Thermophysical Properties of the Pure Ionic Liquid 1-Butyl-1

Article pubs.acs.org/jced

Thermophysical Properties of the Pure Ionic Liquid 1‑Butyl-1methylpyrrolidinium Dicyanamide and Its Binary Mixtures with Alcohols Emilio J. González,† Begoña González,*,‡ and Eugénia A. Macedo† †

LSRE-Laboratory of Separation and Reaction Engineering, Associated laboratory LSRE/LCM, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, s/n, Porto 4200-465, Portugal ‡ Advanced Separation Processes Group, Department of Chemical Engineering, University of Vigo, Campus Lagoas-Marcosende, 36310 Vigo, Spain S Supporting Information *

ABSTRACT: Experimental density, speed of sound, viscosity, and refractive index data for the pure ionic liquid 1-butyl-1-methylpyrrolidinium dicyanamide, [BMpyr][dca], are reported from T = (293.15 to 343.15) K, together with the molar isobaric heat capacity from T = (293.15 to 333.15) K. Moreover, a thermal analysis was carried out for the pure ionic liquid using a differential scanning calorimetry. The density, speed of sound, refractive index, and molar isobaric heat capacity data were fitted to a simple polynomial (first and/or second order), while viscosity data were fitted to the Vogel−Fulcher− Tamman (VFT) equation. From the experimental density values, the thermal expansion coefficient was also calculated. For the binary systems {1-propanol, or 2-propanol, or 1butanol + [BMpyr][dca]}, density, speed of sound, and refractive index data were also measured over the whole composition range at T = (298.15, 313.15 and 328.15) K and p = 0.1 MPa. From these data, the excess molar volumes and excess molar isentropic compressions were calculated and satisfactorily fitted to the Redlich−Kister equation. Finally, the obtained results are discussed in terms of interactions and structure factors in these binary mixtures.

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INTRODUCTION In the past decade numerous researchers have focused their work on the study of ionic liquids (ILs), mainly due to their fascinating properties such as very low vapor pressure at normal temperature and pressure conditions, their wide liquid range, or their ability to dissolve a large number of substances. Many of these studies have led to new possible applications for this kind of salt.1−6 Nevertheless, in order to transfer the ILs from laboratory to industry and designing future processes and equipments involving these ionic compounds, an accurate knowledge about their physical properties, either for pure ILs or mixed with other solvents, is crucial. Regarding the study of physical properties for binary mixtures of alcohol + ionic liquid, a large number of works have been published in recent years,7−19 showing the interest of the scientific community for this field. Before the year 2010, most of the papers reported experimental data for binary mixtures using 1-alkyl-3-methylimidazolium-based ILs with different anions such as chloride, ethylsulfate, trifluoromethanesulfonate, thiocyanate, or tetrafluoroborate,7−13 but in most recent studies new ILs with other cations like 2-hydroxyethylammonium,15 N-octylpyridinium,18 or N-octylisoquinolinum19 are being included. In this study, a thermophysical study of the ionic liquid 1butyl-1-methylpyrrolidinium dicyanamide, [BMpyr][dca], was carried out at several temperatures and atmospheric pressure. © XXXX American Chemical Society

This salt was selected because the dicyanamide anion is a ligand that produces low melting point and low viscosity ILs. Density, speed of sound, refractive index, and viscosity data of this pure compound were measured from T = (293.15 to 343.15) K, and the experimental molar isobaric heat capacity was also determined from T = (293.15 to 333.15) K. The experimental density values were used to calculate the coefficient of thermal expansion for [BMpyr][dca]. On the other hand, densities, speeds of sound, and refractive indices for the binary mixtures {1-propanol, or 2-propanol, or 1-butanol + [BMpyr][dca]} were also measured at T = (298.15, 313.15 and 328.15) K. These experimental data were employed to obtain excess molar volumes and excess molar isentropic compressions. For the pure ionic liquid, density, speed of sound, refractive index, and molar isobaric heat capacity data were adjusted to a simple polynomial, and viscosity data were fitted to the Vogel− Fulcher−Tamman (VFT) equation.20−22 The corresponding excess properties were fitted to a Redlich−Kister type equation.23 To our knowledge, only little density, viscosity, conductivity, and surface tension data for the pure [BMpyr][dca] ionic liquid Received: March 30, 2012 Accepted: May 2, 2013

A

dx.doi.org/10.1021/je300384g | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

2) for these properties are 5 × 10−5 g·cm−3 and 0.6 m·s−1, respectively. For the density and speed of sound of the pure ionic liquid, experimental uncertainties, which include the impurities in the sample, are 0.001 g·cm−3 and 1 m·s−1. This equipment has a temperature controller that keeps the samples at working temperature with an accuracy of 0.01 K. Moreover, the equipment automatically detects the presence of bubbles in the cell. The apparatus was calibrated by measuring Millipore quality water and air, according to the manual instructions. An automatic refractometer Abbemat-HP Dr. Kernchen was used to measure refractive indices. For this property, the standard uncertainty in the measurements is 4 × 10−5 and the combined expanded uncertainty (k = 2) is 8 × 10−5. For the pure ionic liquid (purity, in mass fraction: 0.98), the experimental uncertainty was estimated to be 0.001.This equipment keeps the samples at working temperature with an accuracy of 0.01 K. The apparatus was checked by measuring Millipore quality water and pure liquids before each series of measurements. Kinematic viscosities were determined with an automatic viscosimeter Lauda PVS1 using an Ubbelhode microcapillary Type II (diameter = 1.13 × 10−3 m) with an uncertainty in experimental measurement of 0.03 mPa·s. Taking into account the impurity level of the pure ionic liquid, experimental uncertainty was estimated to be 1 mPa·s. The microcapillary was maintained in a D20KP LAUDA thermostat with an accuracy of 0.01K. The equipment is connected to a control unit PVS1 (Processor Viscosity System) that is a PC-controlled instrument for the precise measurement of the fall time, using standardized glass capillaries. The microcapillary was calibrated and credited by the company. The water content of the pure ILs was measured with a Metrohm 870 KF Titrino using Titran 2, supplied by Merck, as titrant. The uncertainty for the water content of the pure ionic liquid is 150 ppm. Finally, a Mettler Toledo Differential Scanning Calorimeter (DSC822e) was used to carry out the thermal analysis and to determine the molar isobaric heat capacity for the pure ionic liquid. The experimental uncertainties for temperature and molar isobaric heat capacity are 1 K and 1 J·mol−1·K−1, respectively. These data were used to calculate the excess molar isentropic compression for the binary mixtures {alcohol + ionic liquid} at the studied temperatures. All binary mixtures were prepared by weighing using a Mettler AX-205 Delta Range balance with an uncertainty of 3 × 10−4 g. In order to avoid changes in composition of the binary mixtures, all samples were prepared inside a glovebox under inert atmosphere.

were found in literature,24−29 and no data for the binary systems studied in this paper were found in the literature.

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EXPERIMENTAL SECTION Chemicals. The ionic liquid [BMpyr][dca], whose ionic structure is shown is Figure 1, was supplied by Iolitec GmbH

Figure 1. Structure of the ionic liquid 1-butyl-1-methylpyrrolidinium dicyanamide, [BMpyr][dca].

(Germany), and alcohols were supplied by specialized companies. The supplier, the purity, the density, and the refractive index of all of the pure components at T = 298.15 K and atmospheric pressure are reported in Table 1. Density and refractive data found in the literature24−26,30 for the pure studied chemicals are also included in this table in order to compare the experimental data reported in this work with those previously published by other authors. As can be observed from Table 1, the experimental density values for the pure components agree quite well with literature data. The density data for the ionic liquid is in concordance with density values published by Blahut et al. (purity, in mass fraction: > 0.99; water content, in mass fraction: 1 × 10−4)24 and McHale et al. (purity, in mass fraction: 0.98; water content, in mass fraction: 2.35 × 10−4),25 whereas a big discrepancy can be observed with the value published by Galán-Sanchez et al. (purity, in mass fraction: > 0.98; water content, in mass fraction: 5.70 × 10−4)26 for this ionic liquid. This fact appears to indicate that the data reported in ref 26 are erroneous as was previously discussed by Blahut et al.24 Prior to its use, the ionic liquid was subjected to vacuum (p = 2 × 10−1 Pa) at moderate temperature (T = 323.15 K) for 48 h in order to remove water and volatile compounds. Once dried, the water content of the ionic liquid was lower than 1.5 × 10−3, in mass fraction. Regarding the studied alcohols, they were degassed ultrasonically and dried over molecular sieves type 4 × 10−10 m, supplied by Aldrich, without further treatment. All chemicals used in this work were kept in an inert atmosphere (argon gas) to avoid contact with air. Apparatus and Procedure. Densities and speeds of sound were obtained with Anton Paar DSA-5000 M digital vibratingtube densimeter with an uncertainties of 3 × 10−5 g·cm−3 and 1 m·s−1, respectively. The combined expanded uncertainties (k =

Table 1. Supplier, Purity, Density, ρ, and Refractive Index, nD, for the Pure Components at T = 298.15 K and Atmospheric Pressurea ρ/(g·cm−3) compound

supplier

purity, mass fraction

exp.

[BMpyr][dca]

Iolitec

> 0.980

1.013

1-propanol 2-propanol 1-butanol

Sigma-Aldrich Riedel de Haën Sigma-Aldrich

> 0.999 > 0.998 > 0.999

0.79967 0.78160 0.80571

nD lit.

1.01345b,c 1.013d 1.11431e,c 0.79960f 0.78126f 0.80575f

exp.

lit.

1.497

n.a.

1.38309 1.37507 1.39734

1.38370f 1.3752f 1.39741f

a Standard uncertainty: ρ(ionic liquid) is 0.001g·cm−3, nD (ionic liquid) is 0.001, ρ(alcohol) is 0.00003 g·cm−3, nD (alcohol) is 0.00004. bReference 24. cInterpolated value from literature data. dReference 25. eReference 26. fReference 30.

B



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RESULTS AND DISCUSSION Pure Ionic Liquid. Density, ρ, speed of sound, u, refractive index, nD, and kinematic viscosity, ν, of the pure ionic liquid were experimentally measured from T = (293.15 to 343.15) K and atmospheric pressure. The experimental kinematic viscosities were used to calculate the corresponding dynamic viscosities, η, using the following equation: η = ν·ρ (1)

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, ρ, Speed of Sound, u, Refractive Index, nD, and Molar Isobaric Heat Capacity, Cp, for the Ionic Liquid [BMpyr][dca] a −3

ρ/g·cm u/m·s−1 nD Cp/ J·mol−1·K−1

Density, ρ, speed of sound, u, refractive index, nD, and dynamic viscosity, η, for the pure ionic liquid, at the studied conditions, are reported in Table 2. From these values, it is possible to

ρ

K

g·cm

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 338.15 343.15

103η

u −3

1.016 1.013 1.011 1.008 1.005 1.002 1.000 0.997 0.994 0.991 0.989

m·s

−1

1823 1810 1797 1785 1772 1760 1748 1736 1724 1712 1700

nD

Pa·s

1.498 1.497 1.495 1.494 1.492 1.491 1.490 1.488 1.487 1.485 1.484

42 34 29 25 22 19 17 15 13 12 11

η/mPa·s

−0.016

1.60·10−4 3.37·10−4 2.96·10−5 1.34·10−3

(5)

A

k

To

σ

0.232

737.6

150.9

1.097

with the standard relative deviation, σ, defined in eq 4. From σ value, it is possible to conclude that the VFT equation provides a good fit of the experimental data. This result agrees with that published in a previous paper about the temperature dependence and the structural influence on the thermophysical properties of several commercial ionic liquids.31 As mentioned in the Introduction, several data were found in the literature on density and viscosity data for the pure [BMpyr][dca] ionic liquid.24−29 In order to compare the experimental and literature data, the deviations of our experimental data and those available in literature for density were plotted in Figure 2. From this figure, it can be inferred that, in general, our experimental density data agree with those found in literature for the same ionic liquid,24,25,27 except for the data published by Galán et al.,26 for which a deviation of 10% was obtained. This fact appears to indicate that the data reported in ref 26 are erroneous, as has already been discussed by other authors.24 Regarding the viscosity for the pure ionic liquid, only three single values for [BMpyr][dca] ionic liquid were found in literature, (41 and 50) mPa·s at T = 293.15 K27,28 and 36.5 mPa·s at T = 298.15 K.25 The differences between experimental and literature data may be attributed to a different level of impurities in samples. Finally, a thermal analysis was carried out and experimental molar isobaric heat capacity, Cp, for [BMpyr][dca] were determined from T = (293 to 333) K. The rate for the thermal analysis was 10 K·min−1 and for the Cp determination was 20 K·min−1. The results show that [BMPyr][dca] only presents a glass transition temperature, Tg, at T = 172 K, as shown in Figure 3. The obtained Cp data are shown in Table 5. Unlike the other properties studied in this work, Cp values increase

(2)

Since the variation of ln ρ versus T is linear, αp was considered a temperature-independent constant, and the corresponding value for [BMpyr][dca] was 5.5·10−4 K−1, with an uncertainty of 0.5·10−4 K−1. The variation of density, speed of sound, refractive index, and molar isobaric heat capacity with the temperature were satisfactorily fitted to a simple polynomial (first or second order): (3)

where z is ρ, u, nD, or Cp, T is the absolute temperature in K, and a, b, and c are adjustable parameters. The fitting parameters, a, b, and c for each studied property are shown in Table 3, together with the correlation coefficient squared, R2, and the standard relative deviation, σ, defined in eq 4: ndat i

σ

0.9989 0.9998 0.9999 0.9985

Table 4. Fitting Parameters of VFT Equation Together with the Standard Relative Deviations of the Fit, σ, for the Viscosity, η, for the Ionic Liquid [BMpyr][dca]

conclude that all the studied properties decrease as the temperature increases. The viscosity decreases exponentially while all other studied properties decrease linearly, as can be observed in Figure S1, available as Supporting Information (SI). The experimental density values as a function of temperature were used to calculate the coefficient of thermal expansion, αp, defined as:

σ = {∑ ((z − zcal)/zcal)2 /ndat}1/2

−5.5·10 −2.449 −3·10−4 11.225

where A, k, and T0 are adjustable parameters. The values of these adjustable parameters are reported in Table 4, together

Standard uncertainty: T is 0.01 K, ρ is 0.001 g·cm−3, u is 1 m·s−1, nD is 0.001, and η is 1 mPa·s.

z = a + bT + cT 2

R2

η = A exp(k /(T − T0))

a

αp = −1/ρ(∂ρ /∂T )p = −(∂ ln ρ /∂T )

1.176 2540 1.585 −1467

c −4

where z and zcal are the values of experimental and calculated property, respectively, and ndat is the number of experimental points. Furthermore, the dynamic viscosity values, η, were represented using the Vogel−Fulcher−Tamman (VFT) equation:20−22

Table 2. Density, ρ, Speed of Sound, u, Refractive Index, nD, and Dynamic Viscosity, η, for the Ionic Liquid [BMpyr][dca] at Several Temperatures and Atmospheric Pressurea T

b

(4) C



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Table 5. Molar Isobaric Heat Capacity, Cp, for the Ionic Liquid [BMpyr][dca] at Several Temperatures and Atmospheric Pressurea T K 293.15 294.15 295.15 296.15 297.15 298.15 299.15 300.15 301.15 302.15 303.15 304.15 305.15 306.15

Figure 2. Relative deviations between the density data measured in this work, ρexp, and reported in the literature, ρlit, as a function of temperature. Symbols: ×, (ref 24); △, (ref 25); ▲, (ref 26); ■, (ref 27).

a

Cp J·mol ·K 490 492 495 497 500 502 504 506 508 510 512 514 515 517

−1

K 307.15 308.15 309.15 310.15 311.15 312.15 313.15 314.15 315.15 316.15 317.15 318.15 319.15 320.15

Cp −1

J·mol ·K 519 521 522 524 525 526 528 529 530 532 533 534 536 537

−1

T

Cp

K

J·mol−1·K−1

321.15 322.15 323.15 324.15 325.15 326.15 327.15 328.15 329.15 330.15 331.15 332.15 333.15

538 539 541 542 543 544 546 547 548 549 551 552 554

Standard uncertainty: Cp is 1 J·mol−1·K−1.

V E = Vm −

with temperature. This behavior agrees with other results found in literature for other ILs.32−35 Binary Mixtures. In this work, densities, speeds of sound and refractive indices for the binary mixtures 1-propanol (1), 1butanol (1), or 2-propanol (1) + [BMpyr][dca] (2) were measured at T = (298.15, 313.15, and 328.15) K and atmospheric pressure. These experimental data are reported in Tables 6−8. For all of the studied systems, these physical properties decrease with the increase in alcohol concentration, x1, and with temperature. The experimental density and speed of sound data were used to calculate the corresponding excess molar volumes, VE, and excess molar isentropic compressions, KES,m, for the binary mixtures studied in this work. The excess molar volumes were calculated using the following expression:

T

−1

∑ xiVi* i

(6)

where Vm is the molar volume of the mixture and xi and V*i represent the mole fraction and the molar volume of component i, respectively. From density and speed of sound data the isentropic compressibility κs, was obtained using the Laplace equation: κs = −Vm−1(∂Vm/∂p)S = ρ−1u−2 = Vm/(M mu 2)

(7)

where Mm is the molar mass of the mixture. To achieve agreement with the other thermodynamic quantities, it is appropriate to shift from the volume-intensive κs to the mole-intensive quantity KS,m, calculated as36,37 KS,m = −(∂Vm/∂p)S = Vmκs = Vm2/(M mu 2)

(8)

Figure 3. DSC scan for pure [BMpyr][dca] ionic liquid. D



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Table 6. Densities, ρ, Speeds of Sound, u, Refractive Indices, nD, Excess Molar Volumes, VE, and Excess Molar Isentropic Compressions, KES,m, for the Binary Mixture 1-Propanol (1) + [BMpyr][dca] (2) at the Studied Temperaturesa ρ x1

g·cm

0.0000 0.0669 0.1894 0.2912 0.3998 0.5140 0.5970 0.6944 0.8002 0.8940 0.9437 1.0000 T = 313.15 K 0.0000 0.0669 0.1894 0.2912 0.3998 0.5140 0.5970 0.6944 0.8002 0.8940 0.9437 1.0000 T = 328.15 K 0.0000 0.0669 0.1894 0.2912 0.3998 0.5140 0.5970 0.6944 0.8002 0.8940 0.9437 1.0000

VE

u −3

m·s

−1

1.01344 1.00891 0.99951 0.98988 0.97754 0.96137 0.94664 0.92526 0.89503 0.85867 0.83431 0.79967

1810 1796 1766 1734 1693 1639 1590 1523 1434 1339 1281 1206

1.00508 1.00051 0.99094 0.98120 0.96867 0.95220 0.93726 0.91548 0.88473 0.84766 0.82286 0.78744

1773 1758 1728 1695 1653 1598 1549 1480 1390 1292 1233 1155

0.99681 0.99219 0.98247 0.97259 0.95987 0.94313 0.92794 0.90575 0.87440 0.83655 0.81117 0.77480

1736 1722 1690 1657 1615 1559 1509 1439 1346 1247 1186 1105

nD T = 298.15 K 1.49681 1.49446 1.48947 1.48457 1.47813 1.46962 1.46189 1.45057 1.43439 1.41492 1.40174 1.38309

ρ

KES,m −1

cm ·mol 3

Table 7. Densities, ρ, Speeds of Sound, u, Refractive Indices, nD, Excess Molar Volumes, VE, and Excess Molar Isentropic Compressions, KES,m, of the Binary Mixture 2-Propanol (1) + [BMpyr][dca] (2) at the Studied Temperaturesa

−1

−1

m ·TPa ·mol 3

0.000 −0.182 −0.524 −0.739 −0.937 −1.086 −1.121 −1.096 −0.974 −0.689 −0.459 0.000

0.0000 −0.0202 −0.0553 −0.0805 −0.1038 −0.1221 −0.1289 −0.1298 −0.1162 −0.0839 −0.0542 0.0000

1.49248 1.49003 1.48499 1.48002 1.47348 1.46485 1.45700 1.44557 1.42936 1.40968 1.39657 1.37698

0.000 −0.205 −0.571 −0.814 −1.034 −1.193 −1.240 −1.213 −1.083 −0.767 −0.516 0.000

0.0000 −0.0241 −0.0672 −0.0979 −0.1266 −0.1495 −0.1594 −0.1608 −0.1459 −0.1058 −0.0694 0.0000

1.48821 1.48535 1.48071 1.47547 1.46890 1.46017 1.45239 1.44087 1.42432 1.40433 1.39109 1.37055

0.000 −0.230 −0.633 −0.906 −1.153 −1.335 −1.393 −1.366 −1.225 −0.875 −0.589 0.000

0.0000 −0.0303 −0.0814 −0.1196 −0.1556 −0.1843 −0.1970 −0.2001 −0.1819 −0.1345 −0.0886 0.0000

a Standard uncertainty: x is 0.0001, ρ is 0.00003 g·cm−3, u is 1 m·s−1, E is 0.0001 nD is 0.00004, V E is 0.007 cm3·mol−1, and K S,m 3 −1 −1 m ·TPa ·mol .

x1 T = 298.15 K 0.0000 0.0466 0.0896 0.1849 0.2967 0.4039 0.5056 0.6018 0.6997 0.8066 0.8920 0.9461 1.0000 T = 313.15 K 0.0000 0.0466 0.0896 0.1849 0.2967 0.4039 0.5056 0.6018 0.6997 0.8066 0.8920 0.9461 1.0000 T = 328.15 K 0.0000 0.0466 0.0896 0.1849 0.2967 0.4039 0.5056 0.6018 0.6997 0.8066 0.8920 0.9461 1.0000

(9)

where is obtained using the approach developed by Benson and Kiyohara38 ⎡ ⎡ (∑ x E * )2 ⎤ * )2 ⎤ (Ep,i i i p,i ⎥ ⎢ ⎥ * = ∑ x i KS,i + T − T⎢ * ⎥⎦ * ⎢⎣ ⎢⎣ ∑i x iCp,i Cp,i ⎥⎦ i

m·s

nD

KES,m −1

cm ·mol 3

m ·TPa−1·mol−1 3

1.01344 1.00979 1.00648 0.99807 0.98658 0.97301 0.95729 0.93871 0.91491 0.88081 0.84527 0.81697 0.78160

1810 1799 1789 1761 1723 1676 1622 1559 1483 1382 1287 1219 1141

1.49681 1.49494 1.49327 1.48899 1.48321 1.47614 1.46842 1.45947 1.44786 1.43078 1.41191 1.39615 1.37507

0.000 −0.102 −0.246 −0.503 −0.804 −1.018 −1.173 −1.230 −1.192 −0.999 −0.749 −0.483 0.000

0.0000 −0.0177 −0.0346 −0.0682 −0.1052 −0.1341 −0.1556 −0.1670 −0.1679 −0.1485 −0.1106 −0.0692 0.0000

1.00508 1.00139 0.99803 0.98952 0.97787 0.96414 0.94821 0.92931 0.90508 0.87032 0.83402 0.80504 0.76851

1773 1761 1750 1723 1684 1637 1582 1518 1440 1337 1240 1170 1088

1.49248 1.49057 1.48892 1.48451 1.47867 1.47160 1.46382 1.45505 1.44323 1.42556 1.40663 1.39076 1.36846

0.000 −0.120 −0.279 −0.572 −0.912 −1.163 −1.347 −1.415 −1.380 −1.171 −0.887 −0.579 0.000

0.0000 −0.0212 −0.0414 −0.0841 −0.1298 −0.1669 −0.1943 −0.2099 −0.2120 −0.1899 −0.1438 −0.0914 0.0000

0.99681 0.99310 0.98971 0.98108 0.96927 0.95535 0.93915 0.91994 0.89524 0.85973 0.82250 0.79261 0.75455

1736 1724 1713 1685 1646 1598 1543 1478 1398 1293 1193 1120 1034

1.48821 1.48622 1.48449 1.48012 1.47391 1.46727 1.45892 1.45002 1.43809 1.42034 1.40098 1.38454 1.36145

0.000 −0.147 −0.331 −0.668 −1.059 −1.355 −1.571 −1.665 −1.639 −1.415 −1.086 −0.714 0.000

0.0000 −0.0267 −0.0518 −0.1045 −0.1623 −0.2091 −0.2453 −0.2666 −0.2710 −0.2462 −0.1891 −0.1213 0.0000

molar isobaric expansion of the pure component i, E*p,i, is the product of the molar volume and the coefficient of thermal expansion, αp,i, and Cp,i * is the molar isobaric heat capacity of the pure component i. As commented above, the αp,i for [BMpyr][dca] ionic liquid was considered a temperatureindependent constant and its value is 5.5 × 10−4 K−1, while the Cp,i * data were experimentally determined from T = (293.15 to 333.15) K and they are reported in Table 5. For the studied alcohols, the values for αp,i and C*p,i were taken from literature.39

KidS,m

id KS,m

−1

a Standard uncertainty: x is 0.0001, ρ is 0.00003 g·cm−3, u is 1 m·s−1, E is 0.0001 nD is 0.00004, VE is 0.007 cm3·mol−1, and KS,m m3·TPa−1·mol−1.

where KS,m is the molar isentropic compression. The excess molar isentropic compression, KES,m is calculated by the following equation: E id KS,m = KS,m − KS,m

g·cm

VE

u −3

(10)

where K*S,i is the product of the molar volume, Vi*, and the isentropic compressibility, κ*S,i, of the pure component i. The E



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corresponding fitting parameters of the Redlich−Kister equation for the studied temperatures, together with the corresponding standard relative deviations, σ, are given in Tables 9−11.

Table 8. Densities, ρ, Speeds of Sound, u, Refractive Indices, nD, Excess Molar Volumes, VE, and Excess Molar Isentropic Compressions, KES,m, of the Binary Mixture 1-Butanol (1) + [BMpyr][dca] (2) at the Studied Temperaturesa ρ x1 0.0000 0.0464 0.0945 0.1898 0.2990 0.4012 0.4989 0.5996 0.6947 0.7995 0.8965 0.9464 1.0000 T = 313.15 K 0.0000 0.0464 0.0945 0.1898 0.2990 0.4012 0.4989 0.5996 0.6947 0.7995 0.8965 0.9464 1.0000 T = 328.15 K 0.0000 0.0464 0.0945 0.1898 0.2990 0.4012 0.4989 0.5996 0.6947 0.7995 0.8965 0.9464 1.0000

g·cm

VE

u −3

m·s

−1

1.01344 1.00974 1.00578 0.99695 0.98502 0.97168 0.95651 0.93773 0.91635 0.88699 0.85309 0.83226 0.80571

1810 1799 1787 1759 1720 1674 1624 1564 1500 1420 1339 1295 1240

1.00508 1.00133 0.99732 0.98839 0.97631 0.96280 0.94743 0.92848 0.90678 0.87687 0.84242 0.82120 0.79412

1773 1761 1749 1720 1680 1635 1583 1522 1457 1376 1293 1246 1190

0.99681 0.99303 0.98898 0.97992 0.96769 0.95402 0.93844 0.91923 0.89717 0.86672 0.83160 0.80994 0.78211

1736 1724 1712 1682 1642 1596 1544 1482 1416 1333 1247 1199 1140

nD T = 298.15 K 1.49681 1.49508 1.49327 1.48922 1.48332 1.47745 1.47048 1.46149 1.45140 1.43728 1.42111 1.41049 1.39734 1.49248 1.49066 1.48888 1.48478 1.47876 1.47280 1.46568 1.45660 1.44628 1.43205 1.41557 1.40464 1.39115 1.48821 1.48612 1.48426 1.48014 1.47416 1.46814 1.46117 1.45174 1.44129 1.42668 1.40973 1.39877 1.38481

KES,m −1

cm ·mol 3

0.000 −0.145 −0.312 −0.594 −0.850 −1.014 −1.104 −1.121 −1.068 −0.864 −0.583 −0.377 0.000

0.0000 −0.0153 −0.0309 −0.0589 −0.0864 −0.1053 −0.1183 −0.1239 −0.1207 −0.1028 −0.0701 −0.0447 0.0000

0.000 −0.157 −0.337 −0.646 −0.927 −1.110 −1.214 −1.252 −1.197 −0.965 −0.657 −0.423 0.000

0.0000 −0.0178 −0.0368 −0.0705 −0.1039 −0.1290 −0.1448 −0.1529 −0.1502 −0.1298 −0.0898 −0.0557 0.0141

0.000 −0.176 −0.376 −0.712 −1.026 −1.238 −1.362 −1.414 −1.358 −1.107 −0.760 −0.495 0.000

Table 9. Fitting Parameters and Standard Relative Deviations, σ, for the Binary Mixture 1-Propanol (1) + [BMpyr][dca] (2) at the Studied Temperatures

m ·TPa−1·mol−1 3

excess property VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1 VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1 VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1

excess property VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1 VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1 VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1

0.0000 −0.0218 −0.0448 −0.0853 −0.1269 −0.1579 −0.1790 −0.1903 −0.1885 −0.1646 −0.1145 −0.0725 0.0000

T = 298.15 K −4.225 −1.713 −1.536 −0.476 −0.250 −0.206

−1.644 −0.168

0.024 0.023

T = 313.15 K −4.655 −1.922 −1.769 −0.584 −0.319 −0.276

−1.864 −0.231

0.028 0.023

T = 328.15 K −5.202 −2.233 −2.092 −0.717 −0.405 −0.367

−2.146 −0.307

0.030 0.033

B2

B3

σ

T = 298.15 K −4.612 −1.905 −1.145 −0.613 −0.329 −0.276

−1.928 −0.221

0.042 0.027

T = 313.15 K −5.275 −2.289 −1.552 −0.764 −0.422 −0.380

−2.379 −0.336

0.042 0.032

T = 328.15 K −6.150 −2.830 −2.277 −0.961 −0.557 −0.538

−3.001 −0.473

0.044 0.038

B0

B1

B2

The values of the excess properties at the studied temperatures are also reported in Tables 6-8, together with the corresponding physical properties. Moreover, excess molar volumes, VE, and excess molar isentropic compressions, KES,m, versus x1, at the three studied temperatures, are also plotted in Figure S2, available in the Supporting Information (SI). Table 11. Fitting Parameters and Standard Relative Deviations, σ, for the Binary Mixture 1-Butanol (1) + [BMpyr][dca] (2) at the Studied Temperatures excess property VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1

The excess molar volumes and excess molar isentropic compressions at the studied temperatures were satisfactorily fitted to a Redlich−Kister type equation23

VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1

M

∑ Bp(xi − xj)p p=0

σ

B1

Table 10. Fitting Parameters and Standard Relative Deviations, σ, for the Binary Mixture 2-Propanol (1) + [BMpyr][dca] (2) at the Studied Temperatures

a Standard uncertainty: x is 0.0001, ρ is 0.00003 g·cm−3, u is 1 m·s−1, E is 0.0001 nD is 0.00004, V E is 0.007 cm3·mol−1, and K S,m m3·TPa−1·mol−1.

ΔQ ij = xixj

B3

B0

(16)

where ΔQij is the excess property, x is the mole fraction, Bp is the fitting parameter, and M is the degree of the polynomial expansion, which was optimized using the F-test.40 The

VE/cm3·mol−1 KES,m/ m3·TPa−1·mol−1 F

B3

σ

T = 298.15 K −4.405 −0.962 −0.878 −0.471 −0.178 −0.139

−1.204 −0.121

0.028 0.022

T = 313.15 K −4.865 −1.257 −1.008 −0.577 −0.240 −0.186

−1.212 −0.161

0.029 0.016

T = 328.15 K −5.448 −1.580 −1.298 −0.712 −0.322 −0.258

−1.405 −0.212

0.030 0.021

B0

B1

B2



Article

From these data, it is possible to observe that VE and KES,m values are negative over the whole composition range, showing asymmetrical curves, which are quite typical in systems containing components with a large molar volume difference. As it is known, the VE is affected by the intermolecular forces between the components of the mixtures, and by the packing due to the differences in size and shape of molecules. Therefore, the negative VE values can be attributed to strong interactions between the studied alcohols and [BMpyr][dca] ionic liquid. Moreover, the small studied alcohols fit well into the free volume between the relatively large ions of the ionic liquid, resulting in these negative VE values. These negative deviations from ideal behavior are quite usual for binary mixtures alcohol + ionic liquid in which the alcohol has a short chain. As example, negative VE values were also obtained by other authors studying binary mixtures containing small alcohols mixed with ILs such as 1-ethyl-3-methylimidazolium ethylsulfate,10 1-ethyl-3-methylimidazolium trifluoromethanesulfonate,11 1-butyl-3-methylimidazolium tetrafluoroborate,13 imidazolium octanoate,14 2-hydroxyethylammonium acetate,15 1-methylimidazolium acetate,16 and N-octyl-pyridinium nitrate.18 Nevertheless, it is important to remark that the sign of the VE values for this kind of mixtures is quite related to the alcohol chain length, and several papers were found in literature in which the VE values change from negative to positive as the alcohol alkyl-chain length increase.14,16−19 Regarding the effect of the temperature on the excess properties for the studied mixtures, the value of this magnitude decreases; that is, they become more negative when the temperature increases, as seen in figure S2, available as Supporting Information (SI). This behavior is quite usual for this kind of mixtures and several publications were found in literature, in which negative excess molar volumes for binary mixtures alcohol + ionic liquid deviate from the ideality as the temperature increases.10−12,15,19,41 Anouti et al.41 indicate that temperature is a factor that, in alcoholic mixtures, contributes to the contraction. These authors relate this behavior to a special “iceberg structure” of the hydroxyl short molecules which is especially sensitive to globular or linear polar molecules, leading the molecules of the alcohol in the mixture to a greater steric hindrance than the pure alcohol. With the aim of studying the effect of the alcohol on the studied excess properties, the variation of these magnitudes against the molar fraction of alcohol, as well as the Redlich− Kister fits, was plotted in Figure 4 for the binary systems alcohol (1) + [BMpyr][dca] (2) at T = 298.15 K. As can be observed in Figure 4a, the behavior of VE for the binary systems 1-propanol (1), 2-propanol (1), or 1-butanol + [BMpyr]][dca] (2) is quite similar. In all cases, VE values are negative and they present a minimum at high values of the alcohol mole fraction. Comparing the studied systems containing primary alcohols, the obtained results show that the minimum shifts to smaller values of x1 when the alcohol chain increases. This shift of the minimum to higher mole fraction of the ionic liquid was also observed by Vercher et al.,11 who studied volumetric properties of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate with primary alcohols, and Domanska et al.,12 who measured excess molar volumes of binary mixtures of 1-butyl-3-methylimidazolium thiocyanate mixed with 1-heptanol, or 1-octanol, or 1-nonanol, or 1decanol. Furthermore, the mixture containing 2-propanol is the one which presents a larger deviation from ideality, suggesting that

Figure 4. (a) Excess molar volumes, VE and (b) excess molar isentropic compression, KES,m; for the binary systems alcohol (1) + [BMpyr][dca](2) at T = 298.15 K. Symbols: ●, 1-propanol; ▲, 2propanol; and ■, 1-butanol.

the position of the hydroxyl group appears to play an important role on the interactions between the ionic liquid and the alcohol and, therefore, also on the excess molar volume. Similar conclusions can be obtained from the variation of KES,m versus x1, which is plotted in Figure 4b.

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CONCLUSIONS In this study, experimental physical properties (density, speed of sound, refractive index and dynamic viscosity) for 1-butyl-1 methylpyrrolidinium dicyanamide were determined from T = (293.15 to 343.15) K. Moreover, a thermal analysis for the pure ionic liquid was carried out using a differential scanning calorimeter, and the molar isobaric heat capacity was obtained from T = (293.15 to 333.15) K. The VFT equation was used to fit experimental viscosities while the rest of studied properties were fitted to a simple polynomial. All the studied thermophysical properties decrease with the temperature, except the molar isobaric heat capacity. Moreover, densities, speeds of sound and refractive indices for the binary mixtures 1-propanol (1), 2-propanol (1), or 1butanol (1) + [BMpyr][dca] (2) were also measured over the whole composition range at T = (298.15, 313.15, and 328.15) K and atmospheric pressure. G



Article

(8) González, E. J.; González, B.; Calvar, N.; Domínguez, A. Physical properties of binary mixtures of the ionic liquid 1-ethyl-3methylimidazolium ethylsulfate with several alcohols at T = (298.15, 313.15 K, and 328.15) K and atmospheric pressure. J. Chem. Eng. Data 2007, 52, 1641−1648. (9) González, B.; Calvar, N.; González, E.; Domínguez, A. Density and viscosity experimental data of the ternary mixtures 1-propanol or 2-propanol + water + 1-ethyl-3-methylimidazolium ethylsulfate. Correlation and prediction of physical properties of the ternary systems. J. Chem. Eng. Data 2008, 53, 881−887. (10) Lehmann, J.; Rausch, M. H.; Leipertz, A.; Fröba, A. P. Density and excess molar volumes for binary mixtures of ionic liquid 1-ethyl-3methylimidazolium ethylsulfate with solvents. J. Chem. Eng. Data 2010, 55, 4068−4074. (11) 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. (12) Domanska, U.; Królikowska, M. Density and viscosity of binary mixtures of {1-butyl-3-methylimidazolium thiocyanate + 1-heptanol, 1octanol, 1-nonanol, or 1-decanol}. J. Chem. Eng. Data 2010, 55, 2994− 3004. (13) Rilo, E.; Ferreira, A. G. M.; Fonseca, I. M. A.; Cabeza, O. Densities and derived thermodynamic properties of ternary mixtures 1-butyl-3-methyl-imidazolium tetrafluoroborate + ethanol + water at seven pressures and two temperatures. Fluid Phase Equilib. 2010, 296, 53−59. (14) Anouti, M.; Jacquemin, J.; Lemordant. Volumetric properties, viscosities, and isobaric heat capacities of imidazolium octanoate protic ionic liquid in molecular solvents. J. Chem. Eng. Data 2010, 55, 5719− 5728. (15) Alvarez, V. H.; Mattedi, S.; Martin-Pastor, M.; Aznar, M.; Iglesias, M. Thermophysical properties of binary mixtures of {ionic liquid 2-hydroxyethylammonium acetate + (water, methanol, or ethanol). J. Chem. Thermodyn. 2011, 43, 997−1010. (16) Qian, W.; Xu, Y.; Zhu, H.; Yu, C. Properties of pure 1methylimidazolium acetate ionic liquid and its binary mixtures with alcohols. J. Chem. Themodyn. 2012, 49, 87−94. (17) Gómez, E.; Calvar, N.; Macedo, E. A.; Domínguez, A. Effect of the temperature on the physical properties of pure 1-propyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide and characterization of its binary mixtures with alcohols. J. Chem. Thermodyn. 2012, 45, 9−15. (18) Jiang, H.; Wang, J.; Zhao, F.; Qi, G.; Hu, Y. Volumetric and surface properties of pure ionic liquid n-octylpyridinium nitrate and its binary mixtures with alcohols. J. Chem. Thermodyn. 2012, 47, 203− 208. (19) Domanska, U.; Zawadzki, M.; Lewandrowska, A. Effect of temperature and composition on the density, viscosity, surface tension, and thermodynamic properties of binary mixtures of N-octylisoquinolinium bis(trifluoromethylsulfonyl)imide with alcohols. J. Chem. Thermodyn. 2012, 48, 101−111. (20) Vogel, H. The law of the relation between the viscosity of liquids and the temperature. Phys. Z. 1921, 22, 645−646. (21) Fulcher, G. S. Analysis of recent measurements of the viscosity of glasses. J. Am. Ceram. Soc. 1925, 8, 339−355. (22) Tammann, G.; Hesse, W. Z. The dependence of viscosity upon the temperature of supercooled liquids. Anorg. Allg. Chem. 1926, 156, 245−257. (23) Redlich, O.; Kister, A. T. thermodynamics of nonelectrolyte solutions, algebraic representation of thermodynamic properties and the classificacion of solutions. Ing. Eng. Chem. 1948, 40, 345−348. (24) Blahut, A.; Dohnal, V. Interactions of volatile organic compounds with the ionic liquid 1-butyl-1-methylpyrrolidinium dycianamide. J. Chem. Eng. Data 2011, 56, 4909−4918. (25) McHale, G.; Hardacre, C.; Ge, R.; Doy, N.; Allen, R. W. K.; MacInnes, J. M.; Bown, M. R.; Newton, M. I. Density-viscosity

From experimental data, the excess molar volume, and excess molar isentropic compression were calculated and these data were satisfactorily fitted to Redlich−Kister equation. Excess molar volume and excess isentropic compression show a similar behavior. Both properties are negative over the whole composition range and present a minimum at x1 ≈ 0.6. Moreover, both excess properties deviate more strongly from ideality as the temperature increases. Comparing the studied mixtures at the same temperature, it was possible to conclude that the largest deviations from ideality were obtained with the system containing the secondary alcohol.

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ASSOCIATED CONTENT

S Supporting Information *

Temperature dependence of density, speed of sound, viscosity, and refractive index data for the pure ionic liquid [BMpyr][dca]. Excess molar volumes and excess molar isentropic compressions versus alcohol composition for the binary systems alcohol (1) + [BMpyr][dca] (2) at the studied temperatures. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +34 986 812 305. Fax: +34 986 812 380. Funding

The authors are grateful to the Xunta de Galicia (Spain) for financial support through the project 10PXIB314124PR. This work was partially supported by project PEst-C/EQB/LA0020/ 2011, financed by FEDER through COMPETE, Programa Operacional Factores de Competitividade and by Fundaçaõ para a Ciência e a Tecnologia, FCT, (Portugal). B.G. is also grateful to the Comisión Interministerial de Ciencia y Tecnologiá (Spain) for financial support via the Ramón y Cajal Programme (RYC-2008-02388), and E.J.G. is thankful to FCT for his postdoctoral Grant (SFRH/BPD/70776/2010). Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Zhou, F.; Liang, Y.; Liu, W. Ionic liquid lubricants: designed chemistry for engineering applications. Chem. Soc. Rev. 2009, 38, 2590−2599. (2) Quijano, G.; Couvert, A.; Amrare, A. Ionic liquids: applications and future trends in bioreactor technology. Bioresour. Technol. 2010, 101, 8923−8930. (3) Lewandowski, A.; Swiderska-Mocek, A. Ionic liquids as electrolytes for Li-ion batteries - An overview of electrochemical studies. J. Power Sources 2009, 194, 601−609. (4) Tarasova, N. P.; Smetanniko, Y. V.; Zanin, A. A. Ionic liquids in the synthesis of nanoobjects. Russ. Chem. Rev. 2010, 79, 463−477. (5) Han, D.; Row, K. H. Recent applications of ionic liquids in separation technology. Molecules 2010, 15, 2405−2426. (6) Olivier-Bourbigou, H.; Magna, L.; Morvan, D. Ionic liquids and catalysis: recent progress from knowledge to applications. Appl. Catal. A 2010, 373, 1−56. (7) González, E. J.; Alonso, L.; Domínguez, A. Physical properties of binary mixtures of the ionic liquid 1-methyl-3-octylimidazolium chloride with methanol, ethanol, and 1-propanol at T = (298.15, 313.15 K, and 328.15) K and at p = 0.1 MPa. J. Chem. Eng. Data 2006, 51, 1446−1452. H



Article

product of small-volume ionic liquid samples using quartz crystal impedance analysis. Anal. Chem. 2008, 80, 5806−5811. (26) Galán Sanchez, L.; Ribé Espel, J.; Onink, F.; Meindersma, G. W.; de 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. (27) MERCK Ionic liquid brochure. Electrochemistry; Merck: Whitehouse Station, NJ, 2011. (28) MacFarlane, D. R.; Forsyth, S. A.; Golding, J.; Deacon, G. B. Ionic liquids on imidazolium, ammonium and pyrrolidinium salts of the dicyanamide anion. Green Chem. 2002, 4, 444−448. (29) Yu, C.; Shreeve, J. M. Rapid and accurate estimation of densities of room-temperature ionic liquids and salts. J. Phys. Chem. A. 2007, 111, 1456−1461. (30) Riddick, J. A.; Bunger, W. B.; Sakano, T. K. Organic Solvents: Physical Properties and Methods of Purification, 4th ed.; Wiley: New York, 1986. (31) 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. (32) 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. (33) Strechan, A. A.; Paulechka, Y. U.; Kabo, A. G.; Blokhin, A. V.; Kabo, G. J. 1-Butyl-3-methylimidazolium tosylate ionic liquid: heat capacity, thermal stability, and phase equilibrium of its binary mixtures with water and caprolactam. J. Chem. Eng. Data 2007, 52, 1791−1799. (34) Yu, Y. H.; Soriano, A. N.; Li, M. H. Heat capacities and electrical conductivities of 1-n-butyl-3-methylimidazolium-based ionic liquids. Thermochim. Acta 2009, 482, 42−48. (35) Ferreira, A. F.; Simões, P. N.; Ferreira, A. G. M. Quaternary phosphonium-based ionic liquids: Thermal stability and heat capacity of the liquid phase. J. Chem. Thermodyn. 2012, 45, 16−27. (36) Douhéret, 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. Chem. Phys. Chem. 2001, 2, 148−161. (37) Douhéret, G.; Davis, M. I.; Reis, J. C. R.; Fjellanger, I. J.; Vaage, M. B.; Holiand, H. Aggregative processes in aqueous solutions of isomeric 2-butoxyethanols at 298.15 K. Phys. Chem. Chem. Phys. 2002, 4, 6034−6042. (38) Benson, G. C.; Kiyohara, O. Evaluation of excess isentropic compressibilities and isochoric heat capacities. J. Chem. Thermodyn. 1979, 11, 1061−1064. (39) Yaws, C. L. Chemical Properties Handbook. Physical, Thermodynamic, Enviromental, Transport, Safety, and Health Related Properties for Organic and Inorganic Chemicals; McGraw-Hill: New York, 1999. (40) Bevington, P. Data Reduction and Error Analysis for the Physical Sciences; McGraw-Hill: New York, 1969. (41) Anouti, M.; Vigeant, A.; Jacquemin, J.; Brigouleix, C.; Lemordant, D. Volumetric properties, viscosity and refractive index of the protic ionic liquid, pyrrolidinium octanoate, in molecular solvents. J. Chem. Thermodyn. 2010, 42, 834−845.

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Thermophysical Properties of the Pure Ionic Liquid 1-Butyl-1

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