Density, Speed of Sound, Viscosity, and Excess Properties of Binary

Article pubs.acs.org/jced

Density, Speed of Sound, Viscosity, and Excess Properties of Binary Mixtures Formed by Ethanol and Bis(trifluorosulfonyl)imide-Based Ionic Liquids Rocio Salinas, Jordi Pla-Franco, Estela Lladosa,* and Juan B. Montón Departamento de Ingeniería Química, Escuela Técnica Superior de Ingeniería, Universitat de València, 46100 Burjassot, Valencia, Spain ABSTRACT: In this work, viscosities, densities, and speeds of sound of three binary mixtures containing the ionic liquids 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide, [emim][NTf2], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][NTf2], and 1-hexyl-3-methylimidazo-lium bis(trifluoromethylsulfonyl)imide, [hmim][NTf2], mixed with ethanol were measured at atmospheric pressure in the range of (278.15 to 338.15) K, covering the entire range of compositions. From these experimental data, the excess isentropic compressibility and molar isentropic compressibility of pure components and mixtures have been calculated. Additionally, excess properties, such as viscosity deviation, excess molar volume, excess isentropic compressibility, and excess molar isentropic compressibility, have been calculated and fitted with the Redlich−Kister polynomial equation.

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INTRODUCTION Ionic liquids (ILs) find a wide range of application as alternatives to the organic solvents for different processes,1,2 and they are being used as separation agents with very promising results, but experimental data of physical properties are still limited. Density and viscosity are, among other properties, important physical properties in the design of multiple processes. For example, the density is important to developing equations of state, while the excess volume is of great importance when studying the nature of the molecular interactions present in mixtures. On the other hand, viscosity can be required for the design of different equipment related to liquid flow. Due to the fact that most of the chemical and technological applications of ILs take place in mixtures, the interest of an increasing number of research groups worldwide3−7 has been focused on properties such as physical properties, liquid−liquid equilibrium, and vapor−liquid equilibrium of mixtures containing ILs. Moreover, owing to an almost unlimited number of potential combinations of cations and anions, ILs can be tailored to specific applications. However, this task has to be assisted by theoretical models8 due to the extensive number of ILs9 (approximately 106). The most commonly used cations are those of the 1-alkyl-3methylimidazolium family [Cnmim]+. On the other hand, bis(trifluoromethylsulfonyl)imide [F3CSO2)2N], (abbreviated herein as [NTf2]−), has gained in recent years some importance among the commonly used anions due to its stability to moisture, air, and high-temperature conditions. Moreover, [NTf2]− anion has good hydrolytic and electrochemical stability.10 Therefore, the main objective of this work was the determination of density, speed of sound, and viscosity for the IL family of bis(trifluoromethanesulfonyl)imide anion with © XXXX American Chemical Society

Table 1. Specifications of Chemical Samples chemical name

source

initial mass fraction purity

purification method

analysis method

[emim][NTf2]a [bmim][NTf2]b [hmim][NTf2]c ethanol

IoLiTec IoLiTec IoLiTec Sigma-Aldrich

> 0.990 > 0.990 > 0.990 0.999

none none none none

KFd KFd KFd GCe

a

[emim][NTf 2 ] = 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. b[bmim][NTf2] = 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. c[hmim][NTf2] = 1-hexyl-3-methylimidazolium bis(trifluorome-thylsulfonyl)imide. dKF = Karl Fischer Titration. eGC = gas−liquid chromatography.

ethanol at (278.15 to 338.15) K. For this purpose, the properties of three commercially available ILs 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([emim][NTf2]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([bmim][NTf 2]), and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([hmim][NTf2]) with ethanol were measured.

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EXPERIMENTAL SECTION Chemicals. All the ionic liquids were supplied by Iolitec with purity higher than 99.0 %, by mass. The water content, ww, and halide content, whalide, for all ionic liquids were certificated by the company, and their values are ww < 70 ppm and whalide < 100 ppm, respectively. Received: June 27, 2014 Accepted: January 8, 2015

A

DOI: 10.1021/je500594z J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 2. Densities ρ, Speeds of Sound u, vi.Scosities η, Molar Volumes Vm, Isentropic Compressibility κS, and Molar Isentropic Compressibility KS,m of Pure Ethanol, [emim][NTf2], [bmim][NTf2], and [hmim][NTf2]a T K

ρ kg·m

η

u −3

−1

m·s

278.15 298.15 318.15 338.15

802.39 785.32 767.84 749.54

1212.93 1143.07 1075.67 1009.39

278.15 298.15 318.15 338.15

1538.23 1517.76 1497.65 1477.86

1284.91 1240.12 1196.62 1155.76

278.15 298.15 318.15 338.15

1453.69 1434.23 1415.13 1396.34

1273.78 1227.52 1183.99 1142.70

278.15 298.15 318.15 338.15

1390.30 1371.64 1353.31 1335.25

1274.62 1226.82 1182.03 1139.28

106 Vm

mPa·s Ethanol 1.59 1.08 0.77 0.56 [emim][NTf2] 75.08 32.02 17.32 10.82 [bmim][NTf2] 139.82 51.22 24.36 13.94 [hmim][NTf2] 211.31 70.46 30.22 16.82

m ·mol 3

−1

κS TPa

1015 KS,m −1

m ·mol−1·Pa−1 3

57.416 58.664 60.000 61.464

847.116 974.554 1125.572 1309.438

48.638 57.171 67.534 80.483

254.389 257.821 261.283 264.78

393.761 428.420 466.313 506.56

100.168 110.456 121.839 134.13

288.480 292.394 296.339 300.327

423.975 462.727 504.088 548.457

122.309 135.299 149.381 164.716

321.815 326.193 330.611 335.084

442.720 484.393 528.865 577.001

142.474 158.006 174.848 193.344

Standar uncertainties: ρ = 7·10−3 kg·m−3, u = 0.02 m·s−1, η (1−10 mPa·s) = 0.002 mPa·s, η (11−50 mPa·s) = 0.01 mPa·s, η (>50 mPa·s) = 0.05 mPa·s, Vm = 7·10−15 m3·mol−1, κS = 0.05 TPa−1, KS,m = 6.5·10−24 m3·mol−1·Pa−1.

a

Table 3. Fitting Parameters of eq 3 Together with the Correlation Coefficient Squared (R2) and the Standard Relative Deviations of the Fit (σ) for the Density and the Speed of Sound of the Studied ILs [emim][NTf2] [bmim][NTf2] [hmim][NTf2]

−3

ρ/kg·m u/m·s−1 ρ/kg·m−3 u/m·s−1 ρ/kg·m−3 u/m·s−1

A

B

R2

σ

1817.9 1883.3 1719.4 1880.0 1645.3 1900.3

−1.0061 −2.1548 −0.9558 −2.1839 −0.9174 −2.254

0.9999 0.9996 0.9999 0.9994 0.9999 0.9994

1.128·10−4 8.243·10−4 1.187·10−4 1.031·10−3 1.113·10−4 1.050·10−3

Figure 1. Density, ρ, and fitted curves from eq 1 of the studied ionic liquids as a function of temperature:●, [emim][NTf2]; ■, [bmim][NTf2]; ▲, [hmim][NTf2]. B



Article

Figure 2. Speed of sound, u, and fitted curves from eq 1 of the studied ionic liquids as a function of temperature:●, [emim][NTf2]; ■, [bmim][NTf2]; ▲, [hmim][NTf2].

Table 4. Fitting Parameters of eq 3 and the Standard Relative Deviations of the Fit (σ) for the Density of Several [1-alkyl-mim] [NTf2] ILs equation parameters

1-prophyl 1-butyl

1-hexyl 1-heptyl

B

C

1.0627

−0.0253

ref

temp. range, K

σ

alkyl group

ref

temp. range, K

σ

this work 11 12 14 15 16 17 18 19 20 20 this work 12 14 15

[278.15−338.15] [298.15−343.15] [292.88−391.28] [278.15−308.15] [296.15−333.65] [273.15−363.15] [293.49−414.92] [293.15−393.15] [278.15−328.15] [293.15−473.15] [293.15−473.15] [278.15−338.15] [292.88−391.28] [278.15−308.15] [296.45−333.65]

1.503·10−4 2.263·10−4 2.262·10−4 1.603·10−4 1.126·10−3 1.685·10−4 2.521·10−4 3.738·10−4 2.632·10−4 7.493·10−4 4.183·10−4 5.901·10−3 1.083·10−3 1.984·10−3 1.748·10−3

1-butyl

17 19 20 21 22 23 24 20 this work 11 14 20 21 23 25

[293.49−414.92] [278.15−328.15] [293.15−473.15] [273.15−363.15] [298.15−323.15] [278.15−333.15] [298.15−328.20] [293.15−473.15] [278.15−338.15] [298.15−343.15] [278.15−308.15] [293.15−473.15] [293.15−338.15] [278.15−333.15] [298.15−373.15]

4.828·10−3 1.772·10−3 5.630·10−4 1.117·10−3 1.728·10−2 1.422·10−3 1.477·10−3 3.552·10−4 1.503·10−4 6.957·10−5 1.945·10−3 5.633·10−4 2.423·10−4 1.337·10−3 4.576·10−4

26 27 18 20

[258.15−373.15] [293.15−338.15] [293.15−393.15] [293.15−473.15]

7.872·10−5 2.423·10−4 2.297·10−3 5.633·10−4

1-octyl

14 18 20

[278.15−308.15] [293.15−393.15] [293.15−473.15]

1.945·10−3 4.160·10−3 1.499·10−3

alkyl group 1-ethyl

A 1913.55

1-pentyl 1-hexyl

AG245, which has a precision of 0.0001 g. Taking into account the mass of each component placed into the vial and the balance accuracy, the uncertainty in mole fraction of all of the samples was estimated to be less than 0.00002 for any case. All samples were prepared immediately prior to measurements to avoid variations in composition due to evaporation of solvent or pickup of water by the IL. Densities, ρ, and speeds of sound, u, of pure components and binary mixtures were carried out using a digital vibratingtube densimeter and speed of sound analyzer (Anton Paar DSA 5000M) with a proportional temperature controller that keeps samples at working temperature with an accuracy of 0.001 K.

Ethanol (99.9% mass, for analysis ACS) was supplied by Sigma-Aldrich and was used without further purification after chromatography failed to show any significant impurities. The water content, determined using a Karl Fischer volumetric automatic titrator (Metrohm, 701 KF Titrino), was small in all chemicals ( 50 mPa·s) = 0.05 mPa·s, Vm = 7·10−15 m3·mol−1, VEm = 1·10−14 m3·mol−1, κS = 0.05 TPa−1, κES = 0.1 TPa−1, KS,m = 6.5·10−24 m3· mol−1·Pa−1, KES,m = 8.5·10−24 m3·mol−1·Pa−1. a

deviation, σ, of the experimental properties measured from their fitting was calculated following eq 2 ndat

σ=

∑ i

((z − zcal)/zcal)2 ndat

decrease with increasing temperature. Moreover, it was observed that as the alkyl chain length increases in trifluorosulfonyimide-based ILs, the value of the density (and the speed of sound) decreases. According with Kolbeck et al.,14 this behavior is caused by the increase of the ILs nonpolar regions (composed by the alkyl groups). As these regions occupy more space than the polar regions, the final result is a decrease in density. IL density can be expressed as a function of the temperature and the alkyl-chain length:

(2)

where z and zcal are the values of experimental and calculated property and ndat is the number of experimental points. The σ values are also shown in Table 3. As it can be inferred from the low deviations obtained, linear equations properly fit the experimental data. The temperature dependence of density and of speed of sound for the ILs studied has been plotted in Figures 1 and 2, respectively. These figures confirm that both properties

ρ = (A + BT )e−CNC −3

(3) −3

−1

where A (kg·m ), B (kg·m ·K ), and C are the adjustable parameters, T is the absolute temperature in K, and NC is the carbon number of the alkyl chain bounded to the 3-methylimidazolium E



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Table 7. Densities ρ, Speeds of Sound u, Viscosities η, Excess Viscosities ηE, Molar Volumes Vm, Excess Molar Volumes VEm, Isentropic Compressibility κS, Excess Isentropic Compressibility κES , Molar Isentropic Compressibility KS,m, and Excess Molar Isentropic Compressibility KES,m of the Binary Mixtures [Cnmim][NTf2] (1) + Ethanol (2) at T = 298.15 Ka ρ x1

kg·m

η

u −3

m·s

−1

mPa·s

0.000 0.051 0.102 0.198 0.292 0.402 0.501 0.619 0.710 0.811 0.907 1.000

785.32 927.85 1033.54 1171.44 1261.14 1335.52 1384.32 1429.22 1456.41 1481.59 1501.19 1517.76

1143.07 1139.30 1142.58 1158.16 1174.52 1190.87 1203.00 1214.59 1221.97 1228.98 1234.39 1240.12

1.08 1.57 2.16 3.47 5.02 7.16 9.66 13.22 16.41 20.91 25.67 32.02

0.000 0.049 0.096 0.194 0.288 0.390 0.484 0.591 0.696 0.818 0.900 1.000

785.32 921.49 1013.65 1143.26 1222.07 1281.27 1321.04 1355.98 1382.23 1406.65 1420.19 1434.23

1143.07 1142.44 1146.39 1160.70 1174.61 1187.98 1197.38 1206.18 1213.19 1219.85 1223.63 1227.52

1.08 1.71 2.35 4.13 6.64 9.50 12.92 17.30 22.86 31.21 38.05 51.22

0.000 0.047 0.097 0.198 0.292 0.390 0.470 0.596 0.694 0.799 0.903 1.000

785.32 915.22 1008.17 1127.27 1195.96 1244.05 1273.50 1308.27 1328.48 1346.07 1360.48 1371.64

1143.07 1145.72 1152.54 1168.44 1181.86 1192.30 1200.59 1209.19 1214.06 1218.93 1223.11 1226.82

1.08 1.73 2.61 4.98 7.97 12.10 15.94 23.72 31.30 41.44 53.70 70.46

ηE mPa·s

106 Vm

106 VmE

−1

m ·mol 3

m ·mol 3

−1

[emim][NTf2] (1) + Ethanol (2) 58.664 0.000 68.464 −0.269 78.592 −0.353 97.770 −0.387 116.514 −0.339 138.483 −0.294 158.126 −0.236 181.663 −0.200 199.824 −0.146 220.185 −0.090 239.164 −0.036 257.821 0.000 [bmim][NTf2] (1) + Ethanol (2) 0.00 58.664 0.000 −1.83 69.896 −0.250 −3.54 80.681 −0.344 −6.68 103.564 −0.389 −8.88 125.639 −0.315 −11.13 149.589 −0.237 −12.43 171.582 −0.160 −13.41 196.776 −0.110 −13.12 221.200 −0.059 −10.88 249.802 −0.030 −8.16 269.079 −0.013 0.00 292.394 0.000 [hmim][NTf2] (1) + Ethanol (2) 0.00 58.664 0.000 −2.61 71.080 −0.238 −5.20 84.247 −0.323 −9.84 111.221 −0.306 −13.37 136.655 −0.240 −16.04 162.730 −0.169 −17.75 184.154 −0.126 −18.71 217.978 −0.066 −17.93 244.233 0.002 −15.07 272.428 0.035 −10.03 300.349 0.020 0.00 326.193 0.000 0.00 −1.09 −2.08 −3.74 −5.09 −6.36 −6.92 −7.01 −6.64 −5.26 −3.47 0.00

κS

κES −1

−1

1015 KS.m −1

1015 KES.m −1

m ·mol ·Pa 3


(TPa )

(TPa )

974.554 830.318 741.141 636.420 574.797 527.986 499.151 474.289 459.829 446.872 437.180 428.420

0.000 −47.120 −61.023 −63.942 −57.043 −46.090 −36.394 −25.664 −18.260 −10.879 −4.659 0.000

57.171 56.847 58.248 62.223 66.972 73.117 78.929 86.161 91.885 98.394 104.558 110.456

0.000 −3.462 −5.079 −6.523 −6.860 −6.551 −5.881 −4.762 −3.719 −2.436 −1.130 0.000

974.554 831.460 750.666 649.255 593.084 553.019 527.982 506.901 491.542 477.750 470.277 462.727

0.000 −44.741 −56.085 −56.015 −47.987 −38.962 −30.578 −22.244 −15.326 −8.426 −4.387 0.000

57.171 58.116 60.565 67.239 74.515 82.725 90.592 99.746 108.729 119.343 126.541 135.299

0.000 −3.347 −4.802 −6.075 −6.231 −5.969 −5.336 −4.435 −3.420 −2.120 −1.186 0.000

974.554 832.376 746.716 649.769 598.622 565.447 544.768 522.774 510.698 500.004 491.336 484.393

0.000 −42.606 −53.632 −50.672 −42.299 −33.082 −27.617 −18.527 −12.291 −7.151 −2.999 0.000

57.171 59.165 62.908 72.268 81.805 92.015 100.321 113.953 124.729 136.215 147.572 158.006

0.000 −3.236 −4.777 −5.850 −5.934 −5.484 −5.158 −4.074 −3.001 −1.930 −0.891 0.000

Standar uncertainties: ρ = 7·10−3 kg·m−3, u = 0.02 m·s−1, η (1−10 mPa·s) = 0.0006 mPa·s, η (1−10 mPa·s) = 0.002 mPa·s, η (11−50 mPa·s) = 0.01 mPa·s, η (> 50 mPa·s) = 0.05 mPa·s, Vm = 7·10−15 m3·mol−1, VEm = 1·10−14 m3·mol−1, κS = 0.05 TPa−1, κES = 0.1 TPa−1, KS,m = 6.5·10−24 m3· mol−1·Pa−1, KES,m = 8.5·10−24 m3·mol−1·Pa−1. a

Table 2 lists the experimental viscosity data for the three ILs. If viscosity values are compared with those reported in literature, it is concluded that no significant differences can be found. As proof, deviations between experimental and published data are 1.44%11 and 4,60%16 for the [emim][NTf2]; 0.33%21 for the [bmim][NTf2] and 1.68%,11 0.25%19 and 3.35%25 for the [hmim][NTf2]. The viscosity, η, can be expressed as a function of the temperature in various ways. A common way28 is by using an equation with the structure of the Arrenhius law:

cation. Experimental density data from this work have been used to calculate parameters of eq 3. Values of these parameters are given in Table 4. Experimental reported data11,12,14−27 have been compared with values calculated with eq 3. In this way, Table 4 shows the standard relative deviations. According to the results, eq 3 works correctly at temperatures between (273 and 473) K and for a NC between 2 and 7. Regarding the influence of chain alkyl length in speed of sound, it can be said that at low temperatures is negligible. As a result, the values of the speed of sound of [bmim][NTf2] and [hmim][NTf2] are very close. In addition to data for density and speed of sound, viscosity data were obtained at atmospheric pressure from T = (278.15− 338.15) K for [emim][NTf2], [bmim][NTf2] and [hmim][NTf2].

η = Ae(−B / RT )

(4)

where the viscosity at infinite temperature, A (mPa·s) and the activation energy for viscous flow, B (J·mol−1) are the F



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kg·m

η

u −3

m·s

−1

ηE

mPa·s

mPa·s

0.000 0.051 0.102 0.198 0.292 0.402 0.501 0.619 0.710 0.811 0.907 1.000

767.84 909.21 1014.18 1151.39 1240.83 1315.11 1363.99 1408.90 1436.15 1461.40 1481.05 1497.65

1075.67 1079.42 1087.30 1107.66 1126.45 1144.47 1157.59 1170.01 1177.86 1185.35 1191.16 1196.62

0.77 1.09 1.46 2.27 3.21 4.59 5.85 7.84 9.67 11.96 14.35 17.32

0.00 −0.52 −1.00 −1.78 −2.39 −2.83 −3.21 −3.17 −2.85 −2.23 −1.43 0.00

0.000 0.049 0.096 0.194 0.288 0.390 0.484 0.591 0.696 0.818 0.900 1.000

767.84 903.02 994.64 1123.77 1202.45 1261.65 1301.51 1336.54 1362.91 1387.44 1401.04 1415.13

1075.67 1082.05 1090.03 1109.13 1125.52 1140.52 1150.77 1160.65 1168.28 1175.60 1179.73 1183.99

0.77 1.18 1.57 2.61 3.95 5.62 7.52 9.76 12.42 16.16 19.03 24.36

0.00 −0.75 −1.46 −2.74 −3.61 −4.35 −4.67 −4.95 −4.77 −3.91 −2.97 0.00

0.000 0.047 0.097 0.198 0.292 0.390 0.470 0.596 0.694 0.799 0.903 1.000

767.84 896.92 989.44 1108.22 1176.89 1225.05 1254.61 1289.55 1309.88 1327.59 1342.08 1353.31

1075.67 1085.05 1095.93 1116.28 1131.92 1143.84 1153.05 1162.64 1168.00 1173.41 1178.03 1182.03

0.77 1.18 1.71 3.05 4.64 6.70 8.61 12.33 15.72 20.13 24.94 30.22

0.00 −0.97 −1.92 −3.55 −4.73 −5.56 −6.00 −5.99 −5.49 −4.17 −2.42 0.00

106 Vm m ·mol 3

106 VEm

−1

m ·mol 3

−1

κS

κES −1

(TPa )

[emim][NTf2] (1) + Ethanol (2) 60.000 0.000 1125.572 69.868 −0.308 943.968 80.092 −0.405 834.039 99.472 −0.442 707.887 118.421 −0.389 635.130 140.632 −0.336 580.535 160.483 −0.279 547.115 184.283 −0.230 518.492 202.642 −0.172 501.895 223.227 −0.109 487.011 242.416 −0.047 475.871 261.283 0.000 466.313 [bmim][NTf2] (1) + Ethanol (2) 60.000 0.000 1125.572 71.326 −0.285 945.821 82.223 −0.387 846.168 105.360 −0.434 723.367 127.690 −0.352 656.489 151.915 −0.264 609.333 174.157 −0.184 580.196 199.638 −0.127 555.413 224.336 −0.074 537.574 253.261 −0.041 521.516 272.756 −0.020 512.842 296.339 0.000 504.088 [hmim][NTf2] (1) + Ethanol (2) 60.000 0.000 1125.572 72.530 −0.269 946.996 85.841 −0.363 841.485 113.134 −0.339 724.151 138.869 −0.263 663.183 165.253 −0.182 623.899 186.927 −0.135 599.510 221.143 −0.073 573.683 247.701 −0.003 559.607 276.221 0.031 547.062 304.467 0.019 536.921 330.611 0.000 528.865

−1

(TPa )

1015 KS.m −1

1015 KES.m −1

m ·mol ·Pa 3


0.000 −63.213 −81.857 −85.067 −75.326 −60.495 −47.656 −33.577 −23.955 −14.456 −6.524 0.000

67.534 65.954 66.800 70.415 75.213 81.642 87.803 95.549 101.705 108.714 115.359 121.839

0.000 −4.727 −6.927 −8.813 −9.196 −8.723 −7.814 −6.315 −4.945 −3.281 −1.604 0.000

0.000 −59.092 −74.023 −73.576 −62.749 −50.594 −39.397 −28.705 −19.691 −10.818 −5.622 0.000

67.534 67.462 69.575 76.214 83.827 92.567 101.045 110.882 120.597 132.080 139.881 149.381

0.000 −4.501 −6.443 −8.098 −8.266 −7.860 −6.975 −5.805 −4.459 −2.761 −1.544 0.000

0.000 −56.082 −70.344 −66.105 −54.894 −42.859 −35.630 −23.890 −15.850 −9.276 −3.942 0.000

67.534 68.686 72.234 81.926 92.096 103.101 112.065 126.866 138.615 151.110 163.475 174.848

0.000 −4.338 −6.369 −7.746 −7.812 −7.204 −6.746 −5.327 −3.928 −2.545 −1.190 0.000

Standar uncertainties: ρ = 7·10−3 kg·m−3, u = 0.02 m·s−1, η (1−10 mPa·s) = 0.002 mPa·s, η (11−50 mPa·s) = 0.01 mPa·s, η (> 50 mPa·s) = 0.05 mPa·s, VEm = 1·10−14 m3·mol−1, κS = 0.05 TPa−1, κES = 0.1 TPa−1, KS,m = 6.5·10−24 m3·mol−1·Pa−1, KES,m = 8.5·10−24 m3·mol−1·Pa−1.

a

where the three adjustable parameters are A (mPa·s), B (K), and the glass transition temperature, T0. (K). A slightly modification can be done in last expression to obtain the mVFT equation:29,34

adjustable parameters. In this equation the ideal gas constant R is 8.3144 J·mol−1·K−1. According to Okoturo and VanderNoot,29 if the cation is 1-butyl-3-methylimidazolium eq 4 fits viscosity data well in those cases where the anion is symmetrical. Equation 4 also works well if the anion is an imide and the cation has a low symmetry. None of these conditions are met in the ionic liquids studied here so a new equation is required. In this way, viscosity and temperature data were fitted to the Vogel−Fulcher−Tammann (VTF) equation.30−32 This expression is recommended for those cases when the ILs are formed by the imide anion and large cations29,33 (110 < cation molar mass < 170) and it is expressed as η = Ae(−B / T − T0)

η = AT 0.5e(−B / T − T0)

(6)

where the three adjustable parameters are again A (mPa·s), B (K), and the glass transition temperature, T0. (K). Litovitz35 introduced an equation where the viscosity is a cubic function of the inverse of the temperature, expressed as 3

η = Ae(−B / RT )

(7)

where A (mPa·s) and B (J·mol−1) are the adjustable parameters. As in the previous equation, R is 8.31 J·mol‑1·K‑1.

(5) G



Article


kg·m

η

u −3

m·s

−1

ηE

mPa·s

mPa·s

0.000 0.051 0.102 0.198 0.292 0.402 0.501 0.619 0.710 0.811 0.907 1.000

749.54 889.98 994.40 1131.14 1220.47 1294.80 1343.74 1388.81 1416.16 1441.50 1461.23 1477.86

1009.39 1020.73 1033.24 1058.32 1079.67 1099.70 1113.92 1127.34 1135.61 1143.69 1149.96 1155.76

0.56 0.79 1.05 1.60 2.23 3.16 3.99 5.23 6.35 7.70 9.11 10.82

0.00 −0.29 −0.56 −0.99 −1.33 −1.52 −1.71 −1.68 −1.49 −1.18 −0.76 0.00

0.000 0.049 0.096 0.194 0.288 0.390 0.484 0.591 0.696 0.818 0.900 1.000

749.54 883.95 975.18 1104.04 1182.73 1242.06 1282.08 1317.28 1343.80 1368.47 1382.15 1396.35

1009.39 1022.47 1034.50 1058.47 1077.42 1094.23 1105.77 1116.53 1124.94 1133.00 1137.58 1142.70

0.56 0.85 1.12 1.79 2.71 3.70 4.86 6.26 7.79 9.83 11.28 13.94

0.00 −0.37 −0.72 −1.37 −1.70 −2.08 −2.18 −2.21 −2.08 −1.67 −1.32 0.00

0.000 0.047 0.097 0.198 0.292 0.390 0.470 0.596 0.694 0.799 0.903 1.000

749.54 878.04 970.28 1088.96 1157.75 1206.10 1235.83 1271.01 1291.50 1309.35 1323.94 1335.25

1009.39 1025.63 1040.64 1065.52 1083.47 1096.99 1107.22 1117.99 1124.01 1130.04 1135.19 1139.28

0.56 0.85 1.20 2.06 3.03 4.25 5.36 7.44 9.32 11.59 13.80 16.82

0.00 −0.47 −0.94 −1.72 −2.28 −2.65 −2.84 −2.81 −2.52 −1.96 −1.44 0.00

106 Vm m ·mol 3

106 VEm

−1

−1

m ·mol 3

κS

κES −1

(TPa )

[emim][NTf2] (1) + Ethanol (2) 61.464 0.000 1309.438 71.378 −0.366 1078.446 81.686 −0.483 941.972 101.253 −0.529 789.312 120.397 −0.471 702.895 142.838 −0.412 638.631 162.901 −0.343 599.759 186.948 −0.288 566.561 205.502 −0.219 547.556 226.308 −0.142 530.359 245.705 −0.066 517.508 264.781 0.000 506.560 [bmim][NTf2] (1) + Ethanol (2) 61.464 0.000 1309.438 72.865 −0.334 1082.111 83.864 −0.452 958.197 107.243 −0.504 808.463 129.819 −0.414 728.359 154.312 −0.316 672.421 176.796 −0.230 637.902 202.557 −0.164 608.951 227.527 −0.102 588.041 256.772 −0.058 569.254 276.485 −0.027 559.090 300.327 0.000 548.457 [hmim][NTf2] (1) + Ethanol (2) 61.464 0.000 1309.438 74.090 −0.317 1082.688 87.536 −0.424 951.703 115.135 −0.396 808.847 141.165 −0.311 735.788 167.850 −0.222 688.986 189.768 −0.172 660.047 224.368 −0.105 629.470 251.226 −0.029 612.865 280.070 0.011 598.078 308.637 0.007 586.130 335.084 0.000 577.001

−1

(TPa )

1015 KS.m −1

1015 KES.m −1

m ·mol ·Pa 3


0.000 −86.002 −111.024 −113.939 −100.047 −79.977 −62.685 −44.054 −31.242 −18.853 −8.563 0.000

80.483 76.977 76.946 79.920 84.627 91.221 97.702 105.917 112.524 120.025 127.154 134.127

0.000 −6.564 −9.578 −12.015 −12.424 −11.720 −10.439 −8.412 −6.547 −4.344 −2.139 0.000

0.000 −78.721 −98.628 −97.446 −82.584 −66.107 −51.408 −37.088 −25.251 −13.638 −6.893 0.000

80.483 78.848 80.358 86.702 94.555 103.763 112.779 123.347 133.795 146.169 154.580 164.716

0.000 −6.124 −8.749 −10.907 −11.057 −10.434 −9.247 −7.619 −5.808 −3.536 −1.921 0.000

0.000 −75.490 −94.196 −87.873 −72.536 −56.550 −46.825 −31.481 −21.059 −12.486 −5.528 0.000

80.483 80.216 83.308 93.126 103.868 115.646 125.256 141.233 153.968 167.503 180.901 193.344

0.000 −5.960 −8.689 −10.473 −10.491 −9.657 −9.007 −7.133 −5.309 −3.490 −1.702 0.000

Standar uncertainties: ρ = 7·10−3 kg·m−3, u = 0.02 m·s−1, η (1−10 mPa·s) = 0.002 mPa·s, η (11−50 mPa·s) = 0.01 mPa·s, η (> 50 mPa·s) = 0.05 mPa·s, Vm = 7·10−15 m3·mol−1, VEm = 1·10−14m3·mol−1, κS = 0.05 TPa−1, κES = 0.1 TPa−1, KS,m = 6.5·10−24 m3·mol−1·Pa−1, KES,m = 8.5·10−24 m3·mol−1·Pa−1. a

Ghatee et al.36 proposed a linear correlation between the temperature and the fluidity (1/η) ⎛ 1 ⎞φ ⎜ ⎟ = A + B·T ⎝η⎠

listed. According to the results, it can be say that the best way to fit the viscosity data is by the VFT and mVFT equations. However, these deviations increase as the chain length of the cation also increases. Figure 3 shows the dependence between viscosity and temperature for [emim][NTf2], [bmim][NTf2], and [hmim][NTf2]. In this way, experimental values have been plotted together with calculated values of the viscosities. These values have been obtained using eq 5. As can be seen in Figure 3, viscosity is affected by temperature in a higher degree than density and speed of sound. Viscosity is higher at lower temperatures with an exponential relationship. The viscosity increases as the alkyl chain on the imidazolium ring increases. This behavior is in accordance with that reported in the

(8)

where the adjustable parameters are A (mPa−1·s−1) and B (mPa−1·s−1·K−1)). φ is a characteristic exponent used to improve the relationship between temperature and fluidity. According to the Ghatee et al.,36 φ has a value equal to 0.3 for most of ILs. Table 5 shows the calculated values of the adjustable parameters of viscosity equations (eq 4−8). Moreover, the correlation square coefficient and the standard relative deviations are also H



Article

Figure 4. Density ρ for the IL (1) + ethanol (2) binary systems at different temperatures; ●, 278.15 K; ▲, 298.15 K; ■, 318.15 K and x, 338.15 K. IL: (a) [emim][NTf2], data taken from Yao et al.:39 △, 298.15 K, ■, 318.15 K; (b) [bmim][NTf2], data taken from Andreatta et al.:40 △, 298.15 K; (c) [hmim][NTf2].

Figure 5. Speed of sound u for the IL (1) + ethanol (2) binary systems at different temperatures; ●, 278.15 K; ▲, 298.15 K; ■, 318.15 K and x, 338.15 K. IL: (a) [emim][NTf2], (b) [bmim][NTf2], (c) [hmim][NTf2].

Vm =

literature.11,15,16,19,21,25 The cause of this behavior has not been established yet, and many theories can be found in the literature.37,38 However, the general idea is that this increase in viscosity is the result of the van der Waals interactions, which prevail over electrostatic terms. The obtained experimental data allow the determination of various volumetric properties. Thereby, molar volumes of the mixtures, Vm, can be determined from density values using the following expression:

Mm ρ

(9)

where Mm is the molar mass of the mixture, defined as Mm = ΣxiM0i , where xi is the mole fraction of the component i and M0i is the molar mass of pure component, i. Isentropic compressibility, κS, defined as κS = − I

1 ⎛ ∂Vm ⎞ 1 ⎛ ∂ρ ⎞ ⎜ ⎟ = ⎜ ⎟ ⎠ ⎝ Vm ∂P S ρ ⎝ ∂P ⎠

(10) DOI: 10.1021/je500594z J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

⎛ ∂V ⎞ V 2 ΚS,m = −⎜ m ⎟ = Vmκs = m 2 ⎝ ∂P ⎠S M mu

Table 2 lists values of these three properties (Vm, κS and KS,m). As explained above, molar volume is the product of the molar mass and the inverse of the density. Therefore, the molar volume increases with temperature and the length of the alkyl chain. The same behavior is observed for the isentropic compressibility and molar isentropic compressibility. Volumetric Properties of Liquid Mixtures. Tables 6, 7, 8, and 9 list experimental values of density, ρ, speed of sound, u, viscosity, η, molar volume, Vm, isentropic compressibility κS and isentropic molar compressibility, KS,m; corresponding to different systems formed by an ionic liquid and ethanol at (278.15, 298.15, 318.15, and 338.15) K, respectively. These systems are [emim][NTf2] (1) + ethanol (2); [bmim][NTf2] (1) + ethanol (2) and [hmim][NTf2] (1) + ethanol (2). All mixtures are miscible over the entire range of compositions. The density, the speed of sound, and the viscosity have been plotted as a function of the IL molar fraction x1 at various temperatures in Figures 4, 5 and 6, respectively. In addition, Figures 4 and 6 include ethanol + [emim][[NTf2] data from Yao et al.39 and ethanol + [bmim][[NTf2] data from Andreatta et al.40 In all mixtures, the density increases exponentially when x1 also increases. This behavior is not surprising because ILs are much more dense than ethanol. For a fixed composition the density decreases linearly with the temperature. According to Figure 4a,b, density data from this work are in agreement with those reported in the literature.39,40 The way to vary the speed of sound with respect to the mole fraction of IL depends largely on temperature. Generally, the speed of sound increases with x1. However, in some mixtures, the low temperatures favor a decrease in speed of sound with increasing x1. However, this effect disappears at x1 values above 0.15. In all cases the speed of sound decreases linearly with temperature. Similarly to the previous properties, the addition of any IL to ethanol results in an exponential increase in viscosity at low temperatures and in an linear increase at high temperatures. Moreover, the viscosity decreases as temperature is increased. This relationship is also exponential. Viscosity data published previously39,40 are also plotted in Figure 6a,c. As can be seen, these data are similar to those obtained in the present work. However, this time there are small differences at low ethanol concentrations for the mixture with [emim][NTf2]. The molar volume is the quotient between the molar mass and the density. Both properties increase with the IL molar fraction. However, the molar mass does it in a more meaningful way. As a result, the molar volume increases linearly with the IL molar fraction. The molar volume linearly grows with the temperature as the density increases with temperature. The isentropic compressibility decays exponentially with the IL molar fraction and increases lineally with the temperature. This behavior is explained because the isentropic compressibility has been defined as the inverse of the product of the density and the square of the speed of sound. On the other hand, the isentropic molar compressibility increases linearly when temperature and IL molar fraction are increased. Clearly, definition of the molar isentropic compressibility (eq 12) explains this behavior. Excess Properties of Liquid Mixtures. Excess properties QE are defined as the difference between the actual value of the property in the mixture, Q, and that corresponding for an ideal mixture at the same thermodynamic condition, Qid:

Figure 6. Viscosity η for the IL (1) + ethanol (2) binary systems at different temperatures; ●, 278.15 K; ▲, 298.15 K; ■, 318.15 K and x, 338.15 K. IL: (a) [emim][NTf2], data taken from Yao et al.:39 △, 298.15 K, ■, 318.15 K; (b) [bmim][NTf2], data taken from Andreatta et al.:40 △, 298.15 K; (c) [hmim][NTf2].

This property is related to density and speed of sound by the Newton−Laplace equation:

κS =

Vm 1 = 2 ρu M mu 2

(12)

(11)

The molar isentropic compressibility, KS,m, can be defined from isentropic compressibility as

Q E = Q − Q id J

(13) DOI: 10.1021/je500594z J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

Table 10. Fitting Parameters of eq 22 to Obtain the Coefficients of eq 21 and Standard Absolute Deviations σ, for Viscosity Deviation ηE of the Binary Mixtures [Cnmim][NTf2] (1) + Ethanol (2) σ z

A0z

A1z

a b c

−2.93·10−2 19.209 −3157.8

−1.52·10−2 9.870 −1602.4

a b c

−6.72·10−2 49.958 −7189.2

−3.54·10−2 23.103 −3761.9

a b c

−1.10·10−1 71.64 −11684.0

−5.61·10−2 36.44 −5901.0

A2z

A3z

[emim][NTf2] (1) + Ethanol (2) −8.30·10−3 −9.80·10−3 5.307 6.339 −848.1 −1027.8 [bmim][NTf2] (1) + Ethanol (2) −1.44·10−2 −1.38·10−2 9.449 9.178 −1553.1 −1527.8 [hmim][NTf2] (1) + Ethanol (2) −4.44·10−2 −1.55·10−2 29.01 10.18 −4729.6 −1673.9

A4 z

mPa·s

−9.70·10−3 6.371 −1042.6

1.6791

−1.49·10−2 9.868 −1632.5

1.4833

1.76·10−2 −11.50 1875.4

2.1894

Table 11. Fitting Parameters of eq 22 to Obtain the Coefficients of eq 21 and Standard Absolute Deviations σ, for Excess Molar Volume VE of the Binary Mixtures [Cnmim][NTf2] (1) + Ethanol (2) 106 σ z

A0z

A1z

a b c

−1.2470·10−4 6.8533·10−2 −10.3341

3.1700·10−5 −1.4824·10−2 2.2883

a b c

−7.1254·10−5 3.8479·10−2 −5.7552

2.5626·10−5 −1.1444·10−2 2.3018

a b c

−6.9847·10−5 3.8657·10−2 −5.7552

1.8890·10−5 −1.0020·10−2 2.3018

A2z

A3z

[emim][NTf2] (1) + Ethanol (2) 1.2020·10−4 1.1940·10−4 −8.2243·10−2 −5.7138·10−2 13.2031 8.8056 [bmim][NTf2] (1) + Ethanol (2) 1.5740·10−5 1.7447·10−4 −1.5863·10−2 −9.1915·10−2 2.0245 13.7918 [hmim][NTf2] (1) + Ethanol (2) 2.8606·10−5 1.7658·10−4 −1.5252·10−2 −9.1546·10−2 2.0245 13.7918

A4z

m3·mol‑1

−3.0740·10−4 0.17407 −26.6484

0.0094

−8.2023·10−5 3.3826·10−2 −4.2361

0.0066

−1.0110·10−4 3.4002·10−2 −4.2361

0.0063

Table 12. Fitting Parameters of eq 22 to Obtain the Coefficients of eq 21 and Standard Absolute Deviations, for Excess Isentropic Compressibility κES of the Binary Mixtures [Cnmim][NTf2] (1) + Ethanol (2) 106 σ z

A0z

A1z

a b c

−1.7322·10−2 8.2809 −1075.0

1.7715·10−2 −8.2206 1041.8

a b c

−1.1058·10−2 5.0052 −626.3

1.5102·10−2 −7.1170 909.5

a b c

−1.1509·10−2 5.4763 −711.6

1.0210·10−2 −4.6451 593.0

A2z

A3z

[emim][NTf2] (1) + Ethanol (2) −8.3712·10−3 5.7917·10−2 2.9225 −29.1299 −289.9 3872.7 [bmim][NTf2] (1) + Ethanol (2) −9.3544·10−3 4.7381·10−2 3.7569 −23.4357 −410.4 3129.4 [hmim][NTf2] (1) + Ethanol (2) −2.5326·10−3 5.5644·10−2 0.6081 −27.8492 −41.4 3724.0

QE = Q −

Taking to account that an ideal-mixture property is defined as follows: Q id =

∑ xiQ i0

∑ xiQ i0

A4z

m3·Pa‑1

−7.7883·10−2 41.5262 −5732.1

2.6405

−5.5144·10−2 27.1296 −3546.0

2.6516

−7.7335·10−2 40.1561 −5483.0

2.7409

(15)

Thus, eq 15 is used to calculate the excess volume molar, VEm, and the viscosity deviation, ηE. Meanwhile, ideal isentropic compressibility, κidS , and ideal molar isentropic compressibility, KidS,m, can be calculated using the following expressions (Douhéret et al.41 and Benson and Kiyohara42):

(14)

where xi is the mole fraction of component i and Q0i is the property of pure component i at the mixture temperature and pressure, excess properties were calculated using the expression: K



Article

Figure 7. Viscosity deviation ηE for the IL (1) + ethanol (2) binary systems at different temperatures; ●, 278.15 K; ▲, 298.15 K; ■, 318.15 K and x, 338.15 K. The solid lines represent values obtained with eq 21 using parameters listed in Table 10. IL: (a) [emim][NTf2], data taken from Yao et al.:39 △, 298.15 K, ■, 318.15 K; (b) [bmim][NTf2], data taken from Andreatta et al.:40 △, 298.15 K; (c) [hmim][NTf2].

κSid =

ΚSid =

⎡

∑ ϕκi s,0i + T ⎢⎢∑

ϕiV i0(αp,0 i)2

⎣

⎡

∑ xiΚ 0s,i + T ⎢⎢∑ ⎣

Cp,0 i

xi(Ep,0 i)2 Cp,0 i

−

−

id 2 ⎤ Vmid(αp,m ) ⎥ id Cp,m ⎥⎦

id 2 ⎤ (Ep,m ) ⎥ id Cp,m ⎥⎦

Figure 8. Excess molar volume VE for the IL (1) + ethanol (2) binary systems at different temperatures; ●, 278.15 K; ▲, 298.15 K; ■, 318.15 K and x, 338.15 K. The solid lines represent values obtained with eq 21 using parameters listed in Table 11. IL: (a) [emim][NTf2], data taken from Yao et al.:39 △, 298.15 K, ■, 318.15 K; (b) [bmim][NTf2], data taken from Andreatta et al.:40 △, 298.15 K; (c) [hmim][NTf2], data taken from Lachwa et al.:48 △, 298.15 K.

where ϕi = xiV0i /Vidm is the volume fraction of component i, while κidS , KidS , α0p,i, C0p,i, and E0p,i are the isentropic compressibility, the molar isentropic compressibility, the isobaric thermal expansivity, the isobaric molar heat capacity, and the molar isobaric expansion, respectively, of pure component i at the mixture temperature and pressure. On the other hand, αidp,m, Cidp,m, and

(16)

(17) L



Article

Figure 9. Excess isentropic compressibility κES for the IL (1) + ethanol (2) binary systems at different temperatures; ●, 278.15 K; ▲, 298.15 K; ■, 318.15 K and x, 338.15 K. The solid lines represent values obtained with eq 21 using parameters listed in Table 12. IL: (a) [emim][NTf2], (b) [bmim][NTf2], (c) [hmim][NTf2].

Figure 10. Excess molar isentropic compressibility KES,m for the IL (1) + ethanol (2) binary systems at different temperatures; ●, 278.15 K; ▰, 298.15 K; ■, 318.15 K and x, 338.15 K. The solid lines represent values obtained with eq 21 using parameters listed in Table 13. IL: (a) [emim][NTf2], (b) [bmim][NTf2], (c) [hmim][NTf2].

Eidp,m are the isobaric thermal expansivity, the molar heat capacity, and the molar isobaric expansion, respectively, of the ideal mixture defined as id αp,m =

0 ∑ ϕα i p, i

(18)

id Cp,m =

∑ xiCp,0i

(19)

id Ep,m =

∑ xiEp,0 i

(20)

The combined standard uncertainty for ideal properties is the same as that for the actual properties. Excess properties were correlated with the IL mole fraction for each temperature studied, using the Redlich−Kister43 equation: M



Article

Table 13. Fitting Parameters of eq 22 to Obtain the Coefficients of eq 21 and Standard Absolute Deviations σ, for Excess Molar Isentropic Compressibility KES.m of the Binary Mixtures [Cnmim][NTf2] (1) + Ethanol (2) 1015 σ z

A0z

A1z

a b c

−3.1632·10−3 1.55074 −204.70

2.0730·10−3 −0.99843 128.50

a b c

−2.2331·10−3 1.03229 −130.00

2.1499·10−3 −1.07949 144.40

a b c

−2.422710−3 1.16836 −152.43

1.6923·10−3 −0.81734 107.10

A2z

A3z

[emim][NTf2] (1) + Ethanol (2) −5.960510−4 3.2525·10−3 0.20471 −1.64112 −17.10 216.20 [bmim][NTf2] (1) + Ethanol (2) −8.7849·10−4 3.6130·10−3 0.39440 −1.86555 −47.90 253.60 [hmim][NTf2] (1) + Ethanol (2) −8.3569·10−4 3.2631·10−3 0.44295 −1.61539 −62.30 212.00

m

(21)

where QE represents the excess property, xi is the mole fraction of component i, Ap is the polynomial coefficient, and m is the degree of the polynomial expansion. Some authors44,45 expressed the polynomial coefficients as a second degree polynomial function of temperature to reduce the total number of coefficients present in a determined system. A p = A pa T 2 + A pbT + A pc

(22)

where APa, APb and APc are the fitting parameters. In Tables 10, 11, and 12 are given values of these parameters for each binary mixture, together with the corresponding standard absolute deviations, σ, which were calculated using the following expression: ndat

σ=

∑ i

(zexp − zcalc)2 ndat

m3·Pa‑1·mol‑1

−5.6450·10−3 3.08357 −431.20

0.1324

−2.9047·10−3 1.40928 −181.10

0.1215

−5.4361·10−3 2.86298 −393.40

0.1138

concentration. From this point the absolute VE values start to decrease until a point that depends on the IL. Thus, if the IL is the [emim][NTf2] or [bmim][NTf2], the molar volume deviations are always negative. On the other hand, the mixture with [hmim][NTf2] reaches positive values of VE and has a maximum from which VE values return to decrease until practically zero. The higher deviations correspond to the IL with the shortest chain; the [emim][NTf2]. Generally, VE absolute values increase with the temperature. However, this description is not applicable for some points in the [hmim][NTf2] system. As can be seen in Figure 8, the VE obtained at 278.15 K is higher in terms of absolute value than that obtained at 298.15 K for high concentrations of IL. Anyway, in all cases the temperature has greater influence on VE at small IL concentrations. Figure 8 also shows values from other works. In this way, data from Yao et al.,39 Andreatta et al.,40 and Lachwa et al.48 are plotted in Figure 8a−c, respectively. As can be seen in these plots, deviations between the data of this work and those reported in literature are significant, especially for the case of Yao et al. data. In contrast to VE values, all κES and KES,m values are negative. According to Figures 9 and 10, the two excess properties have a similar relationship with the IL molar fraction. At lower x1 both deviations increase until a maximum point. Then, values increase with x1 although they never reach positive deviations. κES and KES,m values decrease with the chain length of the alkyl substituent of IL cation. Thus, the lowest values are obtained for the ethanol and [emim][NTf2] system. Once again the temperature produces an increase in the absolute values, especially at low IL molar fractions.

Q E = xixj ∑ A p(xi − xj) p p=0

A4z

(23)

where zexp is the property experimental value, zcalc is the calculated value, and ndat is the total number of experimental points. By comparing the deviation obtained with eq 23, it can be said that eq 21 makes the best predictions for the [hmim][NTf2] + ethanol system. The experimental values of ηE, VE, κES , and KES,m as a function of the IL molar fraction at different temperatures have been plot in Figures 7, 8, 9, and 10, respectively. In addition, the curves obtained with parameters listed in Tables 10, 11, 12, and 13 have also been included. The viscosity deviations are higher at lower temperatures and increase with the length of the alkyl chain. This behavior is the same as described in the literature.46,47 Thus, maximum absolute values of ηE are obtained for the ethanol and [hmim][NTf2] mixture at 278.15 K. The maximum deviation of each series is reached for an ethanol mole fraction close to a 0.5 value. However, at low temperatures this point is shifted to higher ethanol concentrations. The Yao et al.40 and Andreatta et al.41 data are also plotted in Figure 7a,c, respectively. Although some differences can be seen, the trend of the data is similar. The relationship between excess molar volume values and the IL molar fraction is the same as described in literature.40,41 At low IL concentrations the absolute values of VE increases if the x1 increases. This trend continues only until a certain IL

■

CONCLUSIONS Experimental values of density ρ, viscosity η and speed of sound u have been determined for mixtures formed by an IL ([emim][NTf2], [bmim][NTf2], or [hmim][NTf2]) and ethanol. Determinations were carried out at four different temperatures [(278.15, 298.15, 318.15, and 338.15) K] and atmospheric pressure across the entire range of compositions. The relationship between density and viscosity of pure ILs and the temperature has been discussed and a pair of equations for each mixture has been obtained. These properties have also been used to calculate the viscosity deviation ηE, excess molar volume VE, excess isentropic compressibility κES and excess molar isentropic compressibility KES,m. N



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Then, the values of excess properties were fit in each series to a Redlich−Kister equation. The Redlich−Kister parameters obtained for the same system were correlated with temperature to obtain new temperature dependent parameters. The maximum variation between ideal and experimental viscosity is reached at a certain x1 near the equimolar composition. From this point, ηE increases by adding either ethanol or IL. Regarding the excess molar volumes, at low IL concentrations they have negative values and they decrease as the IL molar fraction, x1, increases. However, this decrease stops at a certain x1 and then VE values begin to increase with IL molar fraction. In some systems positive values of VE are obtained and then a second VE decline is observed. Regarding κES and KES,m behavior, at low IL molar fraction their values begin to decrease to a minimum value and then they start to increase as x1 increase although all values are always negative. An increase in the temperature also causes a VE, κES , and KES,m decrease.

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(11) Seoane, R. G.; Corderí, S.; Gómez, E.; Calvar, N.; González, E. J.; Macedo, E. A.; Domínguez, A. Temperature Dependence and Structural Influence on the Thermophysical Properties of Eleven Commercial Ionic Liquids. Ind. Eng. Chem. Res. 2012, 51, 2492−2504. (12) Jacquemin, J.; Husson, P.; Padua, A. A.; Majer, V. Density and Viscosity of Several Pure and Water-Saturated Ionic Liquids. Green Chem. 2006, 8, 172−180. (13) Dominguez, I. Application of Ionic Liquids in Organic Compounds Separation; Ph.D. Thesis, University of Vigo: Vigo, Spain, 2012. (14) Kolbeck, C.; Lehmann, J.; Lovelock, K. R. J.; Cremer, T.; Paape, N.; Wasserscheid, P.; Fröba, A. P.; Maier, F.; Steinrück, H. P. Density and Surface Tension of Ionic Liquids. J. Phys. Chem. B 2010, 114, 17025−17036. (15) Fredlake, C. P.; Crosthwaite, J. M.; Hert, D. G.; Aki, S. N. V. K.; Brennecke, J. F. Thermophysical Properties of Imidazolium-Based Ionic Liquids. J. Chem. Eng. Data 2004, 49, 954−964. (16) Fröba, A. P.; Kremer, H.; Leipertz, A. Density, Refractive Index, Interfacial Tension and Viscosity of Ionic Liquids [Emim][Etso4], [Emim][Ntf2], [Emim][N(Cn)2], and [Oma][Ntf2] in Dependence on Temperature at Atmospheric Pressure. J. Phys. Chem. B 2008, 112, 12420−12430. (17) Jacquemin, J.; Husson, P.; Mayer, V.; Cibulka, I. High-Pressure Volumetric Properties of Imidazolium-Based Ionic Liquids: Effect of the Anion. J. Chem. Eng. Data 2007, 52, 2204−2211. (18) Gardas, R. L.; Freire, M. G.; Carvalho, P. J.; Marrucho, I. M.; Fonseca, I. M. A.; Ferreira, A. G. M.; Coutinho, J. A. P. PρT Measurements of Imidazolium-Based Ionic Liquids. J. Chem. Eng. Data 2007, 52, 1881−1888. (19) Wandschneider, A.; Lehman, J. K.; Heintz, A. Surface Tension and Density of Pure Ionic Liquids and Some Binary Mixtures with 1propanol and 1-butanol. J. Chem. Eng. Data 2008, 53, 596−599. (20) Tariq, M.; Serro, A. P.; Mata, S. L.; Saramago, B.; Esperança, J. M. S. S.; Lopes, J. N. C.; Rebelo, L. P. N. High-Temperature Surface Tension and Density Measurements of 1-Alkyl-3-Methylimidazolium Bistriflamide Ionic Liquids. Fluid Phase Equilib. 2000, 294, 131−138. (21) Harris, K. R.; Kanakubo, M.; Woolf, L. A. Temperature and Pressure Dependence of the Viscosity of the Ionic Liquids 1-Hexyl-3methylimidazolium hexafluorophosphate and 1-Butyl-3-methylimidazolium bis(Trifluoromethylsulfonyl)imide. J. Chem. Eng. Data 2007, 52, 1080−1085. (22) Dzyuba, S. V.; Bartsch, R. A. Influence of Structural Variations in 1-Alkyl(Aralkyl)-3-methylimidazoium hexafluorophosphates and Bis(Trifluoromethylsulfonyl)imides on Physical Properties of the Ionic Liquids. ChemPhysChem 2002, 3, 161−166. (23) Gomes de Azevedo, R.; Esperança, J. M. S. S.; Szydlowski, J.; Visak, Z. P.; Pires, P. F.; Guedes, H. J. R.; Rebelo, L. P. N. Thermophysical and Thermodynamic Properties of Ionic Liquids Over an Extended Pressure Range: [Bmim][Ntf2] and [Hmim][Ntf2]. J. Chem. Thermodyn. 2005, 37, 888−899. (24) Troncoso, J.; Cerdeiriña, C. A.; Sanmamed, Y. A.; Romaní, L.; Rebelo, L. P. N. Thermodynamic Properties of Imidazolium-Based Ionic Liquids: Densities, Heat Capacities, and Enthalpies of Fusion of [Bmim][PF6] and [Bmim][Ntf2]. J. Chem. Eng. Data 2006, 51, 1856− 1859. (25) Kandil, M. E.; Marsh, K. N.; Goodwin, A. R. H. Measurement of the Viscosity, Density, and Electrical Conductivity of 1-Hexyl-3methylimidazolium bis(trifluorosulfonyl)imide at Temperatures Between (288 and 433) K and Pressures Below 50 MPa. J. Chem. Eng. Data 2007, 52, 2382−2387. (26) Widegren, J. A.; Magee, J. W. Density, Viscosity, Speed of Sound, and Electrolytic Conductivity for the Ionic Liquid 1-Hexyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide and Its Mixtures With Water. J. Chem. Eng. Data 2007, 52, 2331−2338. (27) Esperança, J. M. S. S.; Guedes, H. J. R.; Lopes, J. N. C.; Rebelo, L. P. N. Pressure-Density-Temperature (P-ρ-T) Surface of [C6mim][Ntf2] II. J. Chem. Eng. Data 2008, 53, 867−870. (28) Seddon, K. R.; Stark, A.; Torres, M. J. Viscosity and Density of 1-Alkyl-3-Methylimidazolium Ionic Liquids. In Clean Solvents;

AUTHOR INFORMATION

Corresponding Author

*Tel.: +34963543549. Fax: +34963544898. E-mail: estela.lladosa@ uv.es. Funding

Financial support from the Ministerio de Ciencia y Tecnologiá of Spain, through project No. CTQ2010-18848/PPQ and the FEDER European Program are gratefully acknowledged. J. Pla-Franco is deeply grateful for the grant BES-2011-04636 received from the Ministerio de Economiá y Competitividad. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Earle, M. J.; Seddon, K. R. Ionic Liquids: Green Solvents for the Future. Pure Appl. Chem. 2000, 72, 1391−1398. (2) Brennecke, J. F.; Maginn, E. J. Ionic Liquids: Innovative Fluids for Chemical Processing. AIChE J. 2001, 47, 2384−2389. (3) Heintz, A. Recent Developments in Thermodynamics and Thermophysics of Non-Aqueous Mixtures Containing Ionic Liquids: A Review. J. Chem. Thermodyn. 2005, 37, 525−535. (4) Huddleston, J. G.; Willauer, H. D.; Swatloski, R. P.; Visser, A. E.; Rogers, R. D. Room Temperature Ionic Liquids as Novel Media for “Clean” Liquid-Liquid Extraction. Chem. Commun. 1998, 1765−1766. (5) Selvan, M. S.; McKinley, M. D.; Dubois, R. H.; Atwood, J. L. Liquid-Liquid Equilibria for Toluene + Heptane + 1-Ethyl-3methylimidazolium Triiodide and Toluene + Heptane + 1-Butyl-3methylimidazolium Triodide. J. Chem. Eng. Data 2000, 45, 841−845. (6) Vercher, E.; Miguel, P. J.; Llopis, F. J.; Orchillés, A. V.; MartínezAndreu, A. Volumetric and Acoustic Properties of Aqueous Solutions of Trifluoromethanesulfonate-Base Ionic Liquids at Several Temperatures. J. Chem. Eng. Data 2012, 57, 1953−1963. (7) González, B.; Calvar, N.; Domínguez, I.; Domínguez, A. Synthesis and Physical Properties of 1-Ethylpyridinium Ethylsulfate and Its Binary Mixtures with Ethanol and 1-Propanol at Several Temperatures. J. Chem. Eng. Data 2009, 54, 1353−1358. (8) Palomar, J.; Ferro, V. R.; Torrecilla, J. S.; Rodríguez, F. Density and Molar Volume Predictions Using COSMO-RS for Ionic Liquids: An Approach to Solvents Design. Ind. Eng. Chem. Res. 2007, 46, 6041− 6048. (9) Borra, E. F.; Seddiki, O.; Angel, R.; Eisenstein, D.; Hickson, P.; Seddon, K. R.; Worden, S. P. Deposition of Metal Films on an Ionic Liquid as a Basis for a Lunar Telescope. Nature 2007, 447, 979−981. (10) Bonhote, P.; Dias, A. P.; Papageorgiou, N.; Kalyanasundaram, K.; Gratzel, M. Hydrophobic, Highly Conductive Ambient-Temperature Molten Salts. Inorg. Chem. 1996, 35, 1168−1178. O



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Abraham, M., Moens, L., Eds.; ACS Symposium Series 819; American Chemical Society: Washington, DC, 2002. (29) Okoturo, O. O.; Vandernoot, T. J. Temperature Dependence of Viscosity for Room Temperature Ionic Liquids. J. Electroanal. Chem. 2004, 568, 167−181. (30) Vogel, H. Phys. Z. 1921, 22, 645. (31) Fulcher, G. S. J. Am. Ceram. Soc. 1925, 8, 645−6. (32) Tammann, G.; Hesse, W. The Dependence of Viscosity upon the Temperature of Supercooled Liquids. Z. Anorg. Allg. Chem. 1926, 156, 245−257. (33) Wilkes, J. S. Properties Of Ionic Liquid Solvents For Catalysis. J. Mol. Catal. A 2004, 214, 11−17. (34) Gomez, E.; Calvar, N.; Domínguez, A.; Macedo, E. A. Synthesis ́ and Temperature Dependence of Physical Properties of Four Pyridinium-Based Ionic Liquids: Influence of the Size of the Cation. J. Chem. Thermodyn. 2010, 42, 1324−1329. (35) Litovitz, T. A. Temperature Dependence of the Viscosity of Associated Liquids. J. Chem. Phys. 1952, 20, 1088−1089. (36) Ghatee, M. H.; Zare, M.; Zolghadr, A. R.; Moosavi, F. Temperature Dependence of Viscosity and Relation with the Surface Tension of Ionic Liquids. Fluid Phase Equilib. 2010, 291, 188−194. (37) Bonhôte, P.; Dias, A. P.; Papageorgiou, N.; Kalyanasundaram, K.; Gratzel, M. Hydrophobic, Highly Conductive Ambient-Temperature Molten Salts. Inorg. Chem. 1996, 35, 1168. (38) Tokuda, H.; Hayamizu, K.; Ishii, K.; Susan, M. A. B. H.; Watanabe, M. Physicochemical Properties and Structures of Room Temperature Ionic Liquids. 2. Variation of Alkyl Chain Length in Imidazolium Cation. J. Phys. Chem. B 2005, 109, 6103−6110. (39) Yao, H.; Zhang, S.; Wang, J.; Zhou, Q.; Dong, H.; Zhang, X. Densities and Viscosities of the Binary Mixtures of 1-ethyl-3methylimidazolium bis (trifluoromethylsulfonyl) imide with Nmethyl-2-pyrrolidone or Ethanol at T = (293.15 to 323.15) K. J. Chem. Eng. Data 2012, 57, 875−881. (40) Andreatta, A. E.; Arce, A.; Rodil, E.; Soto, A. Physico-Chemical Properties of Binary and Ternary Mixtures of Ethyl acetate+ Ethanol+ 1-butyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) imide at 298.15 K and Atmospheric Pressure. J. Solution Chem. 2010, 39, 371− 383. (41) Douheret, G.; Davis, M. I.; Reis, J. C. R.; Blandamer, M. J. Isentropic Compressibilities-Experimental Origin And The Quest For Their Rigorous Estimation In Thermodynamically Ideal Liquid Mixtures. ChemPhysChem 2001, 2, 148−161. (42) Benson, G. C.; Kiyohara, O. Evaluation of Excess Isentropic Compressibilities and Isochoric Heat Capacities. J. Chem. Thermodyn. 1979, 11, 1061−1064. (43) Redlich, O.; Kister, A. T. Algebraic Representation of Thermodynamic Properties and The Classification of Solutions. Ind. Eng. Chem. 1948, 40, 345−348. (44) Vercher, E.; Orchillés, A. V.; Miguel, P. J.; Martínez-Andreu, A. Volumetric and Ultrasonic Studies of 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate Ionic Liquid with Methanol, Ethanol, 1Propanol, and Water at Several Temperatures. J. Chem. Eng. Data 2007, 52, 1468−1482. (45) Singh, T.; Kumar, A. Self-Aggregation of Ionic Liquids in Aqueous Media: A Thermodynamic Study. Colloids Surf., A 2008, 318, 263−268. (46) Zhou, Q.; Wang, L. S.; Chen, H. P. Densities and Viscosities of 1-butyl-3-methylimidazolium tetrafluoroborate+ H2O Binary Mixtures from (303.15 to 353.15) K. J. Chem. Eng. Data 2006, 51, 905−908. (47) Tu, C. H.; Lee, S. L.; Peng, I. H. Excess Volumes and Viscosities of Binary Mixtures of Aliphatic Alcohols (C1-C4) with Nitromethane. J. Chem. Eng. Data 2001, 46, 151−155. (48) Lachwa, J.; Morgado, P.; Esperança, J. M.; Guedes, H. J.; Canongia Lopes, J. N.; Rebelo, L. P. N. Fluid-Phase Behavior of {1hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, [C6mim][Ntf2],+ C2-C8 N-alcohol} Mixtures: Liquid-Liquid Equilibrium And Excess Volumes. J. Chem. Eng. Data 2006, 51, 2215−2221.

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