Solubility and solution thermodynamics of glucose and fructose in three asymmetrical dicationic ionic liquids from 323.15 K to 353.15 K

Solubility and solution thermodynamics of glucose and fructose in three asymmetrical dicationic ionic liquids from 323.15 K to 353.15 K

J. Chem. Thermodynamics 139 (2019) 105879 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locat...

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J. Chem. Thermodynamics 139 (2019) 105879

Contents lists available at ScienceDirect

J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct

Solubility and solution thermodynamics of glucose and fructose in three asymmetrical dicationic ionic liquids from 323.15 K to 353.15 K Xuzhao Yang a,b, Jun Wang b, Yun Fang a,⇑ a b

The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China Henan Provincial Key Laboratory of Surface and Interface Science, School of Material and Chemical Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, China

a r t i c l e

i n f o

Article history: Received 16 March 2019 Received in revised form 24 July 2019 Accepted 24 July 2019 Available online 25 July 2019 Keywords: Glucose Fructose Dicationic ionic liquid Solubility Thermodynamics

a b s t r a c t Experimental solubility of D-(+)-glucose and D-()-fructose in three asymmetrical dicationic ionic liquids (DILs), 1-(3-(trimethylammonio)prop-1-yl)-3-methylimidazolium bis(dicyanamide) ([MIMC3N111] [N(CN)2]2), 1-(3-(trimethylammonio)prop-1-yl)-1-methylpiperidinium bis(dicyanamide) ([MPiC3N111] [N(CN)2]2) and 1-(3-(trimethylammonio)prop-1-yl)pyridinium bis(dicyanamide) ([PyC3N111][N(CN)2]2), was determined through an isothermal technique from 323.15 K to 353.15 K at 0.1 MPa. The solubility of the two sugars in selected DILs increased with elevating temperature and the solubility decreased in the following order: D-()-fructose > D-(+)-glucose. The Apelblat, kh, NRTL, Wilson and UINQUAC models were respectively employed to correlate the experimental solubility values with temperature. The thermodynamics of dissolution of D-(+)-glucose and D-()-fructose in the studied DILs, enthalpy of dissolution (D0dissH), Gibbs energy of dissolution (D0dissG) and entropy of dissolution (D0dissS), were also evaluated based on the experimental solubility data. The results indicated that enthalpic contributions were dominant in the dissolution process of D-(+)-glucose and D-()-fructose in those DILs. Ó 2019 Elsevier Ltd.

1. Introduction Lignocellulose may be the most abundant biomass resources in nature and can be divided into cellulose, hemicellulose and lignin [1]. A variety of bio-products can be generated from such biomasses by chemical or biological approaches through pretreatment, hydrolysis and conversion [2]. The effective conversion can be performed through the platform molecules as 5hydroxymethylfurfural (HMF) produced from glucose and fructose, and polymers of hexoses by the means of dehydration, hydrolysis isomerization and catalysis [3]. Furthermore, HMF can be converted into precursors of numerous fine chemicals, such as biofuels and pharmaceuticals [4]. In the above-mentioned conversion processes, solvents, such as water [5–10], organic solvents [11–14] and organic-water mixtures [15–19], play a crucial role by ensuring the dissolution of sugars [5]. In recent years, ionic liquids (ILs) have attracted considerable interest as solvents in such conversion owing to their unique physicochemical characteristics, such as non-volatility, wide liquid range, high stability, and tailored solvency for various inorganic and organic molecules [20–23]. ILs also possess a plenty of

⇑ Corresponding author. E-mail addresses: [email protected] (X. Yang), [email protected] (Y. Fang). https://doi.org/10.1016/j.jct.2019.105879 0021-9614/Ó 2019 Elsevier Ltd.

excellent solvent characteristics for the conversion of sugars to HMF including high dissolving capacity of sugars, easy recyclability and providing relatively mild reaction environment, resulting in high selectivity and yield of HMF. Moreover, ionic liquids have also been proved to act as reaction promoters for conversion of sugars to HMF [20–23], thereby requiring considerable solubility of sugars in selected ILs. The solid-liquid phase equilibrium knowledge of the systems containing ILs and sugars (glucose and fructose) is thus of vital importance for the conversion process. Meanwhile, such equilibrium behaviour can also provide fundmental thermodynamic understanding for recovery of ILs and separation of HMF. Nowadays, although there has existed some solubility data of glucose and fructose in different ILs [24–27], it is still scarce and far from being enough to have a deep understanding on phase behaviour and their modelling involving those components. According to the literature [28–30], the solubility of sugars (glucose and fructose) in ILs is more significantly influenced by the nature of the anion in ILs, due to the strong intermolecular interaction (H-bonded type interaction) between the anion in ILs and the hydroxyl groups in sugars [25]. The sugar-dissolving capacity in ILs is mainly associated to ILs with the dicyanamide (N(CN)2) anion owing to the hydrogen bond acceptor characteristics. In our previous work [31,32], three asymmetrical dicyanamide-based dicationic ionic liquids (DILs) consisting of two unlike cationic head groups, a linkage and two hydrophilic counter monoanions [33],

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1-(3-(trimethylammonio)prop-1-yl)-3-methylimidazolium bis (dicyanamide) ([MIMC3N111][N(CN)2]2), 1-(3-(trimethylammonio) prop-1-yl)-1-methylpiperidinium bis(dicyanamide) ([MPiC3N111] [N(CN)2]2) and 1-(3-(trimethylammonio)prop-1-yl)pyridinium bis (dicyanamide) ([PyC3N111][N(CN)2]2) were respectively synthesized and chemically characterized and their volumetric and viscosity properties have been systematically investigated. Hence, in the present study, the solubility of D-(+)-glucose and D-()fructose was experimentally determined in the above three asymmetrical dicyanamide-based DILs through an isothermal technique from 323.15 K to 353.15 K at the pressure of 0.1 MPa. The modified Apelblat, kh, Wilson and NRTL models were used to correlate the experimental solubility results. The solution thermodynamics of dissolution of glucose and fructose in selected DILs, dissolution enthalpy (40dissH), dissolution Gibbs energy (40dissG) and the dissolution entropy (40dissS), were also evaluated based on the experimental solubility data at various temperatures. To our present knowledge, it is the first report on the solubility of D-(+)-glucose and D-()-fructose in DILs, which may provide a fundamental basis for the conversion of sugars in such DILs in our next investigations. 2. Experimental 2.1. Materials and chemicals D-(+)-Glucose (C6H12O6), D-()-Fructose (C6H12O6) were supplied from Aladdin with >0.990 mass fraction purity and dried under vacuum at 353.15 K before the measurements. (3bromopropyl) trimethylammonium bromide (TAP-Br, C6H15Br2N), 1-butyl-3-methylimidazolium dicyanamide ([BMIM][N(CN)2]) (C10H15N5), 1-methylimidazole (C4H6N2), pyridine (C5H5N), 1methylpiperidine (C6H13N), sodium dicyanamide (C2N3Na) and silver nitrate (AgNO3) were also purchased from Aladdin and used directly without further purification. All compounds employed in present investigation are tabulated in Table 1. [MIMC3N111][N(CN)2]2, [PyC3N111][N(CN)2]2 and [MPiPyC3N111] [N(CN)2]2 were respectively obtained according to our previous

literature [31,32] (NMR spectrum for [MIMC3N111][N(CN)2]2 see literature [31], NMR spectra in DMSO d6 for [MPiPyC3N111][N (CN)2]2 and [PyC3N111][N(CN)2]2 see Figs. S1–S4). Chemical structures of the selected three DILs are depicted in Fig. 1. After drying under vacuum, the water contents of three DILs, D-(+)-Glucose, and D-()-Fructose were determined to be <100  106 by Karl-Fisher Titration technique (Aquastar V-200 Titrator). Purity analyses were performed by a Waters 600E HPLC with a C18 column (150 mm  4.6 mm; 5 lm). The eluent was methanol and the flow rate was 1.0 mLmin1. The UV detection wavelength was set to 220 nm and the injection volume was 20 lL. All DILs and sugars were all maintained in a dry nitrogen atmosphere to prevent moisture and any other contamination absorption before solubility determinations. 2.2. Experimental solubility determination The experimental determination of the solubility of D-(+)Glucose and D-()-Fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111] [N(CN)2]2 and [PyC3N111][N(CN)2]2 from 323.15 K to 353.15 K under 0.1 MPa were performed by an isothermal method described in detail in the literature [24–27]. In each measurement, approximately 10 g DIL were added in 20 mL jacketed equilibrium glass vessel with continuous magnetic stirring. A mercury-in-glass thermometer with an uncertainty of ±0.05 K was placed into the inner chamber of the glass vessel to measure the liquid0 s temperature controlled and maintained through a thermostatic recirculation water bath (JULABO F12-ED) with a precision of ± 0.1 K connected to the glass vessel. After the desired temperature was achieved, each sugar in excess was placed in to the glass vessel with vigorous magnetic stirring. The mixture in the glass vessel was constantly stirred for at least 48 h to reach the liquid-solid phase equilibrium and sustained for at least 5 h at the desired temperature. During the procedure, the sugar particles in the vessel bottle can be seen and the sugar is considered to be excessive. After the sedimentation of excessive sugar, DIL-saturated solution was withdrawn from the top of the inner glass vessel and diluted into ultra-pure water. The concentration of sugar in the solution was quantified

Table 1 Specification of chemical samples used in this investigation.

a b c

chemical name

CAS No.

Molar mass/ (gmol1)

Purity (mass fraction)

Water content (mass fraction)c

Source

D-(+)-glucose D-()-fructose (3-bromopropyl)trimethylammonium bromide sodium dicyanamide silver nitrate ethyl acetate 1-butyl-3-methylimidazolium dicyanamide 1-(3-(trimethylammonio)prop-1-yl)-3-methylimidazolium bis(dicyanamide) 1-(3-(trimethylammonio)prop-1-yl)-1-methylpiperidinium bis(dicyanamide) 1-(3-(trimethylammonio)prop-1-yl)pyridinium bis(dicyanamide)

50-99-7 57-48-7 3779-42-8 1934-75-4 7761-88-8 141-78-6 448245-52-1 None 2252313-60-1 2252313-59-8

180.16 180.16 261.00 89.03 169.87 88.11 205.26 315.38 332.44 312.37

>0.999b 0.990b >0.990b >0.960b >0.990b >0.995b >0.990b >0.990 (HPLCa) >0.990 (HPLCa) >0.990 (HPLCa)

<0.00001 <0.00001 <0.0001 <0.0001 <0.0001 <0.0001 0.000085 0.000055 0.000047 0.000042

Aladdin Aladdin Aladdin Aladdin Aladdin Aladdin Aladdin Synthesized own Synthesized own Synthesized own

High-performance liquid chromatography. provided by the suppliers. Determined by KF titration method.

Fig. 1. Chemical structures of the studied DILs in this investigation.

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for absorption measurements at 540 nm with the classical colorimetric method of dinitrosalicylic acid (DNS) described in the literature [27]. A comparative test was carried out to investigate the effect of studied DILs on colorimetric method for the sugar analysis. The absorbance of dinitrosalicylic acid (DNS) aqueous solution and (DNS + [MIMC3N111][N(CN)2]2) aqueous solution was measured with an SP-721E UV–VIS spectrophotometer (Shanghai, China) within the wave length range of (480–600) nm. DNS and DIL all show no absorption at the measurement wavelength of 540 nm. The absorbance measurements at 540 nm for DNS glucose and DNS fructose determination in the presence or absence of 25 mmolL1 [MIMC3N111][N(CN)2]2 were carried out at room temperature (see Fig. S5). From the measurements, the presence or absence of the ionic liquid has little effect on absorption with an error of <1%, indicating that the selected DILs have no effect on colorimetric method for the sugar analysis. The relative uncertainty of the solubility measurement in the present experiment was estimated to be <2%. The experimental solubility of sugar in each DIL was determined for the average of our three measurements. The saturated mole fraction of sugar, x1, in DIL-saturated solution can be evaluated as follows:

x1 ¼

w=M 1 w=M 1 þ ð1  wÞ=M2

ð1Þ

Here, w denotes the saturated mass fraction of sugar in the mixture, and M1 (gmol1) and M2 (gmol1) stand for the molar masses of sugar and DIL, respectively. Furthermore, the measured solubility (x1) of D-(+)-Glucose in [BMIM][N(CN)2] at various temperatures was compared with the available literature [25,27,28] to confirm the procedure and reproducibility of the present measurements (see Table S1). The measured values show good agreement with literature data.

Table 2 Mole fraction, x1, of D-(+)-glucose and D-()-fructose in selected DILs at various temperatures and at pressure p = 0.1 MPa a, x1, of D-(+)-glucose and D-()-fructose. T/K

D-(+)-Glucose

D-()-fructose

[MIMC3N111][N(CN)2]2 323.15 328.15 333.15 338.15 343.15 348.15 353.15

0.4783 0.5152 0.5475 0.5758 0.6002 0.6225 0.6425

0.6068 0.6373 0.6635 0.6855 0.7084 0.7267 0.7432

[MPiC3N111][N(CN)2]2 323.15 328.15 333.15 338.15 343.15 348.15 353.15

0.3311 0.3466 0.3605 0.3723 0.3838 0.3962 0.4072

0.3752 0.3952 0.4136 0.4308 0.4496 0.4608 0.4715

[PyC3N111][N(CN)2]2 323.15 328.15 333.15 338.15 343.15 348.15 353.15

0.2250 0.2463 0.2682 0.2874 0.3065 0.3285 0.3445

0.4116 0.4398 0.4665 0.4924 0.5080 0.5316 0.5455

a Standard uncertainties u are u(T) = ±0.01 K and u (p) = 1.0 kPa. Relative uncertainty ur is ur(x1) = 0.02.

3. Results and discussion 3.1. Experimental solubility values Considering the thermal stabilities of D-(+)-glucose and D-()fructose [25] and the high viscosities of selected DILs [31], the range of experimental temperature for the solubility measurements in present investigation was selected to be from 323.15 K to 353.15 K to prevent long dissolution time, thermal degradation and chemical comversion of sugars. Experimental solubility data of D-(+)-glucose and D-()-fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111][N(CN)2]2 and [PyC3N111][N(CN)2]2 from 323.15 K to 353.15 K at 0.1 MPa are tabulated in Table 2 and depicted in Figs. 2 and 3. From Table 2 and Figs. 2 and 3, the large sugar-dissolving capacity of the [MIMC3N111][N(CN)2]2, [MPiC3N111][N(CN)2]2 or [PyC3N111][N(CN)2]2 can be ascribed to the strong intermolecular H-bonded type interaction between the hydroxyl groups in D-(+)-glucose and D-()-fructose and the lone pair electrons of nitrogen atoms in the [N(CN)2] anion. For D-(+)-glucose and D-()-fructose, the solubility in three selected DILs increased with elevating temperature, indicating an endothermic dissolution processes of D-(+)-glucose and D-()-fructose in studied DILs. The solubilities of D-(+)-glucose and D-()-fructose in three studied DILs were all larger than those in monocationic ILs with the same [N (CN)2] anion, due to the larger number of [N(CN)2] anion in DILs. As seen in Table 2 and Figs. 2 and 3, solubility of D-(+)-glucose and D-()-fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111] [N(CN)2]2 and [PyC3N111][N(CN)2]2 at constant temperatures increased in the following order: D-(+)-glucose < D-()-fructose, which can be attributed to the characteristics of D-(+)-glucose and D-()-fructose [25]. According to the literature [25,34–36], melting characteristics of D-(+)-glucose and D-()-fructose were

Fig. 2. Experimental mole fraction x1 of D-(+)-glucose in studied DILs. j, [MIMC3N111][N(CN)2]2; d, [MPiC3N111][N(CN)2]2; ▲, [PyC3N111][N(CN)2]2. The symbols stand for the experimental data, and the solid curves are values evaluated by Apelblat equation.

listed in Table 3. As structural isomers, D-()-fructose owns relatively lower melting temperature and enthalpy of fusion, due to its more stable and lower energetic structure. From the solubility data listed in Table 2, the cations in selected DILs also play a determinant role in the sugar-dissolving capability of DILs with the same [N(CN)2] anion. According to the literature [37,38], the smaller cation in DILs and increased relaxation of the sugar structure could have a positive entropic effect on the dissolution of sugars in DILs because of intermolecular H-bonded type interaction between the oxygen atoms of the hydroxyl groups in D-(+)-glucose and D-()-fructose and the hydrogen atoms of the cations in selected DILs. The protons in the cations involved in

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D-(+)-glucose or D-()-fructose also has a considerable effect on the sugar-dissolving capability of DILs. The greater mole solubility of D-()-fructose in [PyC3N111][N(CN)2]2 and D-(+)-Glucose in [MPiC3N111][N(CN)2]2 at the same temperature indicates that the stronger interactions take into account the comprehensive role of the factors mentioned above. 3.2. Solid-liquid equilibrium models The variation of x1 with T for each sugar-DIL binary mixture can be quantitatively estimated by semi-empirical equations and local composition models. 3.2.1. Semi-empirical equations Modified Apelblat model [41]:

lnx1 ¼ A þ

Fig. 3. Experimental mole fraction x1 of D-()-fructose in studied DILs. j, [MIMC3N111][N(CN)2]2; d, [MPiC3N111][N(CN)2]2; ▲, [PyC3N111][N(CN)2]2. The symbols stand for the experimental data, and the solid curves are values evaluated by Apelblat equation.

the studied DILs ([MIM]+, [MPi]+ and [Py]+), especially for the most acidic H2 proton (near the nitrogen atom in the cationic ring), will directly interact with the oxygen atoms of hydroxyl groups in D(+)-glucose and D-()-fructose [38]. Furthermore, the cation, [MIM]+, in [MIMC3N111][N(CN)2]2 has the most acidic protons and could be considered to have a strongest intermolecular interaction with D-(+)-glucose and D-()-fructose than [MPi]+ in [MPiC3N111][N(CN)2]2 and [Py]+ in [PyC3N111][N(CN)2]2, resulting in the largest dissolution ability of D-(+)-glucose and D-()fructose, which was consistent with the experimental results. It has been well known that the cationic structure and the hydrogen bond donor ability (hydrogen bond acidity, a) of DILs can also have a considerable effect on the sugar-dissolving capability of DILs with the same [N(CN)2] anion [38]. The larger values of a of DIL cation and the greater degree of saturation of six-membered ring in cation ([MPi]+ or [Py]+), the stronger the sugar-dissolving ability of DIL with the same [N(CN)2] anion. According to the literature [39,40], the value of a of [Py]+ in pyridinium-based IL was greater than that of [MPi]+ in methylpiperidinium-based IL with the same anion and side chain. Nevertheless, the degree of saturation for [MPi]+ ring was larger than that of [Py]+ ring. The decrease in the degree of delocalization of positive charges of cationic ring in DILs may result in the increase of the strength of Coulomb interaction between cation and [N(CN)2] anion in DILs and the decrease of the strength of H-bonded type interaction between the cations in DIL and the hydroxyl groups in D-(+)-glucose and D-()-fructose. From this point of view, the degree of delocalization of positive charges in [Py]+ ring was bigger because of its p-conjugated delocalization than that in [MPi]+ ring. On the other hand, the intermolecular van der Waals interaction between DILs with

B þ ClnðT=KÞ ðT=KÞ

ð2Þ

In this equation, x1 is the saturated mole fraction, T (K) refers to the absolute temperature, and A, B and C represent equation parameters. kh equation [42]:

    1 1 1 ¼ kh  ln 1  k þ k x1 ðT=KÞ ðT m =KÞ

ð3Þ

Here x1 is the saturated mole fraction, T (K) and Tm (K) denote the absolute temperature and the melting point of sugar, and k and h stand for equation parameters. 3.2.2. Local composition models Local composition models have been widely employed to correlate the solid-liquid equilibrium data involving sugars in ILs [24– 26]. In these models, the equilibrium solubility of sugars in selected DILs can be evaluated from the thermal natures of the pure sugars (such as melting point and enthalpy of fusion) and the activity coefficients [24–26]:

lnc1 ¼

    Dfus Hm 1 1 DC p;m T m DC p;m T m  T   lnx1  ln þ Tm T T R R T R ð4Þ

Here x1 is the saturated mole fraction, c1 denotes the activity coefficient of sugar in DIL, Tm (K) is the melting point of sugar, DfusHm (kJmol1) represents the enthalpy of fusion of solute, R (8.3145 JK1mol1) denotes the universal gas constant, T (K) is the absolute temperature, and DCp,m (JK1mol1) refers to the difference in heat capacities of liquid-state sugar and solid-state one at normal melting point. In present investigation, the experimental temperatures are respectively near to normal melting property, thus Eq. (4) can be simplified as follows [43]:

lnc1 ¼

  Dfus Hm 1 1  lnx1  Tm T R

ð5Þ

The thermal characteristics (Tm and DfusHm) of D-(+)-glucose and D-()-fructose have been listed in Table 3 according to the literature [35,36]. Thus, the activity coefficient (c1) of D-(+)-glucose

Table 3 Thermal characterics of D-(+)-glucose and D-()-fructose at pressure p = 0.1 MPa.a Sugar D-(+)-glucose D-()-fructose a b c d

Molar mass/(gmol1) 180.16 180.16

Standard uncertainty u is u (p) = 1.0 kPa. From Ref. [25]. From Ref. [34,35]. From Ref. [36].

4fusH/(kJmol1)

Tm/K b,c

423.15 378.15b,c

b,c

32.432 26.030b,c

q/(gmL1) 1.5440 1.6000

d d

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and D-()-fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111] [N(CN)2]2 and [PyC3N111][N(CN)2]2 can be respectively evaluated based on Eq. (5). NRTL Model [44,45]:

lnðc1 Þ ¼

x22

s21 G221 ðx1 þ x2 G21 Þ2

þ

s12 G12

!

ð6Þ

ðx2 þ x1 G12 Þ2

Here G12, G21, s12, and s21 are the model parameters, and can be calculated from these expressions:

G12 ¼ expða12 s12 Þ g 12  g 22 RT

s12 ¼

s21 ¼

G21 ¼ expða12 s21 Þ

ð7Þ

g 21  g 11 RT

ð8Þ

Here (g12–g22) (Jmol1) and (g21–g11) (Jmol1) are binary cross parameters, a12 is the adjustable parameter. In present study, parameter a12 is estimated to be 0.3 in the calculation of the activity coefficients. Wilson Model [46,47]:

lnc1 ¼ lnðx1 þ K12 x2 Þ þ x2



K12 K21  x1 þ K12 x2 x2 þ K21 x1



ð9Þ

Here K12 (Jmol1) and K12 (Jmol1) are the adjustable parameters and can be calculated from these expressions:

K12 ¼

    V m2 k12  k11 V m1 k21  k22 exp  K21 ¼ exp  V m1 RT V m2 RT

ð10Þ

In this model, Vm1 (cm3mol1) and Vm2 (cm3mol1) denote the mole volumes of sugar and DIL, (k12–k11) (Jmol1) and (k21–k22) (Jmol1) are binary interaction parameters. UNIQUAC Model [48]:

  Z h1 r1 þ q1 ln þ u2 l1  l2  q1 lnðh1 þ h2 s21 Þ x1 2 u1 r2   s21 s12 þ h2 q1 ð11Þ  h1 þ h2 s21 h2 þ h1 s12

lnðc1 Þ ¼ ln

u1

with

r 1 x1 r 1 x1 þ r 2 x2

u2 ¼

q1 x1 q 1 x1 þ q 2 x2

h2 ¼

u1 ¼ h1 ¼

r 2 x2 r 1 x1 þ r 2 x2

ð12Þ

q 2 x2 q1 x1 þ q2 x2

ð13Þ

Z Z ðr 1  q1 Þ  ðr 1  1Þ l2 ¼ ðr 2  q2 Þ  ðr 2  1Þ 2 2     Du12 Du21 ¼ exp s21 ¼ exp RT RT

l1 ¼

s12

ð14Þ ð15Þ

Here x1 and x2 refer to the mole fractions of sugar and DIL in the saturated sugar-DIL solution, u stands for the average segment fraction, h is the average area fraction, Z and li represent the coordination number and bulk factor and were respectively estimated to be 10 and 1. r and q are respectively volume parameter and surface parameter. The values of r1 and q1 of D-(+)-glucose and D-()-fructose for the UNIQUAC model can be found in the literature [49,50]. For the three studied DILs, an empirical equation can be employed to calculate the values of r2 and q2 with following expressions [51]:

r 2 ¼ 0:029281

q2 ¼

M

q

Z2 2ð1  l2 Þ r2 þ Z Z

ð16Þ

ð17Þ

In these expressions, M (gmol1) is the molar weight of the selected DIL, and q (gcm3) refers to the density of the selected DIL at the temperature of 298.15 K. The densities of [MIMC3N111] [N(CN)2]2, [MPiC3N111][N(CN)2]2 and [PyC3N111][N(CN)2]2 at 298.15 K are respectively (1.15373, 1.11037 and 1.15504) gcm3 [31,32] determined by a digital vibrating tube densimeter (Anton Paar DMA 5000 M). Table 4 summarizes the structural parameters of the sugars (D-(+)-glucose and D-()-fructose) and three selected DILs ([MIMC3N111][N(CN)2]2, [MPiC3N111][N(CN)2]2 and [PyC3N111] [N(CN)2]2). The adjustable interaction parameters of NRTL, Wilson and UNIQUAC models can be evaluated by means of the average absolute relative deviation (AARD):

AARD ¼

exp  PNp xcal x1  1 i¼1  xexp  1

Np

 100%

ð18Þ

Here Np refers to the number of solubility data points, and xexp and 1 xcal represent the experimental and calculated mole fraction of 1 sugar in DIL, respectively. The model parameters of the two semi-empirical equations (Apelblat and kh) and three local composition models (NRTL, Wilson and UNIQUAC) of D-(+)-glucose and D-()-fructose solubilities in [MIMC3N111][N(CN)2]2, [MPiC3N111][N(CN)2]2 and [PyC3N111][N(CN)2]2 were evaluated and shown Table 5, together with the values of AARD. As seen in Table 5, the two semiempirical equations and three local composition models correlate quite well the experimental solubility with the temperature based on the AARDs of the correlation equations. Moreover, the values of AARD determined by modified Apelblat and kh equations are lower than those obtained by three local composition models (NRTL, Wilson and UNIQUAC). The Apelblat equation represents the most accurate than the other models. Among local composition models, the correlation with UNIQUAC model was very satisfactory with AARD value smaller than 4% in all the binary mixtures. 3.3. Thermodynamics of dissolution Three apparent thermodynamic functions, enthalpy of dissolution (D0dissH), Gibbs energy of dissolution (D0dissG) and entropy of dissolution (D0dissS) can represent the dissolution behaviour of sugars in selected DILs [52]. The values of D0dissH, indicating whether the dissolution process of sugar in selected DIL is endothermic or exothermic, can be evaluated directly from the slope of a plot of ln(x1) against (1/T  1/Thm) depicted in Figs. 4 and 5.

2 3 D0diss H 4 @lnx1 5   ¼  R @ 1 1 T

T hm

ð19Þ

p

Here x1 is the mole fraction of D-(+)-glucose or D-()-fructose in selected DIL, R (8.3145 Jmol1K1) represents the universal gas constant, T (K) denotes the absolute temperature, the subscript p refers to isobaric conditions, and Thm (K) stands for the harmonic average temperature determined by [52]:

Table 4 Structural parameters in UNIQUAC model. Compound

r

q

D-(+)-Glucose D-()-fructose [MIMC3N111][N(CN)2]2 [MPiC3N111][N(CN)2]2 [PyC3N111][N(CN)2]2

5.80 5.80 8.00 8.77 7.92

4.84 4.92 6.40 7.01 6.34

6

Table 5 Parameters of Apelblat, kh, Wilson, NRTL, and UNIQUAC models for D-(+)-glucose and D-()-fructose in studied DILs at pressure p = 0.1 MPa.a Solute

DIL

D-(+)glucose

D-()fructose

Wilson

UNIQUAC

A

B

C

AARD/%

k

h

AARD/%

(g12  g22)/ (Jmol1)

(g21  g11)/ (Jmol1)

AARD/%

(k12  k11)/ (Jmol1)

(K21-k22)/ (Jmol1)

AARD/%

412/ (Jmol1)

421/ (Jmol1)

AARD/ %

[MIMC3N111] [N(CN)2]2 [MPiC3N111][N(CN)2]2 [PyC3N111][N(CN)2]2

220.95

11910.8

31.99

0.16

1.93

785.55

0.91

2412.30

8089.58

5.54

7865.80

108969.70

4.18

2739.54

3757.44

3.48

69.54 163.45

4154.12 9537.84

10.00 23.44

0.15 0.23

0.27 0.32

3862.50 3108.13

0.72 1.09

2654.29 21589.80

1853.93 6405.81

3.13 1.80

5837.31 4738.21

113669.67 3949.89

5.27 8.68

92037.64 7083.98

4017.80 3481.61

3.61 1.19

[MIMC3N111] [N(CN)2]2 [MPiC3N111][N(CN)2]2 [PyC3N111][N(CN)2]2

124.60

6839.79

17.99

0.10

0.93

2025.37

1.14

59145.22

7579.43

2.32

5414.85

93899.88

3.12

6556.79

3819.59

2.45

147.56 193.92

8096.69 10548.60

21.37 28.07

0.18 0.22

0.57 0.55

8551.50 5401.95

2.11 2.13

3806.86 3974.31

1258.33 1334.42

9.49 6.46

2710.79 3455.91

4806.19 4738.31

10.42 7.37

110680.90 9628.58

3231.68 3322.39

2.16 2.02

Standard uncertainty u is u (p) = 1.0 kPa.

Fig. 4. Plot of ln x1 versus ((1/T)(1/Thm)) for D-(+)-glucose in selected DILs. j, [MIMC3N111][N(CN)2]2; d, [MPiC3N111][N(CN)2]2; ▲, [PyC3N111][N(CN)2]2.

ð20Þ

Fig. 5. Plot of lnx1 versus ((1/T)(1/Thm)) for D-()-fructose in selected DILs. j, [MIMC3N111][N(CN)2]2; d, [MPiC3N111][N(CN)2]2; ▲, [PyC3N111][N(CN)2]2.

1 i¼1 T i

N T hm ¼ PNp

ð21Þ

ð22Þ

In this expression, N equals the number of temperature data, Ti (K) represents the real experimental temperature. 0 The values of Ddiss G, representing whether dissolution process of sugar in selected DIL is spontaneous or non-spontaneous, can be determined by [52]:

0 Ddiss G ¼ RT hm k

0 0 Ddiss H  Ddiss G T hm

Here k stands for the value of lnx1 at the harmonic average temperature (Thm) and can be determined directly from the intercept of a plot of ln(x1) against (1/T  1/Thm) depicted in Figs. 4 and 5. 0 The values of Ddiss S, revealing the more favourable state at pure material or in the mixed state, can be calculated from the following expression [52]:

0 Ddiss S¼

X. Yang et al. / J. Chem. Thermodynamics 139 (2019) 105879

a

NRTL (a = 0.3)

kh

Apelblat

7

X. Yang et al. / J. Chem. Thermodynamics 139 (2019) 105879 Table 6 Calculated values of D0dissH, D0dissG and D0dissS for dissolving process of D-(+)-glucose and D-()-fructose in studied DILs at pressure p = 0.1 MPa.a Solute

DIL

Thm/K

D0dissH/(kJmol1)

D0dissG/(kJmol1)

D0dissS/(JK1mol1)

% fH

% fTS

D-(+)-glucose

[MIMC3N111][N(CN)2]2 [MPiC3N111][N(CN)2]2 [PyC3N111][N(CN)2]2 [MIMC3N111][N(CN)2]2 [MPiC3N111][N(CN)2]2 [PyC3N111][N(CN)2]2

337.85

9.22 6.46 13.50 6.37 7.32 8.90

1.60 2.79 3.54 1.08 2.39 2.04

22.554 10.863 29.481 15.658 14.592 20.305

54.75 63.77 57.54 54.63 59.76 56.47

45.25 36.23 42.46 45.37 40.24 43.53

D-()-fructose

a

Standard uncertainty u is u (p) = 1.0 kPa.

The values of D0dissH, D0dissG and D0dissS of the dissolution process of sugars in selected DILs have been evaluated and tabulated in Table 6. The calculated values of D0dissH for the studied systems are all positive, indicating the endothermic processes of D-(+)glucose and D-()-fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111] [N(CN)2]2 and [PyC3N111][N(CN)2]2. The evaluated positive values of D0dissG suggest that the dissolving process of D-(+)-glucose and D-()-fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111][N(CN)2]2 and [PyC3N111][N(CN)2]2 are all non-spontaneous. As seen in Table 6, the lower D0dissH and D0dissG values for D-()-fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111][N(CN)2]2 and [PyC3N111][N (CN)2]2 represented higher solubility in the three selected DILs and lower energy to establish new sugar-DIL intermolecular interactions [25]. The contribution values of dissolution enthalpy and dissolution entropy to dissolution Gibbs energy (% fH and % fTS) during the dissolution process of sugar in selected DIL can be evaluated by the following expressions [47]:

   0  Ddiss H     %fH ¼     0 0 Ddiss H þ T hm  Ddiss S

%fTS

    0 T hm  Ddiss S    ¼     0 0 Ddiss H þ T hm  Ddiss S

ð23Þ

ð24Þ

The values of % fH and % fTS are listed in Table 6. As can be seen in Table 6, the main contributor is dissolution enthalpy for the simple reason that the values of % fH are higher than 54% during the dissolving processes of D-(+)-glucose and D-()-fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111][N(CN)2]2 and [PyC3N111] [N(CN)2]2 within the investigated temperature range between 323.15 K and 353.15 K. 4. Conclusions The solid-liquid equilibrium solubility of D-(+)-glucose and D-()-fructose in [MIMC3N111][N(CN)2]2, [MPiC3N111][N(CN)2]2 and [PyC3N111][N(CN)2]2 within the temperature range of 323.15–353.15 K at 0.1 MPa were systematically performed by using an isothermal approach. The results showed that the solubility of D-()-fructose in three studied DILs is greater than those of D-(+)-glucose due to its stable and low energetic structure and lower thermal properties. The greatest solubility values of D-(+)-glucose and D-()-fructose in [N111C3MIM][DCA]2 are due to the strongest intermolecular H-bonded type interaction between the hydroxyl groups in D-(+)-glucose and D-()-fructose and the [MIM]+ cation in [MIMC3N111][N(CN)2]2. The value of a, degree of saturation, the degree of positive charge delocalization in cationic group, and strength of Coulomb interaction between cation and anion can also have considerable effect on the dissolving capacity of DILs. The experimental solubility values were fitted by Apelblat, kh, NRTL, Wilson and UNIQUAC models. The results show that the modified Apelblat is more suitable than other models owing to

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JCT 2019-240