Determination of Infinite Dilution Activity Coefficients of Several

Article pubs.acs.org/jced

Determination of Infinite Dilution Activity Coefficients of Several Organic Solutes in N‑Butylpyridinium Nitrate/N‑Octylpyridinium Nitrate by Blend Inverse Gas Chromatography Xinyu Pan,†,‡ Yali Chen,†,§ Lishuang Deng,†,‡ and Qiang Wang*,†,‡ †

Center for Physical and Chemical Analysis, Xinjiang University, Urumqi 830046, P. R. China Key Laboratory of Coal Cleaning Conversion and Chemical Engineering Process, Xinjiang Uyghur Autonomous Region, College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi, Xinjiang, 830046, P. R. China § Service Center of Public Technology Xinjiang Institute of Ecology and Geography CAS, Chinese Acadamy of Sciences, Urumqi, 830046, P. R. China ‡

S Supporting Information *

ABSTRACT: The miscibility behavior of N-butylpyridinium nitrate/ N-octylpyridinium blends with different compositions was studied using the inverse gas chromatography (IGC) technique. Twenty-one solvents, including alkanes, cycloalkane, aromatic hydrocarbons, alcohols, ethyl ether, acetone, and esters, with different chemical properties were studied to evaluate the interaction between N-alkylpyridinium nitrates and solvents. The interaction parameters of different ionic liquids [ILs] have been calculated. Results were consistent with the activity coefficients at infinite dilution and weight fraction activity coefficient. In addition, the miscibility term ΔH1S was significantly different in each obtained IL blend. The solubility parameters of N-butylpyridinium nitrate/N-octylpyridinium blends were derived using the calculation δ12/(RT) − χ∞ 12/V1 versus δ1 of probes. The altered values of the solubility parameters were consistent with those of the studied ILs based on the methylimidazolium cation.

1. INTRODUCTION Green solvent ionic liquids (ILs) have been extensively studied in both academic and industrial fields. This type of IL has prominent physicochemical properties, such as excellent solvation, low vapor pressure, thermal stability even in high temperatures, wide electrochemical windows, and good thermal conductivity,1−3 which are primarily caused by their ionic inherent nature. However, high viscosity, polarity, and costs of pure ILs limit their application in industrial production. Therefore, the design and synthesis of better ILs that address these challenges are imperative. This study reveals that using a combination of different IL mixtures and other cosolvents reduces IL viscosity and polarity and cuts down costs.4−6 Pyridinium-based ILs are significantly useful in fine-tuning the physicochemical properties of industrial materials by changing the alkyl chain length.7−9 Mixing different ILs changes their extraction properties. These properties affect the capability and selectivity of ILs to separate mixtures. Studying the thermodynamic properties and characteristics of ILs is vital for their applications in various fields, such as pharmaceutical, minerals, and inorganic compounds.10 Furthermore, this study analyzes polymer application and develops simulation tools.11 A series of parameters are used to characterize these systems; the most common of which are the © 2017 American Chemical Society

Hildebrand solubility parameter and IL−solvent interaction parameter. Flory−Huggins theory and the material (2)−material (3) interaction parameter, χ23, which is an extension of the Flory−Huggins theory model, were chosen and have been very helpful in evaluating the interaction between the two components. The dissolution behavior of IL blends was studied by assessing the enthalpic and noncombinatorial entropy of mixing contributions. Both Flory−Huggins and solubility parameters are calculated through intrinsic viscosity measurements, swelling, and inverse gas chromatography (IGC) evaluations.12 However, precisely measuring the properties with the aforementioned techniques is difficult. A suitable technology may be selected to improve the accuracy of results. IGC is useful in studying IL thermodynamic properties. IGC has been used since 1969 in characterizing inorganic materials, polymers, carbon blacks, and other materials.13−16 IGC underwent several improvements and is now used in characterizing ILs and IL blends.17−19 When a liquid solute (probe) is injected into the column, the probe vaporizes and interacts with stationary-phase ILs; thus, Received: March 8, 2017 Accepted: September 6, 2017 Published: September 20, 2017 3095

DOI: 10.1021/acs.jced.7b00244 J. Chem. Eng. Data 2017, 62, 3095−3104

Journal of Chemical & Engineering Data

Article

Table 1. Probe Description Table chemical name n-hexane (n-C6) n-heptane (n-C7) n-octane (n-C8) n-nonane (n-C9) n-decane (n-C10) n-undecane (n-C11) n-dodecane (n-C12) dichloromethane acetone chloroform ethyl acetate tetrahydrofuran ethyl ether carbon tetrachloride methyl acetate cyclohexane benzene toluene o-xylene ethanol methanol N-butylpyridinium nitrate ([Bpy][NO3]) N-octylpyridinium nitrate ([Opy][NO3])

CASRN 110-54-3 142-82-5 111-65-9 111-84-2 124-18-5 1120-21-4 112-40-3 27-63-9 67-64-1 67-66-3 141-78-6 109-99-9 60-29-7 56-23-5 79-20-9 110-82-7 71-43-2 108-88-3 95-47-6 64-17-5 67-56-1

source

initial mole fraction purity

J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. J&K Scientific Ltd. Chengjie Chemical Co. Ltd. Chengjie Chemical Co. Ltd.

0.998 0.985 0.98 0.99 0.98 0.98 0.98 0.995 0.995 0.995 0.995 0.99 0.99 0.995 0.98 0.995 0.995 0.995 0.98 0.997 0.999 0.97 0.97

retention time can then be determined. This method is directly applicable in analyzing mixtures. The material−material interaction parameters of χ23 have been previously studied. These studies determined the interaction of several probes or solvents (1) with each material, χ12 and χ13, and with the blend, χl,i. Taieb Aouak20 studied the miscibility behavior of polybenzyl methacrylate−poly(ethylene oxide) blends at different compositions. Etxeberria21 estimated the interaction parameters of a poly(hydroxy ether of bisphenol A)/poly(vinyl methyl ether) blend. Santos and Guthrie22 analyzed the interaction in multicomponent polymeric systems. In addition, many other researchers obtained the accurate values of IL thermodynamic and physicochemical parameters through IGC.23−25 However, to the best of our knowledge, miscibility and thermodynamic data of mixtures relating to the IL−IL blend are limited.6,26 When designing new ILs, knowledge of several elementary characteristics is important. In the present study, the experimental data were collected using IGC. Analysis results reflected the compatibility of N-butylpyridinium nitrate/N-octylpyridinium blends. Twenty-one solvents were used as solute probes to determine the weight fraction activity coefficient and the Flory−Huggins interaction parameter using the IGC method. Meanwhile, activity coefficients at infinite dilution and solubility parameters at different temperatures were also determined. The results of this evaluation provide a basis for future research on pyridinium-based IL blends.

purification method none none none none none none none none none none none none none none none none none none none none none low pressure, 8h, 363 K low pressure, 8h, 363 K

analysis method

final mole fraction purity

water content

0.999

water content

0.999

On the basis of the IGC technique, the weight fraction activity coefficient (Ω∞ 1 ), molar heat (enthalpy) of the probe absorption in the IL (ΔHS1), molar heat of mixing at infinite dilution (ΔH∞ l ), and the heats of vaporization (ΔHv) for the probes, can be calculated according to literature.28 IGC is a widely used method that is easy to perform. The activity coefficients at infinite dilution γ∞ 12 for solute (1) in a nonvolatile liquid (2), referred to as the IL in this study, is calculated from the solute retention behavior according to the following equation:29 ⎛ n RT ⎞ 2B − V1∞ B − V10 JP0 ln γ12∞ = ln⎜ 2 0 ⎟ − P10 11 + 13 RT RT ⎝ VnP1 ⎠ (1)

In this formula, n2 is the number of moles of the stationaryphase component inside the column, R is the ideal gas constant, and T is the oven temperature. The partial molar volumes of the solutes at infinite dilution and the molar volume are computed as follows: V∞ 1 ≅ V10; B11 is the second virial coefficient of the solute in the gaseous state, which can be calculated through the following equation: B11/Vc = 0.430 − 0.886(Tc/T) − 0.694(Tc/T)2 − 0.0375(n−1)(Tc/T)4.5, where n is the amount of carbon atoms in the probe, and P01 is the probe vapor pressure. B11 and P01 were calculated at temperature T. B13 is the mutual virial coefficient between solute 1 and the carrier gas nitrogen (denoted by “3”); the formula for computing the virial coefficient is as follows:

2. IGC THEORY IGC is generally used to study the infinite dilution in which the interactions between the adsorbed probe molecules are negligible. The specific retention volume Vg0 of a given probe and the net retention volume Vn of the solute are computed based on the calculations from literature.27

Bij Vij

= 0.430 − 0.886 ⎛ Tij ⎞4.5 ⎜ ⎟ ⎝T ⎠

3096

⎛ Tij ⎞2 − 0.694⎜ ⎟ − 0.0375(nij − 1) T ⎝T ⎠

Tij

(2) DOI: 10.1021/acs.jced.7b00244 J. Chem. Eng. Data 2017, 62, 3095−3104


Article

where i is the solute, j is the carrier gas, and n is the effective number of carbon atoms (for normal gas, n is 1; for n-alkanes and n-alkenes, n is the number of carbon atoms contained). On the basis of the IGC solution theory, the Flory−Huggins interaction parameter can be determined from the equation through an IGC experiment.30,31 Similarly, when the column component is an IL blend, eq 3 allows the calculation of the ternary interaction parameter (solute (1)−IL (2)−IL (3)), χ1(23). On the basis of the Scott− Tompa approximation, which describes the ternary system as a simple balance of the corresponding binary systems, the IL−IL interaction parameter χ23 can be calculated as follows:32,33 χ(1)23 = χ12 ϕ2 + χ13 ϕ3 − χ23

V1ϕ2ϕ3 V2

(3)

In this expression, ϕi is the volume fraction of the ILs. In the framework of the Flory−Huggins theory, a reference volume must be defined to calculate the interaction parameter. Thus, the polymer−polymer interaction parameter related to the solvent volume is calculated as follows: ′ χ(1)23 = χ23

V1 V2

(4)

However, previous studies have demonstrated that in these identical experimental conditions of flow, temperature, and inlet and outlet pressure conditions, the IL−IL interaction parameter determination χ23 ′ is significantly simplified with IGC measurement. Only the specific volumes are needed to acquire the ′23 values20,34 in the following condition: ln ′ = χ23

0 V g,b

υb

− ϕ2 ln

0 V g,,2

υ2

− ϕ3 ln

ϕ2ϕ3

0 V g,3

υ3

(5)

0 0 0 In this equation, V g,2 ,V g,3 , and V g,23 are the specific retention volumes for probe in ILs 2, 3, and 23; νi is the molar volume of ILs, which is an additive-specific volume for the IL blend; and Vg,b = w2Vg2 + w3Vg3, where wi is the weight fraction of IL i in the blend. Solubility is widely used to determine interactions. The solubility parameter of the studied material (δ2) can be calculated from the solubility parameter of the probe (δ1) through the following equation:35,36

∞⎞ ⎛ δ2 χ1.2 ⎛ 2δ ⎞ δ2 1 ⎟ = ⎜ 2 ⎟δ1 − 2 ⎜ − V1 ⎠ ⎝ RT ⎠ RT ⎝ RT

Figure 1. Plot of ln V0g versus 1/T for the probes.

chemicals are presented in Table 1. Silicon alkylation 202 monomer support (80−100 mesh) was used as solid support for the ILs in the stationary phase. Dichloromethane was used to dissolve the pure ILs and IL blends (the mass ratios of [Bpy][NO3]/[Opy][NO3] are 1:4,1:1 and 4:1), and removed the redundancy dichloromethane by rotary evaporator. Each solution was then deposited on a weighed amount of solid support. The stationary phase consisted of 10% of the ILs. The support was allowed to equilibrate at T = 333.15 K for 6 h. A stainless steel column (0.2 cm × 150 cm) was washed with acetone prior to use and then prepared for the measurements. Four columns were conditioned (carrier gas and temperature) for approximately 8 h prior to the experiment. The IGC experiments were conducted using Chemstation software (revision B.02.01) and a commercial Hewlett-Packard 6890 gas chromatograph equipped with a flame ionization detector. The injector and detector temperatures were set at 523.15 K during the experiments. Oven temperatures were kept at 333.15, 343.15, 353.15, 363.15, and 373.15 K. High-purity nitrogen with was used as carrier gas to obtain adequate retention times, and the flow rate was 20 mL/min. Methane was used to determine the column holdup time for calculating the net retention time of other probe solvents. Each solvent

(6)

The δ2 is calculated from the slope of a straight line with a slope of 2δ2/RT. The application of the solubility parameter is expanded with IGC.

3. EXPERIMENTAL SECTION The ILs N-butylpyridinium nitrate ([Bpy][NO3]) and N-octylpyridinium nitrate ([Opy][NO3]) investigated in this study were purchased from Chengjie Chemical Co. Ltd., China. All ILs were purified before the experiment. The ionic liquid was further dried under vacuum for 8 h at 363 K to remove trace moisture and volatile chemicals. An analytical-grade homologous series of organic solvents were used without any purification. These were purchased from J&K Scientific Ltd. The names, source, initial mole fraction purity, purification method, final mole fraction purity, analysis method of used 3097



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Table 2. Molar Heat (Enthalpy) of Probe Absorption ΔH1S, and the Molar Heat of Mixing at Infinite Dilution ΔHl∞ between IL Blends and Probes for the Hypothetical Liquid at Zero Pressure and Temperature T = 373.15 Ka −ΔH1S/ (kJ/mol)

ΔHl∞/ (kJ/mol)

n-C6

28.28

−2.338 −3.045 −2.21 −3.202

[Bpy]NO3: [Opy] NO3

n-C7

28.99 28.15 33.75

−3.686 −3.121 −3.853

[Bpy]NO3: [Opy] NO3

n-C8

34.23 33.67 38.97

−3.782 −3.599 −3.79

[Bpy]NO3: [Opy] NO3

n-C9

38.9 38.72 43.85

−3.784 −3.695 −2.849

[Bpy]NO3: [Opy] NO3

n-C10

43.84 43.75 47.28

−3.255 −3.877 −2.269

[Bpy]NO3: [Opy] NO3

n-C11

47.69 48.31 51.05

−2.654 −2.278 −2.039

[Bpy]NO3: [Opy] NO3

n-C12

51.43 51.06 54.91

−2.322 −2.679 −9.054

[Bpy]NO3: [Opy] NO3

dichloromethane

55.2 55.55 32.94

−9.426 −9.694 −7.155

[Bpy]NO3: [Opy] NO3

acetone

33.31 33.58 33.35

−6.643 −7.566 −12.74

[Bpy]NO3: [Opy] NO3

chloroform

32.84 33.76 38.35

−13.5 −13.2 −6.836

[Bpy]NO3: [Opy] NO3

ethyl acetate

39.11 38.81 36.69

IL [Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3

[Bpy]NO3: [Opy] NO3 a

probe 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1

IL

−ΔH1S/ (kJ/mol)

ΔHl∞/ (kJ/mol)

tetrahydrofuran

36.05 37.78 32.37

−6.189 −7.918 6.087

ethyl ether

32.1 33.61 26.61

6.356 4.845 7.501

26.39 32.26 35.56

7.726 1.857 −8.326

methyl acetate

35.39 35.67 34.43

−8.161 −8.438 −6.667

cyclohexane

33.31 35.29 31.41

−5.546 −7.522 −3.709

benzene

30.22 31.64 35.56

−2.521 −3.941 14.63

toluene

35.39 35.71 39.13

14.8 14.48 −6.609

o-xylene

39.17 39.34 43.25

−6.647 −6.824 −16.01

ethanol

43.55 43.45 41.66

−16.31 −16.21 −4.244

methanol

41.45 41.76 38.91

−4.043 −4.351 −5.769

38.69 39.24

−5.555 −6.107

probe 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1 1:1 1:4 4:1

carbon tetrachloride

Standard uncertainties are ur(T) = 0.5 K.

In the cases of the tested n-alkanes, alcohols, esters, and benzenes, V0g increases as the number of carbon atoms of the probes increases. When comparing the V0g of probes with similar boiling points, such as n-C6, and cyclohexane, the lowest value is observed for n-C6. 4.2. Thermodynamic Sorption Parameters. The molar heat (enthalpy) of probe absorption in the IL and ΔH1S and the molar heat of mixing at infinite dilution ΔHl∞ values of [Bpy][NO3]/ [Opy][NO3] were computed. The ΔH1S and ΔHl∞ values in the temperature ranging from 333.15 to 373.15 K are listed in Table 2. The chemical structure of the probes directly affects the molar heat of sorption. As shown in Table 2, with the increasing numbers of methylene groups in the probe molecule, the ΔH1S of the solutes, including n-alkanes, esters, alcohols, and benzenes, also increased. This phenomenon indicated that when the methylene group in the probe molecule was longer, the interaction between the

was injected into the column at least thrice to confirm reproducibility.

4. RESULTS AND DISCUSSION 4.1. Solute−IL Specific Retention Volume. On the basis of the IGC experiments, the retention behavior can be illustrated in diagrams (thermal isotherms) of the IL system. The V0g values of the 21 probes were obtained at a series of temperatures (Supporting Information, Table S1) using eq 1. To generate the retention diagram of the probes, ln V0g was plotted versus T between 333.15 and 373.15 K. For example, in the V0g of 50% [Bpy][NO3]/50%[Opy][NO3] (Figure 1), the V0g of all probes decreased as the temperature increased. The negative slope of the straight-line region is due to the increase in vapor pressure, which is in turn caused by an increase in water temperature. Apart from temperature dependence, V0g values are also affected by the chemical structure of the probes. 3098



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Figure 2. Comparison of γ12∞for mixture ionic liquids at T = 333.15 K.

[Opy][NO3], and [Bpy][NO3]−[Opy][NO3] blends, which are designated as χ12, χ13, and χ1(23), respectively. The interaction between [Bpy][NO3] and [Opy][NO3] is then designated as χ′23. Results show that χ12 obtained from the binary system (solvent 1 IL 2) is different from that of the ternary system (solvent 1 ILs 2 and 3) because of the presence of IL 3; thus, the designation χ13. Consequently, different solvents of known properties of test solutes were injected, and their retention times were recorded to determine the interaction. All the interaction parameters were calculated according to eqs 3−5 at temperatures ranging from 333.15 to 373.15 K. Results for χ12, χ13, and χ1(23) are listed in Table 3. Table 3 shows that the χ of some probes, including dichloromethane, chloroform, acetone, ethyl acetate, toluene, carbon tetrachloride, methyl acetate, and o-xylene, increased as the temperature increased. The χ of the other probes, such as n-C6 to n-C12, tetrahydrofuran, ethyl ether, benzene, cyclohexane, ethanol, and methanol, decreased as the temperature increased. The increase and decrease of the χ may be attributed to the following χ contributions: entropic χs and enthalpic χH.37 The χs contribution is related to the free volume of the solvent, which increased with increasing temperature. The χH contribution is related to the intermolecular forces between the materials and the solvents, which decreased with increasing temperature. The decrease in χ value indicates that IL−solute interactions become stronger; if IL and solute have strong interactions, their solubility is good. Thus, the exothermic reaction has a negative χ value; if the interactions are weak, χ values are likely positive (endothermic) and an immiscible phase will occur. According to Flory−Huggins theory, when the solution is totally miscible, the permissible value is 0.5.38 The values obtained at different temperatures indicate that dichloromethane, acetone, chloroform, o-xylene, ethanol, and methanol are the most compatible of all solvents because their χ1,i are the lowest. Ethyl acetate, carbon tetrachloride, toluene, and methyl acetate are solvents compatible with [Bpy][NO3] and [Opy][NO3]. Finally, as shown in Table 3, the compatibility of n-C6 to n-C12, tetrahydrofuran, ethyl ether, benzene, and cyclohexane

probes and [Bpy][NO3]/[Opy][NO3] is strengthened. Dichloromethane, chloroform, ethyl ether, acetone, ester, and other solvents with comparable boiling points exhibited different ΔH1S values. Results show that polar and hydrogen-bonding solvents, such as ketones and alcohols, present additional interactions with respect to hydrocarbons. 4.3. Activity Coefficients at Infinite Dilution of ILs. In the previous studies, the activity coefficients at infinite dilution γ12∞ of various solutes in ILs were measured. In the present study, the γ12∞ values were calculated according to eq 1. The values of 21 solvents, including alkanes, cycloalkane, benzene, alkylbenzenes, alcohols, and other classical solvents, in the IL blends obtained in temperatures ranging from 333.15 to 373.15 K are listed in Table S3. In Figure 2, the ln γ12∞ in the IL blends describes the function of temperature for all probes investigated. Figure 2 also indicates that at the same temperature, the increasing weight fractions of [Bpy][NO3] causes an increase in γ12∞ of the same solute in the IL blends. This finding clearly indicates that solutes interact weakly with pyridinium-based ILs. Chloroform, dichloromethane, carbon tetrachloride, o-xylene, toluene, benzene, acetone, esters, and alkanols had lower γ12∞ values than C6−C12, tetrahydrofuran, cycloalkane, and ethyl ether. This result shows that the IL blends and solutes had stronger interactions. Furthermore, the interaction between the p-delocalized electrons in aromatics and polar group of the polar solutes and the polar structure of the ILs are enhanced, thereby giving low γ12∞ values. In addition, the polar parts of THF, esters, and acetone strongly interact with polar ILs because oxygen in these compounds has no surrounding blocking group. Ethyl ether, a compound that contains oxygen, has weaker interaction than the above-mentioned polar compounds. However, alcohols containing a hydroxyl group have a strong interaction with the remaining primary hydroxyl group, giving low γ12∞values. 4.4. Miscibility of the IL and IL Pair. The miscibility of the IL and IL pair was studied by assessing the interaction parameters between solutes and pure [Bpy][NO3], pure 3099



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Table 3. Flory-Huggin Interaction Parameter χ∞ 1,i between Probes and Different ILs at Various Temperatures for the Hypothetical Liquid at Zero Pressurea χ∞ 1,i IL [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3

probes n-C6 1:1 1:4 4:1 n-C7 1:1 1:4 4:1 n-C8 1:1 1:4 4:1 n-C9 1:1 1:4 4:1 n-C10 1:1 1:4 4:1 n-C11 1:1 1:4 4:1 n-C12 1:1 1:4 4:1 dichloromethane 1:1 1:4 4:1 acetone 1:1 1:4 4:1 chloroform 1:1 1:4 4:1 ethyl acetate 1:1 1:4 4:1 tetrahydrofuran 1:1

333.15 K

343.15 K

353.15 K

363.15 K

373.15 K

3.245 2.599 2.832 2.522 2.845 2.865 2.247 2.418 2.206 2.629 2.752 2.173 2.323 2.117 2.5 2.691 2.158 2.295 2.131 2.469 2.725 2.254 2.394 2.206 2.552 2.828 2.377 2.517 2.329 2.655 2.889 2.492 2.627 2.445 2.741 −0.4731 −0.4066 −0.2195 −0.4246 −0.3077 −0.5751 0.241 0.3677 0.2329 0.2552 −0.9738 −1.092 −0.8544 −1.119 −0.8794 0.06827 0.5761 0.7287 0.5669 0.6541 2.344 2.217 2.404

3.249 2.589 2.813 2.523 2.82 2.853 2.233 2.405 2.2 2.616 2.742 2.151 2.319 2.113 2.493 2.679 2.149 2.292 2.127 2.464 2.717 2.239 2.379 2.197 2.537 2.808 2.357 2.495 2.315 2.639 2.882 2.473 2.606 2.43 2.728 −0.4288 −0.3554 −0.171 −0.3826 −0.2507 −0.5828 0.2547 0.3934 0.2396 0.2868 −0.9043 −1.019 −0.7702 −1.03 −0.7885 0.04046 0.5907 0.7462 0.568 0.6893 2.382 2.251 2.438

3.231 2.557 2.788 2.5 2.794 2.841 2.214 2.392 2.19 2.603 2.73 2.141 2.314 2.108 2.486 2.667 2.144 2.288 2.123 2.459 2.711 2.222 2.372 2.188 2.513 2.798 2.334 2.481 2.297 2.62 2.877 2.449 2.59 2.41 2.715 −0.3831 −0.3209 −0.1243 −0.3358 −0.2056 −0.5958 0.2695 0.4228 0.2617 0.3097 −0.8273 −0.9371 −0.6863 −0.9395 −0.7032 0.00508 0.6058 0.7697 0.5807 0.7097 2.419 2.270 2.470

3.226 2.532 2.763 2.477 2.77 2.829 2.193 2.38 2.183 2.59 2.718 2.133 2.309 2.102 2.479 2.655 2.137 2.283 2.118 2.454 2.705 2.213 2.354 2.18 2.549 2.779 2.317 2.458 2.285 2.602 2.869 2.431 2.565 2.396 2.702 −0.3396 −0.2785 −0.0888 −0.2864 −0.155 −0.6235 0.2867 0.44 0.2837 0.3384 −0.749 −0.8568 −0.6098 −0.8538 −0.6187 −0.04477 0.6258 0.7917 0.604 0.7527 2.448 2.344 2.482

3.219 2.507 2.739 2.46 2.746 2.816 2.175 2.368 2.175 2.576 2.706 2.124 2.305 2.097 2.473 2.644 2.131 2.279 2.113 2.448 2.699 2.208 2.344 2.172 2.534 2.762 2.304 2.447 2.274 2.585 2.865 2.414 2.552 2.38 2.689 −0.2949 −0.2395 −0.04887 −0.2423 −0.1127 −0.6528 0.3027 0.4612 0.3036 0.3665 −0.6697 −0.7783 −0.5339 −0.7698 −0.5415 −0.1067 0.642 0.8128 0.625 0.7817 2.471 2.363 2.498

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Table 3. continued χ∞ 1,i IL [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3 [Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 [Bpy]NO3:[Opy]NO3 a

probes 1:4 4:1 ethyl ether 1:1 1:4 4:1 carbon tetrachloride 1:1 1:4 4:1 methyl acetate 1:1 1:4 4:1 cyclohexane 1:1 1:4 4:1 benzene 1:1 1:4 4:1 toluene 1:1 1:4 4:1 o-xylene 1:1 1:4 4:1 ethanol 1:1 1:4 4:1 methanol 1:1 1:4 4:1

333.15 K

343.15 K

353.15 K

363.15 K

373.15 K

2.248 1.147 1.957 1.775 2.002 1.724 −0.783 0.6628 0.4321 0.6323 0.4066 0.6076 −0.2643 0.5553 0.6855 0.5399 0.5177 2.596 1.839 2.111 1.879 2.24 0.3808 0.2442 0.3923 0.2189 0.4092 0.613 0.3638 0.514 0.3348 0.5871 0.2247 0.4575 0.6047 0.4203 0.6947 −0.5681 −0.4882 −0.284 −0.486 −0.3891 −0.7313 −0.4792 −0.2588 −0.4416 −0.4473

2.267 1.245 1.911 1.673 2.005 1.717 −0.669 0.6882 0.4649 0.6755 0.4408 0.6539 −0.2974 0.5637 0.7037 0.5303 0.5429 2.57 1.825 2.105 1.825 2.236 0.3929 0.2606 0.4217 0.2377 0.4395 0.6413 0.3773 0.5353 0.3527 0.6079 0.2315 0.4594 0.6175 0.4330 0.7101 −0.5816 −0.5141 −0.2928 −0.4982 −0.3962 −0.7167 −0.4635 −0.2507 −0.4408 −0.4353

2.293 1.334 1.884 1.610 1.990 1.696 −0.576 0.7225 0.4828 0.7134 0.487 0.689 −0.3371 0.5674 0.7235 0.5426 0.5597 2.547 1.807 2.099 1.819 2.232 0.4169 0.2834 0.4535 0.2645 0.4681 0.6629 0.3979 0.5575 0.3762 0.6316 0.2412 0.4474 0.6307 0.4497 0.7249 −0.592 −0.5237 −0.2958 −0.5039 −0.4014 −0.7058 −0.4509 −0.2378 −0.4321 −0.4226

2.318 1.417 1.918 1.642 1.923 1.703 −0.464 0.7515 0.4966 0.7501 0.5272 0.7353 −0.3957 0.5703 0.7425 0.5583 0.5985 2.532 1.801 2.093 1.817 2.228 0.4398 0.3073 0.4760 0.2928 0.5001 0.6812 0.4204 0.5806 0.4031 0.6609 0.2437 0.4951 0.6435 0.4685 0.7409 −0.6007 −0.5303 −0.299 −0.5073 −0.3997 −0.6972 −0.4392 −0.227 −0.4214 −0.4054

2.327 1.488 1.782 1.670 2.019 1.695 −0.372 0.7863 0.5091 0.7877 0.5478 0.7649 −0.4602 0.5757 0.7617 0.5679 0.6274 2.514 1.799 2.086 1.795 2.224 0.4655 0.3330 0.5019 0.3206 0.5236 0.706 0.4438 0.6098 0.4299 0.6895 0.2509 0.5073 0.6624 0.4884 0.7598 −0.607 −0.5342 −0.2982 −0.5084 −0.3994 −0.6848 −0.4301 −0.2162 −0.4068 −0.3913

Standard uncertainties are ur(T) = 0.5 K, and the combined relative standard uncertainty of ur (χ∞ 1,i) = 0.2.

is very low mainly because the increasing χ value reflects the progress of the hardening process. For all weight fractions, the [Bpy][NO3]−[Opy][NO3] interaction parameters χ′23 were calculated according to eq 6 (Table S2). As can be seen from Figure 3, families with interaction force, such as dichloromethane, acetone, ethyl acetate, methyl acetate chloroform, o-xylene, ethanol, and methanol, showed more exothermic χ′23 values. When the weight fraction is 80% [Bpy][NO3]−20%[Opy][NO3], [Bpy][NO3] and [Opy][NO3] are highly compatible. Hydrogen bonds and

dipole−dipole forces have stronger interactions than the dispersive forces. Figure 4 shows as an example the IL−IL interaction parameter χ′23 as a function of the weight percentage of [Bpy]NO3 in the blend using heptane as molecule probe for the three [Bpy][NO3]−[Opy][NO3] mixtures. The data curves show that the χ23 ′ values are strong and closer to 0.8−3.6 in this temperature range. The IL−IL interaction parameter χ′23 decreases weakly and linearly when the temperature increases. Meanwhile, as the weight percentage of [Bpy]NO3 increased, the χ23 ′ value decreased. 3101



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Figure 3. Comparison of χ′23 mixture ionic liquids at T = 333.15 K.

Figure 5. Relation between δ1 and δ12/(RT) - χ∞ 12/V1 of [Bpy]NO3/ [Opy]NO3 = 1:1 at 333.15 K.

Figure 4. IL−IL interaction parametersχ23 ′ of [Bpy]NO3/[Opy]NO3 blend as a function of the weight percentage of [Bpy]NO3 in the blend. The heptane was used as molecule probe.

4.5. Solubility Parameters. Selecting an appropriate solvent for a particular purpose is one of the most imperative concepts in practical applications. The solubility parameters of ILs are important and guide the selection of appropriate solvents for ILs as it works on the basic principle “like dissolves like”.39 This principle means that the closer is the solubility of the parameters, the higher is the compatibility of the solute in a particular solvent. The δ2 for [Bpy]NO3/[Opy]NO3 blends are determined through δ12 RT

−

χ2∞ V1

versus δ1 (Figure 5). To determine the temperature

dependence of δ2 for the [Bpy]NO3/[Opy]NO3 blends, the δ2 values of each IL blend were measured at five temperatures. As shown in Figure 6, the δ2 values decreased as the temperature increased, which fitted an empirical relationship (Table S4, Figure 6). In addition, as can be inferred from Figure 6, the δ2 values of the IL blends were between [Bpy]NO3 and [Opy]NO3 ILs, and they decreased as the [Bpy]NO3 compositions decreased.

Figure 6. Relation between solubility parameter of ILs, δ2, and temperatures.

weight fraction activity coefficient and Flory−Huggins interaction parameter of ILs and IL blends, selected n-C6, n-C7, n-C8, n-C9, n-C10, n-C11, and n-C12; ethyl ether; cyclohexane; and tetrahydrofuran are found to be nonsolvents for

5. CONCLUSIONS Based on the results obtained in this study, the IGC method is suitable for the researched system. From the results of the 3102



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[Bpy]NO3/[Opy]NO3 blends. In addition, the probes dichloromethane, chloroform, ethanol, and methanol are preferred solvents. IGC results also confirmed the miscibility of the binary blend [Bpy]NO3/[Opy]NO3 in the composition range studied. This finding suggests that interactions between [Bpy]NO3 and [Opy]NO3 are relatively high as the weight percentage of [Bpy]NO3 increased. The activity coefficients at infinite dilution χ∞ 12 for 21 polar and nonpolar organic solutes (alkanes, cycloalkanes, aromatic compounds, alcohols, esters, and ketone) at five temperatures were also examined. The solubility parameters δ2 of [Bpy]NO3/[Opy]NO3 blends with different compositions at temperatures ranging from 333.15 to 373.15 K were calculated to be 17.59−19.85 (J·cm −3)0.5.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00244. Specific retention volume, V0g, between probes and [Bpy]NO3:[Opy]NO3(1:1) at different temperatures for the hypothetical liquid at zero pressure; mass fraction activity coefficients Ω1∞of probes at various temperatures of mixture ILs for the hypothetical liquid at zero ′ at various pressure; IL−IL interaction parameter χ23 temperatures for the hypothetical liquid at zero pressure; activity coefficients at infinite dilution γ12∞ of probes at various temperatures of mixture ILs for the hypothetical liquid at zero pressure; solubility parameter δ2 of mixture ILs at various temperatures for the hypothetical liquid at zero pressure (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86 991 8582966. Fax: +86 991 8582966. ORCID

Qiang Wang: 0000-0002-5248-6466 Funding

This work was supported by the National Natural Science Foundation of China under Grant 21366029 and 21566036. Notes

The authors declare no competing financial interest.

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Determination of Infinite Dilution Activity Coefficients of Several

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