Ionic Liquids-Based Aqueous Biphasic Systems with Citrate

Article pubs.acs.org/jced

Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Ionic Liquids-Based Aqueous Biphasic Systems with Citrate Biodegradable Salts Elena Gómez,† Irene Domínguez,‡ Á ngeles Domínguez,‡ and Eugénia A. Macedo*,† †

Associate Laboratory of Separation and Reaction EngineeringLaboratory of Catalysis and Materials (LSRE-LCM), Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, s/n, Porto 4200-465, Portugal ‡ Advanced Separation Processes Group, Department of Chemical Engineering, University of Vigo, Campus Lagoas-Marcosende, 36310 Vigo, Spain ABSTRACT: New ionic liquids−aqueous biphasic systems (ABS) containing the imidazolium and pyrrolodinium cation combined with dicyanamide anion and citrate organic salts are investigated. Several ionic liquids (five in total) were evaluated toward their capacity to create aqueous biphasic systems in the presence of two low environmental impact organic salts: potassium and sodium citrate. The capacity of these ILs to form two liquid phases is discussed regarding the alkyl chain length and the cation core of the IL. Besides, the effect of the citrate salt on the phase behavior has been also addressed. To study the capacity of the ABS the binodal curves were determined at T = 298.15 K and atmospheric pressure. Finally, a comparison between the experimental results obtained here and the literature values was carried out.

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INTRODUCTION In the mid-1950s, Albertsson1 presented the aqueous biphasic systems (ABS) as a clean alternative to conventional liquid− liquid equilibria (LLE) systems since they are mainly composed of water. ABS are based on the separation of an immiscible mixture of three components in two liquid phases at equilibrium. Each of the phase has different properties, which enables the separation of different molecules depending on the affinity of these molecules to each phase. In 2003 Rogers and co-workers2 reported a pioneering work about the ability of ionic liquids (ILs) to act as salting out agents in ABS. The research on IL-based ABS has increased in the last years,3−26 but the majority of the salts used on ABS are inorganic salts; the application of salts more environmentally friendly, such as citrates or tartrates, have seldom been investigated.3,9,12,21−23,27−29 For this reason, in this paper the binodal curves of the ternary systems composed of {ionic liquid (1) + sodium citrate tribasic dihydrate or potassium citrate tribasic monohydrate (2) + water (3)} in which the selected ionic liquids were 1-alkyl-3-methylimidazolium dicyanamide with n = 2, 3, 4, and 6 (CnMim DCA with n = 2, 3, 4 and 6) and 1-butyl-1methylpyrrolidinium dicyanamide (C4pyr DCA) have been determined at T = 298.15 K and atmospheric pressure. The Merchuk equation30 was used to represent and predict the binodal curves. The effect of both the alkyl chain side length of the cation as of the cation core of the ionic liquid on the ABS was evaluated with imidazolium and pyrrolidinium ionic liquids and dycianamide anion. To better evaluate how the characteristics of the salts affect to ABS the following salts were selected: potassium citrate tribasic monohydrate and sodium citrate tribasic dihydrate. © XXXX American Chemical Society

Finally, the obtained results for the system {C4Mim DCA (1) + potassium citrate tribasic monohydrate (2) + water (3)} were compared with literature values.3

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EXPERIMENTAL SECTION Materials. All ionic liquids were acquired at IoLiTec, the ILs were dried at T = 343 K and moderate vacuum to lower the water and the volatile contents before their use. The sodium citrate tribasic dihydrate and potassium citrate tribasic monohydrate salts with mass fraction purity higher than 0.99 were purchased from Sigma-Aldrich, and these salts were dried by lyophilization (Scan vac. Cool-safe 55-4) before their use. The solutions were prepared using double distilled deionized water and all weighing was carried out on a Mettler AX-205 Delta Range balance with an uncertainty of 3 × 10−4 g. In Table 1 the mass fraction purities of the all components are presented.

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APPARATUS AND PROCEDURE

The cloud point technique31 was used for the measurement of binodal curves. Mixtures of known compositions of ionic liquids and citrate salt were prepared in test glasses and intensively shaken with a vortex (VWR, model VV3). They were then immersed in a thermostatic bath (Techne, Tempette TE-8D) with an uncertainty of the measurement of the temperature of 0.2 K. Special Issue: In Honor of Cor Peters Received: September 25, 2017 Accepted: March 17, 2018

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DOI: 10.1021/acs.jced.7b00849 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Table 2. Binodal Curve Data (Weight Fraction Percentage, wi) for the All Ternary Systems {Ionic Liquid (1) + Sodium Citrate Tribasic Dihydrate (2) or Potassium Citrate Tribasic Monodydrate + Water (3)} Determined Experimentally at T = 298.15 K and p = 0.1 MPaa

Table 1. Names, Suppliers, and Purities of the Ionic Liquids and Salts ionic liquid or salt C2Mim DCA C3Mim DCA C4Mim DCA C6Mim DCA C4Mpyr DCA C6H5Na3O7 C6H5K3O7

name 1-ethyl-3-methylimidazolium dicyanamide 1-propyl-3-methylimidazolium dicyanamide 1-butyl-3-methylimidazolium dicyanamide 1-hexyl-3-methylimidazolium dicyanamide 1-butyl-1-methylpyrrolinium dicyanamide Sodium citrate tribasic dihydrate Potassium citrate tribasic monohydrate

supplier

purity (weight fraction)

Iolitec

≥0.99

Iolitec

≥0.99

Iolitec

≥0.98

Iolitec

≥0.99

Iolitec

≥0.98

SigmaAldrich SigmaAldrich

≥0.99

w1

≥0.99

Aqueous solutions of potassium and sodium citrate salts (40 wt % approx.) and of the ionic liquids (from 50 wt % to 90 wt %) were prepared for the calculation of the binodal curves. Dropwise addition of the aqueous solution of organic salt to each ionic liquid solution was carried out until the detection of a cloudy solution. After, a known amount of water was added dropwise to the glasses until a homogeneous phase was achieved. To ensure that the whole range of compositions was covered, the pure ionic liquid was added to the salt solution. The ternary system compositions were determined by weight quantification within an uncertainty of the measurement of ±5 × 10−3 g. Curve fitting to the experimental data points was achieved using the equation given by Merchuk et al.30 with three temperature-dependent adjustable parameters. [IL] = a exp[(b[salt]0.5 ) − ([(c[salt]3 )]

w2

w1

w2

w1

w2

{C2Mim DCA (1) + Sodium Citrate Tribasic Dihydrate (2) + Water (3)} 55.049 2.893 33.567 11.209 20.230 20.229 52.620 3.450 32.763 11.671 18.482 21.618 40.678 7.612 31.875 12.235 16.425 23.176 40.138 7.797 31.227 12.752 14.810 24.616 38.956 8.457 30.355 13.300 13.252 26.067 38.425 8.653 29.211 14.048 12.323 27.043 37.506 9.145 27.799 15.051 11.198 28.243 36.464 9.684 25.644 16.445 10.241 29.395 35.592 10.146 23.824 17.666 9.391 30.470 34.618 10.568 21.838 19.040 8.462 31.749 {C3Mim DCA (1) + Sodium Citrate Tribasic Dihydrate (2) + Water (3)} 68.594 0.528 40.811 5.829 15.097 20.027 58.891 1.837 38.644 6.579 12.583 22.224 56.302 2.147 35.933 7.754 10.254 24.295 54.691 2.369 32.825 9.298 9.083 25.996 53.188 2.590 27.894 12.074 7.637 28.155 52.232 2.820 24.048 14.255 6.224 29.844 50.153 3.221 21.206 15.866 5.757 30.834 48.974 3.640 19.677 16.841 5.412 31.523 46.806 3.713 18.764 17.459 4.912 32.384 46.284 3.911 18.267 17.818 4.613 33.985 43.725 4.694 17.549 18.293 4.340 35.369 {C4Mim DCA (1) + Sodium Citrate Tribasic Dihydrate (2) + Water (3)} 58.239 1.430 17.631 14.291 24.045 11.236 55.781 1.644 15.564 15.449 22.859 11.780 54.231 1.859 13.215 16.891 21.774 12.234 52.526 2.229 10.900 18.692 20.357 12.949 50.621 2.589 8.533 20.956 19.273 13.431 49.140 2.764 58.198 1.676 17.064 14.702 47.885 3.041 54.960 1.882 14.781 15.911 46.932 3.227 53.334 2.112 12.333 17.559 46.016 3.455 51.474 2.558 10.402 19.090 44.070 3.890 49.450 2.909 7.942 21.627 41.835 4.394 47.937 3.080 2.740 34.488 39.115 5.207 46.445 3.384 3.137 33.083 36.391 6.124 45.535 3.554 3.297 31.400 33.532 7.250 44.896 3.798 3.691 29.808 31.073 8.207 43.316 4.164 4.489 27.675 28.365 9.309 40.676 4.913 5.444 25.600 25.474 10.572 38.175 5.555 6.307 24.272 24.032 11.166 35.752 6.450 7.724 22.258 22.832 11.775 32.832 7.562 9.567 20.201 21.833 12.197 30.792 8.425 9.742 19.827 20.708 12.771 28.175 9.520 3.240 34.560 19.598 13.328 25.530 10.592 3.400 32.747 {C6Mim DCA (1) + Sodium Citrate Tribasic Dihydrate (2) + Water (3)} 0.809 38.614 3.673 18.188 16.181 8.225 1.047 36.149 4.617 16.088 17.804 7.771 1.335 33.318 6.109 13.875 18.858 7.521 1.538 29.890 9.516 10.914 20.348 7.057 1.795 28.073 10.475 10.451 22.762 6.575 2.157 26.305 11.721 9.799 26.286 5.827 2.307 24.261 13.115 9.216 37.683 3.877 2.561 21.850 14.458 8.736 {C4Mpyr DCA (1) + Sodium Citrate Tribasic Dihydrate (2) + Water (3)} 2.652 35.282 21.726 10.838 37.889 4.532 3.159 31.734 23.274 10.112 39.878 4.043

(1)

where [IL] and [salt] are the ionic liquids and salts compositions in weight fraction percentage, respectively, and a, b, and c are the adjustable parameters.

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RESULTS AND DISCUSSION In this work, 10 novel ILs-based ABS were studied. To assess the ability of the IL to form ABS the following ionic liquids were selected: CnMim DCA (with n = 2, 3, 4, and 6) and C4pyr DCA. The effect of the salt on the phase behavior was assessed with the selection of the two organic salts: potassium and sodium citrate. The binodal data for all ternary systems measured experimentally at T = 298.15 K and atmospheric pressure are summarized in Table 2 and are graphically presented in Figure 1 (a, b, and c). Table 3 lists the parameters obtained by eq 1 together with the standard deviations for all studied systems. The solubility curves are presented in weight fraction percentage, and it can be observed that the larger is this region, the higher is the ability of IL to form two phases. The experimental solubility curves are divided into three figures: The first figure (Figure 1a) presents the systems composed of sodium salt and the five ionic liquids. In the second figure (Figure 1b) the results obtained with the same ionic liquids but with the potassium salt are shown, and finally in Figure 1c a comparison of the data obtained with the two salts is displayed. Influence of Cation Alkyl Chain Side Length and the Cation Nature of the Ionic Liquid. In Figure 1a the effects of the cation alkyl chain side length and of the cation core of the ionic liquid on the ability to form ABS with the sodium citrate salts can be evaluated. In this figure it can be observed that the larger is the cation alkyl chain length, the better is B



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Table 2. continued w1

w2

Table 2. continued w1

w2

w1

w2

w1

{C4Mpyr DCA (1) + Sodium Citrate Tribasic Dihydrate (2) + Water (3)} 3.546 29.580 24.999 9.342 42.325 3.510 3.997 28.117 25.336 8.901 43.880 3.090 4.360 26.659 25.603 8.772 64.469 0.705 4.954 25.418 26.508 8.420 59.978 1.014 5.321 24.397 27.486 8.073 57.489 1.281 5.666 23.401 28.316 7.705 54.857 1.563 6.224 22.858 29.224 7.371 52.709 1.743 6.505 22.011 29.705 7.181 47.900 2.331 8.821 18.914 30.377 6.926 44.033 3.221 11.045 16.888 31.179 6.666 40.458 4.033 13.334 15.000 32.051 6.343 36.755 5.026 16.541 13.291 33.164 5.987 32.696 6.340 18.166 12.393 34.090 5.663 29.127 7.671 19.917 11.549 35.943 5.073 26.228 8.804 {C2Mim DCA(1) + Potassium Citrate Tribasic Monodydrate (2) + Water (3)} 73.342 0.579 4.976 42.882 19.657 23.283 69.551 1.094 5.336 41.871 21.531 21.818 65.743 1.433 5.713 41.111 22.949 20.764 62.546 1.949 5.945 40.219 24.725 19.578 60.106 2.563 6.183 39.178 27.016 18.037 58.384 2.875 6.511 38.606 28.542 17.005 56.881 3.300 6.780 37.978 31.025 15.365 55.308 3.697 7.122 37.404 32.989 14.066 53.171 4.280 8.047 36.004 35.011 12.836 50.166 5.279 9.123 34.046 36.133 11.830 45.052 7.404 10.152 32.626 37.825 10.903 40.467 9.795 11.385 31.402 39.178 10.148 35.956 12.262 11.851 30.489 40.357 9.515 30.943 15.418 13.038 29.199 41.583 8.919 27.878 17.371 13.717 28.262 42.623 8.411 24.575 19.668 14.793 27.286 43.666 7.890 21.300 22.012 16.089 26.084 45.083 7.295 4.539 44.027 18.217 24.542 45.890 6.895 {C3Mim DCA(1) + Potassium Citrate Tribasic Monodydrate (2) + Water (3)} 66.153 1.368 39.891 3.862 15.521 21.669 61.832 1.943 38.834 4.086 17.551 20.524 58.548 2.477 37.154 4.755 18.749 19.728 54.940 3.370 35.841 5.018 20.213 18.721 52.298 3.719 34.551 5.436 21.675 17.746 50.972 4.051 33.753 5.705 23.404 16.701 49.632 4.605 33.238 5.976 25.000 15.784 48.320 5.082 32.746 6.194 26.852 14.689 47.338 5.277 32.191 6.535 28.637 13.806 46.356 5.542 31.312 7.110 29.810 13.070 45.318 5.855 30.469 7.425 31.241 12.186 42.218 7.078 29.798 7.798 32.393 11.553 40.200 7.752 29.026 8.252 33.524 11.004 36.783 9.567 27.570 9.494 34.375 10.478 33.368 11.282 26.406 10.474 35.359 9.960 30.759 12.353 25.096 11.673 36.286 9.505 28.627 13.458 23.818 12.894 37.073 9.117 24.720 15.782 22.662 14.304 37.875 8.728 {C4Mim DCA(1) + Potassium Citrate Tribasic Monodydrate (2) + Water (3)} 64.531 1.074 22.282 13.553 9.112 22.818 58.652 1.934 21.332 14.067 10.203 21.694 55.187 2.383 19.941 14.732 10.923 20.931 52.478 2.902 18.144 15.684 11.534 20.338 49.495 3.375 2.425 38.961 12.202 19.672

w2

w1

w2

w1

w2

{C4Mim DCA(1) + Potassium Citrate Tribasic Monodydrate (2) + Water (3)} 46.444 4.165 2.706 37.328 13.925 18.444 44.123 4.686 2.977 36.067 15.208 17.525 39.671 6.142 3.234 35.119 16.866 16.465 37.286 7.111 3.601 33.756 18.446 15.553 36.422 7.474 3.782 32.623 20.169 14.676 34.453 8.147 4.461 31.492 22.067 13.739 32.887 8.756 4.983 29.691 23.514 13.098 31.152 9.529 6.093 28.027 24.778 12.417 29.728 10.238 6.776 26.754 26.462 11.604 28.346 10.835 7.377 25.488 27.933 11.024 27.134 11.413 7.828 24.725 29.161 10.532 24.495 12.474 8.431 23.902 30.285 9.991 {C6Mim DCA(1) + Potassium Citrate Tribasic Monodydrate (2) + Water (3)} 55.436 2.027 18.299 8.652 3.919 19.826 50.970 2.287 16.898 9.098 4.030 19.404 48.878 2.546 1.300 38.452 4.218 18.992 45.685 2.782 1.428 33.815 4.573 18.291 42.692 3.456 1.643 31.538 4.936 17.778 40.975 3.539 2.051 27.838 5.597 16.212 39.095 3.902 2.128 27.006 6.142 15.477 37.592 4.116 2.269 25.906 6.479 15.062 35.643 4.544 2.519 25.089 6.859 14.701 32.701 5.073 2.843 24.232 7.276 14.179 30.300 5.631 2.986 23.115 7.942 13.520 27.556 6.213 3.050 22.220 8.901 12.759 24.082 7.038 3.298 21.765 9.640 12.179 22.523 7.455 3.432 21.127 11.363 11.260 20.892 8.042 3.616 20.579 13.563 10.426 19.561 8.353 3.763 20.139 15.763 9.616 {C4Mpyr DCA(1) + Potassium Citrate Tribasic Monodydrate (2) + Water (3)} 65.150 1.040 22.176 12.683 3.433 28.527 59.256 1.359 21.230 13.018 4.174 27.075 51.927 2.355 19.835 13.552 4.838 25.695 47.069 3.128 18.432 14.127 5.789 24.409 45.795 3.454 17.491 14.651 6.659 22.941 42.768 4.130 16.593 15.062 7.535 21.692 39.424 5.154 15.839 15.435 8.754 20.434 37.849 5.613 1.294 41.413 10.179 19.011 36.043 6.366 1.495 39.138 11.844 17.725 33.851 7.014 1.679 36.592 13.523 16.551 31.550 8.000 1.749 34.166 15.006 15.679 30.019 8.498 2.033 32.654 16.707 14.660 25.456 11.347 2.773 31.335 18.930 13.537 24.121 11.813 2.996 29.995 21.560 12.312 a

Standard uncertainty, u, are u(T) = 0.2 K, u(p) = 10 kPa, u(w) = 10−3.

the capacity of ILs to form two phases. The same results are presented in Figure 1b for the systems containing the potassium citrate salt. These conclusions are in good accordance with previous values presented in the literature by several authors for other IL-based ABS which contain other ionic liquids and salts, in which the biphasic area also increases with the increase of the cation alkyl chain side length.3,5,6,16,19 This effect is directly related to the hydrophobicityof the IL, so the longer aliphatic chains of the cation contribute to an enhanced hydrophobicity of the ionic liquid. C



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Table 3. Adjustable Parameters (a, b, and c) Obtained by Merchuck Equation (eq 1) and Standard Deviation for the Experimental Binodal Curves Data system {C2Mim DCA (1) + C6H5Na3O7 (2) + water (3)} {C3Mim DCA (1) + C6H5Na3O7 (2) + water (3)} {C4Mim DCA (1) + C6H5Na3O7 (2) + water (3)} {C6Mim DCA (1) + C6H5Na3O7 (2) + water (3)} {C4Mpyr DCA (1) + C6H5Na3O7 (2) + water (3)} {C2Mim DCA (1) + C6H5K3O7 (2) + water (3)} {C3Mim DCA (1) + C6H5K3O7 (2) + water (3)} {C4Mim DCA (1) + C6H5K3O7 (2) + water (3)} {C6Mim DCA (1) + C6H5K3O7 (2) + water (3)} {C4Mpyr DCA (1) + C6H5K3O7 (2) + water (3)} a

a

b

σa

c −5

88.325

−0.277

2.63 × 10

89.197

−0.323

3.43 × 10−5

0.716

95.225

−0.392

5.18 × 10−5

0.998

273.370

−0.990

3.45 × 10−6

0.631

91.940

−0.416

5.79 × 10−5

0.737

90.396

−0.257

1.95 × 10−5

0.743

95.778

−0.308

3.01 × 10−5

0.680

95.979

−0.357

4.88 × 10−5

0.956

146.846

−0.680

7.04 × 10−5

0.981

94.326

−0.383

6.59 × 10−5

0.890

0.174

Standard deviation:

⎧ ndat ⎫1/2 2 σ = ⎨∑ ((z − zcal)) /ndat ⎬ ⎩ i ⎭ ⎪

⎪

⎪

⎪

where (z and zcal are the values of the experimental and calculated property and ndat is the number of experimental data points).

good agreement between our data and the literature data. For all the other ternary systems presented in this work no literature data were found. Regarding the effect of the cation nature of ionic liquid on the ABS phase behavior, Figure 1 shows that an increase of the length of the alkyl chain of the cation of the IL leads to an increase of the biphasic in the order C4Mpy DCA > C4Mim DCA for the studied salts. The results measured in this work agree with those obtained for other anions,3,21 where the IL cation ability to form ABS follows the order py > pip > pyr > im. Influence of Salt. In Figure 1c a comparison between the experimental binodal curves for the two salts used in this work, is presented. From this figure, the ability of the organic salts (sodium citrate tribasic dehydrate and potasium citrate tribasic monohydrate) to increase the biphasic region with different ionic liquids can be evaluated, and as can be observed the systems composed of sodium salt present a just slightly higher biphasic region. A sodium cation presents a better capacity to form ABS than a potassium cation; this effect may be due to the salting-out effect and can be explained by the Hofmeister series.32 Finally, as can be observed in Table 3 good correlation coefficients were achieved with eq 1 for all the 10 studied systems.

Figure 1. (a) Binodal curve of the ternary systems composed of {ionic liquid (1) + sodium citrate tribasic dihydrate salt (2) + water (3)} at T = 298.15 K and atmospheric pressure. The symbols represent the experimental data and the line corresponds to the fitting by eq 1: (●) C2Mim DCA; (■) C3Mim DCA; (▲) C4Mim DCA; (×) C6Mim DCA and (△) C4Mpy DCA. (b) Binodal curve of the ternary systems composed of {ionic liquid (1) + potasium citrate tribasic monohydrate salt (2) + water (3)} at T = 298.15 K and atmospheric pressure. The symbols represent the experimental data and the line corresponds to the fitting by eq 1: (●) C2Mim DCA; (■) C3Mim DCA; (▲) C4Mim DCA; (×) C6Mim DCA, (△) C4Mpy DCA, and (+)C4Mim DCA (ref 3). (c) Binodal curve of the ternary systems composed of {ionic liquid (1) + salt (2) + water (3)} at T = 298.15 K and atmospheric pressure: (●) {C2Mim DCA (1) + sodium citrate tribasic dihydrate salt (2) + water (3)}; (○) {C2Mim DCA (1) + potasium citrate tribasic monohydrate salt (2) + water (3)}; (▲){C4Mim DCA (1) + sodium citrate tribasic dihydrate salt (2) + water (3)}; (△){C4Mim DCA (1) + potasium citrate tribasic monohydrate salt (2) + water (3)}; (■){C6Mim DCA (1) + sodium citrate tribasic dihydrate salt (2) + water (3)} and (□){C6Mim DCA (1) + potasium citrate tribasic monohydrate salt (2) + water (3)}.

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CONCLUSIONS In this paper, 10 novel ILs-based ABS were studied. The ILs selected for this work were CnMim DCA (with n = 2, 3, 4, and 6) and C4pyr DCA, and were combined with two organic salts, sodium citrate tribasic dihydrate and potassium citrate tribasic monohydrate. The binodal curves were experimentally calculated at T = 298.15 K and atmospheric pressure. With the selection of the ionic liquids and the organic salts, three influences on the ABS can be evaluated: the alkyl chain length

The system {C4Mim DCA (1) + potasium citrate tribasic monohydrate (2) + water (3)} has already been reported by Freire et al.,3 and as can be observed in Figure 1b, there is a D



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of the cation of the ionic liquid, the cation core, and the cation of the salt. The capacity of the ILs to increase the biphasic area increases as follows: C6Mim DCA > C4Mim DCA > C3Mim DCA > C2Mim DCA. This behavior is in good accordance with previous data for other ionic liquids reported by other authors. This order is the same for the two organic salts studied. To assess the influence of the cation core of the ionic liquid on the ABS, C4Mim DCA and C4Mpyr DCA ionic liquids were selected. It was found that the two-liquid phases formation in the investigated systems increases in the order: C4Mpy DCA > C4Mim DCA. Finally, regarding the ability of the organic salts, sodium citrate tribasic dihydrate and potassium citrate tribasic monohydrate, the best results were observed for the systems composed by saturation with a sodium cation.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +351 22508 1653. Fax: +351 22508 1674. E-mail: [email protected]. ORCID

Á ngeles Domínguez: 0000-0002-6695-4064 Eugénia A. Macedo: 0000-0003-3324-4733 Funding

This work is a result of project “AIProcMat@N2020-Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF) and of Project POCI-01-0145FEDER-006984, Associate Laboratory LSRE-LCM funded by ERDF through COMPETE2020, Programa Operacional Competitividade e Internacionalizaçaõ (POCI); and by national funds through FCTFundaçaõ para a Ciência e a Tecnologia and to the Ministerio de Industria y Competitividad of Spain (project CTQ2016-77422-C2-1-R). Elena Gómez acknowledges funding support from Project AIProcMat@N2020-0145-FEDER-006984 ́ and Irene Dominguez is grateful to the Xunta de Galicia (Spain) for her scholarship (ED481B2014/104-O). Notes

The authors declare no competing financial interest.

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REFERENCES

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Ionic Liquids-Based Aqueous Biphasic Systems with Citrate

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