Studies on the Dissolution of Glucose in Ionic Liquids and Extraction

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Studies on the Dissolution of Glucose in Ionic Liquids and Extraction Using the Antisolvent Method El-Sayed R. E. Hassan, Fabrice Mutelet,* Steve Pontvianne, and Jean-Charles Moïse Université de Lorraine, Ecole Nationale Supérieure des Industries Chimiques, Laboratoire Réactions et Génie des Procédés (UPR CNRS 3349), 1 rue Grandville, 54000 Nancy, France S Supporting Information *

ABSTRACT: Biomass, the fibrous material derived from plant cell walls, is a potentially clean and renewable nonfood feedstock for liquid fuel and chemical production in future biorefineries. The capability of ionic liquids to act as selective solvents and catalysts for biomass processing has already been proven. Thus, they are considered as an alternative to conventional solvents. Nevertheless, phase equilibria with biomass derived compounds is still lacking in the literature. To overcome the lack of experimental data on phase equilibria of biomass carbohydrates in ionic liquids, the solubility of D-glucose in four ionic liquids was measured within a temperature range from 283 to 373 K. Solubility data were successfully correlated with local composition thermodynamic models such as NRTL and UNIQUAC. In this work, the possibility of extracting glucose from these ionic liquids using the antisolvent method has been also evaluated. The parameters affecting the extraction process are the ionic liquid type, ethanol/ionic liquid ratio, temperature, water content, and time. Results indicate that ethanol can be successfully used as an antisolvent to separate glucose from ionic liquids.

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INTRODUCTION Biomass, as a fuel source, is renewable, environmentally friendly, and abundant in the natural world.1 It is very important to produce green energy and bioproducts from lignocellulose which is the most abundant biomass.2,3 A lignocellulosic material contains up to 35−50% cellulose4 which is the most abundant biopolymer on the earth and, thus, is a valuable source of raw materials.5 The first attempts to dissolve cellulose date back to the early 1920s.6 Several cellulose solvents have been discovered since then, but all of them suffer either from high environmental toxicity or from insufficient solvation power.7 In general, cellulose dissolution processes require relatively harsh conditions and the use of expensive and uncommon solvents, which usually cannot be recovered after the process.7−11 At the end of the twentieth century, a new class of solvents was proposed to the cellulose research community. Swatloski et al. reported the use of an ionic liquid (IL) as a solvent for cellulose both for the regeneration of cellulose and for the chemical modification of polysaccharide.8 Ionic liquids are organic salts, liquids around or below 100 °C. These solvents have unique physicochemical properties such as high thermal stability, wide electrochemical window, and negligible vapor pressure, and so they are considered to be green solvents. They have been suggested to replace volatile organic compounds in industrial separation processes, as well as applications in chemical synthesis, electrochemistry, polymer chemistry, and nanotechnology.12−16 Imidazolium-based ILs could dissolve large amounts of © XXXX American Chemical Society

cellulose that, when precipitated with water or ethanol, produce an amorphous cellulose product which could be rapidly hydrolyzed into glucose by commercial cellulase mixtures.8,9,17−19 This led to the discovery of ILs that can dissolve lignocellulose10,20−23 and pretreat biomass prior to enzymatic hydrolysis, fractionating it into its principal components.24−27 With increasing interest in the use of lignocellulosic biomass for the production of renewable transportation fuels, new approaches for biomass pretreatment have been of considerable interest.28,29 The conversion of biomass cellulose to watersoluble sugars is currently one of the most intensive demands worldwide.30 Cellulose can be degraded to glucose efficiently in ILs,31−35 but this process is restricted by the difficulty of glucose separation from ILs. Nowadays, the antisolvent method appears to have great advantages in the field of separation and purification.36 When an antisolvent is added to a binary solution (solute + solvent), the original solubility of the solute in the binary solution is reduced, so the solute is crystallized and precipitated because of supersaturation.37 Until now, the literature mainly concerned the application of ILs in the modification of cellulose trapped in the lignocellulosic biomass.38 Studies on the dissolution and extraction of carbohydrates other than cellulose in ILs are Received: October 1, 2012 Revised: December 11, 2012 Accepted: February 11, 2013

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dx.doi.org/10.1021/es303884n | Environ. Sci. Technol. XXXX, XXX, XXX−XXX

Environmental Science & Technology

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limited.39,40 The data reported in the literature concerning the solubility of glucose in ionic liquids are far from enough to have a good knowledge of phase equilibria. In most cases, these data are not available in a sufficiently large range of temperature.41 In 2000, Sheldon et al. were the first to connect ILs and carbohydrates by exploring their potential as media for carbohydrates transformations.42 In 2001, two different research groups reported the solubility of glucose in ILs based on the imidazolium unit.40,43,44 In 2009, Rosatella et al. studied the dissolution of carbohydrates in ionic liquids and their extraction from aqueous phase using dichloromethane.40 In 2011, Liu et al. studied the solubility of glucose in a binary mixture containing an IL and ethanol.37 In 2012, Carneiro et al. were the first team to study the solubility of monosaccharides in ILs using the NRTL and UNIQUAC thermodynamic models to achieve the correlation of the solubility data.41 Several molecular dynamics (MD) simulation studies were employed to investigate glucose solvation in ionic liquids. These MD simulations showed that there is no significant change in anion−cation interactions.45,46 Other MD simulations of the interactions of cellulose with 1ethyl-3-methylimidazolium acetate indicate that ILs interact strongly with cellulose through hydrogen bonding, and hydrophobic interactions may play a role in the dissolution of cellulose by ILs.47,48 This work aims to study the solubility of glucose in ionic liquids in a temperature range from 283 to 373 K using an isothermal method. Solubility data have been successfully correlated with local composition thermodynamic models such as NRTL and UNIQUAC. The second part of the article is devoted to the solubility of glucose in binary mixtures {ethanol + ionic liquids} in order to evaluate the possible use of the antisolvent method for the extraction of glucose from ionic liquids. The influence of different parameters such as temperature, ionic liquid/ethanol ratio, and water content, and also the structure of the IL, is evaluated. 23 Full-Factorial Design is used to evaluate the interaction between different parameters on the glucose solubility in a binary mixture of (BMIMCl + EtOH). Then, the antisolvent method is tested for the extraction of the glucose from 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium thiocyanate.

was maintained constant using a thermostatic bath (polystat 5D +37, Fisher Scientific) with a precision of ±0.1 K. The internal temperature of the cells was also measured with a calibrated platinum probe Pt100 with an accuracy of ±0.1 K. The mixtures, with compositions inside the immiscible region of the system, are weighed using a Mettler analytical balance with a precision of ±0.0001 g. For the solubility of glucose in pure ILs, desired amounts of pure IL and glucose were loaded into a prepared cell. The cell was sealed and connected to the temperature controller. The mixture was vigorously stirred for 6 h and was then heated very slowly (about 1 K.h−1) until complete dissolution of the glucose in the ionic liquid. The solubility measurements were confirmed by the visual observation of the solution under a microscope. For the experiments of solubility of glucose in a binary mixture (IL + EtOH), a desired amount of ethanol was loaded into a prepared cell, and then, a desired amount of IL with a given mass ratio of ethanol to IL was added quickly into the above ethanol solution. The cell was sealed and connected to the temperature controller until a transparent solution was formed. When the temperature of the system attained a desired value, an excessive amount of glucose was added to the mixture. At different time intervals, samples were withdrawn, filtered with 0.45 μm film, and analyzed by high-performance liquid chromatography (HPLC) to determine the glucose concentration. An HPLC (Shimadzu, USA) with a Shodex Asahipak NH2− 50 4E column (Shodex, Japan) and a differential refractive index detector (Shimadzu, USA) was employed for analyzing concentrations of glucose in the mixtures. The column oven temperature was 308 K, the mobile phase was a mixture of acetonitrile and water with a ratio 75:25, and the flow rate was 1 mL/min. The correlation coefficient of the glucose standard curve by HPLC reached a value of 0.999. The expanded relative uncertainty of glucose solubility in IL and antisolvent mixtures was estimated at 1.0%. The equilibration temperature was measured with an uncertainty of 0.2 K.

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RESULTS AND DISCUSSION Only a limited number of ionic liquids available have been used until now in the various applications including the solubility studies. In this work, three ionic liquids, 1-ethanol-3methylimidazolium chloride, 1-butyl-1-methylpyrrolidinium chloride, and 1,3-dimethyl-imidazolium methyl phosphonate, were investigated in order to increase the number of the potentially interesting solvents for carbohydrates. Two other classical ILs, BMIMCl and EMIMSCN used in the biomass conversion process, were also studied to evaluate their behavior in the presence of glucose. Solubility of Glucose in Pure Ionic Liquids. Four imidazolium based ionic liquids were used in this study to investigate the solubility of glucose. To our knowledge, the measurements of solubility of glucose in 1-ethanol-3-methylimidazolium chloride, 1,3-dimethyl-imidazolium methyl phosphonate, are the first published in the literature. Solid−liquid equilibria of binary systems (IL + glucose) were carried out in a large range of temperatures 283−383 K and compositions (up to 60 wt % of glucose) (see Table S1 for the solubility data of glucose in ILs, Supporting Information). Figure 1 presents the results of solubility of glucose in ILs; it is obvious that high glucose solubility is obtained at high temperatures for all imidazolium based ionic liquids. At high temperature, the

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EXPERIMENTAL TECHNIQUES Materials. D-(+)-Glucose anhydrous was purchased from Merck. Ethyl alcohol absolute with a mass fraction purity of 0.999 was from Carlo Erba. Acetonitrile with a mass fraction purity of 0.999 was from Sigma-Aldrich. The ionic liquids used in this work, 1-butyl-3-methylimidazolium chloride (BMIMCl), 1-ethanol-3-methylimidazolium chloride (EtOHMIMCl), 1-butyl-1-methylpyrrolidinium chloride (BMPyrCl), and 1,3-dimethyl-imidazolium methyl phosphonate (DMIMMPh), with purity 98%, were from Solvionic, and 1-ethyl-3-methylimidazolium thiocyanate (EMIMSCN) with purity 95% was from Sigma Aldrich. These ionic liquids were dried under vacuum for 3 h at 363 K before use. Apparatus and Procedures. Solid−liquid equilibrium phase diagrams of the studied systems were obtained at atmospheric pressure and at temperature ranges starting from 283 to 373 K. The solubility experiments of glucose in pure ILs and in a binary mixture of IL with ethanol have been performed in jacketed glass cells using a dynamic method described in the literature.49 The experimental setup consists of a cell with an internal volume of about 50 cm3. The temperature of the cell B



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excellent indicators to estimate their ability to dissolve glucose. The compilation of our data on the solubility of glucose in EMIMSCN and the data in BMIMSCN published in the literature56 proved that the solubility of glucose increases with a decrease of the alkyl chain length. Results obtained on the solubility of glucose in BMIMCl correspond well to those published in the literature.57 At 343.15 K, the solubility of glucose was found to be 0.059 wt % in this work and 0.05 wt % in the literature. The solubility curves of glucose in BMIMCl and EtOHMIMCl follow the same trend. The glucose solubility is higher in BMIMCl than in EtOHMIMCl. The influence of a functional group grafted on the cation on the dissolution of the glucose is not neglected. Similar behavior was observed concerning the solubility of cellulose in ILs.58 The presence of a hydroxyl end-group in the cation decreases the solubility of the glucose in the corresponding ILs, presumably by competing with glucose for hydrogen bond donation to the anion. Computational Theory. In the present work, the nonrandom two-liquid equation (NTRL) proposed by Renon and Prausnitz59 and the universal quasi-chemical (UNIQUAC) theory developed by Abrams and Prausnitz60 were used for the correlation of the (solid + liquid) phase equilibrium at atmospheric pressure. The solubility of glucose in the ILs was determined using a simplified thermodynamic equation relating temperature, TSLE, and the mole fraction of the glucose, x2 in the solvent61

Figure 1. Plot of the experimental and calculated SLE of {ionic liquid (1) + glucose (2)} binary systems: ■, EMIMSCN; ●, DMIMMPh; ×, BMIMCl; ▲, EtOHMIMCl. The solid lines have been calculated using the NRTL model.

solubility of glucose increases in the following order: EMIMSCN < EtOHMIMCl < BMIMCl < DMIMMPh. The chloride anion is known to have a stronger hydrogen-bonding basicity.8 Recent studies on the dissolution of cellulose in BMIMCl indicate that the anion of the IL acts as a hydrogen bond acceptor which interacts with the hydroxyl groups of the cellulose.8 Numerous solvation models may be found in the literature to describe the solute−solvant interactions in complex systems. Among others, the Kamlet−Taft parameters (α, hydrogen bond acidity; β, hydrogen bond basicity; and π*, polarity) can be used to explain the solubility of glucose in ILs (see Table S2 for the solvatochromic parameters α, β, and π* of different ILs and various classical solvents,22,50−55 Supporting Information). The EMIMMPh and BMIMCl ILs displayed high β and π* values compared to classical solvents. In the literature, methyl phosphonate based ionic liquids have a stronger hydrogen bond basicity compared to BMIMCl.22,51 In general, an increase of the alkyl chain of the imidazolium cation decreases the values α and π* while the β value increases. This work demonstrates that the interaction between the glucose and the anion of the IL is predominant compared to the interactions of the glucose with the cation. However, the solubility of glucose in IL is not only governed by the anion. Indeed, it was shown in numerous applications that the solubility of organic compounds in ILs decreases with an increase of the alkyl chain length grafted in the cation. Moreover, Swotloski et al. also found that the solubility of cellulose in ILs decreased with the increasing size of the cations such as lengthy alkyl groups substituted on the imidazolium ring.8 It is suggested that, in salt solutions with small, strong polarizing cations and large polarizable anions, intensive interactions with cellulose occur. In this work, the solubility of the glucose in ionic liquids increases with increasing the order of the hydrogen bond basicity of the ionic liquids. The solubility curves of glucose in EMIMSCN and in DMIMMPh presented in Figure 1 indicate that glucose is more soluble in EMIMSCN than in DMIMMPh at low temperature. This tendency is reversed for temperatures higher than 310 K. This behavior may be related to different physicochemical properties of ILs. IL viscosity may play a role in carbohydrate dissolution. Indeed, it is generally considered that ILs with low viscosity are more efficient in dissolving carbohydrates or cellulose. Nevertheless, viscosity is not the key factor of the solubility of glucose in ILs. Basicity and polarity of ILs are also

−ΔfusH2 ⎛ 1 1 ⎞ ⎟⎟ ·⎜⎜ SLE − R Tfus,2 ⎠ ⎝T

ln(x 2γ2) =

(1)

where ΔfusH2 and Tfus,2 denote melting enthalpy and temperature of the glucose, and x2 stands for the solubility of the glucose at the saturated temperature TSLE. NRTL Model. For the NRTL model, the activity coefficient γi, for any component i of the ternary system, is given by m

ln γi =

∑ j = 1 τjiGjixj m

∑l = 1 Glixl

m

+

∑ j=1

m ⎛ ∑r = 1 xrτrjGrj ⎞ ⎜ ⎟ τ − ij m m ∑l = 1 Gljxl ⎟⎠ ∑l = 1 Gljxl ⎜⎝

xjGij

(2)

with Gji = exp(−αjiτji), τji = [(gji − gii)/RT] = Δgji/RT, and αji = αij = α where g is an energy parameter characterizing the interaction of species i and j, xi is the mole fraction of component i, α the nonrandomness parameter. Although α can be treated as an adjustable parameter, in this study α was set equal to 0.2 according to the literature.62 UNIQUAC Model. For the UNIQUAC model, the activity coefficient γi, for any component i of the binary system is given by ln γi = ln

Φi Φ θ z + qi ln i + li − i Φi xi xi 2

m

∑ xjlj − qi ln(θτj ji) j=1

m

θτ j ji m j = 1 ∑k = 1 θkτkj

+ qi − qi ∑

(3)

where Φi = θi = = (z/2)(rj − qj) − (rj − 1), and τji = exp(−Δuij/RT). Here, the lattice coordination number z is assumed to be equal to 10, ri and qi are, respectively, a relative volume and surface area of the pure component i. Parameters ri and qi are, respectively, relative to molecular van der Waals volumes and molecular surface areas. The binary parameters for glucose were rixi/∑jm= 1rjxj,

C

qixi/∑jm= 1qjxj, lj



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Table 1. Correlation of the Solid−Liquid Equilibria Data by Means of the NRTL and UNIQUAC Equationsa solvent

a

NRTL parameters

rmsd

ionic liquid

a12/(J.mol−1)

a21/(J.mol−1)

b12/(J.mol−1.K−1)

BMIMCl DMIMMPh EMIMSCN EtOHMIMCl solvent

110290.7 34164.2 33568.6 147202

76188.6 8957.3 6678.3 90547.2

ionic liquid

a12/(J.mol−1)

a21/(J.mol−1)

b12/(J.mol−1.K−1)

b21/(J.mol−1.K−1)

σT

BMIMCl DMIMMPh EMIMSCN EtOHMIMCl

45000.0 7434.9 7434.9 45000.0

19999.9 3355.3 3354.9 20000.0

−122.6 −29.4 −9.1 −124.4

−62.4 −8.0 −20.6 −56.8

1.00 0.83 0.74 0.34

−316.3 −126.6 −64 −409.2 UNIQUAC parameters

b21/(J.mol−1.K−1)

σT

−218.5 −25.9 −49.5 −253.3

0.51 1.04 2.84 0.12 rmsd

σT is the temperature deviation.

taken from the literature.41 The required van der Waals parameters ri and qi of the UNIQUAC model for the ionic liquids were estimated with the correlation proposed by Domanska.63

Effect of the Structure of the Ionic Liquid. Figures 2−5 indicate that the solubility of glucose increases in the following

ri = 0.029281 × Vi (cm 3. mol−1) qi =

(z − 2) × ri 2 + z z

(4)

where Vi is the molar volume of the ionic liquid at T = 298.15 K and z is the coordination number assumed to be equal to 10 (see Table S3 for the van der Waals volume and surface area parameters of ILs, Supporting Information). To obtain a better description of the (solid + liquid) phase equilibrium simultaneously, temperature-dependent model parameters (Δgij or Δuij) were assumed: Δg12(J. mol−1) = g12 − g11 = a12 + b12 ·T (K ) Δg21(J. mol−1) = g21 − g22 = a 21 + b21·T (K )

Figure 2. Effect of EtOH/IL ratio by weight on the solubility of glucose in the mixture at temperature 298 K, time 300 min, with water content neglected.

(5)

A total of four adjustable parameters per binary Δgji or Δuji have to be set for each model. The model adjustable parameters of both models were found by minimization of the following objective function (OF): n

OF =

∑ (Texp ,i − Tcalc,i)2 i=1

(6)

The root-mean-square deviation (RMSD) of temperature, σT, was calculated according to the following definition: 2 ⎞1/2 ⎛ n (T exp , i − Tcalc, i) ⎟ σT = ⎜⎜∑ ⎟ n−2 ⎝ i=1 ⎠

(7)

The NRTL and UNIQUAC parameters obtained after the regression of the experimental data are listed in Table 1. As can be seen in the results depicted in Figure 1, the experimental data correlate well with both thermodynamic models. Solubility of Glucose in a Binary Mixture of (IL + EtOH). The dissolution of glucose in binary mixtures {ionic liquid + ethanol as an antisolvent} was evaluated in five ionic liquids: 1-butyl-3-methylimidazolium chloride (BMIMCl), 1ethanol-3-methylimidazolium chloride (EtOHMIMCl), 1,3dimethyl-imidazolium methyl phosphonate (DMIMMPh), 1ethyl-3-methylimidazolium thiocyanate (EMIMSCN), and 1butyl-1-methylpyrolidinium chloride (BMPyrCl).

Figure 3. Effect of temperature (K) on the solubility of glucose in the mixture at EtOH/IL ratio by weight 10, time 300 min, with water content neglected.

order: BMPyrCl < EMIMSCN < BMIMCl < EtOHMIMCl < DMIMMPh. Compared with other ionic liquids, the methyl phosphonate based ionic liquid shows higher solubility of glucose, which indicates that methyl phosphonate based ionic liquids have high dissolving power to glucose due to its strong hydrogen bond basicity. The solubility of glucose in chloride based ionic liquids increases in the following order: BMPyrCl < D



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Consequently, it is expected that these (cosolvent + BMIMCl) mixtures can have reduced affinity with polar compounds compared to pure IL. Moreover, the hydrogen bond basicity values of mixtures are also lower than in pure IL. As discussed previously, a decrease of these both solvatochromic parameters may lead to a decrease of the solubility of glucose in solvents. This indicates the high efficiency of ethanol as an antisolvent. A high ethanol/ionic liquid ratio is recommended for the satisfactory extraction of glucose from its mixtures. Effect of Temperature. Figure 3 shows the effect of temperature on the solubility of glucose in a mixture of IL + ethanol. As expected, the glucose solubility increases with increasing temperature for all ionic liquid mixtures. For example, the solubility of glucose increases from 4.663 to 14.526 g/L with increasing temperature from 298 to 333 K in a binary mixture of BMIMCl + ethanol. The increase of temperature increases the molecular thermal motion of the entire system and the volatility of a nonvolatile solute37 resulting in an increase of the solubility of glucose in IL + ethanol mixtures, and then, low temperature is recommended for the satisfactory extraction of glucose from its mixtures. Effect of Water Content. Water is one of the major impurities in ionic liquids and has a strong impact on the solubility of carbohydrates in ILs. It significantly modifies the solvation ability of ionic liquids.39 The solubility of glucose in water reaches 1100 g/L, so it would greatly affect the solubility of glucose in mixtures.37 Figure 4 shows the effect of water content on the solubility of glucose in the mixtures of IL + ethanol. The glucose solubility increases with increasing water content for all ionic liquids. For example, the solubility of glucose increases from 4.663 to 6.486 g/L with increasing water content from 0% to 4% in a binary mixture of BMIMCl + ethanol. Therefore, negligible water content is recommended for the satisfactory extraction of glucose from its mixtures. This observation corresponds well to results obtained by dynamic simulations. Indeed, dynamic simulations showed that the water molecules initially located around the glucose molecules are rapidly taken up by anions of the IL and most of the water shell around the glucose is replaced by anions. Calculations show that water acts as a solubility enhancer which disrupts glucose− glucose interaction and enhances glucose−solvent interaction (water + IL) resulting in higher glucose solubility. Dissolution Rate of Glucose Solubility. Figure 5 shows the dissolution rate of the solubility of glucose in the binary mixtures (BMIMCl + ethanol) at different temperatures (see Figure S1 for other binary mixtures (IL + ethanol), Supporting Information). It is obvious that most of the glucose dissolution occurs during the first 5 min for the binary mixtures. The solubility of glucose at temperature 298 K increases rapidly from 0 to 3.89 g/L during the first five minutes and then increases slowly up to 4.664 g/L. During the first minutes, the dissolution rate of glucose in (BMIMCl + ethanol) is 0.8 g/L/ min at 298 K, but after ten minutes the dissolution rate decreases greatly to be 0.002 g/L/min. As expected, the dissolution rate depends on the temperature of the system. It increases from 0.8 to 2.32 g/L/min when the temperature increases from 298 to 333 K. After ten minutes, the values of the dissolution rate are 0.002 and 0.018 g/L/min at 298 and 333 K, respectively. Thus, the equilibration time is prolonged when the temperature is increased. In all cases, the mixture reaches equilibrium before 200 min. Applying 23 Full-Factorial Design. An experimental design technique, 23 Full-Factorial Design, is used to optimize the

Figure 4. Effect of water content (%) on the solubility of glucose in the mixture at EtOH/IL ratio by weight 10, time 300 min, and temperature 298 K.

Figure 5. Dissolution rate of glucose in a mixture of (BMIMCl + EtOH) at EtOH/IL ratio by weight = 10, water content neglected, and temperature = ⧫, 298; ■, 313; ▲, 323; and ×, 333 K.

BMIMCl < EtOHMIMCl. The ionic liquids with a shorter chain cation have a larger dissolving power than those with long chain cations when their anions are identical.38−40 Moreover, imidazolium based ionic liquids have stronger hydrogen bond basicity than pyrollidinium based ionic liquids.43 The solubility of glucose in a binary mixture of (IL + ethanol) follows the same trend as the solubility of glucose in pure ionic liquids with the exception of BMIMCl. The presence of ethanol in a mixture of (IL + glucose) decreases the solubility of glucose. For example, the solubility of glucose in a mixture of (DMIMMPh + ethanol) at 333 K is 26.5291 g/L, while its solubility in pure DMIMMPh is 578 g/L (0.44 mass fraction) at 331.5 K. In conclusion, ethanol has high efficiency when used as an antisolvent for extraction of glucose from different kinds of ionic liquids. Effect of Ethanol/Ionic Liquid Ratio. Figure 2 illustrates the effect of ethanol/ionic liquid ratio by weight on the solubility of glucose in a binary mixture of (IL + ethanol). The glucose solubility increases with decreasing ethanol/ionic liquid ratio for all ionic liquids. For example, the solubility of glucose increases from 2.817 g/L to 6.604 g/L with decreasing ethanol/ ionic liquid ratio by weight from 20 to 5 in a binary mixture of BMIMCl with ethanol. The behavior can be explained using the solvatochromic parameters of binary mixtures (cosolvent + IL). Indeed, Yang et al 64 have shown that the π* values of (cosolvent + BMIMCl) mixtures increase with the concentration of BMIMCl, indicating the important role of an additional cosolvent on reducing the dipolarity/polarizability. E



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(BMIMCl + ethanol), the extraction percentage is equal to 21.91% when the temperature decreases from 313 to 298 K, 51.89% when the temperature decreases from 323 to 298 K, and 72.03% when the temperature decreases from 333 to 298 K. The results of the extraction of glucose from IL using the antisolvent method with different antisolvents are shown in Table 3. For these extractions, a solution containing 0.3 molar

glucose solubility results and to evaluate the interaction between different parameters. The behavior of glucose in binary mixtures of (ILs + EtOH) is quite similar. Therefore, only the case of the glucose solubility in a binary mixture of BMIMCl + EtOH is presented in this section. Such an experiment allows the study of the effect of each factor temperature, EtOH/IL ratio and water content, as well as the effects of interactions between factors on the glucose solubility. The analysis of variance (ANOVA) data for the system indicates the good fitting of the experimental results to the factorial model equation and hence accuracy of this model (see Tables S4, S5 for estimated effects and coefficients for glucose and analysis of variance for glucose (ANOVA), Supporting Information). Figure 6a,b,c shows the interaction between the

Table 3. Extraction % of the Glucose from EMIMSCN and BMIMCl with Different Antisolvents at R = 20, T = 298.15 K, with Water Content Neglected glucose extracted % antisolvents

EMIMSCN

BMIMCl

ethanol dichloromethane acetonitrile

80 95 90

99 99 99

fraction of glucose was prepared in EMIMSCN at 340 K and in BMIMCl at 360 K. After the complete dissolution of glucose, an antisolvent is added at 298 K. Results in Table 3 show the influence of the structure of the ionic liquid on the extraction performance. In conclusion, it was found that ionic liquids may be good solvents for the extraction of glucose from biomass. This work clearly shows the influence of the structure of the IL on the extraction performance. A successful extraction process requires high ethanol/IL ratio, low temperature, and low water content. The considerable decrease of the solubility of glucose in the binary mixtures proves the ability of ethanol to be an excellent antisolvent for separating glucose from various types of ionic liquids.

Figure 6. Interaction between different variables on the solubility of glucose in a binary mixture of BMIMCl + EtOH at time 300 min: (a) at water content 2%, (b) at EtOH/IL ratio by weight 12.5, (c) at temperature 315.5 K.

different factors and their effect on the solubility of glucose in this system. It is obvious that no important interaction between the different factors is observed. The glucose solubility increases with increasing both temperature and water content and with decreasing the EtOH/IL ratio. It is also clear that the main effective parameter on the glucose solubility is the temperature (see Figure S2 for the response surface plots of glucose concentration resulting from the main effects of different variables, Supporting Information). Extraction Process Using the Antisolvent Method. From the study of the dissolution of glucose in binary mixtures (ionic liquid + ethanol as an antisolvent), it is possible to evaluate the extraction percentage of glucose from ionic liquids. Table 2 represents the extraction of glucose from five ionic liquids using the antisolvent method described in the previous paragraph. In this study, the extraction is made with an ethanol/ionic liquid ratio equal to 10, neglected water content, and a decrease of temperature from 313 K (or 323 or 333) to 298 K. Results indicate that approximately 70% of glucose may be extracted from ionic liquids and this percentage increases with the increase of the temperature difference. For the binary mixture

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ASSOCIATED CONTENT

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AUTHOR INFORMATION

S Supporting Information *

Additional figures and data tables. This material is available free of charge via the Internet at http://pubs.acs.org. Corresponding Author

*E-mail: [email protected]. Telephone: +33 (0)3.83.17.51.31. Fax: +33 (0)3.83.32.29.75. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Wang, J.; Zheng, Y.; Zhang, S. The application of ionic liquids in dissolution and separation of lignocellulose. Clean energy systems and experiences. Eguchi, K., Ed.; ISBN: 978−953−307−147−3, InTech. 2010, 71−84. (2) Pu, Y.; Zhang, D.; Singh, P. M.; Ragauskas, A. J. The new forestry biofuels sector. Biofuels Bioprod. Bioref. 2008, 2, 58−73. (3) Zhu, S. Use of ionic liquids for the efficient utilization of lignocellulosic materials. J. Chem. Technol. Biotechnol. 2008, 83, 777− 779.

Table 2. Extraction % of the Glucose from Binary Mixtures of the Five Ionic Liquids at R = 10 and Neglected Water Content binary mixture of ethanol + IL

BMPyrCl

EMIMSCN

BMIMCl

DMIMMPh

EtOHMIMCl

Ex. % (from 313 to 298 K) Ex. % (from 323 to 298 K) Ex. % (from 333 to 298 K)

39.05 58.63 73.71

37.15 53.33 72.08

21.91 51.89 72.03

45.13 60.39 69.58

21.76 53.21 69.39

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Studies on the Dissolution of Glucose in Ionic Liquids and Extraction

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