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Mutual Solubility of Aromatic Hydrocarbons in Pyrrolidinium and Ammonium-Based Ionic Liquids and Its Modeling Using the CubicPlus-Association (CPA) Equation of State Patricia Fernández Requejo,† Ismael Díaz,‡ Emilio J. González,‡ and Á ngeles Domínguez*,† †

Advanced Separation Processes Group, Department of Chemical Engineering, University of Vigo, Campus Lagoas-Marcosende, 36310 Vigo, Spain ‡ Department of Industrial Chemical Engineering and Environmental, Technical University of Madrid, E-28006 Madrid, Spain S Supporting Information *

ABSTRACT: In this work, the mutual solubility of 30 binary systems {aromatic hydrocarbon (1) + ionic liquid (2)} involving benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene as aromatics and the ionic liquids, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMpyr][NTf2], 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, [BMpyr][TfO], 1-butyl1-methylpyrrolidinium dicyanamide, [BMpyr][DCA], butyltrimethylammonium bis(trifluoromethylsulfonyl)imide, [N4111][NTf2], and tributylmethylammonium bis(trifluoromethylsulfonyl)imide, [N4441][NTf2], were determined in the temperature range of T = (293.15 to 333.15) K at p = 0.1 MPa. The influence of the temperature and the structural characteristics of the aromatic hydrocarbons as well as the effect of the structure of the ionic liquids on the phase behavior was analyzed. A comparison between the experimental LLE of the binary systems presented in this work and those found in literature was also carried out. Finally, all the binary systems were satisfactorily modeled using the Cubic-Plus-Association (CPA) Equation of State (EoS).

1. INTRODUCTION The extraction of aromatic hydrocarbons from the petrochemical streams is one of the main targets of the petrochemical industry1 since the aromatics are used as basic raw materials for the production of many different chemical products.2 However, this separation is challenging because of the presence of azeotropes and components in the mixtures with close boiling points.3,4 Furthermore, the new environmental regulations demand a reduction of the level of sulfur and of the aromatic hydrocarbons in the petrochemical products (gasoline, diesel fuel, or engine oils) to minimize their environmental impact.5,6 Therefore, the design of processes more efficient from an energetic point of view and less dangerous for the environment as well as the search of new solvents to replace the volatile organic solvents used in many industrial processes are two of the targets tackled by the scientific community. In this background, the ionic liquids (ILs) have been proposed as a suitable alternative to the separation agents used in the petrochemical industry because of their advantageous properties such as a negligible vapor pressure which reduces odor problems and atmospheric pollution, high chemical and thermal stability, nonflammability, and the possibility of modifying their physicochemical properties by combining different anions and cations.7−9 Additionally, the ILs present a very low solubility in the hydrocarbons, both aliphatic and © 2017 American Chemical Society

aromatic hydrocarbons, which allows one to reduce the number of steps of the recovery solvent meaning a reduction of the energy consumption of the separation process. However, before applying the ILs as solvents it is essential to know the mutual solubility of the binary mixtures {aromatic hydrocarbon (1) + ionic liquid (2)} since this information is crucial to design any process on an industrial scale. Moreover, phase equilibrium results allow us to enhance our knowledge about interactions between the ILs and other organic compounds. A database of experimental binary liquid−liquid equilibria (LLE) data of different ILs with a broad range of hydrocarbons has been reported. By inspection of the literature available in the Scopus database, most of the references (25) are related to mixtures containing imidazolium-based ILs, while scarce publications about the phase behavior of binary mixtures with ILs based on other cations such as ammonium (3), phosphonium (3), pyridinium (7), pyrrolidinium (6), or quinolinium (7) have been found.10−54 Because of the large number of {aromatic hydrocarbon (1) + ionic liquid (2)} potential mixtures, new solubility studies are needed since the Received: July 20, 2016 Accepted: December 23, 2016 Published: January 10, 2017 633

DOI: 10.1021/acs.jced.6b00655 J. Chem. Eng. Data 2017, 62, 633−642

Journal of Chemical & Engineering Data

Article

Table 1. Specifications of the Pure Compounds Used in This Worka chemical name

CAS no

source

mass fraction purityg

benzene ethylbenzene toluene o-xylene m-xylene p-xylene [BMpyr][NTf2]b [BMpyr][TfO]c [BMpyr][DCA]d [N4111][NTf2]e [N4441][NTf2]f

71-43-2 100-41-4 108-88-3 95-47-6 108-38-3 106-42-3 223437-11-4 367522-96-1 370865-80-8 258273-75-5 405514-94-5

VWR Sigma-Aldrich VWR Sigma-Aldrich Sigma-Aldrich Fluka IoLiTec IoLiTec IoLiTec IoLiTec IoLiTec

≥0.999 ≥0.998 ≥0.998 ≥0.990 ≥0.990 ≥0.990 >0.99 >0.99 >0.98 >0.99 >0.99

purity method analysisg

purification method

GCi

molecular sieves and degassing

NMRj, ICk

vacuum desiccation

water contenth (ppm)

152 114 72 62 77

a Standard uncertainty: u(water content) = 5 ppm. b1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. c1-Butyl-1-methylpyrrolidinium trifluoromethanesulfonate. d1-Butyl-1-methylpyrrolidinium dicyanamide. eButyltrimethylammonium bis(trifluoromethylsulfonyl)imide. fTributylmethylammonium bis(trifluoromethylsulfonyl)imide. gGiven by the suppliers. hMeasured after the purification method. iGas chromatography. jNuclear magnetic resonance. kIon chromatography.

vacuum (p = 0.2 Pa) for at least 48 h prior to use. Once dried, their water content was measured by Karl Fisher tritation (Mettler Toledo C20 Coulometric KF Titrator) with an uncertainty in the measurement of 5 ppm. In order to prevent water absorption, the ILs were kept and manipulated in a glovebox under argon atmosphere. A summary of the specifications of all of the pure compounds used in this work is shown in Table 1. 2.2. Apparatus. All of the samples were prepared by weighing using a Mettler AX-205 Delta Range balance with an uncertainty in the measurement of 3 × 10−4 g. Densities of both pure compounds and mixtures were measured using an Anton Paar DSA-5000 M digital vibrating tube densimeter with an uncertainty in the measurement of 3 × 10−3 g·cm−3 for the pure ILs and 1 × 10−3 g·cm−3 for the remaining samples. These uncertainties were estimated according to the guidelines reported by Chirico et al.65 The calibration of the densimeter was checked with known densities of pure compounds, Mili-Q water, and some alcohols. To ensure the two-phase equilibrium, a PoliScience thermostatic bath with a digital temperature controller was used, and the temperature was controlled with a digital thermometer ASL model F200 with an uncertainty in the measurement of 0.01 K. 2.3. Experimental Procedure. 2.3.1. Solubility Study. In general terms, the solubility of the aromatic hydrocarbons in the ILs increases when the temperature increases; nevertheless, some binary systems show a decrease in the solubility of the aromatics in the ILs when the temperature increases.11−15,52 Therefore, in order to know the influence of the temperature on the solubility of the aromatics in the selected ILs, previously to the LLE determination, a preliminary study of their solubility was carried out. To this end, the solubilities of the six aromatics in the pyrrolidinium and ammonium-based ILs were determined at three temperatures: room temperature, T = 333.15 K and T = 283.15 K, using the “cloud point” method.66 For this, approximately 3 mL of ionic liquid was placed in a vial, and the aromatic was added dropwise until a slight turbidity in the samples was observed at room temperature; then, the compositions of the samples were determined by weighing. Next, the vial was placed into the thermostatic bath at T = 333.15 K. After a few minutes, if the turbidity of the samples disappeared, the corresponding aromatic hydrocarbon was added drop by drop until turbidity was observed again; then,

solubility of aromatic compounds in the ILs affects their use as extraction media. This article is a continuation of our previous works on solubility studies of aromatic hydrocarbons in different ILs.14,55 In this case, the LLE data of 30 binary systems {aromatic hydrocarbon (1) + ionic liquid (2)} were experimentally determined in the temperature range of (293.15 to 333.15) K at p = 0.1 MPa. The aromatic hydrocarbons used were benzene, toluene, ethylbenzene, and the three xylenes isomers, and the ILs selected were ILs containing 1-butyl-1-methylpyrrolidinium as cation combined with the anions bis(trifluoromethylsulfonyl)imide, [BMpyr][NTf2], trifluoromethanesulfonate, [BMpyr][TfO], and dicyanamide, [BMpyr][DCA], and two ammonium-based ILs, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide, [N4111][NTf2], and tributylmethylammonium bis(trifluoromethylsulfonyl)imide, [N4441][NTf2]. These ILs were chosen since both the pyrrolidinium and the ammonium-based ILs present lower toxicity in comparison with that of the imidazolium and pyridinium-based ILs and because their application as extraction agent has been hardly studied in the literature up to date.56−63 Similar systems, some of them with the same ILs studied in this work, have been previously studied by other authors and, therefore, literature LLE data were also taken into account for comparison purposes.27,39,50,52−54 By comparison of the systems reported in this work, the influence of the structural characteristics of both the aromatic hydrocarbons and the ILs as well as the effect of the temperature on the phase behavior were analyzed. Finally, the experimental LLE data were modeled using the Cubic-Plus-Association (CPA) Equation of State (EoS).64

2. EXPERIMENTAL SECTION 2.1. Chemicals. Benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene were procured from different suppliers with purities greater than 0.99 in mass fraction (provided by the suppliers) in all cases. They were degassed using an ultrasonic cleaner BRANSON 3510 and subsequently dried over molecular sieves of 3 × 10−10 m (Sigma-Aldrich). Then, they were kept in bottles under argon atmosphere without any additional treatment. All of the ILs were supplied by IoLiTec GmbH with high purity. The ILs were dried by heating at T = 343.15 K under 634



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Figure 1. Experimental LLE data of the binary systems: (a) {benzene (1) + ionic liquid (2)}, (b) {toluene (1) + ionic liquid (2)}, (c) {ethylbenzene (1) + ionic liquid (2)}, (d) {o-xylene (1) + ionic liquid (2)}, (e) {m-xylene (1) + ionic liquid (2)}, and (f) {p-xylene (1) + ionic liquid (2)} as a function of the mass fraction of the corresponding aromatic hydrocarbon in the IL-rich phase at T = (293.15 to 333.15) K and at p = 0.1 MPa. Dashed lines represent calculated data using the CPA-EoS. Ionic liquids: (◇) [BMpyr][NTf2], (□) [BMpyr][TfO], (○) [BMpyr][DCA], (△) [N4111][NTf2], and (▲) [N4441][NTf2].

in the determination of density vs composition curves involved in the calculation of the phase compositions. 2.3.2. Liquid−Liquid Equilibrium Determination. In order to determine the experimental LLE data, an immiscible mixture of two compounds was placed inside 15 mL glass vials, the total volume of each sample being 12 mL (4 mL of ionic liquid + 8 mL of aromatic hydrocarbon). This mixture was prepared in a glovebox under argon atmosphere and sealed using a rubber cover to avoid losses by evaporation or absorbance of moisture. Then, the vials were vigorously stirred for at least 3 h in order to ensure intimate contact between both phases at T = 293.15 K. Thereafter, they were settled for at least 3 h in a thermostatic

the sample was weighed, and its composition was calculated. If the turbidity of the samples does not disappear when the temperature rises, they were introduced in a thermostatic water bath at T = 283.15 K in order to determine if the solubility increases when the temperature decreases. Taking into account the results obtained in this preliminary study, it can be concluded that the solubility of the aromatic hydrocarbons in the ammonium-based ILs increases when the temperature is increased, while the solubility of the aromatics in the pyrrolidinium-based ILs decreases with the increase in the temperature. In both cases, this dependence of solubility with temperature is very smooth. These behaviors will be considered 635



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bath to ensure complete phase separation. The temperature was controlled using a digital thermometer. Preliminary tests showed that the chosen time of stirring and of settling was enough to guarantee that equilibrium between phases was reached. Next, a sample of each phase was withdrawn using a syringe, the density of both phases was measured at the corresponding temperature, and the compositions were calculated using the polynomial expression previously obtained, as is described below. This procedure was repeated for each studied temperature from T = (293.15 K to 333.15) K, in 5 K steps. The determination of the IL-rich phase composition was carried out by means of measuring the densities and fitting these values versus the composition (ρ vs xi). Thus, prior to the experimental LLE determination, the density of the miscible binary mixtures with known compositions was determined. Bearing the above-mentioned results in mind, the density of the binary mixtures involving the ammonium-based ILs as solvents was measured at T = 343.15 K in order to ensure the complete miscibility of the binary mixtures, while the density of the binary mixtures containing the pyrrolidinium-based ILs was measured at T = 283.15 K and at p = 0.1 MPa for the same reason. The density values of binary mixtures as well as the polynomial expressions for ρ vs xi are shown in Table S1 and Table S2, respectively (Supporting Information). Besides, two binary mixtures were evaluated in order to obtain the error of the technique used for the determination of the solubility curves with the maximum error found being 0.005 in mole fraction. Finally, due to the fact that the tested ILs are practically immiscible in the aromatic hydrocarbons used in this work at the studied temperature range, the absence of ILs in the aromatic hydrocarbon-rich phase was assumed. This fact was checked with the values of the density of the aromatic hydrocarbon-rich phase since they were practically unchanged from those of the corresponding pure compound.

The effects of the structure of the studied aromatics as well as of ILs included in this work on the LLE data are analyzed below. 3.1.1. Influence of Aromatic Hydrocarbons. As can be inferred by comparing the different items in Figure 1a−e, the trend of the solubility of the aromatic hydrocarbons increases according to benzene > toluene > ethylbenzene in all of the studied ILs. This behavior could be due to the steric hindrance of the aromatics, given that the presence of one substituent as well as an increase in the alkyl chain length of the substituent on the benzene ring can increase steric hindrance and lead to a less effective package of the aromatic molecules in the IL-rich phase.52 Regarding the solubility of the xylene isomers in the ILs, the observed general trend is o-xylene > m-xylene ≥ pxylene. The solubility sequence of xylene isomers could be due to the impact on the aromatic induced dipole moment caused by the different positions of the second methyl group.14−17,52 This general trend can be observed in the LLE of all the presented binary systems with the exception of the binary systems involving [N4441][NTf2] in which the solubility of pxylene is much lower than those of the other xylene isomers in this IL. Finally, the general trend observed by many authors for the solubility of the aromatic hydrocarbons in the ILs is benzene > toluene > ethylbenzene > xylenes;14−17,52 nevertheless, the solubility sequence of the aromatics in the studied ILs follows in general the order benzene > toluene > o-xylene > ethylbenzene > m-xylene ≥ p-xylene (see Figure 1 or Table S2). For a better visualization of the conclusions drawn from the results, by way of example, the LLE data of the binary system {aromatic hydrocarbon (1) + [BMpyr][DCA] (2)} are displayed in Figure 2.

3. RESULTS AND DISCUSSION 3.1. Experimental Data. The experimental LLE data for the binary systems {aromatic hydrocarbon (1) + ionic liquid (2)} in the temperature range of T = (293.15 to 333.15) K, every 5 K, and at p = 0.1 MPa are displayed in Figure 1 and reported in Table S2 provided as Supporting Information. Because of the appreciable differences in the molar masses of the studied ILs, the graphical representation of the LLE data was performed in mass fraction, w, instead of molar fraction, x, in order to make a reliable analysis of the different influences. Moreover, as stated above, the studied ILs were assumed practically immiscible in all of the tested aromatic hydrocarbons at the studied temperature range; therefore, only the compositions of the corresponding aromatic hydrocarbon in the IL-rich phase are plotted in the figures presented in this work. The experimental LLE data presented in Figure 1 allow the analysis of the effect of the temperature on the solubility of the aromatics in the ILs. As has been mentioned in section 2.3.1, although the temperature effect on the phase behavior is small, a slight increase in the solubility of all the aromatics in the ammonium-based ILs with an increase in the temperature is observed at the studied temperature range, while a slight decrease in the solubility of the aromatics is found in the pyrrolidinium-based ILs. Despite the fact that this latter behavior is not typical for the binary systems, this trend has been previously reported for other mixtures.11−15,52

Figure 2. Experimental LLE data of the binary systems {aromatic hydrocarbon (1) + [BMpyr][DCA] (2)} as a function of the mass fraction of the corresponding aromatic hydrocarbon in the IL-rich phase: (●) benzene, (■) toluene, (○) ethylbenzene, (◇) o-xylene, (×) m-xylene, and (△) p-xylene at T = (293.15 to 333.15) K and at at p = 0.1 MPa.

3.1.2. Influence of Ionic Liquids. The effect of the structure of the anion and the cation of the ionic liquid on the phase equilibria can be analyzed from results shown in Figure 1. Comparing the solubilities of the aromatics in the pyrrolidinium-based ILs, two different phase behaviors are observed: when the aromatic hydrocarbon is benzene, the order followed by the solubilities is [BMpyr][DCA] > [BMpyr][NTf2] > 636



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[BMpyr][TfO], while when the aromatic hydrocarbon is other than benzene, the sequence followed is [BMpyr][NTf2] > [BMpyr][DCA] > [BMpyr][TfO]. This unusual behavior observed for the binary system involving benzene may be related to the lower molecular mass and molar volume of the [DCA]− anion since the number of ions of ionic liquid in the vicinity of benzene, which is the smallest aromatic hydrocarbons, is higher than that when the ionic liquid contains a [NTf2]− or [TfO]− anion, with higher molar volumes. However, the comparison of the values of the solubility of the aromatic hydrocarbons in the ammonium-based ILs shows that the solubility sequence is [N4441][NTf2] > [N4111][NTf2] for all the studied aromatics. A possible explanation for this behavior is that the interaction between the IL cation and the aromatic is enhanced by the decrease of the IL cation polarity due to the increase of the alkyl chain length. Furthermore, the entropic effects that contribute to increase the solubility (asymmetry and free volume of the IL) are also enhanced by a longer alkyl chain.52 3.2. Comparison with the Literature. The comparison between the experimental LLE data of the binary systems in the temperature range of T = (293.15 to 333.15) K and at p = 0.1 MPa presented in this work and those data found in the literature27,39,50,52−54,56,62,63 are displayed in Figure 3. To our knowledge, only LLE data for the binary systems {benzene, or toluene or ethylbenzene (1) + [BMpyr][NTf2] (2)},56,62 {benzene, or toluene (1) + [BMpyr][TfO] (2)},27 and {benzene, or toluene, or ethylbenzene (1) + [BMpyr][DCA] (2)}52,63 were previously published. 3.2.1. Comparison of Binary Systems with the Same IL. As can be observed in Figure 3, the experimental LLE data of the systems {benzene or toluene (1) + [BMpyr][TfO] (2)} are in agreement with those found in the literature.27 The same conclusion is possible to draw from the comparison of the experimental and reported LLE data of the systems {benzene or toluene or ethylbenzene (1) + [BMpyr][NTf2] (2)} and {benzene (1) + [BMpyr][DCA] (2)}.56,62,63 Otherwise, some discrepancies are observed in the comparison of the experimental solubility data of the binary systems {benzene or toluene or ethylbenzene (1) + [BMpyr][DCA] (2)} with those reported in literature.52 These differences can be due to the different experimental methodology employed to determine the phase compositions. Paduszyński et al.52 determined the compositions of equilibrium using gravimetry. 3.2.2. Comparison of Binary Systems with the Same Alkyl Chain Length of the IL Cation. The comparison of the experimental LLE data for the systems {benzene or toluene (1) + [BMpyr][TfO] (2)} with those reported for the systems {benzene or toluene (1) + [BMim][TfO] (2)},27 {benzene or toluene (1) + [BM3py][TfO] (2)}27 are presented in Figure 3a,b. The solubilities of the aromatic hydrocarbons follow the order [BMpyr][TfO] ≈ [BMim][TfO] < [BM3py][TfO], both for benzene and for toluene. In the case of the comparison of the systems {benzene or toluene or ethylbenzene (1) + IL (2)} the ILs being [BMpyr][NTf2] and [BM4py][NTf2],39 it can be concluded that the solubility of the three aromatics is lower in [BMpyr][NTf2] than in its pyridinium-based homologue. 3.2.3. Comparison of Binary Systems with Different IL Anions. The influence of the anionic nature of the IL on the solubility of the aromatic hydrocarbons can be analyzed comparing the systems containing benzene, toluene, and ethylbenzene as aromatics and the ILs [BMpyr][NTf2], [BMpyr][TfO], [BMpyr][DCA], [BMpyr][TCM],50 [BMpyr]-

Figure 3. Experimental LLE data of the binary systems: (a) {benzene (1) + ionic liquid (2)}, (b) {toluene (1) + ionic liquid (2)}, and (c) {ethylbenzene (1) + ionic liquid (2)} as a function of the mass fraction of the corresponding aromatic hydrocarbon in the IL-rich phase at the 637



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mixtures {aromatic hydrocarbon (1) + ionic liquid (2)} were obtained from the experimental LLE data. Parameter estimation was carried out using the maximum-likelihood objective function and the Britt-Luecke minimization algorithm.71 The CPA-EoS combines a typical cubic term (SRK) with an association term for the calculation of compressibility factor (Z):

Figure 3. continued studied temperatures and at p = 0.1 MPa. Ionic liquids: (□) [BMpyr][TfO] (this work), (○) [BMpyr][DCA] (this work), (◇) [BMpyr][NTf2] (this work), (■, gray) [BMpyr][TfO],27 (●, gray) [BMpyr][DCA],52 (●) [BMpyr][DCA],63 (▲, gray) [BMpyr][NTf2],62 (◆) [BMpyr][NTf2],56 (■) [BMim][TfO],27 (◪) [BM3py][TfO],27 (◆, gray) [BM4py][NTf2],39 (▽) [BMpyr][TCM],50 (△) [BMpyr][FPA],53 and (▼, gray) [BMpyr][TCB].54

Z = Z cubic + Z assoc

[FPA],53 and [BMpyr][TCB].54 By inspection of Figure 3, it can be inferred that the solubility of benzene follows the order [BMpyr][FPA] < [BMpyr][TfO] < [BMpyr][NTf 2 ] < [BMpyr][DCA] < [BMpyr][TCM] < [BMpyr][TCB], while the order followed for the solubilities of toluene and ethylbenzene is [BMpyr][FPA] < [BMpyr][TfO] < [BMpyr][DCA] < [BMpyr][NTf2] < [BMpyr][TCM] < [BMpyr][TCB]. Furthermore, it is important to comment that the effect of the temperature on the LLE data is rather small for all the studied binary systems and the systems found in the literature. Nevertheless, the dependence of the solubility of the aromatics with the temperature in the binary systems involving the IL [BMpyr][FPA] is significant, given that an increase in the temperature leads to an increase in the solubility of benzene, toluene, and ethylbenzene in this IL. As can be observed in Figure 3, the solubility of benzene and toluene is lower in [BMpyr][FPA] than in the remaining ILs at low temperatures, whereas higher solubilities are found when the temperature is increased. When the aromatic hydrocarbon is ethylbenzene, the solubility values in [BMpyr][FPA] are lower than those obtained for the rest ILs in the comparison. 3.3. Thermodynamic Modeling Using the CPA-EoS. The experimental LLE data were modeled using the CPA-EoS originally developed by Kontogeorgis et al.64 This model has demonstrated a good ability to correlate phase equilibria data for mixtures involving ILs.67−69 Data fitting was carried out using the data regression tool implemented in a commercial process flow sheet simulator (Aspen Plus). First, pure component parameters were obtained by fitting density and vapor pressure, and then binary interaction parameters of the

(1)

Z cubic =

vm a − vm − b RT (vm + b)

Z assoc =

∑ xi ∑ ρi ∑ ⎢⎢⎜⎜ i

Ai

(3)

∑ ∑ xixjaij i

b=

⎤ 1 1 ⎞ δX A i ⎥ − ⎟⎟ 2 ⎠ δρi ⎥⎦ ⎣⎝ X A i ⎡⎛

i

a=

(2)

(4)

j

∑ xibi

(5)

i

aij =

aiaj (1 − kij)

ai = a0i(1 + c1i(1 −

(6)

Tri ))2

(7)

where ρ is the molar density, R is the universal gas constant, a and b are the SRK parameters, vm is the mixture molar volume, xi is the mole fraction of component i, XAi is the fraction of sites of type A at molecule i that does not form any bonds with other active sites, and Tri is the reduced temperature of the component i. This fraction is calculated as X Ai =

1 (1 + ρ ∑i xi ∑ B X BjΔA iBj )

(8)

j

with ⎤ ⎡ ⎛ ε A iBj ⎞ ΔA iBj = bijβ A iBjg (ρ)⎢exp⎜ ⎟ − 1⎥ ⎦ ⎣ ⎝ RT ⎠

(9)

Table 2. CPA Pure Component Parameters Aromatic Hydrocarbon parameter

benzene

toluene

mm Pcm (bar) Tcm (K) εAiBj (K) βAiBj ρ deviation Pv deviation

0.7703 55.02 572.8 0.0 0 toluene > o-xylene > ethylbenzene > m-xylene ≥ p-xylene. Moreover, the analysis of the influence of the change of the anion of the ionic liquid shows that the solubility decrease in the order [BMpyr][NTf2] > [BMpyr][DCA] > [BMpyr][TfO] for all of the studied aromatics with the exception of the solubility of benzene that follows the order [BMpyr][DCA] > [BMpyr][NTf2] > [BMpyr][TfO]. Regarding the effect of the

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