Essential oil deterpenation by solvent extraction using 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate ionic liquid

Essential oil deterpenation by solvent extraction using 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate ionic liquid

Fluid Phase Equilibria 296 (2010) 149–153 Contents lists available at ScienceDirect Fluid Phase Equilibria journal homepage: www.elsevier.com/locate...

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Fluid Phase Equilibria 296 (2010) 149–153

Contents lists available at ScienceDirect

Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid

Essential oil deterpenation by solvent extraction using 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate ionic liquid M. Francisco, S. Lago, A. Soto, A. Arce ∗ Department of Chemical Engineering, University of Santiago de Compostela, E-15782 Santiago de Compostela, Spain

a r t i c l e

i n f o

Article history: Received 15 December 2009 Received in revised form 10 March 2010 Accepted 12 March 2010 Available online 20 March 2010 Keywords: Liquid–liquid equilibrium Deterpenation Ionic liquid

a b s t r a c t Taking into account that heat application can have undesirable effects in essential oil properties, liquid extraction comes up as a promising process instead of distillation for citrus oil deterpenation. In this work the suitability of using the ionic liquid 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate as a solvent for the extraction of linalool from citrus essential oil (which has been simulated as a mixture of limonene and linalool) has been analyzed. Liquid–liquid equilibrium data at three different temperatures (298.15 K, 308.15 K and 318.15 K) have been reported and successfully correlated using NRTL model. The best results were achieved using ˛ = 0.1 for the systems at 298.15 K and 308.15 K and ˛ = 0.2 at 318.15 K. The solute distribution ratio has showed values close to one and high values of selectivity have been achieved. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Lemon essential oil is a liquid mixture of volatile aroma compounds derived from lemon peel. It is basically a mixture of terpenic hydrocarbons and their oxygenated derivatives. The former are insoluble in aqueous and alcoholic solutions, can be oxidized when exposed to air and contribute little to the aroma and flavor of the essential oil, being the oxygenated terpenes the ones that give the organoleptic characteristics to the oil [1]. That is why a separation of the terpenes is required in order to concentrate their oxygenated derivates. Selective elimination of terpenes is called deterpenation. There are different methods to deterpenate essential oils as, extraction with supercritical fluids [2], membrane based separation technologies [3], liquid–liquid extraction [4], microwave extraction with ionic liquids as the absorption medium [5] and the most common one, vacuum distillation [6]. Sometimes, the essential oil components are too sensible to high temperatures and can be denatured causing undesirable effects in its properties. In this case, liquid extraction with a solvent comes up as suitable process instead of distillation. Ionic liquids have received a great increase in attention during the last years due to their interesting properties [7]. Particularly significant is the low vapor pressure in most instances which contrast the environmental problems of volatile organic solvents. These characteristics make them a good option to be used as solvents

in liquid–liquid extraction processes [8]. An ionic liquid is a salt with melting point under 100 ◦ C. They are composed of big organic cations and usually smaller anions and can be custom-designed by modification of its anion and/or cation. This characteristic makes it possible to find the suitable ionic liquid for a given application just by studying the physical and chemical properties of the anion and the cation that constitute it. Several reports about essential oil deterpenation with ionic liquids [8,9] can be found but these results are not good enough. Ionic liquids with better properties need to be found. In this work, lemon essential oil is simulated as a mixture of its two main components, the monoterpene hydrocarbon limonene and the desired oxygenated terpenoid linalool. Ionic liquid 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate ([C2 mim][Meesu]) has been selected as solvent for extraction purpose according to the acquired experience in our previous solubility proofs of linalool and limonene in different ionic liquids. No information about human toxicity and this IL has been found on bibliography, this must be carefully taken into consideration in the food/aroma applications. Liquid–liquid equilibrium data at three different temperatures (298.15 K, 308.15 K and 318.15 K) are reported and correlated using NRTL model and suitability of this solvent is evaluated in terms of solute distribution ratio and selectivity. 2. Experimental procedure 2.1. Reagents

∗ Corresponding author at: University of Santiago de Compostela, School of Engineering, E-15782 Santiago de Compostela, Spain. Tel.: +34 981563100x16790. E-mail address: [email protected] (A. Arce). 0378-3812/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2010.03.019

The (R)-(+)-limonene (Lim) was supplied by Sigma–Aldrich and the (±)-linalool was supplied by SAFC. Their nominal

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M. Francisco et al. / Fluid Phase Equilibria 296 (2010) 149–153

Table 1 Physical properties of the pure components at 298.15 K and atmospheric pressure. Compound

Limonene Linalool [C2 mim][Meesu]

Water content (ppm)

 (g cm−3 )

Experimental

Experimental

Literature

Experimental

Literature

152 204 289

0.83868 0.85683 1.23861

0.8383 [11] 0.85760 [12] 1.2367 [14]

1.47081 1.45961 1.48113

1.4701 [11] 1.4601 [13] Not found

purities were 97 mass% and ≥97 mass%, respectively. The chemicals were used without further purification. Ionic liquid 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy)ethylsulfate [C2 mim][Meesu] was synthesized in the laboratory following the publication of Himmler et al. [10]. The ionic liquid was prepared by reaction 1:3 of 1-ethyl-3methylimidazolium ethylsulfate ([C2 mim][EtSO4 ]) and di(ethylene glycol) methyl ether (Sigma–Aldrich, ≥99%), catalyzed by a small quantity (1:0.1) of methane sulfonic acid (Merck, ≥99%). The [C2 mim][EtSO4 ] was synthesized following the publication of Arce et al. [8] being prepared by reaction of 1-methylimidazole (Sigma–Aldrich, 99%) in a excess quantity of toluene (Sigma–Aldrich, 99.5+%, ACS reagent) and adding dropwise a equimolecular quantity of diethyl sulfate (Fluka, ≥99%, GC) under inert atmosphere and putting ice in the bath to keep the temperature under 40 ◦ C. After 2 h of reaction the excess of toluene is separated in a funnel and the ionic liquid is washed three times with fresh toluene. Finally, the flask is put into a rotatory evaporator (70 ◦ C, 1–2 h) and under vacuum (70 ◦ C, 48 h) to remove residual volatile compounds. A molar relation 1:2 of [C2 mim][EtSO4 ] and di(ethylene glycol) methyl ether was mixed with methane sulfonic acid in a bottom flask. The reaction was carried out at 70 ◦ C, argon atmosphere and constant stirring during 5 h. Afterwards, the ethanol formed was removed introducing the flask first in a rotatory evaporator (1–2 h, 70 ◦ C) and later under vacuum (70 ◦ C, 12 h). Then, the rest of the di(ethylene glycol) methyl ether is added to the flask and the reaction is carried out during 30 min at the same conditions as above. The same procedure as above is repeated to eliminate the ethanol formed. The ionic liquid is washed with a two folder excess of diethyl ether (Sigma–Aldrich, 99+%, ACS reagent) and this step is repeated five times. To remove the residual volatile compounds left in the ionic liquid the flask is introduced first in a rotatory evaporator (1–2 h, 70 ◦ C) and later under vacuum (70 ◦ C, 48 h). 1 H and 13 C NMR were obtained to check that the ionic liquid synthesized was 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate. In Table 1 water content of pure compounds is reported, and their experimental densities and refractive indices are compared with the available values published by other authors [11–14]. 2.2. Apparatus Densities and refractive indices of the pure components were experimentally measured at 298.15 K and atmospheric pressure. The refractive indices were measured by means of an Atago RX5000 refractomer with a Techne Tempunit TU-16A thermostat with an accuracy of ±4 × 10−5 . An Anton Paar DMA 5000 densimeter precise to within ±10−5 g cm−3 was used to measure the density of the chemicals. These physical properties are shown in Table 1. The water content was measured with a Metrohm 737 KF coulometer. All the weighing was carried out in a Mettler Toledo AE 240 analytic balance with a precision of 10−4 g. 2.3. Procedure Liquid–liquid equilibrium data for the ternary System were experimentally (limonene + linalool + [C2 mim][Meesu])

nD

determined by analysis of phases at equilibrium at 298.15 K, 308.15 K and 318.15 K. The liquid mixtures with composition inside the immiscible region are introduced in 30 mL jacketed vessels with constant temperature and vigorous stirring. The vessels were connected to a P. SELECTA ULTRATERM 6000383 thermostat to keep the selected temperature. Uncertainty in temperature measurement is ±0.02 K. Several experiments were done to ensure that the equilibrium was reached after 6 h of stirring. Once the equilibrium was reached, the stirrers of the vessels were turned off and left overnight to settle down. After this time samples of both formed layers were withdrawn using syringes and analyzed by gas chromatography using an internal standard method. For the analysis of (limonene + linalool + [C2 mim][Meesu]) the chromatograph used was a Hewlett–Packard HP 6890 Series gas (GC), equipped with a thermal conductivity detector and a HP5 capillary column (30 m × 0.32 mm × 0.25 ␮m). Helium was used as the mobile phase and injection volume was 1 ␮L with a split ratio of 20:1. The oven temperature was kept at 353.15 K for 3.7 min, it was then increased at 333.15 K/min to 523.15 K, and was kept constant for 1.5 more minutes. An empty precolumn was placed between column and injector to protect the column and collect the ionic liquid that could not be retained by the liner. 3. Results and discussion 3.1. Experimental data The liquid–liquid equilibrium data were determined experimentally at 298.15 K, 308.15 K and 318.15 K. The ends of the tie-lines are shown in Table 2. All of equilibria correspond to type I category showing only one immiscible region and only one pair with immiscibility [15]. 3.2. Correlation The experimental data were correlated using the widely employed NRTL model [16]. The value of the nonrandomness parameter of the NRTL equation, ˛, was previously assigned as 0.1, 0.2 and 0.3 for the correlation in all cases. The binary interaction parameters for NRTL equation were obtained using a computer program described by Sørensen [15], who used two objective functions. First Fa does not require any previous knowledge of parameters, and after convergence the parameters are used in the second function to fit the experimental concentrations, Fb : Fa =

 2  aIijk − aIIijk k

Fb =

 k

i

min

aIijk + aIIijk

j

 i

j

+Q



Pn2

(1)

n

2

(xijk − xˆ ijk ) + Q



  Pn2 + ln

I ˆ S∞ II ˆ S∞

2 ˇ∞ (2)

where x is the experimental mole fraction, xˆ the mole fraction of the calculated tie-line considered, a is the activity, i are the components

M. Francisco et al. / Fluid Phase Equilibria 296 (2010) 149–153

151

Table 2 Experimental tie-lines for (limonene + linalool + [C2 mim][Meesu]) at 298.15 K, 308.15 K and 318.15 K, where x1 , x2 and x3 are the mole fractions of limonene, linalool and [C2 mim][Meesu] respectively. ˇlinalool

S

0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

– 0.61 0.67 0.83 0.98 1.00 1.01 1.01 1.05 1.02

– 24.80 15.66 15.92 6.42 5.62 3.98 3.25 2.57 2.22

0.000 0.075 0.154 0.199 0.284 0.353 0.401 0.434 0.484 0.550

0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

– 0.48 0.73 0.81 0.90 0.97 0.95 1.02 1.04 0.99

– 17.08 15.92 14.49 7.50 5.56 3.63 2.97 2.25 1.55

0.000 0.070 0.176 0.205 0.304 0.413 0.454 0.501 0.572

0.000 0.005 0.009 0.000 0.000 0.000 0.000 0.000 0.000

– 0.31 0.65 0.79 0.83 0.90 0.94 0.99 0.97

– 11.63 13.65 14.96 7.46 3.98 3.08 2.35 1.59

Ionic liquid-rich phase

Limonene-rich phase

x1

x3

x1

x2

x3

0.982 0.938 0.855 0.795 0.608 0.551 0.452 0.398 0.299 0.265

1.000 0.936 0.838 0.804 0.712 0.672 0.613 0.587 0.540 0.503

0.000 0.064 0.162 0.196 0.288 0.328 0.387 0.413 0.460 0.497

0.983 0.938 0.848 0.793 0.658 0.544 0.461 0.364 0.260 0.166

1.000 0.925 0.846 0.801 0.716 0.647 0.599 0.566 0.516 0.450

0.980 0.953 0.846 0.796 0.672 0.498 0.409 0.294 0.183

1.000 0.925 0.815 0.795 0.696 0.587 0.546 0.499 0.428

x2

T = 298.15 K 0.018 0.000 0.023 0.039 0.036 0.109 0.042 0.163 0.109 0.283 0.120 0.329 0.156 0.392 0.183 0.419 0.220 0.481 0.230 0.505 T = 308.15 K 0.017 0.000 0.026 0.036 0.039 0.113 0.045 0.162 0.086 0.256 0.113 0.343 0.157 0.382 0.194 0.442 0.238 0.502 0.288 0.546 T = 318.15 K 0.020 0.000 0.025 0.022 0.039 0.115 0.042 0.162 0.077 0.251 0.132 0.37 0.166 0.425 0.210 0.496 0.261 0.556

of the mixture, j are the phases and k are the tie-lines. Both functions include a penalization term to reduce the risks of multiple solutions associated with parameters of high value, in which Q is a constant and Pn are the adjustable parameters. Fb also includes a term to correctly fit experimental results when working with low solute I II represent the solute activity and ˆ S∞ concentrations, in which ˆ S∞ coefficients calculated at infinite dilution in both phases and ˇ∞ is the solute molar distribution ratio at infinite dilution. The quality of the correlation is measured by the residual function F and by the mean error of the solute distribution ratio, ˇ:

⎡ ⎤0.5   (xijk − xˆ ijk )2 ⎦ min F = 100⎣ k

 ˇ = 100

i

j

6M

 ((ˇ − ˇˆ ))/ˇ k k k k

M

Fig. 1. Experimental tie-lines for ternary system (limonene + linalool + [C2 mim] [Meesu]) at 298.15 K (solid circle, solid line), and correlated tie-lines obtained for NRTL model fixing ˛ = 0.1 (empty circle, dotted line).

Fig. 2. Experimental tie-lines for ternary system (limonene + linalool + [C2 mim] [Meesu]) at 308.15 K (solid circle, solid line), and correlated tie-lines obtained for NRTL model fixing ˛ = 0.1 (empty circle, dotted line).

(3)

0.5 (4)

where M is the total number of tie-lines. Two different ways were used to correlate the experimental data, in a similar manner to the procedure followed by Sørensen. Firstly, the correlation was performed without fixing a previous value for ˇ∞ . Later, an optimal value of this parameter, found by trial and error considering the minimization of ˇ as the optimality criterion, was specified before carrying out the correlation. Obtained correlation parameters are shown in Tables 3–5. Figs. 1–3 show a comparison of experimental tie-lines and those calculated with NRTL at 298.15 K, 308.15 K and 318.15 K, respectively.

Fig. 3. Experimental tie-lines for ternary system (limonene + linalool + [C2 mim] [Meesu]) at 318.15 K (solid circle, solid line), and correlated tie-lines obtained for NRTL model fixing ˛ = 0.2 (empty circle, dotted line).

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M. Francisco et al. / Fluid Phase Equilibria 296 (2010) 149–153

3.3. Solvent evaluation The ability of the ionic liquid to extract the linalool from the essential oil mixture was evaluated from the experimental data at the three different temperatures using the solute distribution ratio, ˇLiOH , and the selectivity, S, parameters: ˇLiOH =

(xLinalool )

Solvent

(5)

(xLinalool )Lim

Table 3 Binary interaction parameters (gij , gji ) and residuals (F, ˇ) for the correlation of (limonene + linalool + [C2 mim][Meesu]) at 298.15 K. Residuals

NRTL, 298.15 K

Table 5 Binary interaction parameters (gij , gji ) and residuals (F, ˇ) for the correlation of (limonene + linalool + [C2 mim][Meesu]) at 318.15 K. Residuals

NRTL, 318.15 K

F 1.449 ˇ 10.5 ˛ = 0.1, optimized ˇ∞ = 4.6 F 1.0708 ˇ 6.2 ˛ = 0.2, not optimized

Parameters

i–j

gij (J mol−1 )

gji (J mol−1 )

F 2.3523 ˇ 19.3 ˛ = 0.2, optimized ˇ∞ = 4.9

1–2 1–3 2–3

−12,059 33,875 544.22

19,864 1021.4 −1442.3

F 1.3218 ˇ 5.5 ˛ = 0.3, not optimized

1–2 1–3 2–3

17,825 39,840 15,911

−13,306 2816.2 11,347

F 2.9086 ˇ 24.3 ˛ = 0.3, optimized ˇ∞ = 4.0

1–2 1–3 2–3

893.31 21,199 1371.8

2678.3 5329.5 2779.4

F ˇ

1–2 1–3 2–3

2828.8 24946 7789.9

−4416.5 9116.0 −5286.9

1–2 F 2.6046 1–3 ˇ 21.5 2–3 ˛ = 0.3, optimized ˇ∞ = 1.60 1–2 F 3.0634 1–3 ˇ 11.0 2–3

1785.3 15,382 3052.1

3397.5 7279.8 2207.9

950.18 13,866 2376.7

4869.3 5620.4 3159.2

F 1.6636 ˇ 5.3 ˛ = 0.1, optimized ˇ∞ = 1.9 F 0.5429 ˇ 2.9 ˛ = 0.2, not optimized F 2.3501 ˇ 11.7 ˛ = 0.2, optimized ˇ∞ = 2.3 F 0.8224 ˇ 4.4 ˛ = 0.3, not optimized

Parameters

i–j

gij (J mol−1 )

gji (J mol−1 )

1–2 1–3 2–3

−13,934 36,347 3659.9

23,738 −136.11 −4435.3

1–2 1–3 2–3

16,242 41,937 14,877

−13,707 1946.3 −10,947

1–2 1–3 2–3

−324.84 21,607 2358.1

4706.5 4711.9 2400.8

1–2 1–3 2–3

638.81 25,543 8321.6

−4964.3 7893.9 −6454.6

1–2 1–3 2–3

1267.7 15,419 3502.0

4387.2 6830.8 2272.0

1–2 1–3 2–3

−16,985 13,767 7976.6

−1993.3 9040.7 −18,594

˛ = 0.1, not optimized

Components

˛ = 0.1, not optimized

Components

1.6845 6.7

Table 4 Binary interaction parameters (gij , gji ) and residuals (F, ˇ) for the correlation of (limonene + linalool + [C2 mim][Meesu]) at 308.15 K. Residuals

NRTL, 308.15 K Components

Parameters

i–j

gij (J mol−1 )

gji (J mol−1 )

1–2 1–3 2–3

−12,514 35,640 2435.4

22,340 16.131 −2855.7

1–2 1–3 2–3

16,292 42,764 12,964

−13,162 2728.5 −10,369

1–2 1–3 2–3

456.66 22,094 2081.8

3514.7 4677.4 2408.8

1–2 1–3 2–3

1289.7 24,835 7498.9

−4430.3 8353.3 −6032.2

1–2 1–3 2–3

1616.6 15,619 3341.6

3780.6 6748.3 2152.1

1–2 1–3 2–3

−27,329 14,400 7188.7

−1104.3 9251.3 −29,039

˛ = 0.1, not optimized F 1.3314 ˇ 6.3 ˛ = 0.1, optimized ˇ∞ = 2.6 F 0.5429 ˇ 2.9 ˛ = 0.2, not optimized F 2.2321 ˇ 14.3 ˛ = 0.2, optimized ˇ∞ = 3.2 F 1.3374 ˇ 4.2 ˛ = 0.3, not optimized F 2.7641 ˇ 20.5 ˛ = 0.3, optimized ˇ∞ = 2.4 F ˇ

1.6887 4.7

Fig. 4. Linalool solute distribution ratio, ˇlinalool , at 298.15 K (), 308.15 K () and 318.15 K (䊉) and correlated values obtained for NRTL model {(· · ·) 298.15 K, (– · – · –) 308.15 K, (– – –) 318.15 K} between ionic liquid [C2 mim][Meesu] and limonene.

Fig. 5. Experimental values of selectivity, Slinalool , at 298.15 K (), 308.15 K () and 318.15 K () and correlated values obtained for NRTL model {(· · ·) 298.15 K, (– · – · –) 308.15 K, (– – –) 318.15 K} for the ionic liquid [C2 mim][Meesu] to extract linalool from its mixtures with limonene at 298.15 K.

M. Francisco et al. / Fluid Phase Equilibria 296 (2010) 149–153

S=

(xlinalool )solvent (xlimonene )Lim (xlinalool )

Lim

(xlimonene )

solvent

=

ˇlinalool ˇlimonene

(6)

where x represents the mole fraction of each component. Values close to one were obtained for the solute distribution ratio which are presented in Table 2. High values of selectivity were found and were also included in this table. Their graphical representation is included together with the calculated values obtained by the correlation model in Figs. 4 and 5. 4. Conclusions Several reports about essential oil deterpenation with ionic liquids [8,9] can be found but these results are not good enough and it is necessary to improve them. For this reason in this work the suitability of using the 1-ethyl-3-methylimidazolium 2-(2methoxyethoxy) ethylsulfate ionic liquid as solvent extraction was analyzed. Liquid–liquid equilibrium data for (limonene + linalool + [C2 mim][Meesu]) were obtained at 298.15 K, 308.15 K and 318.15 K. A type I diagram is obtained when representing the equilibrium data, this means one immiscible region and just one immiscible pair (limonene and [C2 mim][Meesu]). As shown in Figs. 1–3, temperature has a small effect on the liquid–liquid equilibrium for this range of temperatures. The experimental LLE data were satisfactorily correlated using the NRTL model. The value of the nonrandomness parameter of the NRTL equation, ˛, that better fits the experimental data for the systems at 298.15 K, 308.15 K and 318.15 K is 0.1 in the three cases, but optimization of ˇ∞ drives to different results. The residual ˇ is highly reduced by slightly increasing F. In this case the best results are obtained for ˛ = 0.1 for the systems at 298.15 K and 308.15 K, and ˛ = 0.2 for the system at 318.15 K. The values of the solute distribution ratio are unfavorable which is shown in the negative slopes of the tie-lines. However, the low solubility of the limonene in the ionic liquid drives the solvent’s selectivity to a high value. Low solute distribution ratio values imply the use of high amounts of solvent in the extraction process. Even though in the case of the ionic liquid the solvent recovery is total (negligible vapor pressure), the possibility of combining anions and cations to find the ideal ionic liquid for separation purposes calls for further research in essential oil deterpenation with ionic liquids. List of symbols a activity F rms deviation of phase composition Fa activity objective function concentration objective function Fb M number of tie-lines

Pn Q x xˆ

153

parameter value constant experimental mole fraction calculated mole fraction

Greek letters ˛ NRTL non-randomness parameter ˇ experimental solute distribution ratio ˆ ˇ calculated solute distribution ratio ˇ rms relative deviation of solute distribution ratio g optimizable binary NRTL parameters  activity coefficient ˆ calculated activity coefficient Subscripts i component identifier j phase identifier k tie line identifier

n parameter identifier in the term Q n Pn2 ∞ infinite dilution Acknowledgments We want to thank the Ministerio de Educación y Ciencia (Spain) for financial support through Project CTQ 2009-10776. M. Francisco also wants to thank them for the award of the FBI grant with reference DES-2007-16693 through the same project. References [1] A. Arce, A. Soto, in: N. Benkeblia, P. Tennant (Eds.), Tree and Forestry Science and Biotechnology, vol. 2 (Special Issue 1), Global Sciences Books, Ltd., UK, 2009, pp. 1–9. [2] S. Diaz, S. Espinosa, E.A. Brignole, J. Supercrit. Fluids 35 (2005) 49–61. [3] D.J. Brose, M.B. Chidlaw, D.T. Friesen, E.D. LaChapelle, P. van Eikeren, Biotechnol. Prog. 11 (1995) 214–220. [4] A. Arce, A. Marchiaro, J.M. Martinez-Ageitos, A. Soto, Can. J. Chem. Eng. 83 (2005) 366–370. [5] Y. Zhai, S. Sun, Z. Wang, J. Cheng, Y. Sun, L. Wang, Y. Zhang, H. Zhang, A. Yu, J. Sep. Sci. 32 (2009) 3544–3549. [6] G.R. Stuart, D. Lopes, J.V. Oliveira, J. Am. Oil Chem. Soc. 78 (2001) 1041–1044. [7] M.J. Earle, K.R. Seddon, Pure Appl. Chem. 72 (2000) 1391–1398. [8] A. Arce, A. Pobudkowska, O. Rodríguez, A. Soto, Chem. Eng. J. 133 (2007) 213–218. [9] A. Arce, A. Marchiaro, O. Rodríguez, A. Soto, AIChE J. 52 (2006) 2089–2097. [10] S. Himmler, S. Hörmann, R. van Hal, P.S. Schulz, P. Wasserscheid, Green Chem. 8 (2006) 887–894. [11] J.A. Riddick, W.B. Bunger, T.K. Sakano, Organic solvents, in: Physical Properties and Methods of Purification, 4th edn., Wiley, New York, 1986. [12] F. Comelli, S. Ottani, J. Chem. Eng. Data 47 (2002) 93–97. [13] R. Francesconi, C. Castellari, J. Chem. Eng. Data 46 (2001) 1520–1525. [14] A.N. Soriano, B.T. Doma Jr., M.H. Li, J. Chem. Thermodyn. 40 (2008) 1654–1660. [15] J.M. S␾rensen, W. Arlt, Liquid–Liquid Equilibrium Data Collection, DECHEMA Chemistry Data Series, Frankfurt, 1980. [16] H. Renon, J.M. Prausnitz, AIChE J. 14 (1968) 135–144.