = 4, 6, 8, 10, 12) in Aqueous Solutions. J. Phys. Chem. B 2007, 111, 6181−6188. (22) Rilo, E.; Vila, J.; Pico, J.; Garcia-Garabal, S.; SEgade, L.; Varela, L. M.; Cabeza, O. Electrical Conductivity and Viscosity of Aqueous Binary Mixtures of 1-Alkyl-3-methyl Imidazolium Tetrafluoroborate at Four Temperatures. J. Chem. Eng. Data 2010, 55, 639−644. (23) Xu, W.; Cooper, E. I.; Angell, C. A. Ionic Liquids: Ion Mobilities, Glass Temperatures, and Fragilities. J. Phys. Chem. B 2003, 107, 6170−6178.

(24) Angell, C. A.; Byrne, N.; Belieres, J. P. Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications. Acc. Chem. Res. 2007, 40, 1228−1236.

H

dx.doi.org/10.1021/je301347v | J. Chem. Eng. Data XXXX, XXX, XXX−XXX