Separation of 2-Phenylethanol from Water by LiquidâLiquid Extraction

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Separation of 2-Phenylethanol from Water by LiquidLiquid Extraction with Ionic Liquids: New Experimental Data and Modeling with Modern Thermodynamic Tools Kamil Paduszy#ski, Urszula Maria Domanska, Marek Królikowski, and Agnieszka Wróblewska Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b00375 • Publication Date (Web): 28 Apr 2016 Downloaded from http://pubs.acs.org on May 6, 2016

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Industrial & Engineering Chemistry Research

Separation of 2-Phenylethanol from Water by Liquid-Liquid Extraction with Ionic Liquids: New Experimental Data and Modeling with Modern Thermodynamic Tools Urszula Domańska,†,‡ Kamil Paduszyński,∗,† Marek Królikowski,† and Agnieszka Wróblewska† † Department of Physical Chemistry, Faculty of Chemistry Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland ‡ Thermodynamic Research Unit, School of Chemical Engineering University of KwaZulu-Natal, Howard College Campus, King George V Avenue, Durban 4001, South Africa E-mail: [email protected]

Phone: +48 (22) 234 56 40

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Abstract In this work, ionic liquids (ILs) are proposed as candidates for extractive removal of 2phenylethanol (PEA) (well-known rose-like aroma compound) from its aqueous solutions. Four ILs based on different cations, namely, 1-hexyl-1-methylpyrrolidinium, 1-hexyl-1,4-diaza [2.2.2]bicyclooctanium, 1-(2-methoxyethyl)-3-methylimidazolium and 1-(2-methoxyethyl)-1methylpyrrolidinium, and bis(trifluoromethylsulfonyl)imide anion were under study. Thermodynamic data at ambient pressure are presented for pure ILs (including temperature-dependent density data and thermal characterization with DSC) as well as for binary systems {IL + water} and ternary systems {IL + PEA + water}. For the binary systems, (liquid + liquid) equilibrium phase diagrams were determined in temperature range T = (280–370) K. For ternary systems, (liquid + liquid) equilibrium was investigated at T = 308.15 K. An impact of the cation structure on the studied properties is established. The data obtained are discussed in terms of the selectivity and distribution ratio of separation of PEA from water. modeling of the measured properties with two modern chemical engineering thermodynamic tools, namely, non-random two liquid (NRTL) model and perturbed-chain statistical associating fluid theory (PC-SAFT), is demonstrated. The NRTL model is applied in a purely correlative fashion in the case of both binary and ternary systems. In turn, predictive capacity of the PC-SAFT is tested for ternary (liquid + liquid) equilibrium using the combining rules corrections transferred from binary data.


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Introduction Due to the new US Food and Drug Administration and European legislations, production of 2phenylethanol (phenyl ethyl alcohol, PEA) has attracted attention of a growing number of publications concerned with new and alternative solvents. Products obtained by biotechnological methods can be considered natural if the substrate used for the production process is of natural origin. 1,2 However, natural PEA, extracted from the rose’s flowers is very expensive. On the other side, chemically synthesized PEA from benzene or styrene is restricted to be used in food, beverages and cosmetics. 3 Recently, excellent review on an alternatives methods of production of PEA was presented. 1 In particular, in situ product removal techniques seem to be very promising. In this type of methods, selection of the suitable solvent is important for easy and effective removal of a given solute from the aqueous phase, for a minimum loss of the biocatalytic ability, and for easy recovery from entrainer. Thus far, several solvents have been tested in PEA bioproduction, e.g. oleic acid, oleyl alcohol, miglyol, isopropyl myristate, and polypropylene glycol 1200. In particular, oleic acid and S. cerevisiae strain at T = 308.15 K during a long time turned out to be the best extraction system. 1 It was confirmed by recently published data of new solubility measurements of PEA in alcohols, eicosane and oleic acid. 4 Decanol and oleic acid were chosen as the best solvents for PEA extraction and were used in bioproduction using S. cerevisiae strains. The synergistic effect of PEA production can be observed by addition of ethanol to synthesis and the aqueous/organic two-phase bioconversion system succeeded in obtaining high overall PEA production. 5 The nature of ionic liquids (ILs) provides many unique physical and chemical characteristics (e.g. negligible vapor pressure, non-flammability, high solvating capacity), attractive from the point of view of numerous applications. Since the use of volatile organic solvents (VOCs) as extraction media in PEA/water separations may cause significant contamination in industry-scale technologies, the ILs are also perceived as substitute materials for such liquid-liquid extraction process. The requirements of a suitable IL for the separation of PEA are the good or even complete miscibility with PEA and low solubility of water in the IL. This is usually achieved by considering the IL, which interacts strongly with polar OH group of PEA and aromatic rings 3 ACS Paragon Plus Environment


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via the n–π or π–π interactions. Therefore, the mutual solubilities of ILs and PEA/water are essential for the design and development of separation process. Piperidinium-, ammonium- and imidazolium-based ILs with hydrophobic bis(trifluoromethylsulfonyl)imide ([NTf2 ]) anion were used the first time by Sendovski et al. 6 to show an increase of the PEA recovery capability. With regard to the ILs potential application in PEA/water separation process, solubility of 1-hexyl3-methylpyridinium triflate, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate and N-octylisoquinolinium bis(trifluoromethylsulfonyl)imide in PEA has been recently measured in our laboratory and reported. 7,8 The PEA/water partition coefficients for the ILs under consideration were measured and the results revealed that only isoquinolinium-based IL is suitable for the extraction of PEA with a high selectivity. 7 Additionally, the solubilities of other eight ILs based on piperidinium, imidazolium, quinolinium and isoquinolinium cations in PEA and water were presented. 9 The most interesting one was the IL based on 1-hexyl-1-methylpiperidinium cation and [NTf2 ] anion exhibiting complete miscibility with PEA and large miscibility gap with water. 9 Much more important and useful information about the possibility of the separation is the selectivity and the distribution ratio obtained from the ternary (liquid + liquid) equilibrium measurements. In particular, it has been reported by us that the selectivity of the extraction of PEA from water at temperature T = 298.15 K obtained with N-octylisoquinolinium bis(trifluoromethylsulfonyl)imide was higher than 1000. 8 Recently, an interesting review of applications and mechanism of ILs in whole-cell biotransformation was reported by Fan et al. 10 It was shown, that the structure of the IL plays an important role in the enzyme or yeast activity in biotransformation. Unfortunately, rather the old-generation ILs were mentioned. By addition of 1-butyl-3-methylimidazolium tetrafluoroborate to biocatalysis of reduction of (Z)−C6 H5 CH−CXC(−O)CH3 (X = Cl, Br) using S. cerevisiae strains, the better

diasteroselectivity and enantioselectivity was obtained than in pure water. 11 The old work of yeast-

mediated ketone production has shown that 1-butyl-3-methylimidazolium hexafluorophosphate in IL/water biphasic system exhibited less aggregation than in toluene/water system, which is positive for bioconversion. 12 For instance, the hydrophilic imidazolium-based ILs were tested in the pre-


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treatment of lignocellulosic biomass in the context of second-generation of bioethanol production using S. cerevisiae strains. 13 The main problem of this investigation was the toxic effects of ILs to the yeast, in particular the better tolerance was shown by 1-ethyl-3-methylimidazolium methylphosphonate than by 1-ethyl-3-methylimidazolium acetate. 13 Thus, to choose suitable IL is important from many points of view. First, IL has to be strongly hydrophobic to be a good entrainer for the extraction of PEA from the aqueous phase. Furthermore it has to disclose a good biocompatibility with the cells and preferably has to be biodegradable. Based on the presented review one can claim that the selection of the ILs for the bioproduction of PEA is an important scientific activity. That is why we follow our previous papers 4,7–9 and proceed with this kind of research. The aim of this work is to investigate (liquid + liquid) equilibrium phase diagrams of mixtures of four new hydrophobic ILs with water and PEA. The ILs under study are based on four distinct cations, namely, 1-hexyl-1-methyl-pyrrolidinium, 1-hexyl-1,4diaza[2.2.2]bicyclooctanium, 1-(2-methoxyethyl)-3-methylimidazolium and 1-(2-methoxyethyl)1-methylpyrrolidinium, and all of them have in their structure [NTf2 ] anion. These cation-anion combinations were selected based on the results of preliminary screening for ILs which are completely miscible with PEA and disclose very low solubility in water. Besides, an impact of cation structure on the investigated properties is elucidated. From the experimental tie-lines data collected for ternary systems selectivity and the distribution ratio are determined and discussed in terms of extraction of PEA performance. Additionally, pure-fluid properties such as liquid density as function of temperature and thermal characterization of pure ILs are reported. Aside of the experimental data, significant part of this work comprises modeling of the obtained phase equilibrium diagrams using modern thermodynamic tools, namely, non-random two liquid (NRTL) model and perturbed-chain statistical associating fluid theory (PC-SAFT).



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Experimental Chemicals Chemical structures of cations and anion of the ILs under consideration in this paper are shown in Figure 1. Chemical names, abbreviations, CAS number, suppliers are as follows: 1-hexyl1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide, [C6 C1 Pyr][NTf2 ] (380497-19-8, synthesized in our laboratory; preparation, 1 H NMR and

13 C

NMR spectra and elementary anal-

yses are given in the Supporting Information), 1-hexyl-1,4-diaza[2.2.2]bicyclooctanium bis(trifluoromethylsulfonyl)imide, [C6 DABCO][NTf2 ] (898256-50-3, Io-Li-Tec), 1-(2-methoxyethyl)3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C2O1 C1 Im][NTf2 ] (178631-01-1, Io-LiTec) and 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C2O1 C1 Pyr][NTf2 ] (757240-24-7, Merck). Purity of all the ILs was > 0.99 mass fraction. The samples were dried for 24 h at temperature around T = 300 K under reduced pressure to remove volatile impurities and trace water. 2-Phenylethanol, PEA (CAS No. 60-12-8, > 0.99 mass fraction purity), was purchased from Merck. The sample was stored over freshly activated molecular sieves of type 4A (Union Carbide). Doubly distilled and degassed water (PURE LAB Option Q Elga Water System) was used in the phase equilibrium determinations. The density of water was ρ = 0.9984 g · cm−3 and conductivity, κ = 8 µS (at T = 293.15 K). The water content of the chemicals used was determined by means of Karl-Fischer titration. The sample of IL or PEA (was dissolved in anhydrous methanol and titrated with steps of 0.0025 cm3 . Each determination was repeated three times and the results were reproducible within 10 ppm. The final values of mass fraction water contents are as follows: 450 ppm for [C6 C1 Pyr][NTf2 ], 270 ppm for [C6 DABCO][NTf2 ], 250 ppm for [C2O1 C1 Im][NTf2 ], 160 ppm for [C2O1 C1 Pyr][NTf2 ], 130 ppm for PEA. All the experimental methods were applied at atmospheric pressure P = 0.1 MPa. During the weeks of the study, the pressure was stable within 10 kPa. 6 ACS Paragon Plus Environment

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Differential Scanning Calorimetry The basic thermal characteristics of ILs, i.e. melting point and melting enthalpy, temperature of glass transition were measured using a differential scanning calorimetry technique (DSC). All the experiments were performed in heating mode. The applied scanning rate was +5 K · min−1 , with power and recorder sensitivities of 16 mJ · s−1 and 5 mV, respectively. The apparatus (DSC 1 STARa System with Liquid Nitrogen Cooling System purchased from Mettler Toledo) was calibrated with a 0.999999 mass fraction purity indium sample. The repeatability of the melting temperature and glass transition temperature value was 0.1 K, whereas in the case of melting enthalpy it was 0.1 kJ · mol−1 .

Density The density of ILs and solvents was measured at ambient pressure using an Anton Paar GmbH 4500 vibrating-tube densimeter in temperature range T = (288.15–363.15) K with 5 K interval. The densimeter takes into account an automatic correction for the viscosity of the sample. The apparatus resolution was 0.00001 g · cm−3 , and the uncertainty of the measurements was estimated to be 0.0005 g · cm−3 .

Phase Equilibria in Binary Systems The (solid + liquid) and (liquid + liquid) phase equilibrium determinations were carried out at atmospheric pressure with dynamic (synthetic or visual) method, which is described in detail elsewhere. 14 The heterogeneous sample {IL + PEA or water} was prepared at room temperature by weighing. Uncertainty of the mass determination was 0.0001 g, what resulted in combined uncertainty of mole fraction of the mixture at the level of 0.0005. Then, it was heated very slowly (< 2 K · h−1 ) with continuous stirring inside a Pyrex glass cell placed in bath. The thermostat was filled up with water, or acetone with dry ice depending of the range of temperature. The temperature of the



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disappearance of solid or one of the two liquid phases, detected visually, were measured with a calibrated electronic thermometer P 550 (DOSTMANN electronic GmbH) with the probe totally immersed in the water bath. The uncertainty of the phase transition temperature measurement was 0.1 K. The dynamic method was not applicable at very low mole fraction of the IL (< 0.0001) mainly because of uncertainties of the initial samples and extremely high slope of the equilibrium curve. Therefore, static methods based on spectrophotometric (for [C6 DABCO][NTf2 ]) and conductometric (for [C2O1 C1 Im][NTf2 ] and [C2O1 C1 Pyr][NTf2 ]) determination of of IL content were applied in this range of composition. The experimental solubility of [C6 DABCO][NTf2 ] in water was determined by UV-Vis spectrophotometry. The samples of heterogeneous IL-water solutions were prepared by weighing. To about 5 cm3 of water IL was added in such amount so that two liquid phases could be readily detected visually (approx. 0.1–0.5 g of IL). These mixtures were placed into a jacketed glass cell with a volume of 10 cm3 , together with a coated magnetic stirring bar, and properly closed to avoid losses by evaporation or absorption of moisture from the atmosphere. The temperature within the cell was maintained constant by using a thermostatic water bath with coupled with Lauda Alpha A6 temperature control system stabilizing temperature within 0.1 K. The mixtures were stirred for 8 h to reach thermodynamic equilibrium and then the system was allowed to settle for a minimum of 12 h (overnight) to ensure that the equilibrium state was reached. After phase separation, approximately 2.5 cm3 of water-reach phase was carefully taken using glass syringe with coupled stainless steel needle. The sample was mixed with a known amount of 2-propanol (in 6:1 volume ratio) to ensure a complete miscibility. Then the {dilutent + water-rich phase} mixture was finally moved to a quartz cuvette (path length 10 mm). The reference cuvette was filled with the mixture of water and 2-propanol in the same volume proportion as the sample. The probes were analyzed by Perkin Elmer Lambda 25 spectrophotometer at constant temperature (within 0.1 K) by using the spectra recorded between 190 and 240 nm. The calibration curve was determined based on reference aqueous solutions of IL (0.01 g of IL per 5–25 g of water, depending on the concentration


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of the IL in the solution to be obtained), with 2-propanol added in the same ratio as in the analyzed samples. Photometric accuracy (NIST 930D Filter 1A) obtainable with the used spectrophotometer is 0.1%. Absorbance corresponding to the chosen wavelength λ = 201.3 nm was used to construct the ordinates of the calibration curve. The overall uncertainty in IL mole fraction was estimated to be at the level of 10−6 . The solubility of [C2O1 C1 Im][NTf2 ] and [C2O1 C1 Pyr][NTf2 ] in water was determined by a conductometric method, because these ILs do not absorb in the UV-Vis range. Equilibration procedures were the same as in the case of spectrophotometric method. The conductivity of the aqueous solution was measured using a Mettler Toledo FiveEAsy FE 30, coupled with an LE 703 Conductivity Probe as the electrode. In this method, 4 cm3 of the water-rich phase was taken out from the equilibrium glass vials and was mixed with a known amount of 2-propanol (complete miscibility with ILs) in a mass ratio of 1 : 4. Prior to the measurements, the calibration curves were performed for each IL in an adequate concentration range and containing the same amount of 2-propanol. Each stock solution was prepared gravimetrically within 0.0001 g and at least 2 calibration curves were determined for each IL and to confirm that no gravimetric errors occurred during the preparation of each stock solution. Solubility results, at each temperature, are the average of three measurements of individual samples. Conductivity relative uncertainty is 0.5%. The uncertainty of mole fraction solubility determined was at the level of 10−5 .

Phase Equilibria in Ternary Systems The (liquid + liquid) phase equilibrium in ternary systems {IL + PEA + water} is represented by the tie-lines inside the immiscibility range, i.e. the lines connecting mole fraction compositions of IL-rich and water-rich phases. In this work, the equilibrium compositions at T = 308.15 K were determined with gas chromatography (GC). Two-phase ternary samples were prepared by weighing within 0.0001 g and placed in a thermostated jacketed glass cell within a volume of 10 cm3 . The cell was properly closed to avoid losses by evaporation, or pickup of moisture from the atmosphere. The jackets were connected to a 9 ACS Paragon Plus Environment


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thermostatic water bath (LAUDA Alpha A6) to maintain a constant temperature of T = 308.15 K. The uncertainty of temperature measurements was 0.1 K. The mixtures were stirred for 6 h and then allowed to settle for minimum of 12 h to reach the thermodynamic equilibrium. Next, the sample about (0.1–0.3) ·10−3 cm−3 from both phases were taken using glass syringes with coupled stainless steel needles. Sample was placed in an ampoule of a volume of 2 cm3 and the ampoule was closed with septum cap. Acetone (1.0 cm3 ) was added to the samples to avoid phase splitting and to maintain a homogeneous mixture. The ILs reveal very low vapor pressure, thus they cannot be analysed by GC. Therefore, only PEA and water were analysed, whereas the mole fraction of the third component (IL) is then determined from the mass balance. The composition was analysed by GC chromatograph (Perkin Elmer Clarus 580 GC) equipped with auto sampler and FID and TCD detectors. The capillary column of the chromatograph was protected with an pre-column to avoid the non-volatile IL reaching the column in case of leak from the glass wool in the liner. The TotalChrom Workstation software was used to obtain the chromatographic areas for the PEA, water and internal standard (1-butanol was used in this work). Samples were injected three times, and the average value was calculated. Details of the operational conditions of the apparatus are reported in Table S1 in the Supporting Information. The estimated uncertainty in the determination of mole fraction compositions is 0.003 for compositions of the water-rich phase and 0.005 for compositions of IL-rich phase.


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Modeling Phase Equilibria Calculations Thermodynamic phase equilibrium condition requires equality of activities of all the components in all the phases present in the system. In the case of (solid + liquid) equilibrium in binary system {IL (1) + PEA, or water (2)} (where IL act as pure solid phase in equilibrium with the saturated solution), the following simplified relationship between the solubility of IL x 1 and temperature can be derived: ∆m H10 1 * − 1 + − ln γ1 ln x 1 = − 0 R , T Tm,1 -

(1)

0 where R is the universal gas constant, Tm,1 and ∆m H10 denote melting temperature and enthalpy of

pure IL, respectively, and γ1 is the activity coefficient of IL in the saturated solution. Given T, x 1 can be solved numerically. If γ1 = 0 irrespective of T and x 1 , then eq (1) transforms into ideal solubility equation. In the case of binary (liquid + liquid) equilibrium in system {IL (1) + PEA, or water (2)}, the equilibrium condition is usually written as:

x ′1 γ1′ = x ′′1 γ1′′,

(2a)

(1 − x ′1 )γ2′ = (1 − x ′′1 )γ2′′,

(2b)

where x ′1 and x ′′1 denote the IL’s mole fractions in IL-rich and water-reach phase, respectively, whereas the γ’s correspond to activity coefficients of the respective components (given in subscripts) in both phases. The system of equations given in eq (2) can be solved with respect to x ′1 and x ′′1 , when the system temperature T and pressure P are given. In the case of ternary system {IL (1) + PEA (2) + water (3)}, there are four unknowns, namely



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x ′1 , x ′2 , x ′′1 and x ′′2 . Given T and P they can be obtained from the following system of equations: x ′1 γ1′ = x ′′1 γ1′′

(3a)

x ′2 γ1′ = x ′′2 γ2′′

(3b)

(1 − x ′1 − x ′2 )γ3′ = (1 − x ′′1 − x ′′2 )γ3′′

(3c)

z1 = x ′1 β + x ′′1 (1 − β)

(3d)

z2 = x ′2 β + x ′′2 (1 − β)

(3e)

Eqs (3a) to (3c) represent thermodynamic equilibrium condition, whilst Eqs (3d) and (3e) formulate the overall material balance of the IL and PEA distribution between the phases. Symbols z1 and z2 stand for the initial (“feed”) mole fractions of IL and PEA, respectively, and 0 ≤ β ≤ 1 denote the IL-rich phase molar ratio. Thus, finally there are five unknowns present in five relationships given in eq (3). In this work, in-house functions and subroutines coded in Matlab (Mathworks Inc.; ver. 2014b) were used to solve the systems of equations given in eqs (2) and (3).

Thermodynamic Models Activity coefficients required in eqs (2) and (3) can be calculated by using diverse thermodynamic models, in particular excess Gibbs energy (GE ) models, or equations of state (EoS). An example of GE -based model is the well-known non-random two-liquid (NRTL) model developed by Renon and Prausnitz. 15 This model is based on the following expression for the activity coefficient of the i-th component in C-component mixture:

ln γi =

PC

j=1 x j τji G ji PC j=1 x j G ji

+

C X j=1

x j Gi j PC

k=1 x k G k j

PC k=1 x k τk j G k j + *τi j − P C k=1 x k G k j ,

(4)

where Gi j = exp(−αi j τi j ). The model involves binary interaction parameters τi j , τji and nonrandomness parameters αi j = α ji . Thus, there are three parameters of the NRTL model per a pair 12 ACS Paragon Plus Environment

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of components i and j. The non-randomness parameters are usually set as constants, whereas the binary interaction parameters are temperature-dependent. In this work, we adopted the following formula:

τi j = ai j + bi j τji = a ji + b ji

! 1 1 + ci j (T − T0 ) − T T0 ! 1 1 + c ji (T − T0 ) − T T0

(5a) (5b)

where T0 = 308.15 K. The parameters ai j , a ji , bi j , b ji , ci j , c ji are usually obtained by means of fitting them to binary phase equilibrium data, e.g. (vapor + liquid), or (solid + liquid), or (liquid + liquid) equilibrium. This makes the NRTL model a correlative rather than predictive approach. Details regarding NRTL modeling of the systems considered in this work are summarized in the following subsection. A modern molecular-based EoS-based approach applied in this work is the perturbed-chain statistical associating theory (PC-SAFT) proposed by Gross and Sadowski. 16,17 In this model, thermodynamics of a system is expressed as residual Helmholtz free energy Ares , which is assumed to be a sum of several contributions that can be assigned to different types of intermolecular interactions: Ares = Ahc + Adisp + Aassoc + . . .

(6)

Superscripts “hc”, “disp” and “assoc” in eq (6) refer to the hard-chain formation contribution, contribution due to dispersive van der Waals forces, and association, respectively. Detailed expressions for each contribution can be found elsewhere. 16,17 In this paper we only provide a brief summary of the model parameters. In terms of the PC-SAFT molecules of the i-th component of the mixture are pictured as molecular chains built of mi spherical segments of diameter σi , interacting via square-well potential of a depth ui /kB . In the case of associating components, additional parameters defining the strength



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of specific interactions between sites Ai and Bi are introduced, namely, the energy ε Ai Bi /kB and volume κ Ai Bi of association. These parameters are usually obtained by fitting the PC-SAFT calculations to pure-fluid properties like vapor pressure or liquid (saturated or compressed) density. In the case of ILs the vapor pressures are usually unavailable and hence other properties like the Hildebrand’s solubility parameters (δH ) can be employed. 18–20 For mixtures, cross-terms reflecting interactions between dislike molecules appear in the PC-SAFT equations. These parameters, namely, ui j /kB , σi j , ε Ai B j /kB , κ Ai Bi , are typically estimated by using Lorentz-Berthelot (LB) and Wolbach-Sandler (WS) combining rules: √ ui j = ui u j 1 − kiLB j σi + σ j σi j = 2 Ai Bi ǫ + ǫ Aj Bj Ai B j 1 − kiWS ǫ = j 2 ! √ p σi σ j 3 Ai B j A B A B j j i i κ κ = κ σi j

(7a) (7b) (7c) (7d)

WS where kiLB j and ki j are the binary corrections that need to be adjusted to binary data. The advantage

of the PC-SAFT over the NRTL is that the binary parameters shown in eq (7) can be adjusted to binary data other than these under study. In particular, we have evidenced previously 19–22 that phase equilibria in binary and ternary systems with ILs can be accurately calculated with the binary corrections obtained from infinite dilution activity coefficients. In order to achieve better accuracy of the PC-SAFT correlations or predictions, the binary corrections are assumed to be temperature dependent. For example, a simple linear relationship between kiXj (where X = LB or WS) can be proposed: kiXj = ai j + bi j (T − T0 )

(8)

where T0 is a reference temperature, in this work set as 308.15 K. Details for the way of determination of coefficients ai j and bi j are presented in the following section. 14 ACS Paragon Plus Environment

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Finally, the PC-SAFT activity coefficient of a given component is calculated as a ratio of fugacity coefficients of this component in a mixture and in its pure state, γi = ϕi /ϕi0 , wheras the fugacity coefficients are obtained from differentiation of Ares with respect to mole fractions, according to the general thermodynamic formula: res

RT ln ϕi = A

∂ Ares + (Z − 1) − ln Z + ∂ xi

!

T, ρ,x j,i

−

C X j=1

xj

∂ Ares ∂xj

!

(9) T, ρ,x k,j

where Z stands for compressibility factor (Z = P/ρRT) and ρ is the system’s molar density.

Strategies for the Parameters Determination For the investigated systems {IL (1) + PEA (2) + water (3)}, the NRTL parameters τ12 , τ21 , τ13 , τ31 , τ23 , τ32 need to be determined. Of course, different sets of parameters accounting for different types of phase equilibrium data could be determined. However, we decided to obtain a single set of internally consistent NRTL parameters according to the procedure as follows. First, the temperature-dependent parameters τ13 and τ31 , actually, the coefficients given in eqs (5a) and (5b), were obtained by fitting them to binary (liquid + liquid) equilibrium data for systems {IL (1) + water (3)}. In turn, the parameters τ23 and τ32 corresponding to system {PEA (2) + water (3)} were fitted to (liquid + liquid) equilibrium data published by Stephenson and Stuart. 23 Finally, the parameters τ12 and τ21 (with b12 , c12 , b21 and c21 fixed as 0) were adjusted to ternary (liquid + liquid) equilibrium data. In the case of the PC-SAFT, pure-fluid parameters of ILs and PEA were determined first. For ILs, they were fitted to experimental data of liquid density reported in this work and the Hildebrand’s solubility parameters (δH ) obtained from experimental infinite dilution activity coefficients of various molecular solvents in IL (γ ∞ ) reported in literature. 24–27 Detailed procedure for transforming γ ∞ into δH can be found elsewhere. 28 A full list of the obtained values of δH is given in Table S2 in the Supporting Information. To model the ILs, we applied “5 + 5” associating scheme following our previous papers concerning [NTf2 ]-based ILs. 21 The parameters for PEA were ad15 ACS Paragon Plus Environment


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justed to saturated liquid densities and vapor pressures taken from DIPPR database 29 in reduced temperature range from 0.5 to 0.9 (20 equidistant data points). “1 + 1” (2B) association scheme corresponding to a single hydroxyl group was adopted for PEA. The fitting procedure was based on non-linear least squares method minimizing relative relative differences between calculated and experimental properties. Finally, the parameters for water modelled with the “2 + 2” scheme (4C) were taken from literature. 30 The binary corrections included in the PC-SAFT model were obtained similarly as in the case LB and k WS were fitted to (liquid + liquid) equilibrium of the NRTL model, i.e., the parameters k13 13 LB and k WS were fitted to the literature data for data for {IL (1) + water (3)} systems, whereas k23 23

{PEA (2) + water (3)}. In turn, the parameter related to the interactions between ILs and PEA were ∞ ) at T = 308.15 K. The procedure adjusted to infinite dilution activity coefficient of PEA in ILs (γ2,1

rests on a numerical solution of the following equation:

∞ γ2,1

=

ϕ∞ 2,1

(10)

ϕ02

X with ϕ∞ 2,1 depending on k 12 , where X = LB or WS and the fugacity coefficients are obtained from LB or k WS allowed to apply the PC-SAFT in an eq (9). Then, the estimated binary correction k12 12

entirely predictive fashion in ternary (liquid + liquid) equilibrium modeling. Unfortunately, the ∞ experimental data of γ2,1 were not available and therefore, the predicted values were employed.

Linear solvation-energy relationship (LSER) correlations derived from γ ∞ data for each IL indi∞ ; the procedure as well as the resulting LSER models vidually were used to estimate the value of γ2,1 ∞ are summarized in Table S3 in the Supporting Information. For and the calculated values of γ2,1 ∞ [C6 C1 Pyr][NTf2 ], the value of γ2,1 at T = 308.15 K was additionally predicted with modified UNI-

FAC (Dortmund) model using the parametrization of Hector and Gmehling. 31 For the remaining ILs this was not possible because of a lack of appropriate UNIFAC group assignments. In order to check an influence of the type of binary correction (i.e. LB or WS) fitted, we adopted five distinct modeling strategies when attempting to reproduce ternary (liquid + liquid) equilibrium


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LB WS phase diagrams with the PC-SAFT: (0) pure predictions with k12 = k12 = 0; (1) predictions with LB fitted to γ ∞ obtained from LSER; (2) predictions with k WS fitted to γ ∞ obtained from LSER; k12 2,1 2,1 12 LB fitted to γ ∞ obtained from UNIFAC; (2a) predictions with k WS fitted to (1a) predictions with k12 2,1 12 ∞ obtained form UNIFAC. Of course, the strategies (1a) and (2a) were tested only for systems γ2,1

with [C6 C1 Pyr][NTf2 ] IL. The binary parameters determinations were carried out by means numerical optimization of the following objective function:

min f (p) = p

N C−1 X X i=1 j=1

2 xˆ ′j,i − x ′j,i + g 2

2 xˆ′′j,i − x ′′j,i

(11)

where p is the vector of the parameters, x j,i denotes mole fraction of j-th component of the mixture for the i-th tie-line, the “hat” correspond to the calculated values, N stands for the number of tie-lines, C stands for the number of components, ′ and ′′ denote IL-rich and water-rich phases, respectively, and g is the scaling factor incorporated in order to avoid a bias in the objective function caused by the differences in the order of magnitude of IL-rich and water-rich mole fractions. Accuracy of the fits or predictions were assessed with average absolute deviation (AAD) between calculated and experimental mole fractions, defined as: XX 1 xˆ′ − x ′ + xˆ′′ − x ′′ . j,i j,i j,i N (C − 1) i=1 j=1 j,i N C−1

AAD =


(12)


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Results and Discussion Experimental Data Thermal Properties of ILs The thermal properties, i.e. normal melting temperature (Tm0 ), normal enthalpy of fusion (∆m H 0 ) and glass transition temperature (Tg ), obtained from DSC analyses of four ILs are listed in Table 1. DSC thermograms of the investigated ILs are shown in Fig. S1 in the Supporting Information. To our best knowledge, the values of ∆m H 0 for [C6 C1 Pyr][NTf2 ] and [C6 DABCO][NTf2 ] are reported in the open literature for the very first time. On the other hand, the values of Tm0 and Tg for [C6 C1 Pyr][NTf2 ] are in good agreement available reference data extracted from literature. 32–35 In general, the investigated ILs form liquid phase at relatively low temperature. This is also a very important characteristic of a candidate for solvent for extractive purposes. In particular, the melting temperature of [C6 DABCO][NTf2 ] is about 7.5 K higher than that of [C6 C1 Pyr][NTf2 ]. It is also noteworthy that the Tg of [C6 DABCO][NTf2 ] is also much higher compared to other ILs. Density The experimental densities (ρ) of pure ILs as a function of temperature are given in Table S4 in the Supporting Information and plotted in Figure 2. It is evidenced that the density follows the trend: [C6 C1 Pyr][NTf2 ] < [C6 DABCO][NTf2 ] < [C2O1 C1 Pyr][NTf2 ] < [C2O1 C1 Im][NTf2 ]. Furthermore, the data reported in this work are in good agreement with the literature data. 32,33,36–48 For [C6 C1 Pyr][NTf2 ], our data agree with the data by Appetecchi et al. (single data point; measurement priciple not specified) within 0.17%, 45 with the data by Jin et al. (single data point; measured with a pycnometer) within 0.91%, 32 and with the data by Nebig and Gmehling (measured with vibrating U-tube densimeter) within 0.24%. 36 For [C6 DABCO][NTf2 ], our data agree with the data by Marcinkowski et al. (measured with vibrating U-tube densimeter) within 0.43%. 37 The most significant data scatter was observed for [C2O1 C1 Im][NTf2 ]. For this IL, only several data points measured with different techniques were found. The deviations between our data and 18 ACS Paragon Plus Environment

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the data reported by Bonhote et al., 38 Zhang et al., 39 Bara et al. 40 and Shimojo et al. 41 are much higher compared to [C6 C1 Pyr][NTf2 ] and [C6 DABCO][NTf2 ], namely, 5.6%, 8.8%, 5.1% and 3.1%, respectively. It is difficult to explain the observed differences, because for the reference data purity of the sample (e.g. water content) was not always stated. Besides, the mentioned authors used much less accurate experimental techniques to measure density. Finally, for [C2O1 C1 Pyr] the data published in this work and the litrature data are in excellent agreement: Wu et al. (0.06%), 42 Regueira et al. (0.05%), 43 Gacino et al. (0.10%), 44 Appetecchi et al. (0.07%), 45 Zhou et al. (0.04%), 46 Marciniak and Królikowski (0.04%) 47 and Belhocine et al. (0.03%). 48

Binary Systems We checked all the ILs studied in this work exhibit complete miscibility with PEA over wide range of temperature. On the other hand, it was observed that all the considered ILs exhibit immiscibility in the liquid phase when mixed with water. Naturally, this is a necessary condition for the extraction of PEA from its aqueous solutions. The measured solubility curves of [C6 DABCO][NTf2 ] in PEA and water are shown in Figure 3, whereas the data are listed in Table S5 in the Supporting Information. These data can be very useful when designing operating conditions for the extraction process employing ILs (e.g. to avoid the IL precipitation). As can be seen, the IL is better soluble in PEA compared with water. Based on the collected (solid + liquid) equilibrium data one can also observe that the system with PEA basically does not deviate from the ideal behavior. This explains complete miscibility of the ILs under study with PEA. In the case of systems with water, the deviations from ideality are strongly positive what confirmed by the miscibility gaps observed when studying (liquid + liquid) phase behavior. (Liquid + liquid) equilibrium phase diagrams for the binary systems {IL + water} are shown in Figure 4. All the experimental data points are listed in Table S6 in the Supporting Information. The data for both IL-rich and water-rich phases for the system {[C6 C1 Pyr][NTf2 ] + water} were taken from literature. 49 As can be easily noted, all the investigated ILs disclose similar phase behavior and an influence of the cation structure of the phase diagram is not so significant. In particular, 19 ACS Paragon Plus Environment


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phase diagrams with an upper critical solution temperature (UCST) were observed for all systems. However, the UCSTs were too high to be determined by means of the dynamic method. The largest miscibility gap was observed for [C2O1 C1 Pyr][NTf2 ]. In particular, solubility of water in IL increases in the following order: [C6 C1 Pyr][NTf2 ] ≈ [C2O1 C1 Pyr][NTf2 ] < [C2O1 C1 Im][NTf2 ] < [C6 DABCO][NTf2 ]. Due to the high hydrophobic nature of [NTf2 ] anion, the solubility of the studied ILs in water is very low, namely, of the order of 0.001 of mole fraction. An impact of the cation on the solubility is as follows: [C6 C1 Pyr][NTf2 ] < [C6 DABCO][NTf2 ] < [C2O1 C1 Pyr][NTf2 ] < [C2O1 C1 Im][NTf2 ]. Ternary Systems The experimental (liquid + liquid) equilibrium tie-line endpoints of the four ternary systems {IL (1) + PEA (2) + water (3)} at T = 308.15 K and ambient pressure are reported in Table S7 in the Supporting Information. The data are plotted in a form of the Gibbs triangular charts in Figure 5. Based on the data presented, one can observe that in the investigated (liquid + liquid) equilibria, the water-rich phase is basically a pure water. Within uncertainty of the analysis methods applied, the mole fractions of IL and PEA in this phase are very close to zero. This result regarding ternary system is consistent with the binary (liquid + liquid) equilibrium data for {IL + water} reported in this work, as well as with the data for {PEA + water} measured by Stephenson and Stuart. 23 The area of miscibility gap follows the trend of binary data for the systems {IL + water} discussed above. A slight inflection of the binodal curves can be seen in Figure 5. In particular, the binodal curve tends to be concave for lower PEA concentrations as the ternary system approaches the binary system {IL + water}, and concave at low IL concentrations as the ternary system is closer to the binary system {PEA + water}. The feasibility of the entrainer to perform considered PEA/water extraction is quantitatively evaluated by using two common parameters: PEA/water selectivity (S23 ) and PEA distribution


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ratio ( β2 ) defined as: x ′′2 /x ′2 x ′′3 /x ′3 x ′′ β2 = 2′ x2

(13a)

S23 =

(13b)

In further text, we discuss the extractive performance of the studied ILs in terms of average values of β2 and S23 over all the tie-lines measured for a given system. In general, the separation in the system PEA/water, described by the average selectivity is quite high, varying from 293 to 424 for different ILs. For all systems the values of S23 change from the first tie-line via the middle of the area of measures tie-lines to the last one. Our average selectivity results for these four ternary systems at T = 308.15 K increase in the following order: [C2O1 C1 Pyr][NTf2 ] (S23 = 293) < [C6 DABCO][NTf2 ] (S23 = 347) < [C2O1 C1 Im][NTf2 ] (S23 = 394) < [C6 C1 Pyr][NTf2 ] (S23 = 424). The average selectivity for [C6 C1 Pyr][NTf2 ] (424) is more than two times lower then that for N-octylisoquinolinium bis(trifluoromethylsulfonyl)imide ([C8 iQuin][NTf2 ]), 8 but this is quite attractive result for new technologies. The selectivity observed for the ILs with the alkyl chains attached to the cation core, does not differ crucially from the ILs with the oxygen atom incorporated into the cations’ substituents. This is in contrast with the thiophene/heptane separations, for which more significant effect of such cation functionalization was observed. 47 Distribution ratio of PEA ( β2 ) over the two equilibrated liquid phases at T = 308.15 K is similar for the two measured ILs, namely, [C6 C1 Pyr][NTf2 ] (157) and [C6 DABCO][NTf2 ] (155), with slightly smaller value for [C2O1 C1 Im][NTf2 ] (143). The lowest average value was observed for [C2O1 C1 Pyr][NTf2 ] (109). Larger distribution ratios was observed previously for [C8 iQuin][NTf2 ] (> 200). 8 It may be a result of weaker interaction between the cation and anion in that IL and higher interaction with PEA molecules (e.g. via π–π stacking). That is why the [C8 iQuin][NTf2 ] IL is capable of “absorbing” more PEA molecules compared to the ILs investigated in this work.



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Modeling The NRTL model was applied to both binary and ternary (liquid + liquid) equilibrium data as a correlative tool. The resulting parameters τi j and τji (actually, the coefficients defining their temperature dependence) and the final values of AAD are given in Table 2. The experimental versus correlated binodal curves for binary systems {IL + water} (parameters τ13 and τ31 fitted) are shown in Figure 4. As can be seen the model is capable of accurate representing the measured data over the entire range of temperature studied. In particular, both IL-rich and water-rich curves of the phase diagram are captured very accurately and the AAD of equilibrium mole fraction is at the level of 0.001. This is explained by the applied temperature-dependence of the parameters. In fact, we checked that worse correlations (e.g. not describing the variation of the slope in the water-rich phase composition against temperature) were obtained when omitting the second or the third term in eq (5). It is noteworthy that we additionally performed NRTL correlations of the literature data for {PEA + water}. 23 The parameters τ23 and τ32 associated with this system are also given in Table 2. Finally, ternary (liquid + liquid) equilibrium tie-lines were reproduced by the NRTL model by adjusting the parameters τ12 and τ21 . Please note that this parameters are temperature-independent and they are valid only at T = 308.15 K. Based on the values of AAD listed in Table 2, it is seen that these data can be accurately reproduced by the model using only the two parameters, not six at it is usually carried out and reported. The PC-SAFT approach also disclosed a good correlative and predictive abilities when used to model the investigated properties. First of all, the model parametrisation of pure ILs and PEA was performed and the resulting pure-fluid constants are shown in Table 3. It can be noted that the PC-SAFT combined with the proposed association scheme is able to reproduce both liquid density and Hildebrand’s solubility parameters of ILs with average absolute relative deviation below 1%. The experimental versus the PC-SAFT calculated properties of pure ILs are shown in Figure 6. In the case of PEA, an acceptable fit of saturated liquid density and vapor pressure found in DIPPR database 29 was obtained as well. In Figure 4, the correlative power of the PC-SAFT approach against the NRTL is also confronted. 22 ACS Paragon Plus Environment

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The model parameters used to calculate the presented phase diagrams are listed in Table 4. As seen, by using temperature-dependent binary corrections, see eq (8), AAD at the level 0.005 can be achieved regardless of the ILs. The recommended correlations for the system {PEA (2) + water (3)} are as follows: LB k23 = 0.0503 + 3.59 ·10−4 (T/K − 308.15)

(14a)

WS k23 = −0.0358 − 5.40 ·10−5 (T/K − 308.15)

(14b)

with AAD between calculations and experimental data 23 equal to 0.0023. It should be also noted from Figure 4 that NRTL and PC-SAFT represent different qualitative phase behavior. In particular, NRTL tends to reveal the phase diagrams with both upper and lower critical solution temperature, whereas in the case of the PC-SAFT only the UCST is predicted by the model. This is a result of different numbers of adjustable parameters adopted in NRTL and PCSAFT modeling (6 and 4, respectively). In the case of NRTL, the idea was to provide parameters that will reproduce the experimental data as accurately as possible. On the other side, the number of binary parameters as low as possible was desired to be included in our PC-SAFT calculations to test the predictive capacity of this more physically sound approach in ternary systems. In fact, a key problem challenged in this work was modeling of ternary phase diagrams with the PC-SAFT, using solely the pure-fluid and binary data. We have just shown that the systems {IL + water} and {PEA + water} were nicely represented by the model. As discussed above, different LB and k WS were proposed. The complete list strategies for the estimation of binary corrections k12 12

of the obtained parameters (including corresponding to them values of AAD) is summarized in Table 5. As can be seen pure PC-SAFT predictions yield in relatively low values of AAD, even < 0.01 for some systems. In our opinion, this a satisfactory result taking into account complexity of the systems modelled and the simplicity of the molecular schemes used to represent them. Nevertheless, different strategies can be perceived as optimal, depending on the system considered. For the system with [C6 C1 Pyr][NTf2 ] a slight improvement is accuracy is observed when using



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∞ the binary corrections fitted to LSER-predicted γ2,1 (strategies 1 and 2). In particular, the “WS”

correction seems to be more relevant for this system. On the other hand, the corrections obtained ∞ = 0.581 at T = 308.15 K predicted by the modified UNIFAC (Dortmund) 31 (strategies from γ2,1

1a and 2a) resulted in worse predictions, even compared with the “conventional” predictions with LB WS k12 = k12 = 0 (strategy 0). For the ternary systems involving [C6 DABCO][NTf2 ], the results

were basically the same irrespective of the modeling strategy applied. This is a surprisingly result confirming a significant predictive power of the PC-SAFT approach. In turn, for the systems with [C2O1 C1 Im][NTf2 ] and [C2O1 C1 Pyr][NTf2 ] the strategies 1 and 2, respectively, seem to be the best ones. Exemplary calculations for ternary (liquid + liquid) equilibrium are given in Figure 7. In particular, the predictions for ternary system {[C6 DABCO][NTf2 ] + PEA + water} are plotted in WS obtained from LSER- or UNIFACFigure 7a, whereas an impact of the binary correction k12 ∞ is illustrated in Figure 7b. To keep the phase diagram clear, the tie-lines were not predicted γ2,1

plotted in Figure 7. The model predicts extremely low solubility of IL and water and PEA in water so that, the experimental and the calculated tie-lines have basically the same slope. Showing where the calculated tie-lines end is the most informative so that the binodal curves are given only. Unfortunately, this is not a trivial task to unequivocally judge which strategy is the best. As seen from Table 5 that the obtained values of AAD are similar for different systems (with a few exceptions). However, the corrections based on LSER-calculated activity coefficients seem to result in more accurate representation of the phase diagrams. Furthermore, since the difference between LB and WS corrections are basically unnoticeable, one can finally recommend an application of more “traditional” Lorentz-Berthelot cross-terms. This is mainly due to the fact that they are much easier to be implemented in the commercial software for process simulation.


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Concluding Remarks On the basis of the investigated binary (solid + liquid) and (liquid + liquid) equilibrium phase diagrams, we conclude the ILs proposed seem to be very interesting candidates for the extraction of PEA from aqueous phase. The ILs exhibit complete miscibility with PEA and wide miscibility gaps with water. Relatively high values of selectivity in PEA/water separations as well as PEA distribution ratio were obtained. Besides, an impact of the cation of IL on the (liquid + liquid) phase equilibrium was established. Based on the average values of extractive parameters, we conclude that [C6 C1 Pyr][NTf2 ] is the most promising IL for potential recovery of PEA from its aqueous solutions. We also demonstrated the NRTL and the PC-SAFT models as interesting thermodynamic tools for modeling of the investigated properties. In particular, the NRTL was confirmed to be an effective correlative equation for both binary and ternary (liquid + liquid) equilibrium data for systems composed of ILs and molecular solvents. In particular, it was shown that the parameters fitted to binary data can be transferred to represent the ternary tie-lines. In turn, the PC-SAFT approach turned out to be a very promising predictive model for ternary (liquid + liquid) equilibrium when used with the parameters adjusted solely to pure-fluid and binary properties. However, performance of this model depends on the adopted modeling strategy, including the type of binary correction to be fitted and the source of the binary data used to adjust it. Summing up, this study should be perceived as a another step in understanding both experimental and theoretical aspects of possible applications of ILs as new entrainers for modern extraction technologies. We hope that the experimental data and modeling results shown will be useful for chemical engineers in design and optimization of processes involving the compounds studied.



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Supporting Information Available Details for synthesis of [C6 C1 Pyr][NTf2 ]; Figure S1 showing DSC thermograms of the studied ILs; Table S1 presenting operational conditions for GC analyses; Tables S2 and S3 summarizing some additional data applied in the PC-SAFT modeling; Tables S4–S7 presenting all the experimental data points collected in this study.

This material is available free of charge via the Internet at

http://pubs.acs.org/.

Acknowledgement Funding for this research was provided by the project of National Science Center in Poland for years 2015-2018, No. 2014/15/B/ST5/00136. Dr. Maciej Zawadzki is acknowledged for the synthesis of [C6 C1 Pyr][NTf2 ] ionic liquid.


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(34) Furlani, M.; Albinsson, I.; Mellander, B.-E.; Appetecchi, G. B.; Passerini, S. Annealing Protocols for Pyrrolidinium Bis(trifluoromethylsulfonyl)imide Type Ionic Liquids. Electrochim. 2011, 57, 220–227. (35) MacFarlane, D. R.; Meakin, P.; Amini, N.; Forsyth, M. Structural Studies of Ambient Temperature Plastic Crystal Ion Conductors. J. Phys.: Condens. Matter 2001, 13, 8257–8267. (36) Nebig, S.; Liebert, V.; Gmehling, J. Measurements and Prediction of Activity Coefficients at Infinite Dilution (γ ∞ ) Vapor-Liquid Equilibria (VLE) and Excess Enthalpy (H E ) of Binary Systems with 1,1-Dialkyl-pyrrolidinium Bis(trifluoromethylosulfonyl)imide Using Mod. UNIFAC. Fluid Phase Equilib. 2009, 277, 61–67. (37) Marcinkowski, L.; Kloskowski, A.; Namieśnik, J. Physical and Thermophysical Properties of 1-Hexyl-1,4-diaza[2.2.2]bicyclooctanium Bis(trifluoromethylsulfonyl)imide Ionic Liquid. J. Chem. Eng. Data 2014, 59, 585–591. (38) Bonhote, P.; Dias, A.-P.; Papageorgiou, N.; Kalyanasundaram, K.; Grätzel, M. Hydrophobic, Highly Conductive Ambient-Temperature Molten Salts. Inorg. Chem. 1996, 35, 1168–1178. (39) Zhang, J.; Fang, S.; Qu, L.; Jin, Y.; Hirano, S. Synthesis, Characterization, and Properties of Ether-Functionalized 1,3-Dialkylimidazolium Ionic Liquids. Ind. Eng. Chem. Res. 2014, 53, 16633–16643. (40) Bara, J. E.; Gabriel, C. J.; Lessmann, S.; Carlisle, T. K.; Finotello, A.; Gin, D. L.; Noble, R. D. Enhanced CO2 Separation Selectivity in Oligo(ethylene glycol) Functionalized Room-Temperature Ionic Liquids. Ind. Eng. Chem. Res. 2007, 46, 5380–5386. (41) Shimojo, K.; Kamiya, N.; Tani, F.; Naganawa, H.; Naruta, Y.; Goto, M. Extractive Solubilization, Structural Change, and Functional Conversion of Cytochrome c in Ionic Liquids via Crown Ether Complexation. Anal. Chem. 2006, 78, 7735–7742.



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Figure 1. Chemical structures of the cations and anion of ILs considered in this work: (1) 1-hexyl1-methylpyrrolidinium cation, [C6 C1 Pyr]; (2) 1-hexyl-1,4-diaza[2.2.2]bicyclooctanium cation, [C6 DABCO]; 1-(2-methoxyethyl)-3-methylimidazolium cation, [C2O1 C1 Im]; 1-(2-methoxyethyl)1-methylpyrrolidinium cation, [C2O1 C1 Pyr]; bis(trifluoromethylsulfonyl)imide anion, [NTf2 ].



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Figure 2. Density (ρ) of the ILs under study at P = 0.1 MPa as a function of temperature (T) reported in this work (empty markers) and in literature (filled markers). Markers correspond to experimental data, according to the key: circles, [C6 C1 Pyr][NTf2 ]; 32,33,36 squares, [C6 DABCO][NTf2 ]; 37 triangles, [C2O1C1 Im][NTf2 ]; 38–41 diamonds, [C2O1 C1 Pyr][NTf2 ]. 42–48 Solid lines designated by linear fits of ln ρ vs. T.


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Figure 3. Binary (solid + liquid) phase equilibrium diagrams (equilibrium temperature T vs. mole fraction x 1 ) at P = 0.1 MPa for binary systems {[C6 DABCO][NTf2 ] (1) + molecular solvent (2)}. Markers correspond to experimental data, according to the key: circles, 2-phenylethanol; squares, water. Dashed line designated by the ideal solubility equation, see eq (1).



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Figure 4. Binary (liquid + liquid) phase equilibrium diagrams (equilibrium temperature T vs. mole fraction x 1 ) at P = 0.1 MPa for binary systems {IL (1) + water (2)}. Markers correspond to experimental data, according to the key: circles, [C6 C1 Pyr][NTf2 ]; 49 squares, [C6 DABCO][NTf2 ]; triangles, [C2O1 C1 Im][NTf2 ]; diamonds, [C2O1 C1 Pyr][NTf2 ]. Solid and dashed lines designated by the NRTL and the PC-SAFT correlations, respectively.


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Figure 5. Experimental ternary (liquid + liquid) phase equilibrium diagrams at T = 308.15 K and P = 0.1 MPa for systems {IL (1) + PEA (2) + water (3)}. Markers correspond to experimental tieline data, according to the key: circles, [C6 C1 Pyr][NTf2 ]; squares, [C6 DABCO][NTf2 ]; triangles, [C2O1 C1 Im][NTf2 ]; diamonds, [C2O1 C1 Pyr][NTf2 ]. Tie-lines were plotted only for a single IL to keep the figure clear. For the remaining ILs the tie-lines point pure water.



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Figure 6. Experimental vs. the PC-SAFT calculated temperature-dependent properties of pure ILs at P = 0.1 MPa studied in this work: (a) density (ρ) at P = 0.1 MPa; (b) the Hildebrand’s solubility parameters (δH ). Markers correspond to experimental data, according to the key: circles, [C6 C1 Pyr][NTf2 ]; 49 squares, [C6 DABCO][NTf2 ]; triangles, [C2O1 C1 Im][NTf2 ]; diamonds, [C2O1 C1 Pyr][NTf2 ]. Solid lines designated by the PC-SAFT model with the parameters listed in Table 3.


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Figure 7. Experimental vs. the PC-SAFT predicted ternary (liquid + liquid) phase equilibrium diagrams at T = 308.15 K and P = 0.1 MPa for systems: (a) {[C6 DABCO][NTf2 ] (1) + PEA (2) + water (3)}; (b) {[C6 C1 Pyr][NTf2 ] (1) + PEA (2) + water (3)}. Markers and solid lines connecting them correspond to experimental tie-line data. Binodal curves calculated based on different strategies of the PC-SAFT modeling adopted in this work: solid line in a and b, strategy 0; dashed line in b, strategy 2; dotted line in b, strategy 2a.



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Page 40 of 45

Table 1. Summary of Thermal Properties of the ILs Under Study: Melting Temperature T 0m , Melting Enthalpy ∆m H 0 and Glass Transtion Temperature T g at P = 0 . 1 MPa. IL

Tm0 / K

∆m H 0 / kJ · mol−1 Tg / K

Ref.

[C6 C1 Pyr][NTf2 ]

274.0

0.653

this work

271.5

185.9 191.5

275.9

34

276.1

35 190

[C6 DABCO][NTf2 ]

33

305.8a

5.033

219.5

306.3b

32 this work this work

[C2O1 C1 Im][NTf2 ]

192

this work

[C2O1 C1 Pyr][NTf2 ]

183.3

this work

a

Measured with DSC (onset).

b

Measured with visual method.


Page 41 of 45

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Table 2. Model Parameters τ i j and τ j i for the NRTL Equation Used in (Liquid + Liquid) Equilibrium Calculations for Systems {IL (1) + PEA (2) + Water (3)} and the Average Absolute Deviations (AAD) between Calculated and Experimental Mole Fractions. τi j

i- j

a

ai j

τji 10−3 bi j / K

ci j / K−1

b

a ji

αi j 10−3 b ji / K

AADc

c ji / K−1

[C6 C1 Pyr][NTf2 ] 1-2 d

3.596

1-3 e

0.06950

−8.488

−0.116

8.998

2.035

0.0328

0.20 0.0014

2-3

0.7744

−3.215

−0.0401

4.920

−3.162

−0.0323

0.35 0.0006

f

0.20 0.0033

−4.551

[C6 DABCO][NTf2 ] 1-2 d

0.3469

1-3 e

1.899

−1.130

−0.0467

7.271

−3.922

−0.0427

0.35 0.0012

2-3

0.7744

−3.215

−0.0401

4.920

−3.162

−0.0323

0.35 0.0006

f

0.20 0.0027

−4.342

[C2O1 C1 Im][NTf2 ] 1-2 d

−4.177

1-3 e

−0.4680

3.118

0.0112

5.708

−9.030

−0.0858

0.20 0.0013

0.7744

−3.215

−0.0401

4.920

−3.162

−0.0323

0.35 0.0006

2-3

f

5.889

0.20 0.0023

[C2O1 C1 Pyr][NTf2 ] 1-2 d

4.420

1-3 e

−0.3090

2-3

f

0.7744

0.20 0.0030

−6.482 0.7079 −3.215

−0.00570

7.076

1.618

0.0173

0.20 0.0005

−0.0401

4.920

−3.162

−0.0323

0.35 0.0006

a

See eq (5a).

b

See eq (5b).

c

See eq (12).

d

Adjusted to ternary (liquid + liquid) equilibrium data. Recommended to be used only at T = 308.15 K.

e

Adjusted to binary (liquid + liquid) equilibrium data for system {IL + water}.

f

Adjusted to literature binary (liquid + liquid) equilibrium data for system {PEA + water}. 23



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Table 3. The PC-SAFT Equation of State Parameters m , σ , u / k B , ǫ AB/ k B and κ AB for the Compounds under Study and the Average Absolute Relative Deviations (AARD) between Calculated and Experimental Liquid Density (ρρ), Hildebrand’s Solubility Parameters (δδ H ; In the Case of ILs), or Vapour Pressure (In the Case of PEA and Water). Compound

Parameters m

σ/Å

AARD u/kB / K

ǫ AB /kB / K

κ AB

ρ

δH

[C6 C1 Pyr][NTf2 ]a

6.8093 4.2353 248.050

1880.36

0.0117 0.23 0.47

[C6 DABCO][NTf2 ]a

6.9342 4.2436 217.389

1823.00

0.0794 0.11 0.87

[C2O1 C1 Im][NTf2 ]a

7.5700 3.7387 208.694

1628.70

0.0286 0.39 0.10

[C2O1 C1 Pyr][NTf2 ]a

7.0103 3.9573 209.102

1707.70

0.0250 0.24 0.13

PEAb

2.6632 3.9332 232.471

3663.82

0.0566 0.51 1.1

waterc

1.5000 2.6273 180.300

1804.22

0.0942 2.6

a

Fitted in this work. Association scheme: “5 + 5”.

b

Fitted in this work. Association scheme: “1 + 1” (2B).

c

Ref. 30. Association scheme: “2 + 2” (4C).


0.91

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WS Table 4. Temperature-dependent Binary Interaction Parameters k LB 13 and k 13 of the PCSAFT Equation of State Fitted to Binary (Liquid + Liquid) Equilibrium Data for {IL (1) + Water (3)} Systems and Average Absolute Deviations (AAD) between Calculated and Experimental Mole Fractions.

IL

LB k13

WS k13

a

a13

AADb

a

104 b13

a13

104 b13

[C6 C1 Pyr][NTf2 ]

0.0241

5.34

0.0611

−7.62

0.0047

[C6 DABCO][NTf2 ]

0.0033

3.40

0.0402

−0.436

0.0068

[C2O1 C1 Im][NTf2 ]

−0.0338

1.93

0.0886

−2.25

0.0015


−0.0215

1.30

0.0832

1.98

0.0009

a

See eq (8).

b

See eq (12).



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Page 44 of 45

WS Table 5. Binary Interaction Parameters k LB 12 and k 12 of the PC-SAFT Equation of State for {IL (1) + PEA (2)} Systems Determined from Infinite Dilution Activity Coefficients of PEA in ILs (γγ ∞ 2,1 ) by Using Different Modeling Strategies and the Resulting Average Absolute Deviations (AAD) between Calculated and Experimental Mole Fractions in Ternary (Liquid + Liquid) Equilibrium Phase Diagrams of Systems {IL (1) + PEA (2) + Water (3)}.

IL

strategya

X

[C6 C1 Pyr][NTf2 ]

0

none

1

[C6 DABCO][NTf2 ]

[C2O1 C1 Im][NTf2 ]


a

X k12

AADb —

0.0137

LB

0.0078

0.0129

2

WS

0.0104

0.0098

1a

LB

−0.0268

0.0163

2a

WS

−0.0253

0.0235

0

none

—

0.0072

1

LB

0.0001

0.0072

2

WS

0.0001

0.0071

0

none

—

0.0064

1

LB

0.0233

0.0053

2

WS

0.0345

0.0124

0

none

—

0.0160

1

LB

0.0119

0.0149

2

WS

0.0160

0.0103

LB = k WS = 0; 1, k LB fitted to γ ∞ at T = 308.15 K obtained from LSER Key: 0, k12 12 2,1 12

WS fitted to γ ∞ at T = 308.15 K obtained from LSER correlations; correlations; 2, k12 2,1 LB fitted to γ ∞ at T = 308.15 K predicted by mod. UNIFAC (Dortmund); 2a, 1a, k12 2,1 WS fitted to γ ∞ at T = 308.15 K predicted by mod. UNIFAC (Dortmund). k12 2,1 b

See eq (12).


Page 45 of 45

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