Ionic Liquids as Promising Solvents for Biomass Derived Mannitol and

Ionic Liquids as Promising Solvents for Biomass Derived Mannitol and Xylitol. Ana Rita C. Morais, Lucinda J. A. Conceição, Rafał Bogel-Łukasik, an...
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Ionic Liquids As Promising Solvents for Biomass Derived Mannitol and Xylitol Ana Rita C. Morais,† Lucinda J. A. Conceiçaõ ,†,‡ Rafał Bogel-Łukasik,*,† and Ewa Bogel-Łukasik‡ †

Unit of Bioenergy, Laboratório Nacional de Energia e Geologia, I.P., Estrada do Paço do Lumiar 22, 1649-038, Lisboa, Portugal REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal

‡

ABSTRACT: Ionic liquids are novel media characterized by tunable physicochemical properties leading to the wide spectrum of application. Up to now ionic liquids have proven their feasibility to dissolve selectively biomass as a whole as well as individually carbohydrates. This work demonstrates solubility of sugar alcohols which can be obtained from biomass. The solubility of mannitol and xylitol has been studied in the temperature range from (318.15 to 414.15) K using a dynamic (synthetic) method. The solubility of sugar alcohols in triflate ([OTf]) ionic liquids is slightly worse than in other hydrophilic ones such as imidazolium ILs containing hydrogen sulfate or thiocyanate or tricyanomethane or 2(2methoxyethoxy)ethylsulfate anions. The obtained results confirm the tailoring of the ionic liquids guides to differentiate sugar alcohol solubility; thus, it can be tuned from extremely high to the negligible one depending on the ionic liquid used. Xylitol is more soluble than mannitol in the examined ionic liquids, and the solubility of both sugar alcohols decreases as the length of the alkyl chain of the IL cation is increasing.

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INTRODUCTION Carbohydrates and their derivatives are one of the most abundant organic compounds found in nature.1 Due to their common presence the recent focus on the processing of carbohydrates to a variety of products has been explored intensively. The concept guiding this conversion is called biorefinery, and the major goal is a maximal exploitation of the carbohydrate-rich raw material to produce energy (fuel, heat, and power) and the high value added products (e.g., chemicals and materials).2 Sugar alcohols are considered to be high value added products and are commodities that can be obtained in the frame of the biorefinery concept. The most popular sugar alcohols are xylitol and mannitol. Xylitol as a building block from the biomass biorefinery is applicable in ample processes guiding the synthesis of many chemicals.3,4 Xylitol is an artificial sweetener characterized by slow adsorption without increasing the sugar level in the blood. Therefore xylitol is considered an alternative sugar for diabetes.5 For this reason xylitol is widely used in “sugar-free” chewing gums, dietary drinks, and foods.6 Furthermore xylitol is also called a “toothfriendly” sugar substitute because of a plaque-reducing effect.7 Mannitol is the second common sugar alcohol obtained by the hydrogenation of sucrose after inversion to glucose-fructose syrop.8 It is also commonly used as artificial sweetener1 and is used as a drug carrier in the human body.9 Analogous to xylitol, mannitol is commonly used as a sweetener and as a booster of a cooling effect in mint candies and chewing gums.10 The practical use of sugar alcohols is almost always associated with wet chemistry; therefore, the efficient methods © XXXX American Chemical Society

of dissolution of these compounds are crucial for their successful application. Sugar alcohols are very soluble in water; however, water, although considered green solvent,11 shows significant limitations in practical use. Water is rather poorly soluble in most organic solvents; therefore, most processes cannot be carried out in a water environment. For this reason, novel solvents for carbohydrates and their derivatives as well as any other organic chemicals are required. Ionic liquids (ILs) seem to be one of these interesting replacements because they reveal a large solvating capacity and are selective solvents for various organic chemicals12−14 ILs as salts are compounds composed solely of ions with immeasurable combinations of anions and cations; therefore, they are considered designer solvents15 with easily and tunable properties. Due to this, ILs facilitate more sustainable applications in reactions16,17 and separations18−21 because of their unique properties, such as a high thermal stability,22 great solvent power,23 and many others. In the last few decades, the number of publications about the use of ionic liquids in carbohydrates chemistry demonstrates a strongly increasing tendency. It is definitively guided by the increasing interest of the scientific community in biomass valorisation. Nevertheless this research field is still in the very beginning although some ground-breaking discoveries were already made. For example the selective and efficient biomass Received: March 22, 2013 Accepted: February 6, 2014

A

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trifluoromethanesulfonate [C10mim][OTf] (purity 100 w ≥ 99). All examined ionic liquids were purchased from Io-Li-Tec GmbH, Heilbronn, Germany. The halide content in all ionic liquids was < 100 ppm according to suppliers’ information. All ionic liquids were treated prior to experiments by being degassed, dried, and freed from any traces of volatile compounds and water by applying a vacuum (0.1 Pa) at moderate temperature (60 °C) for minimum 24 h directly prior to use. The water content in the examined ionic liquids was as follows: [C2mim][OTf] 210 ppm, [C4mim][OTf] 240 ppm, [C6mim][OTf] 200 ppm, [C8mim][OTf] 170 ppm, and [C10mim][OTf] 230 ppm. The anhydrous sugar alcohols (D-mannitol and D-xylitol) were used in this study. Xylitol was bought from Sigma with the stated purity of 100 w ≥ 99. D-Mannitol (Merck art. 5987) was acquired from Merck USA with the HPLC grade (purity 100 w ≥ 99). Solutes (sugar alcohols) were kept under vacuum (0.1 Pa) at moderate 60 °C for at least 24 h prior to use. The water content determined by Karl Fischer procedure was established for D-mannitol at the level of 7840 ppm and for D-xylitol at 11890 ppm. All of the studied compounds underwent drying procedures as described previously, and the fresh samples of each chemical were used to prepare solutions, always immediately before the phase diagram determination. Experimental Procedure. The phase equilibria (solid− liquid, SLE, and liquid−liquid, LLE) were examined at ambient pressure of 0.1 MPa and at temperature range from (318.15 to 414.15) K using a dynamic (synthetic) method described elsewhere.33 The measurement were always carried out at temperature above 318.15 K to reduce the effect of high viscosity of binary samples that obstructed of the last crystal (SLE) or two phase (LLE) disappearance. The solutions were prepared in 5 mL Supelco flasks by weighing the pure components with accuracy of 10−4 g. The experiments were made by heating very slowly (at less 2Kh−1 near the equilibrium temperature) a mixture of sugar alcohol and ionic liquid with continuous stirring inside a Pyrex glass cell, placed in a thermostat. The solubility measurements were confirmed by the visual observation of the solution under the microscope (200× magnifications), and no sugar crystal presence in the IL was noticed.32 For [C10mim][OTf] solvent, the solubility was determined at 363.15 K by continuous addition of a fresh portion of solute up to the moment when no more solute was soluble in the examined ionic liquid at determined temperature. As the thermostatic fluid, silicon oil was used. The temperature of the last crystal disappearance was measured with a calibrated DOSTMANN electronic P600 thermometer equipped in a Pt 100 probe totally immersed in the thermostatting liquid. The uncertainty of the temperature

fractionation in ionic liquids is one of these achievements.24−28 Another attained milestone is the use of ionic liquids in the processing of biomass to high value added products, e.g., to 5-hydroxymethylfurfural.16 Although the works with the use of ionic liquids demonstrate high quality research, very often the deficiency of basic data impedes the applicability of these achievements. Thus it is extremely important to examine simple as well as complex systems containing ionic liquids and biobased molecules such as, e.g., sugar alcohols. In the past decade the solubility of carbohydrates was extensively examined;12,23 however, dissolution of sugar alcohols was studied extremely rarely.29−32 In this work the solubility (solid−liquid and liquid−liquid phase equilibria) of xylitol and mannitol, sugar alcohols in ionic liquids, in a full scale range of composition and temperature up to 413.93 K are presented. This research involves hydrophilic trifluoromethanesulfonate (triflate) ionic liquids to boost a spectrum of the potentially interesting solvents for sugar origin compounds. Furthermore triflate ionic liquids were shown to be good solvents for other value added compounds from biomass such as tannins and flavonoids.13 Therefore the solubility data for other groups of compounds produced from biomass in the biorefinery concept are valuable contributions for the general knowledge. The chemical structures of ionic liquids and sugar alcohols investigated in this work are presented in Figure 1.

Figure 1. Ionic liquids and sugar alcohols used in this study: (a) 1-alkyl(R)-3-methylimidazolium triflate, where R = ethyl, butyl, hexyl, octyl, or decyl; (b) xylitol; and (c) mannitol.

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EXPERIMENTAL SECTION Chemicals. For the purpose of this investigation, the following ionic liquids were selected: 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C2mim][OTf] (purity 100 w ≥ 99), 1-butyl-3methylimidazolium trifluoromethanesulfonate [C4mim][OTf] (purity 100 w ≥ 99), 1-hexyl-3-methylimidazolium trifluoromethanesulfonate [C6mim][OTf] (purity 100 w ≥ 99), 1-methyl3-octylimidazolium trifluoromethanesulfonate [C8mim][OTf] (purity 100 w ≥ 99), and 1-decyl-3-methylimidazolium

Table 1. Solubility Data (x) and Experimental Activity Coefficient (γ1) of Mannitol (1) in the Examined Ionic Liquids at Temperature T and Pressure p = 0.1 MPaa [C2mim][OTf](2)

a

[C4mim][OTf](2)

[C6mim][OTf](2)

[C8mim][OTf](2)

[C10mim][OTf](2)

x1

T/K

γ1

x1

T/K

γ1

x1

T/K

γ1

x1

T/K

γ1

x1

T/K

0.0305 0.0543 0.0802 0.1183 0.1728 0.2176 1.0000a

340.96 351.02 357.59 364.42 370.62 375.57 439.10

0.69 0.60 0.54 0.49 0.43 0.42 1.00

0.0274 0.0489 0.0721 0.1062 0.1549 0.1947 1.0000b

364.69 378.28 387.14 396.37 404.73 411.42 439.10

2.14 2.09 2.02 1.96 1.85 1.89 1.00

0.0273 0.0485 0.0716 0.1055 1.0000a

373.84 388.79 398.54 408.69 439.10

3.13 3.20 3.16 3.15 1.00

0.0258 0.0460 0.0678 1.0000a

386.20 402.99 413.93 439.10

5.43 5.83 5.96 1.00

0.0079

363.15

γ1

Standard uncertainties u are u(T) = 0.03 K, u(x) = 0.0005. bReference 37. B

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C

1.00

6.30

8.20

11.91

18.62

T/K

363.15

x1

0.0146 24.40 33.38

γ1

1.00

5.45

7.10

10.30

T/K

340.66 363.16 366.70 363.18 386.48 363.17 398.07 363.20 404.87 363.20 411.90 365.70

x1

0.0173 0.0275 0.0275b 0.0493 0.0493b 0.0771 0.0771b 0.1121 0.1121b 0.1460 0.1460b 1.0000c 13.38 16.33

γ1

0.97 0.99 1.00

0.96

0.99

1.04

1.17

1.50

2.19

2.52

2.77

a

Standard uncertainties u are u(T) = 0.03 K, u(x) = 0.0005. bLiquid−liquid equilibria. cReference 37.

1.00

5.40

7.05

T/K

340.80 363.16 364.91 363.20 374.30 363.19 379.80 363.18 386.80 365.70

x1

0.0317 0.0562 0.0562 0.0892 0.0892b 0.1294 0.1294b 0.1685 0.1685b 1.0000c 10.69 12.98 10.24

γ1 T/K

334.65 356.57 363.16 365.10 363.20 370.11 363.18 376.47 365.70 0.0319 0.0565 0.0896 0.0896b 0.1304 0.1304b 0.1701 0.1701b 1.0000c

x1 γ1

1.91

[C8mim][OTf](2) [C6mim][OTf](2)

T/K

363.19 372.28 363.19 374.13 363.19 373.14 363.19 369.93 363.19 366.32 363.19 363.83 364.33 365.16 365.70 0.4812 0.4812b 0.6111 0.6111b 0.7873 0.7873b 0.8838 0.8838b 0.9270 0.9270b 0.9588 0.9588b 0.9876 0.9951 1.0000c

x1 γ1

5.41 5.49 5.28 4.69 3.98 3.51 3.23 2.98

where x1, γ1, ΔfusH1, Δfus, Cp1, Tfus,1, and T1 stand for mole fraction, activity coefficient, enthalpy of fusion, difference in solute heat capacity between the solid and liquid at the melting temperature, melting temperature of the solute, and equilibrium temperature, respectively. The aforementioned equation may be used assuming the simple eutectic mixtures have full miscibility in the liquid and immiscibility in the solid phases. In this study, the solute activity coefficients γ1 from the NRTL34 correlation equation that describe the Gibbs excess energy (GE) was used. The molar volume of xylitol and mannitol Vm1 (298.15 K) was calculated by the group contribution method35 and was assumed to be 100.2 cm3·mol−1 for xylitol and 120.2 cm3·mol−1 for mannitol. The molar volume data for solvents were taken from literature or calculated in the same manner as for solute. The Vm2 are as follows: [C2mim][OTf], 187.2;36

T/K

⎤ ΔfusCp1 ⎡ ⎛ T1 ⎞ T ⎢ln⎜⎜ ⎟⎟ + fus,1 − 1⎥ + ln γ1 ⎥⎦ R ⎢⎣ ⎝ Tfus,1 ⎠ T1

318.71 334.94 342.82 347.54 351.4 354.25 358.79 363.19 364.17 363.16 365.89 363.18 368.04 363.19 370.30

−

x1

ΔfusH1 ⎛ 1 1 ⎞ ⎜⎜ − ⎟⎟ R ⎝ T1 Tfus,1 ⎠

0.0354 0.0628 0.0863 0.1145 0.1544 0.1929 0.2450 0.3079 0.3079b 0.3317 0.3317b 0.3652 0.3652b 0.4196 0.4196b

−ln x1 =

[C4mim][OTf](2)

RESULTS Solubility of xylitol and mannitol in triflate ILs was investigated in this work. The tabulated data of the solubility of these sugar alcohols in [C2mim][OTf], [C4mim][OTf], [C6mim][OTf], and [C8mim]OTf] are compiled in Tables 1 and 2. It was found that the solubility of mannitol in the examined triflate ionic liquid is decreasing with an increase of the alkyl chain length in the ionic liquid cation of triflate salts. For example at 363.15K the solubility of mannitol in [C2mim][OTf] determined by the NRTL equation is 0.1118 mol fraction of solute and decreases to 0.0251, 0.0189, and to 0.0113 for [C4mim][OTf], [C6mim][OTf], and [C8mim][OTf], respectively. The comparison of the mannitol solubility in [OTf] ionic liquids is shown in Figure 2. When the obtained data are analyzed, it can be observed that the solubility of mannitol in [C2mim][OTf] at 363.15 K is 5-fold higher than that in [C4mim][OTf]. A similar relation was found for xylitol for which at 363.15 K the solubility in [C2mim][OTf] is more than 4 times higher than that in [C4mim][OTf]. In general the solubility of xylitol in triflate ionic liquids follows the identical trend as observed for mannitol in the same ionic liquids. Thus, the solubility decreases with the increase of the alkyl chain length in the ionic liquid cation. Consequently the solubility of xylitol in [OTf] increases in the following order: [C8mim][OTf] < [C6mim][OTf] < [C4mim][OTf] < [C2mim][OTf]. At 363.15 K xylitol is poorly soluble in [C8mim][OTf] (x1 = 0.0257), while for other ILs the solubility is 0.0570, 0.0888, and 0.3062 for [C6mim][OTf], [C4mim][OTf], and [C2mim][OTf], respectively. The comparison of the solubility data of xylitol in ionic liquids is presented in Figures 3 and 4. In all systems consisting of xylitol and studied ionic liquids, the LLE phase equilibria was observed. The most pronounced LLE was determined for [C2mim][OTf] for which the complete miscibility gap in the liquid phase was noticed (Figure 3, region “2”). The correlation of solid+liquid equilibria has been made using the following equation:

[C2mim][OTf](2)

Table 2. Solid−Liquid (SLE) and Liquid−Liquid (LLE) Solubility Data (x) and Experimental Activity Coefficient (γ1) of Xylitol (1) in the Studied Ionic Liquids at Temperature T and Pressure p = 0.1 MPa.a

■

[C10mim][OTf](2)

γ1

measurements was ± 0.03 K, and that of the mole fraction did not exceed ± 0.0005.

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Figure 2. Mannitol solubility (x1) in [C2mim][OTf] (●), [C4mim][OTf] (○), [C6mim][OTf] (■), and [C8mim][OTf] (□). The dashed line represent the ideal solubility of mannitol in [C2mim][OTf] and dashed-dotted line for system with [C4mim][OTf]. The ideal solubilities for mannitol + [C6mim][OTf] or + [C8mim][OTf] are not presented; however, they are almost identical to the system with [C4mim][OTf].

Figure 4. Solid−liquid and liquid−liquid equilibria for system containing of xylitol and [C4mim][OTf] (●), [C6mim][OTf] (□), and [C8mim][OTf] (■). The idea solubility for the system xylitol + [C4mim][OTf] is represented by solid lines. The idea solubility are omitted for the clarity of the figure.

analysis of the solubility results revealed that mannitol is significantly less soluble than xylitol in series of imidazolium and phosphonium ionic liquids. Furthermore xylitol is soluble in triisobutylmethylphosphonium tosylate ionic liquid contrary to the tetradecyl(trihexyl)phosphonium dodecylbenzenesulfonate ionic liquid previously reported.29 This dissimilarity confirms that, even for the same type of ionic liquid (phosphonium), the alkyl chain substituents as well as anion are important and play a significant role in affecting the solubility data. Paduszynski et al. examined the solubility of sorbitol and xylitol in dicyanamide ionic liquids.31 They found that xylitol is more soluble than sorbitol due to the difference in the melting point but also due to the slightly more hydrophilic structure of xylitol than sorbitol. Furthermore the solubility of sugar alcohols depends on the polarity of the cation and in case of imidazolium cation the aromacity of IL promotes higher solubility.31 When the data obtained in this work is analyzed, it can be concluded that results presented herein are in general agreement with those presented by Conceição et al.32 Therefore, the general conclusion is that xylitol is more soluble than mannitol in [OTf] ionic liquids. This comparison is presented in Figure 5 on 1-hexyl-3-methylimidazolium triflate example. When Figure 5 as well as results for other ionic liquids are examined, it can be clearly stated that xylitol is twice more soluble than mannitol in the same IL. The responsibility for such a difference in solubility can be found in the considerable difference in the melting points and enthalpies of melting of both sugar alcohols. The enthalpy of melting and melting point of mannitol is 56.1 kJ·mol−1 and 439.10 K,37 while for xylitol the solid to liquid phase transition is detectable at 365.70 K with a noticeably lower enthalpy of melting at the level of 37.4 kJ·mol−1.37 These differences in melting point and enthalpy of melting may lead to much higher solubility of xylitol in ionic liquids in comparison to that for mannitol. Additionally, due to the low melting point and low enthalpy of melting, the existence of liquid− liquid phase equilibria for a composition rich in xylitol was observed as miscibility gap presented in Figures 3 and 4 for temperatures higher than 363.15 K.

Figure 3. Solid−liquid and liquid−liquid equilibria for systems containing of xylitol and [C2mim][OTf]. The regions indicate the coexisting phases and they are as follows: (1) crystals of xylitol + liquid saturated with crystals of ionic liquid, (2) liquid L1 + liquid L2, (3) homogeneous liquid, and (4) crystals of xylitol + liquid saturated with crystals of ionic liquid. Lines are given only as a guide to an eye.

[C4mim][OTf], 223.6;36 [C6mim][OTf], 259.5;35 and [C8mim][OTf], 303.035 cm3·mol−1. The values of model parameters obtained by fitting to the solubility results with the corresponding standard deviations are presented in Table 3.

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DISCUSSION To date very scarce data about the solubility of sugar alcohols in ionic liquids have been presented in the literature.29,31,32 Payne and Kerton found that xylitol was insoluble in tetradecyl(trihexyl)phosphonium dodecylbenzenesulfonate. They also showed that xylitol in the concentration of 20 mg·g−1 at 100 °C is soluble in 1-butyl-3-methylimidazolium chloride and 1-butyl-3methylimidazolium hexafluorophosphate as well as in the two eutectic mixtures of choline chloride with oxalic or citric acid.29 Conceiçaõ et al. presented more comprehensive data, and the D

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Table 3. Correlation of the Solubility Data, SLE, of Xylitol or Mannitol (1) + a Solvent (2) by NRTL Equation: Values of Parameters and Deviations

xylitol (1) + [C2mim][OTf] [C4mim][OTf] [C6mim][OTf] [C8mim][OTf] a

(2) (2) (2) (2)

parameters

deviations

parameters

deviations

Δg12, Δg21

σTa

Δg12, Δg21

σTa

J·mol−1

K

J·mol−1

K

2095.87, −3890.81 6229.73, −1044.50 18867.60, 581.55 18096.70, 2626.76

5.07b 0.52b 0.22b 2.54b

7044.10, 6988.89, 3813.18, 1438.20,

1815.53 4494.49 6376.69 9670.89

mannitol (1) + b

1.16 4.70b 4.95b 5.02b

[C2mim][OTf] [C4mim][OTf] [C6mim][OTf] [C8mim][OTf]

(2) (2) (2) (2)

2 1/2 b According to the equation σT = [Σi n= 1(Texp − Tcal i i ) /(n − 2)] , Calculated with the third non randomness parameter α = 0.3.

x1 = 0.0079 at 363.15 K. It shows that the less hydrophilic ionic liquids are, the less selective the solvent as dissolve both sugar alcohols equally well. Comparing the obtained data with the literature one, it can be stated that surprisingly [OTf] ionic liquids are rather poor solvents for sugar alcohols. It is unexpected as [OTf] ionic liquids are known as hydrophilic ionic liquids and are very good solvents for many mono and polyhydroxy alcohols.38 Nevertheless the data presented herein shows that [C4mim][OTf] compared to other 1-alkyl-3-methylimidazolium ionic liquids with hydrogen sulfate, thiocyanate, tricyanomethane, 2(2-methoxyethoxy)ethylsulfate anion, or even to triisobutylmethylphosphonium tosylate is a worse solvent than the previously mentioned ILs.32 However it is also important to notice that all of the referred anions (hydrogen sulfate, thiocyanate, tricyanomethane, 2(2methoxyethoxy)ethylsulfate, and tosylate) are also hydrophilic; therefore, the solubility of sugar alcohols in these ionic liquids might be also as high as in [OTf] ionic liquids or even higher than in the ILs studied in this work. A similar conclusion was found in the literature for [emim][EtSO4] and Aliquat ionic liquids for which in more hydrophobic Aliquat IL the solubility of sugar alcohols was lower than in ethylsulfate ionic liquid.30 Furthermore the examined ILs showed to be less efficient in sugar alcohol dissolution than imidazolium, pyrrolidinium, or piperidinium dicyanamide ILs as reported in the literature.31 The correlation showed that positive deviations from ideality are found for all examined systems except mannitol + [C2mim][OTf]. This confirms that for these systems solubility is lower than ideal ones. The idea solubility for mannitol + [C2mim][OTf] is negative; therefore, the solubility of mannitol in this IL is higher than predicted by the NRTL equation. The average standard deviation (σT), obtained in the correlation of the experimental results, ranged from (0.22 to 5.02) K. When the complexity of systems studied here as well as the little experimental data for some systems are taken into account, the correlation equations gave acceptable σT.

Figure 5. Solubility of {mannitol (○) or xylitol (●)} (1) + [C6mim][OTf] (2).

Furthermore the comparison of solubility of mannitol and xylitol in [OTf] ionic liquids showed that each additional ethyl group in the alkyl chain influences the solubility. However this relation is not linear and depends on the number of carbons in the alkyl chain as it is depicted in Figure 6.

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CONCLUSIONS The results obtained in this work and the previous literature reports confirm that sonic liquids are solvents that exhibit a great solvent power toward sugar alcohols.31,32 The produced data confirms the possibility of using ILs as designer solvents. Xylitol was shown to be more soluble than mannitol in the examined ionic liquids. As expected, the solubility of solid solutes increases with the increase of temperature. Furthermore, the solubility of sugar alcohols decreases as the length of the alkyl chain of the IL cation is increases. The obtained results confirm that by tailoring the ionic liquid, the solubility of the sugar alcohol can be easily modified from the extremely high solubility to the negligible one depending on the ionic liquid used.

Figure 6. Comparison of xylitol (○) and mannitol (●) solubility in [Cnmim][OTf] at 363.15 K as a function of number of carbon atoms in the ionic liquid cation alkyl chain.

Following this trend it can be expected that for, e.g., 1-decyl3-methylimidazolium triflate the difference in solubility is even lower. The solubility tests of both examined sugar alcohols in [C10mim][OTf] confirmed this observation and the solubility of xylitol in this IL equals x1 = 0.0146 while of mannitol is E

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The solid−liquid phase equilibria were described using the NRTL correlation equation which allowed for a good description with the standard deviation of temperature in the acceptable range for examined systems.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +351217163636. Phone: +351210924600 ext. 4224. Funding

This work was supported by the Fundaçaõ para a Ciência e a 336 Tecnologia (FCT, Portugal) through Grants SFRH/BD/ 94297/2013, IF/01643/2013, IF/00424/2013, and PEst-C/ EQB/LA0006/2013. Notes

The authors declare no competing financial interest.

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REFERENCES

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dx.doi.org/10.1021/je400279d | J. Chem. Eng. Data XXXX, XXX, XXX−XXX