Thermodynamics of clouding process in 1-butanol + water mixtures in the presence and absence of sugars

Journal of Molecular Liquids 278 (2019) 164–174

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Thermodynamics of clouding process in 1-butanol + water mixtures in the presence and absence of sugars Nosaibah Ebrahimi a, Rahmat Sadeghi a,⁎, Baram A.H. Ameen b a b

Department of Chemistry, University of Kurdistan, Sanandaj, Iran Department of Science, Charmo University, 46023 Chamchamal-Sualimani, Kurdistan Region, Iraq

a r t i c l e

i n f o

Article history: Received 26 October 2018 Received in revised form 23 December 2018 Accepted 2 January 2019 Available online 6 January 2019 Keywords: Clouding process Soluting-out effect Disaccharides Monosaccharides 1-Butanol Thermodynamic functions

a b s t r a c t This paper deals with liquid-liquid equilibrium of binary {1-butanol + water} and ternary {1-butanol + aqueous sugar solutions} systems in both water-rich and butanol-rich environments. Immiscibility region of 1-butanolwater system is expanded by addition of sugars, and this effect becomes stronger by increasing hydrophilicity and molality of sugars. The soluting-out ability of sugars follows the order maltitol ≈ maltose N sucrose N D(+)-glucose N D-(−)-fructose N xylitol N D-(+)-xylose. The experimental cloud point data were successfully correlated by Setschenow's equation. Thermodynamic functions and relative contributions of entropy and enthalpy to Gibbs free energy of clouding were calculated. From the obtained results, the clouding process of 1-butanol in water mixtures is more spontaneous than that of water in 1-butanol ones. The presence of sugars, in both waterrich and alcohol-rich environments, leads to a more spontaneous liquid-liquid demixing process. The clouding process in the water-rich region is entropy-driven, while in the butanol-rich region is enthalpy-driven. © 2019 Published by Elsevier B.V.

1. Introduction The presence of a non-volatile solute in a mixed solvent system can significantly affect its liquid-liquid and vapor-liquid equilibria behavior. This subject which may appear as soluting-out or soluting-in effects has been advantageously used in distillation and solvent extraction [1,2]. Besides, many reactions and industrial processes are carried out in mixed solvents. Therefore, there is a well-sustained interest in studying the soluting effects of different solutes on solvent mixtures. Studying soluting effects of sugars on the liquid-liquid phase behavior of organic solvent/water systems is useful for industrial applications of biocatalysis [3–5]. The proper design of bioreactors and advancement of products separation from the reaction mixture require the accurate knowledge of the solution behavior of organic/aqueous systems in the presence of sugars [6–8]. 1-Butanol is a beneficial four‑carbon alcohol with several industrial applications, for example as a solvent, reactant, intermediate, or extractant in a wide variety of chemical processes, and in manufacturing of cosmetics, pharmaceuticals, hormones, vitamins, essential oils etc. [9,10]. Unlike the C1–C3 alcohols which are completely water-soluble, 1butanol shows only limited miscibility with water. The liquid-liquid equilibrium data of binary 1-butanol + water solutions have been reported by several authors [11–16]. The soluting effects of various salts on the liquid-liquid phase behavior of 1-butanol/aqueous systems are ⁎ Corresponding author. E-mail address: [email protected] (R. Sadeghi).

https://doi.org/10.1016/j.molliq.2019.01.011 0167-7322/© 2019 Published by Elsevier B.V.

also presented in the literature [1,17–21]. However, despite its importance, as far as we know, there is no article regarding the soluting effects of sugars on the liquid-liquid demixing of 1-butanol + water mixtures. The word “sugar” is a generic name which refers to the low molecular weight carbohydrates, namely monosaccharides, disaccharides, and oligosaccharides. Sugars, as the main source of energy, are among the life protective materials which also play an important role in a wide variety of applications such as biological usages, food industries, pharmaceutical, cosmetics, textile, plastics, etc. [22–26]. Due to a large number of hydroxyl groups in their structure, sugars show a high affinity for water and are prone to act as biodegradable, non-charged and non-toxic soluting-out agent. An overview of the articles published hitherto shows that sugars have been used as the soluting-out agent to produce new types of aqueous biphasic systems (ABS) such as IL-sugar [27], polymer-sugar [28], and acetonitrile-sugar [29] ABS. In the previous paper [30], we studied the soluting-out effect of sugars on the aqueous solutions of completely water-miscible alcohols and reported, for the first time, the possibility of forming propanol-sugar ABS. In continuation of the previous paper, this work addresses the soluting-out effect of various sugars including mono- and di-saccharides and their polyols on the solution behavior and clouding process of 1-butanol + water mixtures. Clouding is a well-known phenomenon observed upon raising or lowering the solution temperature depending on the nature of solute-solvent interactions. For example, aqueous solutions of a thermosensitive polymer (such as polypropylene glycol) [28,31] or a non-ionic surfactant (such as Triton X-114) [32,33] become turbid when temperature increases to critical values known as cloud points. Similarly, a binary

N. Ebrahimi et al. / Journal of Molecular Liquids 278 (2019) 164–174

165

Table 1 Provenance and purity of chemical samples. Chemical name

103 ⋅ Molar mass (kg·mol−1)

Source

Mass fraction puritya

D-(+)-xylose D-(+)-glucose D-(−)-fructose Sucrose Maltose monohydrate Xylitol Maltitol 1-Butanol

150.13 180.16 180.16 342.29 360.32 152.15 344.32 74.12

Merck (Germany) Merck (Germany) Merck (Germany) Merck (Germany) Merck (Germany) Alfa Aesar (US) Alfa Aesar (US) Merck (Germany)

≥0.99 ≥0.995 ≥0.99 ≥0.98 0.99 0.99 0.97 ≥0.99

a

Declared by supplier.

mixture of water + partially water-miscible alcohols (such as 1butanol) undergoes clouding phenomenon by increasing or decreasing the solution temperature. Additives can influence the clouding process and lead to the expansion or restriction of biphasic region of cloud point phase diagrams. The effects of sugars as additives on the clouding thermodynamic parameters of aqueous polymer solution [28] and aqueous non-ionic surfactant solutions [32,33] have been well documented. Herein, thermodynamic factors which control the clouding process in binary {1-butanol + water} system are discussed, then the effect of sugars, as additives, on the clouding thermodynamic parameters at both water-rich and butanol-rich environments is studied. The soluting-out coefficients of sugars on 1-butanol/aqueous mixtures are calculated based on Setschenow equation [34]. Such information would be useful for the proper design of liquid-liquid extractors and chemical industries involving mixed solvents of 1-butanol and water.

2. Materials and methods 2.1. Materials The specifications of the used materials are listed in Table 1. All chemicals were used without further purification. Bidistilled water, with a specific conductivity of 1.2 μS·cm−1 at 25 °C, was used in all

the experiments. Fig. 1 represents the chemical structures of the used materials. 2.2. Experimental procedure The liquid-liquid phase diagram measurements were performed in a collection consists of: (i) a double-shell glassy cell with a volume of 12 cm3 to hold mixtures, (ii) a Julabo thermostat with a precision of ± 0.1 K to circulated water at certain temperatures in the outer shell around the mixtures, and (iii) a magnetic stirrer for the continuous stirring of mixtures throughout experiments. Details on apparatus description have been given in previous works [31,35]. The turbidity titration method, which has been successfully applied to obtain the liquidliquid phase diagram of various systems such as {water + polymer} [28], {water + polymer + amino acid} [28], {water + polymer + salt} [29], {water + propanol + sugar} [30], and {water + polymer + sugar} [31] systems, was used in this work to determine the liquidliquid phase diagrams of {water + 1-butanol} and {water + 1-butanol + sugar} systems. In the water-rich environment, for determining 1butanol mass fraction (wb) corresponded to each cloud point temperature (TCp), pure water or aqueous solutions of (0.2, 0.4, and 0.6) mol·kg−1 of sugars were titrated with pure 1-butanol until the visual detection of a cloudy solution (biphasic system). In the alcohol-rich environment, a cloudy mixture of {1-butanol + water} or {1-butanol

OH D-Glucose

D-Xylose O

D-Fructose

O

HO

O

HO

HO

OH

OH

HO

OH

OH

OH

OH OH

Sucrose CH2OH HO HO

CH2OH

O

HO HO

CH2OH

O

OH

OH

O

Maltose

O

CH2OH

OH

O

CH2OH

CH2OH

OH OH

Maltitol

O

CH2OH

OH

O

HO

O

HO

OH

HO HO

Xylitol HO HO

OH

OH

OH

OH HO OH

1-Butanol OH

OH

Fig. 1. Chemical structures of the studied carbohydrates and alcohol.

CH2OH

166

N. Ebrahimi et al. / Journal of Molecular Liquids 278 (2019) 164–174

One-phase region

0

One-phase region

-2

345

-4

ΔGm / kJ.mol-1

360

TCp / K

330

Two-phase region 315 Butanol-rich branch 300

Water-rich branch

-10

-14

270 0.1

0.2

0.3

0.4

0.5

Water-rich branch

-8

-12

285

0

Butanol-rich branch

-6

0.6

0.7

0.8

0.9

(a)

270

290

310

TCp /K

wb 370

TCp.ΔSm / kJ.mol-1

TCp / K

310

Ref [13] Ref [14]

Two-phase region

290 270 0.06

0.07

0.08

0.09

wb

0.10

0.11

0.12

Butanol-rich branch Water-rich branch

15 10 5 0

(b)

-5

270

290

370

This work

One-phase region

330

Two-phase region

310

Ref [13]

10

Ref [14]

8

Ref [15]

6

290 270 0.70

0.72

0.74

0.76

wb

0.78

0.80

0.82

(c)

310

TCp /K

330

350

370

(b)

12

Ref [12]

ΔHm / kJ.mol-1

TCp / K

350

370

(a)

20

Ref [12]

One -phase region

330

350

25

This work 350

330

Butanol-rich branch

4

Water-rich branch

2 0 -2 -4

Fig. 2. Cloud point temperature, TCp, versus 1-butanol mass fraction, wb, for the binary system of {1-butanol + water}: (a) the overall liquid-liquid phase diagram obtained in this work; (b) comparison of the water-rich branch liquid-liquid phase diagram data with literature; and (c) comparison of the butanol-rich branch liquid-liquid phase diagram data with literature.

+ aqueous solutions of 0.4 mol·kg−1 of sugars}, with the approximate initial 1-butanol mass fraction (wb) of 0.7, was titrated with pure 1butanol until the formation of a transparent system, at each TCp. The

-6

270

290

310

TCp /K

330

350

370

(c)

Fig. 3. (a) Gibbs free energy changes (ΔGm, C); (b) entropy changes (ΔSm, C); and (c) enthalpy changes (ΔHm, C) of clouding process in the binary system of {1-butanol + water}, versus cloud point temperature (TCp) at both water-rich and butanol-rich branches.

Table 2 Thermodynamic functions (Gibbs free energy changes, ΔGm, C, entropy changes, ΔSm, C, and enthalpy changes, ΔHm, C) and relative contributions of entropy (ζS) and enthalpy (ζH) to Gibbs energy for clouding process in the binary system of 1-butanol + water, at both water-rich and butanol-rich branches, as a function of cloud point temperature (TCp) at 845 hPa. TCp/K

283.1

293.1

303.1

313.1

323.1

333.1

343.1

353.1

1-Butanol + water (water-rich branch) ΔGm/(kJ · mol−1) −8.4919 TCp ⋅ ΔSm/(kJ · mol−1) 19.1490 ΔHm/(kJ · mol−1) 10.6571 ζS 0.6425 ζH 0.3575

278.1

−8.8345 19.0512 10.2167 0.6509 0.3491

−9.4830 18.1860 8.7030 0.6763 0.3237

−10.0805 16.4785 6.3979 0.7203 0.2797

−10.5312 14.1106 3.5794 0.7977 0.2023

−10.9774 11.6811 0.7038 0.9432 0.0568

−11.3259 9.5617 −1.7642 0.8442 0.1558

−11.5182 8.0189 −3.4992 0.6962 0.3038

−11.7782 7.4286 −4.3496 0.6307 0.3693

1-Butanol + water (butanol-rich branch) ΔGm/(kJ · mol−1) −1.6057 TCp. ΔSm/(kJ · mol−1) 0.9392 −1 ΔHm/(kJ · mol ) −0.6665 ζS 0.5849 ζH 0.4151

−1.6181 0.7853 −0.8329 0.4853 0.5147

−1.6436 0.4351 −1.2086 0.2647 0.7353

−1.6457 0.0047 −1.6410 0.0029 0.9971

−1.6383 −0.4898 −2.1280 0.1871 0.8129

−1.6274 −1.0384 −2.6658 0.2803 0.7197

−1.5727 −1.6763 −3.2490 0.3403 0.6597

−1.5131 −2.3580 −3.8711 0.3785 0.6215

−1.4410 −3.0838 −4.5248 0.4053 0.5947

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167

360

1.2

Pure water

1

Sucrose 0.2 mol/kg Sucrose 0.6 mol/kg

0.6

TCp / K

ζΗ, ζS

0.8

0.4 0.2 0

Sucrose 0.4 mol/kg

340

320

300

270

290

310

330

350

370

280 0.05

TCp /K

0.06

0.07

0.08

0.09

0.1

wb

Fig. 4. The relative contributions of the entropy (ζS) and enthalpy (ζH) to Gibbs free energy of clouding process in the binary system of {1-butanol + water}, versus cloud point temperature (TCp): ▲, ζS at water-rich branch; ●, ζH at water-rich branch; △, ζS at butanol-rich branch; and ○, ζH at butanol-rich branch.

Fig. 6. Cloud point temperature, TCp, versus 1-butanol mass fraction, wb, for ternary systems of {1-butanol in aqueous solution of sucrose}.

mixture composition was determined using an analytical balance (Sartorius CP124S) with a precision of ±1·10−4 g. To ensure the accuracy and reproducibility of the obtained data, the cloud point measurements for each system, at each TCp, were performed in three replicates, and the average values of wb were reported. A lamp was also situated near the

measuring glassy cell for better visualization and recording the exact alcohol mass fraction related to phase separation at each temperature. The standard uncertainty in determining wb was found to be ±5 ∙ 10−4. Previous studies [28,30] showed that compared to salts, carbohydrates are weaker soluting-out agents. Therefore, the sugars

360 Pure water Xylose 0.4 mol/kg 340

Xylitol 0.4 mol/kg

TCp / K

Fructose 0.4 mol/kg Glucose 0.4 mol/kg 320

Sucrose 0.4 mol/kg Maltose 0.4 mol/kg Maltitol 0.4 mol/kg

300

280 0.055

0.063

360

wb

0.079

0.087

Pure water Xylitol 0.4 mol/kg Glucose 0.4 mol/kg Maltose 0.4 mol/kg

340

TCp / K

0.071

(a)

Xylose 0.4 mol/kg Fructose 0.4 mol/kg Sucrose 0.4 mol/kg Maltitol 0.4 mol/kg

320

300

280 0.7

0.75

0.8

0.85

wb

0.9

0.95

1

(b)

Fig. 5. Cloud point temperature, TCp, versus 1-butanol mass fraction, wb, for ternary systems of {1-butanol + aqueous solutions of 0.4 mol·kg−1 of sugars}: (a) water-rich branch; (b) butanol-rich branch.

168

N. Ebrahimi et al. / Journal of Molecular Liquids 278 (2019) 164–174

0.40 283.1 K 293.1 K

0.30

(iii) Solubility data for ternary systems of 1-butanol + aqueous solutions of 0.4 mol·kg−1 of sugars, in the alcohol-rich environment, at the temperature interval from 293.1 K to 333.1 K.

303.1 K

ln mb

0.20

313.1 K 323.1 K

0.10

333.1 K 343.1 K

0.00

353.1 K -0.10 -0.20 0.00

0.20

0.40

0.60

0.80

ms / mol.kg-1 Fig. 7. Setschenow-type plot for ternary systems of {1-butanol in aqueous solution of sucrose} at different temperatures. The dotted lines obtained by Eq. (6).

All the liquid-liquid equilibrium data are provided in the Supplementary material (Tables S1–S6) as the cloud point temperature (TCp) versus 1-butanol mass fraction (wb). It should be remarked that because of possible contaminations caused by 1-butanol, this work focuses more on the soluting effects of sugars on the water-rich region of the alcohol/ water system. Hence, the temperature and the sugar concentration range investigated in the water-rich environment is wider than those in the alcohol-rich environment. Besides, in the alcohol-rich environment, there is the possibility of sugars precipitation at low temperatures and high sugar molalities. However, there was no trace of sugar precipitation in the temperature and concentration range selected in this work, and all the cloud point data were related to liquid-liquid demixing. 3.1. Clouding process in the binary 1-butanol + water system

concentration should be high enough to insert a detectable soluting effect on the phase behavior of butanol-water mixtures. On the other hand, to avoid the sugars precipitation by addition of alcohol, the aqueous sugar solutions should not be so concentrated. At such sugar concentrations which have been selected in this work (aqueous solutions of 0.2, 0.4 and 0.6 mol·kg−1 of sugars at water-rich branch, and aqueous solutions of 0.4 mol·kg−1 of sugars at alcohol-rich branch) a detectable soluting effect is observed and there is no trace of sugars precipitation (no interference of liquid-liquid equilibrium with solid-liquid equilibrium). 3. Results and discussion This work reports the results regarding the liquid-liquid demixing (clouding process) of binary {1-butanol + water} and several ternary {1-butanol + water + sugar} systems. The investigated sugars are pentose monosaccharide (D-(+)-xylose), hexose monosaccharides (D(+)-glucose and D-(−)-fructose), disaccharides (sucrose and maltose), and sugar polyols (xylitol, and maltitol). The obtained data can be classified as follows: (i) Solubility data for the binary system of 1-butanol + water, in both water-rich and alcohol-rich environments (namely, solubilities of 1-butanol in water and water in 1-butanol), at the temperature interval from 278.1 K to 353.1 K. (ii) Solubility data for ternary systems of 1-butanol + aqueous solutions of (0.2, 0.4, and 0.6) mol·kg−1 of sugars, in the water-rich environment, at the temperature interval from 283.1 K to 353.1 K.

Fig. 2 shows the overall liquid-liquid phase diagram of the binary system of 1-butanol + water obtained in this work (Fig. 2a), as well as compares our data at water-rich (Fig. 2b) and 1-butanol-rich (Fig. 2c) branches with the literature [12–15]. As can be seen, our data and literature are in good agreement. From Fig. 2b, the solubility of 1-butanol in water, first decreases with an increase in temperature, goes through a minimum at about 330 K and then increases at higher temperatures. In other words, a homogenous solution of 1-butanol in water undergoes liquid-liquid demixing by heating at temperatures lower than 330 K, and by cooling at temperatures higher than 330 K. However, as Fig. 2c shows, the solubility of water in 1-butanol always increases with an increase in temperature. The liquid-liquid phase behavior of the butanolwater system in the presence of sugars has also the same behavior, only the area of biphasic/monophasic regions changes, as will be seen later. The Gibbs free energy change of phase separation or clouding process (ΔGm) was calculated from the following equation [36–40]: ΔGm ¼ RT Cp lnX i

ð1Þ

where R is the universal gas constant and Xi is the solute mole fraction corresponding to TCp. The subscript ‘i’ denotes the solute, which is 1-butanol at the water-rich branch, and water at the 1-butanol-rich branch. The entropy change of clouding process (ΔSm) can be calculated from the temperature dependency of ΔGm. For this purpose, first, the dependence of Xi on TCp was determined by a polynomial equation, and then ΔSm was calculated as follows:
ΔSm ¼ −R

ln X i þ T Cp


 d lnX i dT

ð2Þ

Table 3 Values of the soluting-out coefficients (ks) obtained from the linear fits of cloud point data to the Setschenow equation (Eq. (6)) for 1-butanol in aqueous sugar solutions at different temperatures and 845 hPa. TCp/K

ks/kg·mol−1 (R2) 1-Butanol in aqueous sugar solutions

283.1 293.1 303.1 313.1 323.1 333.1 343.1 353.1

Maltitol

Maltose

Sucrose

Glucose

Fructose

Xylitol

Xylose

0.248 (0.972) 0.233 (0.988) 0.177 (0.987) 0.144 (0.950) 0.102 (0.970) 0.077 (0.980) 0.119 (0.925) 0.089 (0.909)

0.244 (0.968) 0.239 (0.995) 0.175 (0.987) 0.147 (0.952) 0.105 (0.981) 0.073 (0.955) 0.118 (0.923) 0.093 (0.905)

0.214 (0.983) 0.198 (0.994) 0.152 (0.996) 0.128 (0.970) 0.092 (0.980) 0.056 (0.993) 0.079 (0.983) 0.058 (0.986)

0.198 (0.982) 0.189 (0.994) 0.124 (0.983) 0.108 (0.958) 0.072 (0.983) 0.046 (0.996) 0.071 (0.993) 0.036 (0.967)

0.186 (0.982) 0.159 (0.968) 0.105 (0.969) 0.099 (0.974) 0.063 (0.979) 0.037 (0.983) 0.062 (0.945) 0.022 (0.987)

0.155 (0.982) 0.129 (0.993) 0.092 (0.972) 0.088 (0.964) 0.056 (0.982) 0.029 (0.963) 0.063 (0.948) 0.017 (0.990)

0.126 (0.995) 0.117 (0.988) 0.055 (0.992) 0.063 (0.986) 0.033 (0.964) 0.012 (0.972) 0.042 (0.946) 0.004 (0.899)

The Data in the parentheses is related to the correlation coefficients (R2).

N. Ebrahimi et al. / Journal of Molecular Liquids 278 (2019) 164–174

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Table 4 Thermodynamic functions (Gibbs free energy changes, ΔGm, C, entropy changes, ΔSm, C, and enthalpy changes, ΔHm, C) and relative contributions of entropy (ζS) and enthalpy (ζH) to Gibbs energy for clouding process in the ternary systems of 1-butanol + aqueous sugar solutions, at the water-rich branch, as a function of cloud point temperature (TCp) at 845 hPa. TCp/K

303.1

313.1

323.1

333.1

343.1

353.1

1-Butanol in aqueous 0.2 mol·kg−1 of D-(+)-xylose solution ΔGm/(kJ · mol−1) −8.9070 −9.5381 TCp ⋅ ΔSm/(kJ · mol−1) 18.4721 17.6485 −1 ΔHm/(kJ · mol ) 9.5651 8.1104 ζS 0.6588 0.6851 ζH 0.3412 0.3149

283.1

293.1

−10.1111 16.0526 5.9415 0.7299 0.2701

−10.5710 13.8715 3.3005 0.8078 0.1922

−10.9959 11.5751 0.5792 0.9523 0.0477

−11.3407 9.5221 −1.8186 0.8396 0.1604

−11.5384 7.9376 −3.6008 0.6879 0.3121

−11.7923 7.1687 −4.6235 0.6079 0.3921

1-Butanol in aqueous 0.2 mol·kg−1 of xylitol solution ΔGm/(kJ · mol−1) −8.9329 −9.5649 TCp ⋅ ΔSm/(kJ · mol−1) 18.4060 17.5814 −1 ΔHm/(kJ · mol ) 9.4730 8.0165 ζS 0.6602 0.6868 0.3398 0.3132 ζH

−10.1142 15.9615 5.8473 0.7319 0.2681

−10.6080 13.8111 3.2031 0.8117 0.1883

−11.0128 11.4825 0.4697 0.9607 0.0393

−11.3445 9.3902 −1.9543 0.8277 0.1723

−11.5465 7.7666 −3.7799 0.6726 0.3274

−11.7959 6.9302 −4.8657 0.5875 0.4125

1-Butanol in aqueous 0.2 mol·kg−1 of D-(−)-fructose solution ΔGm/(kJ · mol−1) −8.9533 −9.5691 TCp ⋅ ΔSm/(kJ · mol−1) 18.0017 17.3350 ΔHm/(kJ · mol−1) 9.0484 7.7659 ζS 0.6655 0.6906 ζH 0.3345 0.3094

−10.1200 15.9245 5.8045 0.7329 0.2671

−10.6152 13.9469 3.3318 0.8072 0.1928

−11.0252 11.6831 0.6579 0.9467 0.0533

−11.3479 9.4840 −1.8639 0.8357 0.1643

−11.5721 7.6227 −3.9494 0.6587 0.3413

−11.7983 6.3599 −5.4384 0.5391 0.4609

1-Butanol in aqueous 0.2 mol·kg−1 of D-(+)-glucose solution ΔGm/(kJ · mol−1) −8.9624 −9.5761 TCp ⋅ ΔSm/(kJ · mol−1) 18.2140 17.4482 ΔHm/(kJ · mol−1) 9.2516 7.8721 ζS 0.6632 0.6891 ζH 0.3368 0.3109

−10.1396 15.9396 5.8000 0.7332 0.2668

−10.6280 13.8692 3.2413 0.8106 0.1894

−11.0388 11.5844 0.5457 0.9550 0.0450

−11.3572 9.4463 −1.9109 0.8317 0.1683

−11.5767 7.7330 −3.8437 0.6680 0.3320

−11.8165 6.7120 −5.1045 0.5680 0.4320

1-Butanol in aqueous 0.2 mol·kg−1 of sucrose solution ΔGm/(kJ · mol−1) −8.9745 −9.5984 TCp ⋅ ΔSm/(kJ · mol−1) 18.4696 17.5823 −1 ΔHm/(kJ · mol ) 9.4950 7.9839 ζS 0.6605 0.6877 ζH 0.3395 0.3123

−10.1673 15.9277 5.7604 0.7344 0.2656

−10.6404 13.7228 3.0823 0.8166 0.1834

−11.0493 11.4014 0.3522 0.9700 0.0300

−11.3721 9.3459 −2.0261 0.8218 0.1782

−11.5882 7.8195 −3.7687 0.6748 0.3252

−11.8301 7.0883 −4.7418 0.5992 0.4008

1-Butanol in aqueous 0.2 mol·kg−1 of maltose solution ΔGm/(kJ · mol−1) −9.0154 −9.6238 TCp ⋅ ΔSm/(kJ · mol−1) 18.0769 17.2539 ΔHm/(kJ · mol−1) 9.0615 7.6301 ζS 0.6661 0.6934 ζH 0.3339 0.3066

−10.1919 15.7540 5.5622 0.7391 0.2609

−10.6581 13.7480 3.0899 0.8165 0.1835

−11.0633 11.6307 0.5674 0.9535 0.0465

−11.4008 9.7531 −1.6477 0.8555 0.1445

−11.6405 8.3455 −3.2950 0.7169 0.2831

−11.8872 7.6465 −4.2407 0.6433 0.3567

1-Butanol in aqueous 0.2 mol·kg−1 of maltitol solution ΔGm/(kJ · mol−1) −9.0144 −9.6192 TCp ⋅ ΔSm/(kJ · mol−1) 18.0296 17.2297 ΔHm/(kJ · mol−1) 9.0152 7.6105 ζS 0.6667 0.6936 ζH 0.3333 0.3064

−10.1867 15.7589 5.5722 0.7388 0.2612

−10.6570 13.7792 3.1222 0.8153 0.1847

−11.0668 11.6715 0.6046 0.9507 0.0493

−11.3948 9.7668 −1.6280 0.8571 0.1429

−11.6394 8.3237 −3.3156 0.7151 0.2849

−11.8860 7.5641 −4.3219 0.6364 0.3636

1-Butanol in aqueous 0.4 mol·kg−1 of D-(+)-xylose solution ΔGm/(kJ · mol−1) −8.9607 −9.5971 TCp ⋅ ΔSm/(kJ · mol−1) 18.3896 17.5192 −1 ΔHm/(kJ · mol ) 9.4290 7.9221 ζS 0.6611 0.6886 ζH 0.3389 0.3114

−10.1473 15.8562 5.7088 0.7353 0.2647

−10.6217 13.6650 3.0433 0.8179 0.1821

−11.0242 11.3464 0.3222 0.9724 0.0276

−11.3559 9.3003 −2.0556 0.8190 0.1810

−11.5734 7.7641 −3.8093 0.6709 0.3291

−11.8024 6.9963 −4.8061 0.5928 0.4072

1-Butanol in aqueous 0.4 mol·kg−1 of xylitol solution ΔGm/(kJ · mol−1) −8.9834 −9.6347 TCp ⋅ ΔSm/(kJ · mol−1) 18.8740 17.7845 −1 ΔHm/(kJ · mol ) 9.8905 8.1498 ζS 0.6562 0.6858 ζH 0.3438 0.3142

−10.1896 15.8430 5.6534 0.7370 0.2630

−10.6588 13.4095 2.7506 0.8298 0.1702

−11.0449 10.9799 −0.0650 0.9941 0.0059

−11.3725 9.0282 −2.3443 0.7939 0.2061

−11.5897 7.7823 −3.8074 0.6715 0.3285

−11.8185 7.4749 −4.3436 0.6325 0.3675

1-Butanol in aqueous 0.4 mol·kg−1 of D-(−)-fructose solution ΔGm/(kJ · mol−1) −9.0126 −9.6831 TCp ⋅ ΔSm/(kJ · mol−1) 18.8484 17.6578 ΔHm/(kJ · mol−1) 9.8358 7.9746 ζS 0.6571 0.6889 ζH 0.3429 0.3111

−10.2087 15.5877 5.3790 0.7435 0.2565

−10.6630 13.1067 2.4437 0.8429 0.1571

−11.0544 10.7420 −0.3124 0.9717 0.0283

−11.3820 8.9381 −2.4439 0.7853 0.2147

−11.5934 7.9024 −3.6909 0.6816 0.3184

−11.8259 7.8702 −3.9556 0.6655 0.3345

1-Butanol in aqueous 0.4 mol·kg−1 of D-(+)-glucose solution ΔGm/(kJ · mol−1) −9.0253 −9.6943 TCp ⋅ ΔSm/(kJ · mol−1) 19.0067 17.7610 ΔHm/(kJ · mol−1) 9.9814 8.0666 ζS 0.6557 0.6877 ζH 0.3443 0.3123

−10.2336 15.6382 5.4046 0.7432 0.2568

−10.6808 13.0968 2.4159 0.8443 0.1557

−11.0731 10.7182 −0.3549 0.9680 0.0320

−11.3964 8.9465 −2.4500 0.7850 0.2150

−11.6171 8.0085 −3.6086 0.6894 0.3106

−11.8495 8.1154 −3.7342 0.6849 0.3151

(continued on next page)

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N. Ebrahimi et al. / Journal of Molecular Liquids 278 (2019) 164–174

Table 4 (continued) 303.1

313.1

323.1

333.1

343.1

353.1

1-Butanol in aqueous 0.4 mol·kg−1 of sucrose solution −9.0436 −9.7076 ΔGm/(kJ · mol−1) TCp ⋅ ΔSm/(kJ · mol−1) 19.1253 17.7864 ΔHm/(kJ · mol−1) 10.0818 8.0788 ζS 0.6548 0.6877 ζH 0.3452 0.3123

TCp/K

283.1

293.1

−10.2599 15.5917 5.3319 0.7452 0.2548

−10.6960 12.9983 2.3023 0.8495 0.1505

−11.0868 10.6509 −0.4359 0.9607 0.0393

−11.4044 8.9861 −2.4183 0.7880 0.2120

−11.6388 8.2486 −3.3902 0.7087 0.2913

−11.8756 8.6195 −3.2562 0.7258 0.2742

1-Butanol in aqueous 0.4 mol·kg−1 of maltose solution ΔGm/(kJ · mol−1) −9.0876 −9.7474 TCp ⋅ ΔSm/(kJ · mol−1) 19.0122 17.6203 −1 ΔHm/(kJ · mol ) 9.9246 7.8729 ζS 0.6570 0.6912 ζH 0.3430 0.3088

−10.2955 15.4323 5.1368 0.7503 0.2497

−10.7341 12.9346 2.2004 0.8546 0.1454

−11.1068 10.7401 −0.3666 0.9670 0.0330

−11.4299 9.3103 −2.1196 0.8146 0.1854

−11.7103 8.8940 −2.8163 0.7595 0.2405

−11.9418 9.5922 −2.3496 0.8032 0.1968

1-Butanol in aqueous 0.4 mol·kg−1 of maltitol solution ΔGm/(kJ · mol−1) −9.0926 −9.7536 TCp ⋅ ΔSm/(kJ · mol−1) 18.8419 17.5332 −1 ΔHm/(kJ · mol ) 9.7492 7.7797 ζS 0.6590 0.6927 ζH 0.3410 0.3073

−10.2980 15.4307 5.1327 0.7504 0.2496

−10.7321 12.9841 2.2520 0.8522 0.1478

−11.1047 10.7785 −0.3262 0.9706 0.0294

−11.4380 9.2673 −2.1707 0.8102 0.1898

−11.7133 8.6733 −3.0400 0.7405 0.2595

−11.9292 9.0969 −2.8324 0.7626 0.2374

1-Butanol in aqueous 0.6 mol·kg−1 of D-(+)-xylose solution −9.0367 −9.6780 ΔGm/(kJ · mol−1) TCp ⋅ ΔSm/(kJ · mol−1) 17.8474 17.0306 ΔHm/(kJ · mol−1) 8.8106 7.3525 ζS 0.6695 0.6985 ζH 0.3305 0.3015

−10.1887 15.4431 5.2543 0.7461 0.2539

−10.6518 13.3926 2.7408 0.8301 0.1699

−11.0573 11.2139 0.1566 0.9862 0.0138

−11.3753 9.2254 −2.1498 0.8110 0.1890

−11.6188 7.6924 −3.9264 0.6621 0.3379

−11.8165 6.7686 −5.0480 0.5728 0.4272

1-Butanol in aqueous 0.6 mol·kg−1 of xylitol solution ΔGm/(kJ · mol−1) −9.0831 −9.6943 TCp ⋅ ΔSm/(kJ · mol−1) 17.6815 16.9309 ΔHm/(kJ · mol−1) 8.5985 7.2366 ζS 0.6728 0.7006 ζH 0.3272 0.2994

−10.2362 15.4701 5.2339 0.7472 0.2528

−10.6941 13.4676 2.7735 0.8292 0.1708

−11.0973 11.2598 0.1625 0.9858 0.0142

−11.4014 9.1337 −2.2677 0.8011 0.1989

−11.6545 7.3935 −4.2610 0.6344 0.3656

−11.8372 6.1570 −5.6802 0.5201 0.4799

1-Butanol in aqueous 0.6 mol·kg−1 of D-(−)-fructose solution ΔGm/(kJ · mol−1) −9.1279 −9.7267 TCp ⋅ ΔSm/(kJ · mol−1) 17.3080 16.5996 −1 ΔHm/(kJ · mol ) 8.1802 6.8729 ζS 0.6791 0.7072 ζH 0.3209 0.2928

−10.2538 15.2173 4.9635 0.7540 0.2460

−10.7147 13.3262 2.6115 0.8361 0.1639

−11.1100 11.1985 0.0885 0.9922 0.0078

−11.4139 9.1082 −2.3057 0.7980 0.2020

−11.6608 7.3292 −4.3316 0.6285 0.3715

−11.8462 5.9932 −5.8530 0.5059 0.4941

1-Butanol in aqueous 0.6 mol·kg−1 of D-(+)-glucose solution ΔGm/(kJ · mol−1) −9.1448 −9.7737 TCp ⋅ ΔSm/(kJ · mol−1) 17.7462 16.7829 ΔHm/(kJ · mol−1) 8.6013 7.0093 ζS 0.6735 0.7054 ζH 0.3265 0.2946

−10.2841 15.0907 4.8066 0.7584 0.2416

−10.7287 12.9863 2.2576 0.8519 0.1481

−11.1247 10.8517 −0.2730 0.9755 0.0245

−11.4288 8.9849 −2.4439 0.7862 0.2138

−11.6708 7.6439 −4.0269 0.6550 0.3450

−11.8706 6.9504 −4.9202 0.5855 0.4145

1-Butanol in aqueous 0.6 mol·kg−1 of sucrose solution ΔGm/(kJ · mol−1) −9.1673 −9.7901 TCp ⋅ ΔSm/(kJ · mol−1) 18.2503 17.0532 ΔHm/(kJ · mol−1) 9.0831 7.2631 ζS 0.6677 0.7013 ζH 0.3323 0.2987

−10.3307 15.1306 4.8000 0.7592 0.2408

−10.7616 12.8109 2.0494 0.8621 0.1379

−11.1582 10.6191 −0.5391 0.9517 0.0483

−11.4489 8.8658 −2.5831 0.7744 0.2256

−11.6830 7.8267 −3.8563 0.6699 0.3301

−11.9093 7.6363 −4.2730 0.6412 0.3588

1-Butanol in aqueous 0.6 mol·kg−1 of maltose solution ΔGm/(kJ · mol−1) −9.2120 −9.8507 TCp ⋅ ΔSm/(kJ · mol−1) 18.1244 16.8626 −1 ΔHm/(kJ · mol ) 8.9125 7.0119 ζS 0.6704 0.7063 ζH 0.3296 0.2937

−10.3643 14.8982 4.5340 0.7667 0.2333

−10.7871 12.6547 1.8676 0.8714 0.1286

−11.1796 10.6459 −0.5337 0.9523 0.0477

−11.4815 9.1751 −2.3064 0.7991 0.2009

−11.7483 8.5048 −3.2435 0.7239 0.2761

−11.9740 8.7147 −3.2593 0.7278 0.2722

1-Butanol in aqueous 0.6 mol·kg−1 of maltitol solution ΔGm/(kJ · mol−1) −9.2162 −9.8385 TCp ⋅ ΔSm/(kJ · mol−1) 17.9038 16.7336 −1 ΔHm/(kJ · mol ) 8.6876 6.8950 ζS 0.6733 0.7082 ζH 0.3267 0.2918

−10.3656 14.9043 4.5387 0.7666 0.2334

−10.7835 12.7471 1.9636 0.8665 0.1335

−11.1759 10.7606 −0.4153 0.9628 0.0372

−11.4831 9.2312 −2.2519 0.8039 0.1961

−11.7498 8.4103 −3.3395 0.7158 0.2842

−11.9700 8.3797 −3.5903 0.7001 0.2999

Finally, the enthalpy change of clouding process (ΔHm) was obtained from the following thermodynamic relation: ΔH m ¼ ΔGm þ T Cp ΔSm

ð3Þ

The values obtained for thermodynamic functions of clouding process in the binary system of 1-butanol + water are presented in

Table 2 and depicted in Fig. 3. As Fig. 3a shows, the values of ΔGm for the water-rich branch are more negative than those for the alcoholrich branch. In other words, the liquid-liquid demixing process for 1butanol in water mixtures is more spontaneous than that for water in 1-butanol ones. It can be seen that ΔGm becomes more negative with increasing temperature at the water-rich branch, while at the alcohol-rich branch ΔGm is almost independent of temperature. From Fig. 3b, the

N. Ebrahimi et al. / Journal of Molecular Liquids 278 (2019) 164–174 Table 5 Thermodynamic functions (Gibbs free energy changes, ΔGm, C, entropy changes, ΔSm, C, and enthalpy changes, ΔHm, C) and relative contributions of entropy (ζS) and enthalpy (ζH) to Gibbs energy for clouding process in the ternary systems of 1-butanol + aqueous sugar solutions, at the butanol-rich branch, as a function of cloud point temperature (TCp) at 845 hPa. TCp/K

293.1

303.1

313.1

323.1

333.1

1-Butanol + aqueous 0.4 mol·kg−1 of D-(+)-xylose solution (butanol-rich branch) ΔGm/(kJ · mol−1) −1.8167 −1.8000 −1.7802 −1.7665 −1.7193 TCp ⋅ ΔSm/(kJ · mol−1) −0.8440 −0.4212 −0.4497 −0.9565 −2.0076 ΔHm/(kJ · mol−1) −2.6607 −2.2212 −2.2300 −2.7231 −3.7269 ζS 0.2408 0.1594 0.1678 0.2600 0.3501 ζH 0.7592 0.8406 0.8322 0.7400 0.6499 1-Butanol + aqueous 0.4 mol·kg−1 of xylitol solution (butanol-rich branch) −1.8370 −1.8353 −1.8183 −1.8098 −1.8016 ΔGm/(kJ · mol−1) TCp ⋅ ΔSm/(kJ · mol−1) 0.0793 −0.2851 −0.4425 −0.3484 0.0107 ΔHm/(kJ · mol−1) −1.7577 −2.1204 −2.2608 −2.1582 −1.7908 ζS 0.0432 0.1185 0.1637 0.1390 0.0060 ζH 0.9568 0.8815 0.8363 0.8610 0.9940 1-Butanol + aqueous 0.4 mol·kg−1 of D-(−)-fructose solution (butanol-rich branch) ΔGm/(kJ · mol−1) −1.9165 −1.9188 −1.8970 −1.8921 −1.8551 TCp ⋅ ΔSm/(kJ · mol−1) −0.0864 −0.1729 −0.4063 −0.7549 −1.2739 −1 ΔHm/(kJ · mol ) −2.0029 −2.0917 −2.3033 −2.6470 −3.1290 ζS 0.0414 0.0764 0.1499 0.2219 0.2893 ζH 0.9586 0.9236 0.8501 0.7781 0.7107 1-Butanol + aqueous 0.4 mol·kg−1 of D-(+)-glucose solution (butanol-rich branch) ΔGm/(kJ · mol−1) −1.9978 −2.0071 −1.9848 −1.9498 −1.9193 TCp ⋅ ΔSm/(kJ · mol−1) 0.8946 −0.2856 −0.9923 −1.1557 −0.7305 ΔHm/(kJ · mol−1) −1.1032 −2.2927 −2.9771 −3.1055 −2.6498 ζS 0.4478 0.1108 0.2500 0.2712 0.2161 ζH 0.5522 0.8892 0.7500 0.7288 0.7839 1-Butanol + aqueous 0.4 mol·kg−1 of sucrose solution (butanol-rich branch) ΔGm/(kJ · mol−1) −3.6611 −3.6585 −3.5461 −3.4333 −3.1997 TCp ⋅ ΔSm/(kJ · mol−1) 0.0999 −1.4096 −3.4849 −5.8598 −8.4616 −1 ΔHm/(kJ · mol ) −3.5612 −5.0681 −7.0310 −9.2931 −11.6613 ζS 0.0273 0.2176 0.3314 0.3867 0.4205 ζH 0.9727 0.7824 0.6686 0.6133 0.5795 −1

1-Butanol + aqueous 0.4 mol·kg ΔGm/(kJ · mol−1) −4.0994 TCp ⋅ ΔSm/(kJ · mol−1) −0.0250 −1 ΔHm/(kJ · mol ) −4.1244 ζS 0.0060 ζH 0.9940

of maltose solution (butanol-rich branch) −4.0779 −4.0145 −3.9315 −3.8276 −1.3192 −2.3463 −3.0923 −3.5868 −5.3971 −6.3608 −7.0238 −7.4144 0.1964 0.2695 0.3057 0.3260 0.8036 0.7305 0.6943 0.6740

1-Butanol + aqueous 0.4 mol·kg−1 of maltitol solution (butanol-rich branch) ΔGm/(kJ · mol−1) −4.1187 −4.0761 −4.0256 −3.9332 −3.8534 TCp ⋅ ΔSm/(kJ · mol−1) −0.5161 −1.5771 −2.2948 −2.7299 −2.8632 ΔHm/(kJ · mol−1) −4.6348 −5.6533 −6.3203 −6.6630 −6.7166 ζS 0.1002 0.2181 0.2664 0.2906 0.2989 ζH 0.8998 0.7819 0.7336 0.7094 0.7011

clouding process in the water-rich region is accompanied by a large entropy increase (high positive values of TCpΔSm), however, no significant change in entropy is observed for phase separation in the alcohol-rich region (small positive or negative values of TCpΔSm). According to Fig. 3c, although, the clouding process in the alcohol-rich region is always exothermic, in the water-rich region it is endothermic and exothermic at temperatures lower and higher than 330 K, respectively. From the results gathered, the main driving force for clouding process at the water-rich branch is often entropy increase. However, at the butanol-rich branch, the enthalpy decrease is mostly the primordial force in the clouding process. It is obvious that the effect of temperature on solvent structure and solute-solvent interactions is different for various types of solvents. The previous studies [41,42] showed that the compressibility of pure alcohols increases by rising temperature while the compressibility of pure water decreases with temperature to a minimum value near 330 K and

171

then increases gradually. This indicates that the structure of alcohols is weakened by elevation of temperature, while water becomes more structured and less compressible with an increase in temperature, at temperatures below 330 K. The temperature effect on the water structure is reversed at temperatures higher than 330 K. In the butanol-rich environment, which 1-butanol act as the solvent, an increases in temperature leads to the breakdown of the solvent (1-butanol) selfassociated molecules from each other, therefore leading to the more hydrogen bonds between solute (water) and solvent (1-butanol) molecules, and eventually leads to transformation of the two-phase system into a one-phase system. Obviously, decreasing in temperature in the butanol-rich environment leads to less solvent-solute and more solvent-solvent interactions and ultimately leads to the exothermic clouding phenomenon. However, in the water-rich environment, which water act as the solvent, increasing in temperature, at temperatures below 330 K, leads to the more structured solvent and the looser hydration sell of solute, resulting in a more distance between 1butanol and water molecules. Therefore, in this case, by increasing temperature (endothermic process), the solute (1-butanol) and solvent (water) molecules become excluded from the vicinity of each other, and ultimately because of the entropic reason the phase separation becomes favorable. By the formation of a biphasic system (two homogenous solutions of water and 1-butanol) the mentioned exclusion vanishes and entropy of system increases. According to above discussion, similar to the alcohol-rich environment, the exothermic clouding process in the water-rich environment at temperatures above 330 K is due to the strengthening of the water structure by reducing the temperature. The relative contributions of the entropy (ζS) and enthalpy (ζH) to Gibbs free energy of clouding were assessed using the following equations [43]: ζS ¼

jTΔSm j jΔH m j þ jTΔSm j

ð4Þ

ζH ¼

jΔH m j jΔH m j þ jTΔSm j

ð5Þ

As illustrated in Table 2 and Fig. 4, the relative contributions of entropy and enthalpy from the Gibbs free energy of phase separation in the binary 1-butanol-waer system follow the orders ζS N ζH at the water-rich branch, and ζH N ζS at the alcohol-rich branch (except at 278.1 K). This result agrees with the above discussion. 3.2. Clouding process in ternary 1-butanol + water + sugar systems The liquid-liquid phase diagrams (clouding diagram) for ternary systems of {1-butanol + aqueous solutions of 0.4 mol·kg−1 of sugars} are depicted in Fig. 5a (water-rich branch) and Fig. 5b (butanol-rich branch). As Fig. 5 shows, all the investigated sugars lead to an expansion in the two-phase region of the clouding diagram, at both water-rich and butanol-rich branches. In other words, the mutual solubility of 1butanol and water (solubility of 1-butanol in water and water in 1butanol) decreases by addition of sugars to their mixtures. The ability of the sugars to facilitate the clouding process, which in fact reflects their soluting-out strength, follows the order: maltitol ≈ maltose N sucrose N glucose N fructose N xylitol N xylose. The same trend was observed in the ternary systems of 1-butanol in aqueous solutions of (0.2 and 0.6) mol·kg−1 of the sugars which their respective clouding diagrams are provided in the Supplementary material (Fig. S1). Indeed, it can be envisaged that the competition between OH group of 1butanol and OH groups of sugars for hydrogen bonding with water molecules is responsible for the soluting-out phenomenon occurring in water-butanol mixtures. The logarithm of the octanol/water partition coefficient (log Kow) for 1-butanol is 0.84, while that for the studied sugars ranges from −1.08 to −5.61 (Table S7) [44]. This indicates that

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N. Ebrahimi et al. / Journal of Molecular Liquids 278 (2019) 164–174

-9.0

Pure water Xylose 0.4 mol/kg

-9.5

Xylitol 0.4 mol/kg

ΔGm / kJ.mol-1

Fructose 0.4 mol/kg

-10.0

-10.5

-10.1

Glucose 0.4 mol/kg

-10.2

Sucrose 0.4 mol/kg

-10.3

Maltose 0.4 mol/kg Maltitol 0.4 mol/kg

-10.4

-11.0

-10.5 -10.6

-11.5

-12.0

-10.7 -10.8 302.5

280

304.5

290

306.5

308.5

300

310.5

312.5

310

314.5

320

330

340

350

(a)

350

(b)

TCp /K -1.0 -1.5

ΔGm / kJ.mol-1

-2.0

Pure water Xylose 0.4 mol/kg Xylitol 0.4 mol/kg

-2.5

Fructose 0.4 mol/kg Glucose 0.4 mol/kg

-3.0

Sucrose 0.4 mol/kg Maltose 0.4 mol/kg Maltitol 0.4 mol/kg

-3.5 -4.0 -4.5

270

280

290

300

310

320

330

340

TCp /K Fig. 8. Gibbs free energy changes, ΔGm, C, versus cloud point temperature, TCp, for ternary systems of {1-butanol + aqueous solutions of 0.4 mol·kg−1 of sugars}: (a) water-rich branch; (b) butanol-rich branch.

sugars hold a higher affinity for water compared to 1-butanol, leading thus to the relative exclusion of 1-butanol from the vicinity of sugars and water, and consequently the facilitation of clouding process. From the obtained results, sugars with the higher number of hydroxyl groups are more prone to induce clouding process, so that their soluting-out ability can be classified as disaccharides N hexose monosaccharides N pentose monosaccharides, agreeing with the general trend of the hydrophilicity degree of sugars [45]. Comparing D-fructose and D-glucose which are structural isomers with the same number of OH groups, it is clear that aldohexoses are more effective in promoting clouding process when compared with ketohexoses. The trend of maltose (composed of two glucose units) and sucrose (composed of a glucose and a fructose unit) conforms the soluting-out ability of their constituent subunits. The results obtained here for the soluting-out ability of sugars are similar to those previously observed in the ternary systems of {propanol + sugar + water} [30] and {polypropylene glycol + sugar + water} [28]. As expected, the soluting-out influence of sugars on the clouding diagram of 1-butanol-water system becomes stronger by increasing the molality of sugars, an example of this fact is provided in Fig. 6.

To quantify the soluting-out effect of sugars on the 1-butanol-water mixtures, the obtained data at the water-rich branch were linearly fitted to Setschenow's equation [34]: m0b ln mb

! ¼ ks ms

ð6Þ

where mb0 and mb refer, respectively, to the solubility of 1-butanol in pure water and in aqueous sugar solutions with molality of ms. ks is the soluting-out coefficient which is specific for a particular sugar/ 1-butanol pair. In this assessment, we used the molality scale to avoid discrepancies resulted from differences in sugars molar mass. Fig. 7 represents the plot of lnmb versus ms for the water solubility of 1-butanol in the presence and absence of sucrose at different temperatures, as an instance of Setschenow-type plots. The values of ks obtained by least-squares linear fitting, along with correlation coefficients (R2) are presented in Table 3. Also, Fig. S2 depicts the values of ks against TCp for the investigated systems. It can be seen that ks generally decreases with increasing temperature, and at a certain

N. Ebrahimi et al. / Journal of Molecular Liquids 278 (2019) 164–174 360 Pure water Sucrose 0.4 mol/kg

TCp / K

340

(C)

(A) (B)

320 Two-phaseregion

One-phase region

300

280 0.65

0.7

0.75

0.8

wb

0.85

0.9

1

(a)

1

(b)

1

(c)

0.95

360 Pure water Maltose 0.4 mol/kg

TCp / K

340

(A) (B)

(C)

320

One-phase region

Two-phase 300

280 0.65

0.7

0.75

0.8

wb

0.85

0.9

0.95

360 Pure water Maltitol 0.4 mol/kg

TCp / K

340

(C)

(A) (B)

One-phase region

320 Two-phase region 300

280 0.65

0.7

0.75

0.8

wb

0.85

0.9

0.95

Fig. 9. The strange behavior of clouding diagram (Cloud point temperature (TCp) versus 1butanol mass fraction (wb)) for ternary systems of {1-butanol + aqueous solutions of 0.4 mol·kg−1 of sucrose/maltose/maltitol} in the butanol-rich environment: (a) sucrose; (b) maltose; and (c) maltitol.

TCp, whose values follow the trend of sugars ability to expand the biphasic region of clouding diagrams (Fig. 5 and Fig. S1). This result demonstrates that Eq. (6) gives a good description of experimental cloud point data. The thermodynamic functions and the relative contributions of entropy and enthalpy to Gibbs free energy of clouding process in the ternary systems of {1-butanol + aqueous sugar solutions}, at both water-rich and butanol-rich branches, were computed from Eqs. (1)–(5) and the obtained results are given in Tables 4 and 5. From these tables, for all the studied systems at the water-rich branch (Table 4), the values of ζS are greater than ζH, while at the butanol-rich branch (Table 5) ζH N ζS. This suggests that similar to the binary 1-butanol + water system, the clouding process in the ternary 1-butanol + water + sugar systems is driven by entropy and enthalpy, respectively, in the water-rich and butanol-rich environments. Fig. 8 shows that the clouding process of 1-butanolwater mixtures, at both water-rich (Fig. 8a) and butanol-rich (Fig. 8b) branches, in the presence of sugars is more spontaneous than that in the absence of them and the magnitude of ΔGm increases with increasing the soluting-out ability of sugars. Moreover, an

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increase in temperature leads to the more negative and less negative values of ΔGm at water-rich and butanol-rich branches, respectively. Fig. 9 displays the strange behavior observed during the clouding experiments for the ternary systems of {1-butanol + aqueous solutions of sucrose/maltose/maltitol} in the butanol-rich environment. When, at constant temperatures, a turbid mixture of {1-butanol + aqueous solution of sucrose, maltose or maltitol}, in the butanol-rich environment, is titrated with pure 1-butanol, a transparent solution appears at certain concentrations shown by line (A) in Fig. 9. However, this transparency is established just for a short concentration range, and by continuing titration the liquid-liquid demixing occurs at line (B) and the mixture becomes turbid again. The turbidity continues until line (C), afterward, a transparent solution appears again and this transparency is stable and doesn't change by the addition of more amounts of 1-butanol. In other words, it can be said that concentrations between lines (A) and (B) in Fig. 9 form a transparent zone in the biphasic regions of {1-butanol + aqueous solutions of sucrose/maltose/maltitol} systems. However, such strange behavior was not observed for the butanol-rich region of the ternary systems of {1-butanol + aqueous solutions of xylose/xylitol/fructose/glucose}, namely, there is not any transparent zone in the biphasic regions of these systems. Indeed, disaccharides have a higher number of OH groups and also a greater hydrocarbon portion in their structures, as compared to monosaccharides. From Fig. 9, it may be envisaged that, although sucrose, maltose, and maltitol because of possessing the higher number of hydrophilic groups induce the greater soluting-out effect on the 1-butanol-water mixtures and provide the broader biphasic region in the clouding diagram, due to their wealthy hydrocarbon contribution, facilitate the solubility of water in 1butanol for a small concentration range. This strange behavior may be a result of a delicate balance between hydrophobic and hydrophilic portions of disaccharides. It should be noted that although this type of liquid-liquid phase diagram is anomalous and it is reported here for the first time, the abundant repetition of our experimental clouding data confirms its correctness. Meanwhile, we couldn't find a trace of sugar precipitation in ternary systems of {1-butanol + aqueous solutions of 0.4 mol·kg−1 of sucrose/maltose/maltitol}. Therefore this anomalous behavior is independent of solid-liquid equilibrium. We also observed that when a turbid mixture of {1-butanol + aqueous solution of 0.4 mol·kg−1 of sucrose, maltose or maltitol}, in the butanolrich environment, is heated at a constant concentration, the mixture becomes transparent at a certain temperature, this transparency is established in a small temperature range, then it becomes turbid again by heating, and finally it becomes transparent with further increase in temperature. This observation is in agreement with the phase diagram depicted in Fig. 9. 4. Conclusion Thermodynamics of clouding behavior for 1-butanol-water solutions in the presence and absence of various sugars was investigated, in a wide temperature range. All the studied sugars induce the soluting-out effect and decrease the mutual solubility of 1-butanol and water. The liquid-liquid demixing becomes more spontaneous by addition of sugars to 1-butanol-water mixtures in both water-rich and butanol-rich environments. The clouding process in the butanol-rich branch is enthalpy-driven, while in the water-rich branch is entropydriven. In the presence and absence of sugars, the Gibbs free energy of clouding for 1-butanol-in water mixtures is more negative than that for water in 1-butanol ones, corroborating the more thermodynamically favorable clouding process in the water-rich environment of these systems, profiting also the more eco-friendly character for scaled-up strategies. The soluting-out coefficient of sugars is enhanced by increasing their hydrophilic nature and follows the order: disaccharides N hexose monosaccharides N pentose monosaccharides. A small transparent zone was found in the biphasic region of ternary 1-butanol + aqueous

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