Temperature Dependence of Physicochemical Properties of

Article pubs.acs.org/jced

Temperature Dependence of Physicochemical Properties of Imidazolium‑, Pyroldinium‑, and Phosphonium-Based Ionic Liquids Mohammad S. AlTuwaim,* Khaled H. A. E. Alkhaldi, Adel S. Al-Jimaz, and Abubaker A. Mohammad Department of Chemical Engineering, College of Technological Studies, P.O. Box 42325, Shuwaikh 70654, Kuwait ABSTRACT: Densities, viscosities, speeds of sound, surface tensions, and refractive indices for nine different imidazolium-, pyroldinium-, and phosphonium-based ionic liquids were measured at temperatures ranging from 298.15 K to 333.15 K and atmospheric pressure. Empirical models were used to correlate the thermophysical properties of the ionic liquids as a function of temperature. The isentropic compressibility, coefficients of thermal expansion, surface properties, and critical temperatures were calculated using the experimental data. Furthermore, the effect of anions and alkyl chains of the different ionic liquids on their thermophysical properties had been investigated.

[BF4]).17−21 As for 1-alkyl-3-methylimidazolium hexafluorophosphate, a literature survey shows that they are one of the most commonly investigated ILs (alkyl = butyl ([bmim][PF 6 ]), 17,22−41 hexyl ([hmim][PF 6 ]), 22,23,34,41−51 octyl ([omim][PF6]),17,22−24,34,42−44,47,48 whereas for 1-octyl-3methylimidazolium chloride ([omim][Cl]) there are several articles.22,23,41,52,53 Thus experimental data of densities (ρ), speeds of sound (c), viscosities (η), refractive indices (nD), and surface tensions (σ) of the above nine pure ILs at T = (298.15 to 333.15) K and atmospheric pressure have been measured. The corresponding isentropic compressibility (κs), coefficients of thermal expansion (αp), surface enthalpies (Hs), surface entropies (Ss), and critical temperatures (Tc) were calculated. Moreover, the dependency of the measured density, viscosity, surface tension, speed of sound, and refractive index on temperature was investigated by fitting experimental data using least-squares method. In addition, the effect of tuning the anions and cations of the different ILs on their thermophysical properties have been studied.

1. INTRODUCTION Ionic liquids (ILs) have gained increasing interest in recent years because of their distinct properties such as negligible vapor pressure, ability to solvate polar and nonpolar compounds, high thermal and chemical stability, and nonflammability. The structure and the composition of ILs play a major role in considering them as green-designed solvents in industry. Their properties lead to wide applications in liquid and gas separation processes, wide range of chemical and catalytic reactions, electrolytes and fuel cells, biotechnology, nanotechnology, and cleaning operations.1−6 The proper design and development of chemical reaction and separation processes in the chemical industry are based on an adequate knowledge of the thermophysical properties of ILs. These properties can be tunable to suit a particular process since the ILs consist of combinations of organic cations and inorganic or organic anions. This flexibility opens a new horizon of potential applications and fields of research for both pure ILs and mixtures of ILs.7−9 Several review articles10−13 have shown that there is a need for physical, chemical, and thermodynamic property data of pure ILs owing to several considerations, one being that the reported data are for a very limited number of ILs. Additionally, further studies are required for most of the ILs since their thermophysical properties can be only obtained from a single source. Moreover, the comparison between multiple literature sources showed differences in the measured properties for the majority of available ILs data,10 which emphasizes the need for more studies in this field. A literature survey for the ionic liquids investigated in this study showed that no research article has been cited for the physical properties of 1-butyl-3-methylimidazolium hydrogen sulfate ([bmim][HSO4]) and tri-isobutylmethylphosphonium tosylate ([ibmp][TOS]), whereas one article has been cited for 1-ethyl-3-methylimidazolium methylsulfate ([emim][MeSO4]),14 and few articles have been cited for both 1,3-dimethylimidazolium methylsulfate ([dmim][MeSO4]),15,16 and N-butyl-4-methylpyridinium tetraflouroborate ([bmpy]© 2014 American Chemical Society

2. EXPERIMENTAL 2.1. Materials. All ILs were manufactured by Aldrich except 1-hexyl-3-methylimidazolium hexafluorophosphate which was obtained from Fluka. The CAS numbers, purities of these substances, and suppliers are listed in Table 1. As shown in Table 2, the measured densities, speeds of sound, viscosities, refractive indices, and surface tensions for some of the investigated ILs were compared with available literature values. 2.2. Apparatus and Procedures. The water content was analyzed using a Mettler Toledo DL39-KF coulometer and found to be less than 0.1 % for all ILs after drying them at moderate temperature and under vacuum for several days. Received: January 27, 2014 Accepted: May 7, 2014 Published: May 20, 2014 1955

dx.doi.org/10.1021/je500093z | J. Chem. Eng. Data 2014, 59, 1955−1963

Journal of Chemical & Engineering Data

Article

viscosity, and refractive index of the ILs as functions of temperature. The experimental data conforms closely with previously published data. In addition, the values for viscosity drop dramatically as the temperature increases for all ILs except for the [MeSO4]-based anions where the drop can be considered moderate compared to the rest. 3.1. Estimation of Properties. The measured density, speed of sound, refractive index, and surface tension are correlated to temperature by least-squares fit using the following equation:

Table 1. Chemicals and Purities compound

CAS No.

supplier

purity

1-butyl-3-methylimidazolium hydrogen sulfate Tri-isobutylmethylphosphonium tosylate 1-ethyl-3-methylimidazolium methylsulfate 1,3-dimethylimidazolium methylsulfate N-butyl-4-methylpyridinium tetraflouroborate 1-butyl-3-methylimidazolium hexafluorophosphate 1-hexyl-3-methylimidazolium hexafluorophosphate 1-octyl-3-methylimidazolium hexafluorophosphate 1-octyl-3-methylimidazolium chloride

262297-13-2

Sigma

≥ 0.95

344774-05-6

Sigma

≥ 0.95

516474-01-4

Sigma

≥ 0.98

97345-90-9 343952-33-0

Sigma Sigma

≥ 0.97 ≥ 0.97

174501-64-5

Sigma

≥ 0.97

304680-35-1

Fluka

≥ 0.97

304680-36-2

Sigma

≥ 0.95

64697-40-1

Sigma

≥ 0.97

X = A 0 + A1T

(1)

where X is ρ, c, nD, or σ, A0 and A1 are fitting parameters, and T is the temperature. Viscosity is fitted to the well-known Vogel− Fulcher−Tamman (VFT) equation:

⎡ A1′ ⎤ η = A 0′ exp⎢ ⎥ ⎣ T − A 2′ ⎦

Anton Paar (DSA 5000) density/sound velocity meter and (SVM 3000 Stabinger) viscometer were used to measure density, speed of sound, and viscosity while ABBE Mark II (model 104810 Cambridge Instrument Inc., USA) refractometer was used to measure refractive index. DCAT 21 tensiometer (Data Physics Instruments GmbH) with automatic calibrating function and software-controlled motorized height positioning of the sample vessel with built-in Pt l00 probe connected to a circulating water bath (HAAKE C25, with temperature control unit F6) was used to measure surface tension. All measurements were done at temperatures between 298.15 Kand 333.15 K. The details of sample preparation, measurements, and calibration of the instruments were described in our earlier work.54,55

(2)

where η is the viscosity, A0′ A1′ and A2′ are fitting parameters. The fitting parameters for surface tension data, namely A0 and A1, are the surface enthalpy and entropy based on the thermodynamics of interface56

σ = H s + S sT

(3)

where Hs = σ −

⎛ dσ ⎞ ⎜ ⎟T ⎝ dT ⎠

(4)

and ⎛ dσ ⎞ S s = −⎜ ⎟ ⎝ dT ⎠

3. RESULTS AND DISCUSSION The experimental values for measured properties of the nine pure ILs at T = (298.15 to 333.15) K and atmospheric pressure are shown in Tables 3 and as expected all properties decrease as the temperature increases. Figures 1 to 10 illustrate the comparison of experimental and available literature values for density,

(5)

The standard deviation (SD) is calculated using ⎡ ∑n (y − y )2 ⎤1/2 i = 1 exp calc ⎥ SD = ⎢ ⎢ ⎥ − 1 n ⎣ ⎦

(6)

Table 2. Experimental Physical Properties of Some Pure ILs at 298.15 K (n.a., Data Not Available) [bmim][PF6] T (K)

exp.

(a) Densities, ρ (g cm−3) 298.15 1.367

[hmim][PF6]

[omim][PF6]

[bmpy][BF4]

lit. [ref]

exp.

lit. [ref]

exp.

lit. [ref]

exp.

lit. [ref]

1.3674 [26] 1.36722 [31] 1.367531 [38]

1.292

1.29322 [51] 1.29341 [46] 1.29145 [50]

1.234

1.2245 [17] 1.23572 [34] 1.236 84 [42]

1.190

1.2144 [17] 1.18424 [18] 1.18349 [20]

1424.4

1424.2 [34]

1404.7

1407.8 [34]

1602.3

n.a.

349.17

n.a.

603.44

732 [26] 690.60 [34]

202.86

196.2 [19] 202.8 [21]

1.4179

1.41787 [26]

1.4217

1.42302 [26]

1.4507

1.4517 [20]

37.2

37.1 [26]

36.1

36.2 [26]

45.4

45.1 [21]

6.072

n. a.

6.147

5.9515 [17]

5.680

5.4287 [17]

(b) Speed of Sound, c (m/s) 298.15 1443.6 1442.41 [27] 1442.8 [34] (c) Viscosity, η (mPa·s) 298.15 273.94 271 [26] 247.06 [34] 282.2 [38] (d) Refractive Index, nD 298.15 1.4101 1.40937 [26] 1.4095 [39] (e )Surface Tension, σ(mN·m−1) 298.15 43.0 42.9 [26] (f) Thermal Expansion Coefficient, αp·104 (K−1) 298.15 6.017 6.1126 [17]

1956


1957

1.224 1.220 1.217 1.214 1.211 1.208 1.204 1.201

1.329 1.323 1.319 1.316 1.312 1.308 1.305 1.302

1.367 1.363 1.359 1.355 1.351 1.347 1.343 1.339

298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

mPa·s

η

[bmim][HSO4] 1689.8 439.36 1676.7 321.95 1664.3 240.81 1652.1 183.54 1640.2 142.55 1628.5 112.37 1615.5 89.95 1601.5 72.88 [dmim][MeSO4] 1811.5 71.70 1799.4 57.60 1787.3 46.93 1775.4 38.81 1763.6 32.52 1751.9 27.59 1740.3 23.67 1728.8 20.50 [bmim][PF6] 1443.6 273.94 1431.6 203.20 1419.8 153.99 1408.3 118.96 1396.9 93.44 1385.8 74.60 1374.7 60.43 1363.8 49.62

m/s

c

1.4101 1.4085 1.4081 1.4070 1.4068 1.4058 1.4053 1.4042

1.4817 1.4811 1.4804 1.4797 1.4792 1.4785 1.4779 1.4771

1.5043 1.5000 1.4965 1.4914 1.4857 1.4813 1.4762 1.4721

nD

43.0 42.6 42.2 41.9 41.7 41.2 40.8 40.5

57.6 57.3 56.8 56.4 56.0 55.5 55.1 54.8

43.6 43.2 42.8 42.4 42.0 41.7 41.3 40.9

mN·m

σ −1 3

1.292 1.288 1.284 1.280 1.276 1.272 1.268 1.264

1.190 1.186 1.183 1.179 1.176 1.173 1.169 1.166

1.068 1.065 1.062 1.059 1.056 1.053 1.050 1.047

g/cm

ρ

1424.4 1411.3 1399.6 1386.7 1374.9 1363.4 1352.1 1340.8

1602.3 1589.7 1577.4 1565.2 1553.2 1541.2 1529.6 1517.9

1628.8 1610.6 1585.6 1567.6 1551.1 1535.7 1521.5 1508.3

m/s

c [ibmp][TOS] 2132.40 1363.20 896.08 606.71 422.49 302.17 221.27 165.53 [bmpy][BF4] 202.86 146.57 108.70 82.49 63.94 50.51 40.60 33.14 [hmim][PF6] 349.17 253.96 188.77 142.99 110.24 86.42 68.87 55.62

mPa·s

η

u(ρ) = 0.001 g·cm−3, u(c) = 0.2 m/s, u(η) = 0.01 mPa·s, u(nD) = 0.0004, u(σ) = 0.1 mN·m−1, u(T) = 0.01 K.

g/cm

K

3

ρ

T

1.4179 1.4161 1.4148 1.4134 1.4115 1.4104 1.4088 1.4075

1.4507 1.4502 1.4495 1.4488 1.4482 1.4475 1.4469 1.4463

1.5185 1.5181 1.5174 1.5160 1.5151 1.5144 1.5123 1.5119

nD

37.2 36.9 36.6 36.3 36.0 35.7 35.4 35.1

45.4 45.1 44.8 44.5 44.2 43.9 43.5 43.2

33.9 33.8 33.6 33.4 33.2 32.9 32.8 32.6

mN·m

σ −1 3

1.234 1.231 1.226 1.223 1.219 1.215 1.211 1.208

1.010 1.007 1.004 1.001 0.998 0.995 0.992 0.989

1.292 1.289 1.285 1.282 1.279 1.275 1.272 1.268

g/cm

ρ

1404.7 1390.3 1376.6 1363.6 1351.0 1338.9 1327.0 1315.5

1687.2 1667.7 1646.1 1619.6 1597.1 1577.4 1559.6 1543.0

1762.1 1750.4 1738.7 1727.0 1715.5 1704.0 1692.6 1681.3

m/s

c

η [emim][MeSO4] 94.91 76.80 61.66 51.28 42.42 35.33 30.11 26.25 [omim][Cl] 13267 7770.4 4755.2 3006.7 1967.6 1323.4 914.13 646.96 [omim][PF6] 603.44 430.88 314.44 234.24 177.79 137.24 107.58 85.58

mPa·s

Table 3. Density ρ, Speed of Sound c, Viscosity η, Refractive Index nD, and Surface Tension σ at Several Temperatures and Atmospheric Pressure

1.4217 1.4211 1.4206 1.4201 1.4195 1.4186 1.4177 1.4167

1.5088 1.5085 1.5061 1.5058 1.5054 1.5048 1.5037 1.5029

1.4741 1.4739 1.4735 1.4721 1.4716 1.4706 1.4702 1.4698

nD

36.1 35.9 35.6 35.3 35.1 34.9 34.6 34.3

32.5 32.2 31.9 31.6 31.3 31.0 30.7 30.4

39.8 39.5 39.2 38.9 38.8 38.4 38.2 38.0

mN·m−1

σ

Journal of Chemical & Engineering Data Article



Article

Figure 4. Comparison of experimental values of density ρ as a function of temperature T with literature for [bmpy][BF4]: ●, this work; □, Sanchez et al. [21]. For [dmim][MeSO4]: ○, this work; ■, Shekaari et al. [63]; ×, Pereiro et al. [15]. For [emim][MeSO4]: ▼, this work; ◇, Wang et al. [62]; ◆, Tome et al. [14]. For [omim][Cl]: △, this work; ▲, Gomez et al. [52]; ▽, Singh et al. [40].

Figure 1. Comparison of experimental values of density ρ as a function of temperature T with literature for[bmim][PF6]: ●, this work; ◇, Soriano et al. [39]; ▼, Gu et al. [17]; □, Fan et al. [38]; ■, Troncoso et al. [30]; △, Harris et al. [26]; ◆, Huo et al. [31]; ○, Pereiro et al. [34].

Figure 5. Experimental values of viscosity η as a function of temperature T for [bmim][PF6]: ●, this work; ○, Pereiro et al. [34]; ▼, Fan et al. [38]; ▲, Rocha et al. [61].

Figure 2. Comparison of experimental values of density ρ as a function of temperature T with literature for [hmim][PF6]: ●, this work; ○, Pereiro et al. [34]; ▼, Harris et al. [51]; ■, Vakili-Nezhaadet al. [50].

Figure 6. Comparison of experimental values of viscosity η as a function of temperature T with literature for [bmpy][BF4]: ○, this work; ■, Sanchez et al. [21]. For [dmim][MeSO4]: ●, this work; □, Shekaari et al. [63]; ▽, Pereiro et al. [15].

Figure 3. Comparison of experimental values of density ρ as a function of temperature T with literature for [omim][PF6]: ●, this work; ○, Pereiro et al. [34]; ▼, Gu et al. [17]; △, Harris et al. [42].

and lower interaction energy between ions57 for ILs compared to other solvents. 3.2. Thermodynamic Properties. The thermal expansion coefficient indicates the change of the liquid volume as the temperature changes and is defined as

where yexp is the experimental value, ycalc is the calculated value, and n is the number of data points. Table 4 shows the fitting parameters and SD for density, speed of sound, refractive index, and surface tension while Table 5 shows the fitting parameters along with standard deviations for viscosity for all investigated ILs. The low surface entropy and surface enthalpy values of the studied ILs may indicate, respectively, an enhancement of the degree of surface orientation

⎛ dρ ⎞ α p = − ρ− 1 ⎜ ⎟ ⎝ dT ⎠ p 1958

(7)



Article

Figure 7. Comparison of experimental values of speed of sound u as a function of temperature T with literature for [dmim][MeSO4]: ●, this work; □, Pereiro et al. [15]. For [omim][Cl]: ○, this work; ■, Singh et al. [53].

Figure 10. Comparison of experimental values of surface tension σ as a function of temperature T with literature for [bmpy][BF4]: ●, this work; □, Sanchez et al. [21]. For [dmim][MeSO4]: ○, this work; ▲, Pereiro et al. [15].

The isentropic compressibility is calculated from Laplace− Newton equation using the experimental values for density and speed of sound: ⎛ ∂V ⎞ 1 κs = −V m−1⎜ m ⎟ = 2 cρ ⎝ ∂p ⎠s

(8)

and the results are shown in Table 7 where κs increases as the temperature increases for all ILs. 3.3. Estimation of Critical and Boiling Temperatures. Critical and boiling temperatures are important relevant thermodynamic properties since they are used in many corresponding states correlations. There is a lack of values for both temperatures for most ionic liquids because many of the ILs start to decompose as the temperature approaches the boiling point. This makes it difficult to experimentally determine these temperatures, and this can be only achieved through empirical correlations. The experimental data for surface tension as a function of temperature can be used to predict the critical temperature for ILs using the Guggenheim empirical equation58

Figure 8. Comparison of experimental values of refractive index nD as a function of temperature T with literature for [dmim][MeSO4]: ○, this work; ■, Shekaari et al. [63]; ▽, Pereiro et al. [15]. For [omim][Cl]: ●, this work; □, Gomez et al. [52].

11/9 ⎡ T⎤ σ = σ0⎢1 − ⎥ Tc ⎦ ⎣

(9)

where σ0 is a fitting parameter. Moreover, the prediction of Tc was used to estimate the boiling point temperature (Tb)59,60 where Tb ≈ 0.6Tc as shown in Table 8. 3.4. Effect of Anions and Alkyl Chains. A comparison of the physical properties of different combinations of anions and alkyl chains emphasizes the fact that the dominant effect on the properties is that of the anions and this conforms with previous studies.21,34 For instance, Figures 11 to 15 depict the influence of alkyl chains and anions on properties of 1-alkyl-3-methylimidazolium hexafluorophosphates versus 1-octyl-3-methylimidazolium chloride. The effect of anion change on the properties of omim[PF6] and omim[Cl] is clearly visible compared to the effect of alkyl chain (1-alkyl-3-methylimidazolium[PF6], alkyl = butyl, hexyl, and octyl) where the influence is less. Furthermore, the trend for an increase in density and viscosity for the different anions follows [Cl]¯ < [TOS]¯ < [BF4]¯ < [HSO4]¯ < [MeSO4]¯, [PF6]¯ and [MeSO4]¯ < [BF4]¯ < [HSO4]¯, [PF6]¯ < [TOS]¯ < [Cl]¯, respectively. In addition, for the other properties the trend is as follows: [PF6]¯ < [BF4]¯ < [TOS]¯ < [Cl]¯ < [HSO4]¯ < [MeSO4]¯ for speed of sound, [PF6]¯ < [BF4]¯ < [MeSO4]¯ < [Cl]¯, [HSO4]¯ < [TOS]¯ for refractive index, and [Cl]¯ < [TOS]¯ < [BF4]¯, [PF6]¯,

Figure 9. Comparison of experimental values of refractive index nD as a function of temperature T with literature for [hmim][PF6]: ●, this work; ○, Pereiro et al. [34]; ▼, Vakili-Nezhaad et al. [50].

The coefficient can be easily calculated due to the linear relation of the density with temperature. The calculated thermal expansion coefficients for the pure liquids are listed in Table 6 where it can be seen that the change in ILs volume is small as the temperature changes which conforms to the fact that these solvents do not expand much17 (the range of αp for the ILs investigated is between 6.3·10−4 K and 5.2·10−4 K−1 compared to (7 to 11)·10−4 K−1 for other solvents such as THF, NMP, phenetole, and DMF). 1959



Article

Table 4. Parameters of Equation (1) and Standard Deviation (SD) A0

Property

A1

ρ·103/(g/cm3) u/(m/s) nD σ/(mN·m−1)

1412.6 2429.90 1.7858 66.27

ρ·103/(g/cm3) u/(m/s) nD σ/(mN·m−1)

1550.7 2515.40 1.520300 82.518

ρ·103/(g/cm3) u/(m/s) nD σ/(mN·m−1)

1612.6 2121.60 1.4554 64.88

SD

[bmim][HSO4] −0.6342 −2.4832 −0.000942 0.0762 [dmim][MeSO4] −0.7498 −2.3624 −0.000129 0.0834 [bmim][PF6] −0.822800 −2.2765 −0.000153 0.0734

A0

A1

0.170802 0.673204 0.000559 0.012017

1251.9 2656.80 1.5794 45.947

0.891791 0.241547 0.000058 0.027124

1391.0 2320.20 1.48880 63.839

0.055035 0.438935 0.000291 0.034752

1525.6 2134.50 1.463600 55.03

A0

SD

[ibmp][TOS] −0.6179 −3.4632 −0.000203 0.0402 [bmpy][BF4] −0.6757 −2.4097 −0.00013 0.0618 [hmim][PF6] −0.7844 −2.3851 −0.000140 0.0599

A1

0.102109 4.141960 0.000392 0.037938

1493.5 2450.90 1.5154 55.118

0.029817 0.394071 0.000056 0.023467

1186.6 2948.90 1.455400 50.083

0.139445 0.853811 0.000253 0.012084

1460.1 2160.20 1.785800 51.23

SD

[emim][MeSO4] −0.675800 −2.3110 −0.000138 0.0515 [omim][Cl] −0.5929 −4.2348 −0.000153 0.059 [omim][PF6] −0.7585 −2.5400 −0.000942 0.0507

0.085209 0.370698 0.000281 0.052170 0.065482 3.303744 0.000291 0.019882 0.0671286 1.158532 0.000559 0.018781

Table 5. Parameters of VFT Equation and Standard Deviation (SD) A0′ 0.091390 0.228000 0.100100

A1′

A2′

A0′

SD

[bmim][HSO4] 1062.0 169.8 [dmim][MeSO4] 722.1 172.6 [bmim][PF6] 1007.0 171.0

0.659014

0.068200

0.028823

0.099020

0.743976

0.073690

A1′

A2′

[ibmp][TOS] 1122.0 189.8 [bmpy][BF4] 855.1 186.0 [hmim][PF6] 1073.0 171.4

A0′

SD

A1′

6.205794

0.074080

0.061997

0.193700

1.889979

0.082630

A2′

[emim][MeSO4] 1053.0 145.7 [omim][Cl] 1084.0 200.8 [omim][PF6] 1116.0 172.7

SD 0.365284 44.905226 0.659014

Table 6. Thermal Expansion Coefficient αp at Several Temperatures and Atmospheric Pressure αp·104/K−1 T/K

[bmim][HSO4]

[ibmp] [TOS]

[emim] [MeSO4]

[dmim] [MeSO4]

[bmpy][BF4]

[omim][Cl]

[bmim][PF6]

[hmim][PF6]

[omim][PF6]

298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

5.183 5.197 5.211 5.223 5.239 5.252 5.266 5.279

5.786 5.805 5.821 5.838 5.855 5.872 5.889 5.907

5.230 5.244 5.258 5.272 5.286 5.300 5.314 5.328

5.642 5.670 5.685 5.700 5.715 5.731 5.746 5.761

5.680 5.697 5.713 5.729 5.746 5.762 5.779 5.796

5.872 5.889 5.906 5.923 5.941 5.960 5.977 5.994

6.017 6.036 6.054 6.073 6.091 6.110 6.128 6.147

6.072 6.091 6.110 6.129 6.147 6.166 6.185 6.204

6.147 6.166 6.185 6.205 6.224 6.243 6.262 6.282

u(αp) = 0.001K−1, u(T) = 0.01 K.

Table 7. Isentropic Compressibility κs at Several Temperatures and Atmospheric Pressure κs/TPa−1 T/K

[bmim][HSO4]

[ibmp] [TOS]

[emim] [MeSO4]

[dmim] [MeSO4]

[bmpy][BF4]

[omim][Cl]

[bmim][PF6]

[hmim][PF6]

[omim][PF6]

298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

286.2 291.5 296. 7 301.7 307.0 312.3 318.1 324.5

353.0 362.2 374.8 384.5 393.8 402.9 411.7 420.2

249.3 253.3 257.4 261.6 265.8 270.18 274.5 278.9

229.3 233.6 237.3 241.2 245.1 249.0 253.0 257.1

327.4 333.6 339.8 346.1 352.5 359.0 365.6 372.3

347.9 357.19 367.69 380.9 392.9 404.0 414.5 424.65

350.9 358.0 365.0 372.1 379.4 386.7 394.2 401.7

381.5 389.8 397.7 406.3 414.6 422.9 431.3 439.9

410.7 420.6 430.36 440.0 449.7 459.2 468.8 478.6

u(κs)) = 0.4 TPa−1, u(T) = 0.01 K.

[HSO4]¯ < [MeSO4]¯ for surface tension. Table 9 summarizes the observations regarding the different anions. As for the effect of alkyl chain, the viscosity and refractive index increase in contrast to the density, speed of sound, and surface tension, which decrease

as the alkyl chain length increases. This applies to the [PF6] anion, while for [MeSO4] anion the same behavior is observed except for the surface tension which decreases as the chain length increases. 1960



Article

Table 8. Estimated Critical and Boiling Point Temperatures ionic liquid

Tc/K

Tb/K

[bmim][HSO4] [ibmp][TOS] [emim][MeSO4] [dmim][MeSO4] [bmpy][BF4] [omim][Cl] [bmim][PF6] [hmim][PF6] [omim][PF6]

992.69 1320.30 1232.20 1138.10 1191.00 966.28 1009.50 1052.30 1163.80

595.61 792.18 739.32 682.86 714.60 579.77 605.70 631.38 698.28

Figure 14. Experimental values of surface tension σ as a function of temperature T for ●, [omim][Cl]; ○, [bmim][PF6]; ▼, [hmim][PF6]; △, [omim][PF6]. Solid line, least-squares fit.

Figure 11. Experimental values of density ρ as a function of temperature T for ●, [omim][Cl]; ○, [bmim][PF6]; ▼, [hmim][PF6]; △, [omim][PF6]. Solid line, least-squares fit. Figure 15. Experimental values of refractive index nD as a function of temperature T for ●, [omim][Cl]; ○, [bmim][PF6]; ▼, [hmim][PF6]; △, [omim][PF6]. Solid line, least-squares fit.

Table 9. Observations Regarding Properties of ILs Based on Anions

Figure 12. Experimental values of viscosity η as a function of temperature T for ●, [omim][Cl]; ○, [bmim][PF6]; ▼, [hmim][PF6]; △, [omim][PF6]. Solid line, least-squares fit.

property

highest

lowest

density speed of sound viscosity refractive index surface tension

[MeSO4]¯ and [PF6] ¯ [MeSO4]¯ [Cl]¯ [TOS]¯ [MeSO4]¯

[Cl]¯ [PF6]¯ [MeSO4]¯ [PF6]¯ [Cl]¯

4. CONCLUSIONS Experimental data for nine ionic liquids at several temperatures and atmospheric pressure are reported. The values of all measured properties decrease as the temperature increases. Viscosity is the most affected property by the temperature change while refractive index and surface tension are the least affected. Density, speed of sound, refractive index, and surface tension are linearly correlated, while viscosity is correlated using the VFT equation. The thermal expansion coefficient is obtained using density measurements for pure ILs. The linear correlation of surface tension data estimates the surface thermodynamic enthalpy and entropy. Furthermore, the Guggenheim empirical equation is used to predict the critical temperatures from surface tension measurements and then used to estimate the boiling point temperatures for the investigated liquids. The measured data show that the physical properties of the studied ionic liquids depend mainly on the nature of the anions, whereas the alkyl chain length has less effect.

Figure 13. Experimental values of speed of sound u as a function of temperature T ffor ●, [omim][Cl]; ○, [bmim][PF6]; ▼, [hmim][PF6]; △, [omim][PF6]. Solid line, least-squares fit. 1961



■

Article

Methyl-n-butylpyridinium Tetrafluoroborate at 25, 40, and 50 °C. J. Solution Chem. 2002, 31, 467−476. (20) Ortega, J.; Vreekamp, R.; Penco, E.; Marrero, E. Mixing Thermodynamic Properties of 1-Butyl-4-Methylpyridinium Tetrafluoroborate [b4mpy][BF4] with Water and with an Alkan-1ol (Methanol to Pentanol). J. Chem. Thermodyn. 2008, 40, 1087−1094. (21) Sanchez, L. G.; Espel, J. R.; Onink, F.; Wytze, G.; Meindersma, G. W.; Haan, A. B. Density, Viscosity, and Surface Tension of Synthesis Grade Imidazolium, Pyridinium, and Pyrrolidinium Based Room Temperature Ionic Liquids. J. Chem. Eng. Data 2009, 54, 2803−2812. (22) Huddleston, J. G.; Visser, A. E.; Reichert, W.; Willauer, H. D.; Broker, G. A.; Rogers, R. D. Characterization and Comparison of Hydrophilic and Hydrophobic Room Temperature Ionic Liquids Incorporating the Imidazolium Cation. Green Chem. 2001, 3, 156−164. (23) Seddon, K. R.; Stark, A.; Torres, M. J. Viscosity and Density of 1Alkyl-3-methylimidazolium Ionic Liquids. ACS Symp. Ser. 2002, 819, 34−49. (24) Kabo, G. J.; Blokhin, A. V.; Paulechka, Y. U.; Kabo, A. G.; Shymanovich, M. P.; Magee, J. W. Thermodynamic Properties of 1Butyl-3-methylimidazolium Hexafluorophosphate in the Condensed State. J. Chem. Eng. Data 2004, 49, 453−461. (25) Tokuda, H.; Hayamizu, K.; Ishii, K.; Susan, M. A. B. H.; Watanabe, M. Physicochemical Properties and Structures of Room Temperature Ionic Liquids. 1. Variation of Anionic Species. J. Phys. Chem B 2004, 108, 16593−16600. (26) Harris, K. R.; Woolf, L. A.; Kanakubo, M. Temperature and Pressure Dependence of the Viscosity of the Ionic Liquid 1-Butyl-3Methylimidazolium Hexafluorophosphate. J. Chem. Eng. Data 2005, 50, 1777−1782. (27) Zafarani-Moattar, M. T.; Shekaari, H. Volumetric and Speed of Sound of Ionic Liquid, 1-Butyl-3-methylimidazolium Hexafluorophosphate with Acetonitrile and Methanol at T (298.15 to 318.15) K. J. Chem. Eng. Data 2005, 50, 1694−1699. (28) Jacquemin, J.; Husson, P.; Padua, A. A. H.; Majer, V. Density and Viscosity of Several Pure and Water-Saturated Ionic Liquids. Green Chem. 2006, 8, 172−180. (29) Tomida, D.; Kumagai, A.; Qiao, K.; Yokoyama, C. Viscosity of [bmim][PF6] and [bmim][BF4] at High Pressure. Int. J. Thermophys. 2006, 27, 39−47. (30) Troncoso, J.; Cerdeirina, C. A.; Sanmamed, Y. A.; Romani, 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. (31) Huo, Y.; Xia, S.; Ma, P. J. Densities of Ionic Liquids, 1-Butyl-3methylimidazolium Hexafluorophosphate and 1-Butyl-3-methylimidazoliumTetrafluoroborate, with Benzene, Acetonitrile, and 1-Propanol at T (293.15 to 343.15) K. J. Chem. Eng. Data 2007, 52, 2077−2082. (32) 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. (33) Navia, P.; Troncoso, J.; Romani, L. Excess Magnitudes for Ionic Liquid Binary Mixtures with a Common Ion. J. Chem. Eng. Data 2007, 52, 1369−1374. (34) Pereiro, A. B.; Legido, J. L.; Rodriguez, A. Physical Properties of Ionic Liquids Based on 1-Alkyl-3-methylimidazolium Cation and Hexafluorophosphate as Anion and Temperature Dependence. J. Chem. Thermodyn. 2007, 39, 1168−1175. (35) Huo, Y.; Xia, S.; Ma, P. Solubility of Alcohols and Aromatic Compounds in Imidazolium-Based Ionic Liquids. J. Chem. Eng. Data 2008, 53, 2535−2539. (36) Kumar, A.; Singh, T.; Gardas, R. L.; Coutinho, J. A. P. Nonideal Behaviour of a Room Temperature Ionic Liquid in an Alkoxyethanol or Poly Ethers at T = (298.15 to 318.15) K. J. Chem. Thermodyn. 2008, 40, 32−39. (37) Machida, H.; Sato, Y.; Smith, R. L. Pressure Volume Temperature (PVT) Measurements of Ionic Liquids ([bmim+][PF6−], [bmim +][BF4−], [bmim+][OcSO4−]) and Analysis with the Sanchez Lacombe Equation of State. Fluid Phase Equilib. 2008, 264, 147−155.

AUTHOR INFORMATION

Corresponding Author

*Tel: +965-22314415. Fax: +965-24811568. E-mail: ms.altuwaim@ paaet.edu.kw. Notes

The authors declare no competing financial interest. Funding

The authors thank the Public Authority for Applied Education and Training for the financial support of this work under the contract (PAAET-TS-12-09).

■

REFERENCES

(1) Seddon, K. R.; Stark, A.; Torres, M. J. Ionic Liquids: Green Solvents for the Future. Pure Appl. Chem. 2000, 72, 1391−1398. (2) Bennecke, J. F.; Mogiun, E. J. Ionic Liquids: Innovative Fluids for Chemical Processing. AIChE J. 2001, 47 (11), 2384−2389. (3) Rogers, R. D.; Seddon, K. R. Ionic Liquids as Green Solvents: Progress and Prospects. ACS Symp. Ser. 2003, 856. (4) Zhao, H.; Xia, S.; Ma, P. Review: Use of Ionic Liquids as ‘Green’ Solvents for Extractions. J. Chem. Technol. Biotechnol. 2005, 80, 1089− 1096. (5) Zhao, H. Innovative Applications of Ionic Liquids as Green Engineering Liquids. Chem. Eng. Commun. 2006, 193, 1660−1677. (6) Joglekar, H. C.; Rahman, I.; Kulkarni, B. D. The Path Ahead for Ionic Liquids. Chem. Eng. Technol. 2007, 30, 819−828. (7) Quijano, G.; Couvert, A.; Amrane, A. Review Ionic liquids: Applications and Future Trends in Bioreactor Technology. Bioresour. Technol. 2010, 101, 8923−8930. (8) Millat, J.; Dymond, J. H.; Nieto de Castro, C. A. Transport Properties of Fluids: Their Correlation,Prediction and Estimation; Cambridge University Press: London, 2005. (9) Franca, J. M. P.; Nieto de Castro, C. A.; Lopes, M. M.; Nunes, V. M. B. Influence of Thermophysical Properties of Ionic Liquids in Chemical Process Design. J. Chem. Eng. Data 2009, 54, 2569−2575. (10) Aparicio, S.; Atilhan, M.; Karadas, F. Thermophysical Properties of Pure Ionic Liquids: Review of Present Situation. Ind. Eng. Chem. Res. 2010, 49, 9580−9595. (11) Heintz, A. Recent Developments in Thermodynamics and Thermophysics of Non-aqueous Mixtures Containing Ionic Liquids. A Review. J. Chem. Thermodyn. 2005, 37, 525−535. (12) Plechkova, N. V.; Sedon, K. R. Applications of Ionic Liquids in the Chemical Industry. Chem. Soc. Rev. 2008, 37, 123−150. (13) Marsh, K. N.; Boxall, J. A.; Lichtenthaler, R. Room Temperature Ionic Liquids and Their MixturesA Review. Fluid Phase Equilib. 2004, 219, 93−98. (14) Tome, L. I. N.; Carvalho, P. J.; Freire, M. G.; Marrucho, I. M.; Fonseca, I. M. A.; Ferreira, A. G. M.; Coutinho, J. A. P.; Gardas, R. L. Measurements and Correlation of High-Pressure Densities of Imidazolium-Based Ionic Liquids. J. Chem. Eng. Data 2008, 53, 1914− 1921. (15) Pereiro, A. B.; Santamarta, F.; Tojo, E.; Rodrı ́guez, A.; Tojo, J. Temperature Dependence of Physical Properties of Ionic Liquid 1,3Dimethylimidazolium Methyl Sulfate. J. Chem. Eng. Data 2006, 51, 952−954. (16) Aparicio, S.; Alclade, R.; Garcı ́a, B.; Leal, J. M. High-Pressure Study of the Methylsulfate and Tosylate Imidazolium Ionic Liquids. J. Phys. Chem. B 2009, 113, 5593−5606. (17) Gu, Z.; Brennecke, J. F. Volume Expansivities and Isothermal Compressibilities of Imidazolium and Pyridinium Based Ionic Liquids. J. Chem. Eng. Data 2002, 47, 339−345. (18) Heintz, A.; Kulikov, D. V.; Verevkin, S. P. Thermodynamic Properties of Mixtures Containing Ionic Liquids. Activity Coefficients at Infinite Dilution of Alkanes, Alkenes, and Alkylbenzenes in 4-Methyl-nbutylpyridinium Tetrafluoroborate Using Gas−Liquid Chromatography. J. Chem. Eng. Data 2001, 46, 1526−1529. (19) Heintz, A.; Klasen, D.; Lehmann, J. K. Excess Molar Volumes and Viscosities of Binary Mixtures of Methanol and the Ionic Liquid 41962



Article

Binary Mixtures of N,N-Dimethylformamide with 1-Alkanols at Different Temperatures. J. Chem. Thermodyn. 2012, 48, 39−47. (56) Adamson, A. W.; Gast, A. P. Physical Chemistry of Surfaces; John Wiley: N.Y., 1997. (57) Guggenheim, E. A. The Principle of Corresponding States. J. Chem. Phys. 1945, 13, 253−261. (58) Kurnia, K. A.; Abdul Mutalib, M. I.; Ariwahjoedi, B. Estimation of Physico-chemical Properties of Ionic Liquids [H2N-C2mim][BF4] and [H2N-C3mim][BF4]. J. Chem. Eng. Data 2011, 56, 2557−2562. (59) Rebelo, L. P. N.; Lopes, J. N.; Esperança, J. M. S. S.; Filipe, E. On the Critical Temperature, Normal Boiling Point, and Vapor Pressure of Ionic Liquids. J. Phys. Chem. B 2005, 109, 6040−6043. (60) Valderrama, J.; Robles, P. Critical Properties, Normal Boiling Temperatures, and Acentric Factors of Fifty Ionic Liquids. Ind. Eng. Chem. Res. 2007, 46, 1338−1344. (61) Rocha, M. A. A.; Ribeiro, F. M. S.; Ferreira, A. I. M. C. L.; Coutinho, J. A. P.; Santos, L. M. N. B. F. Thermophysical Properties of [CN−1C1im][PF6] Ionic Liquids. J. Mol. Liq. 2013, 188, 196−202. (62) Wang, J.; Zhao, F.; Liu, Y.; Wang, X.; Hu, Y. Thermophysical Properties of Pure 1-Ethyl-3-methylimidazolium Methylsulfate and Its Binary Mixtures with Alcohols. Fluid Phase Equilib. 2011, 305, 114−120. (63) Shekaari, H.; Mousavi, S. S. Volumetric Properties of Ionic Liquid 1,3-Dimethylimidazolium Methyl Sulfate + Molecular Solvents at T = (298.15−328.15) K. Fluid Phase Equilib. 2010, 291, 201−207.

(38) Fan, W.; Zhou, Q.; Sun, J.; Zhang, S. Density, Excess Molar Volume, and Viscosity for the Methyl Methacrylate + 1-Butyl-3methylimidazolium Hexafluorophosphate Ionic Liquid Binary System at Atmospheric Pressure. J. Chem. Eng. Data 2009, 54, 2307−2311. (39) Soriano, A. N.; Doma, B. T., Jr.; Li, M. H. Measurements of the Density and Refractive Index for 1-n-Butyl-3-methylimidazolium-Based Ionic Liquids. J. Chem. Thermodyn. 2009, 41, 301−307. (40) Singh, T.; Kumar, A. Volumetric Behavior of 1-Butyl-3methylimidazolium Hexafluorophosphate with Ethylene Glycol Derivatives: Application of Prigogine-Flory-Patterson Theory. J. Mol. Liq. 2010, 153, 117−123. (41) Ghatee, M. H.; Zolghadr, A. R. Surface Tension Measurements of Imidazolium-Based Ionic Liquids at Liquid Vapor Equilibrium. Fluid Phase Equilib. 2008, 263, 168−175. (42) Harris, K. R.; Kanakubo, M.; Woolf, L. A. Temperature and Pressure Dependence of the Viscosity of the Ionic Liquids 1-Methyl-3octylimidazolium Hexafluorophosphate and 1-Methyl-3-octylimidazolium Tetrafluoroborate. J. Chem. Eng. Data 2006, 51, 1161−1167. (43) Gardas, R. L.; Freire, M. G.; Carvalho, P. J.; Marrucho, I. M.; Fonseca, I. M. A.; Ferreira, A. G. M.; Coutinho, J. A. P. High-Pressure Densities and Derived Thermodynamic Properties of ImidazoliumBased Ionic Liquids. J. Chem. Eng. Data 2007, 52, 80−88. (44) Tomida, D.; Kumagai, A.; Kenmochi, S.; Qiao, K.; Yokoyama, C. Viscosity of 1-Hexyl-3-methylimidazolium Hexafluorophosphate and 1Octyl-3-methylimidazolium Hexafluorophosphate at High Pressure. J. Chem. Eng. Data 2007, 52, 577−579. (45) Ahosseini, A.; Scurto, A. M. Viscosity of Imidazolium-Based Ionic Liquids at Elevated Pressures: Cation and Anion Effects. Int. J. Thermophys. 2008, 29, 1222−1243. (46) Muhammad, A.; Abdul Mutalib, M. I.; Wilfred, C. D.; Murugesan, T.; Shafeeq, A. Thermophysical Properties of 1-Hexyl-3-methylimidazolium Based Ionic Liquids with Tetrafluoroborate, Hexafluorophosphate and Bis(trifluoromethylsulfonyl)imide Anions. J. Chem. Thermodyn. 2008, 40, 1433−1438. (47) Klomfar, J.; Souckova, M.; Patek, J. Surface Tension Measurements for Four 1-Alkyl-3-methylimidazolium-Based Ionic Liquids with Hexafluorophosphate Anion. J. Chem. Eng. Data 2009, 54, 1389−1394. (48) Taguchi, R.; Machida, H.; Sato, Y.; Smith, R. L. High-Pressure Densities of 1-Alkyl-3-methylimidazolium Hexafluorophosphates and 1Alkyl-3-methylimidazolium Tetrafluoroborates at Temperatures from (313 to 473) K and at Pressures up to 200 MPa. J. Chem. Eng. Data 2009, 54, 22−27. (49) Li, J.; Hu, Y.; Ling, S.; Zhang, J. Physicochemical Properties of [C6mim][PF6] and [C6mim][(C2F5)3PF3] Ionic Liquids. J. Chem. Eng. Data 2011, 56, 3068−3072. (50) Vakili-Nezhaad, G.; Vatani, M.; Asghari, M.; Ashour, I. Effect of Temperature on the Physical Properties of 1-Butyl-3-methylimidazolium Based Ionic Liquids with Thiocyanate and Tetrafluoroborate Anions, and 1-Hexyl-3-methylimidazolium with Tetrafluoroborate and Hexafluorophosphate Anions. J. Chem. Thermodyn. 2012, 54, 148−154. (51) 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. (52) Gomez, E.; Gonzalez, B.; Dominguez, A.; Tojo, E.; Tojo, J. Dynamic Viscosities of a Series of 1-Alkyl-3-methylimidazolium Chloride Ionic Liquids and Their Binary Mixtures with Water at Several Temperatures. J. Chem. Eng. Data 2006, 51, 696−701. (53) Singh, T.; Kumar, A. Temperature Dependence of Physical Properties of Imidazolium Based Ionic Liquids: Internal Pressure and Molar Refraction. J. Solution Chem. 2009, 38, 1043−1053. (54) Al-Jimaz, A. S.; Al-Kandary, J. A.; Abdul-Latif, A. M. Acoustical and Excess Properties of {Chlorobenzene + 1-Hexanol, or 1-Heptanol, or 1-Octanol, or 1-Nonanol, or 1-Decanol} at (298.15, 303.15, 308.15, and 313.15) K. J. Chem. Eng. Data 2007, 52, 206−214. (55) AlTuwaim, M. S.; Alkhaldi, K. H. A. E.; Al-Jimaz, A. S.; Mohammad, A. A. Comparative Study of Physico-chemical Properties of 1963


Temperature Dependence of Physicochemical Properties of

Recommend Documents