(Liquid + liquid) equilibria for (water + 1-propanol or acetone + β-citronellol) at different temperatures

J. Chem. Thermodynamics 86 (2015) 20–26

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(Liquid + liquid) equilibria for (water + 1-propanol or acetone + b-citronellol) at different temperatures Hengde Li ⇑, Yongtao Han, Cheng Huang, Chufen Yang ⇑ School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China

a r t i c l e

i n f o

Article history: Received 5 November 2014 Received in revised form 12 February 2015 Accepted 14 February 2015 Available online 24 February 2015 Keywords: b-Citronellol LLE 1-Propanol Acetone Model

a b s t r a c t On this paper, experimental (liquid + liquid) equilibrium (LLE) results are presented for systems composed of b-citronellol and aqueous 1-propanol or acetone. To evaluate the phase separation properties of b-citronellol in aqueous mixtures, LLE values for the ternary systems (water + 1-propanol + b-citronellol) and (water + acetone + b-citronellol) were determined with a tie-line method at T = (283.15, 298.15, and 313.15 ± 0.02) K and atmospheric pressure. The reliability of the experimental tie-lines was verified by the Hand and Bachman equations. Ternary phase diagrams, distribution ratios of 1-propanol and acetone in the mixtures are shown. The effect of the temperature on the ternary (liquid + liquid) equilibria was examined and discussed. The experimental LLE values were satisfactorily correlated by extended UNIQUAC and modified UNIQUAC models. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction As environmentally friendly organic solvents, chemical compounds obtained from natural products have been increasing recently in use [1], essential oils have become important in the global economy not only for their medicinal properties but also due to their wide use in the chemical and food industries [2]. Citronellol (C10H20O) is a natural acyclic monoterpenoid and one the of the important fragrance terpenoids. It is abundant in plant essential oils (major constituents are terpenes and oxygenated terpenoids) and commonly used in perfumes, flavours, synthesis, fine chemicals, and biotransformation. Citronellol is present in many plants such as Cymbopogon nardus [3], Cymbopogon citratus, Monarda citriodora, Pelargonium graveolens, and Artemisia scoparia. The residues of Artemisia scoparia could serve as an important bioresource for extraction of monoterpenoid-rich oil (main components: b-citronellol and citronellal) exhibiting antioxidant activity, and thus hold a good potential use in the food and pharmaceutical industry [4]. As part of our research on the Cymbopogon essential oils by (liquid + liquid) extraction with different solvents, this work reports results for (water + 1-propanol or acetone + citronellol) at different temperatures. These solvents have the presence of polar groups as common factor.

⇑ Corresponding authors. Fax: +86 20 3932 2231 (H. Li), +86 20 3932 2231 (C. Yang). E-mail addresses: [email protected] (H. Li), [email protected] (C. Yang). http://dx.doi.org/10.1016/j.jct.2015.02.013 0021-9614/Ó 2015 Elsevier Ltd. All rights reserved.

Propanol and acetone are important organic synthetic raw materials, and are also good solvents and extraction agents. Extraction of essential oils from plants by extraction agents is popularly used in industry. The solubility of the terpenoids dissolved into several kinds of solvents and the experimental LLEs of the multicomponent terpenoid mixtures are indispensable for the proper design of their separation process or for the study of their use as industrial solvents. On the other hand, the (liquid + liquid) equilibria in (water + propanol or acetone + citronellol) systems provide important information in the design of equipment for the separation of propanol or acetone from aqueous mixtures. A survey of the literature on the (liquid + liquid) equilibrium systems containing monoterpenoid (or monoterpene) and alcohol, ternary (linalool + ethanol + water), and (limonene + ethanol + water) systems from T = (293.15 to 323.15) K were studied by Cháfer et al. [2,5]. The (water + ethanol + citral) multicomponent system at T = 303.15 K by Gramajo de Doz [6]; ternary LLE systems (limonene + linalool + 1,2-propanediol or 1,3-propanediol) from T = (298.15 to 318.15) K by Arce et al. [7]; (liquid + liquid) equilibrium data for the system (limonene + carvone + ethanol + water) at T = 298.2 K by Oliveira et al. [8]; ternary LLE (water + acetone + apinene, or b-pinene, or limonene) mixtures by Li and Tamura [9]; and ternary (a-pinene + D3-carene) polar compound systems [10] by Antosik and Stryjek, are available in the literature. Furthermore, ternary (water + terpene + 1-propanol or 1-buthanol) systems at T = 298.15 K [11]; (liquid + liquid) phase behaviour of geraniol in aqueous alcohol mixtures [12]; and ternary LLE for bcitronellol in aqueous alcohol at different temperatures [13] have

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H. Li et al. / J. Chem. Thermodynamics 86 (2015) 20–26

been reported previously. In addition, as far as we know, there are few reports on LLE for (propanol or acetone + terpenoid) mixtures in the literature. In the present paper, to examine the multicomponent phase equilibrium behaviour of b-citronellol in the (water + 1-propanol) or (water + acetone) mixture and the distribution ratios of 1-propanol or acetone between organic and aqueous phases, we determined the LLE tie-lines for (water + 1-propanol or acetone + citronellol) systems at T = (283.15, 298.15, and 313.15) K and atmospheric pressure. The reliability of the experimental LLE tie-lines was verified by the Hand and Bachman equations. The experimental values were correlated using the extended and modified UNIQUAC models. The effect of temperature on (liquid + liquid) phase equilibria was also studied, and its consequences are discussed. 2. Experimental

well-defined interface. The samples of both phases were withdrawn with precision Hamiltion syringes and immediately placed in 2 cm3 chromatographic vials, and their compositions were analysed by gas chromatography (Agilent 7820A) equipped with both a thermal conductivity detector (TCD) and flame ionisation detector (FID), and a 16-sample automatic liquid sampler. The temperatures of the injection port and TCD detector were set at 523.15 K and the oven temperature was increased from (323.15 to 503.15) K at a rate of 0.67 K  s1. The hydrogen flow rate for the separation column was set at 0.0125 cm3  s1 (split ratio 100:1). A GC capillary column (DB-624, 30 m  0.25 mm) was used to separate every component. The peak area of the components, detected to analyse with EzChrom Elite Compact software, was calibrated by gravimetrically weighed mixtures. For each sample solution, three analyses were performed to obtain a value. The accuracy of the tie-line measurements was estimated within ±0.0005 in mole fraction.

2.1. Materials

3. Results and discussion

3,7-Dimethyloct-6-en-1-ol (CAS No. 106-22-9, (±)-b-citronellol), 1-propanol, and acetone were supplied by the Aladdin Company and were used without further purification. Double-distilled water prepared in our laboratory was used throughout the experiment. The purities in mass fraction (by a GC assay) of the chemical reagents used in this work are shown in table 1. Their densities and refractive indices were measured at T = 293.15 K and atmospheric pressure, and are compared with literature values [14,15] in table 1. Densities were measured with an Anton Paar (DMA 4500) densimeter precise to within ±0.00005 g  cm3. Refractive indices were measured with an Anton Paar (Abbemat 500) refractometer with an accuracy of ±0.00002.

3.1. Experimental tie-line and reliability results

2.2. Procedure

The experimental ternary LLE tie-line results for the {water (1) + 1-propanol (2) + b-citronellol (3)} and {water (1) + acetone (2) + b-citronellol (3)} systems at T = (283.15, 298.15, and 313.15) K whose composition are expressed in mole fraction x are reported in tables 2 and 3. The reliability of the experimental tie-line values at each temperature was evaluated by using the Hand [16] and Bachman [17] linear correlation equations, respectively, as follows

ln

 II  I x2 x2 ¼ k1 ln þ b1 x3 x1

xII3 ¼ k2

Ternary (liquid + liquid) equilibria for the (water + 1-propanol + b-citronellol) and (water + acetone + b-citronellol) systems were determined using a tie-line method at the temperatures (283.15, 298.15, and 313.15) K. The experimental temperature was regulated by a high-precision thermostatic bath (type BL5FB, Beijing Bilon Lab equipment Ltd.), accurate to ±0.02 K. The LLE experimental values were determined using equilibrium glass cells with a volume of about 150 cm3. Ternary mixtures of known overall composition within the heterogeneous region were prepared by mass. The mixtures with a volume of approximately 80 cm3 loaded in the equilibrium glass cells were stirred vigorously by using a magnetic stirrer for 5 h, and settled for 5 h [13] at constant temperature enough to reach full phase separation. The headspace of the cell was filled with dry nitrogen gas to eliminate contamination by moisture. After phase separation, samples were divided into two liquid phases including the water rich phase (aqueous phase) in the bottom, and citronellol rich phase (organic phase) in the top. The two liquid phases were clear and transparent at equilibrium, with a

ð1Þ

 II  x3 þ b2 xI1

ð2Þ

where the superscripts I and II denote the aqueous phase and organic phase, respectively; k1, k2 and b1, b2 are slopes and intercepts of the Hand and Bachman equations; table 4 contains these parameters together with the regression coefficients R2. The straight lines plotted by the Hand equation for the system (water + 1-propanol + b-citronellol), and by the Bachman equation for the system (water + acetone + b-citronellol), are shown in figure 1. Good agreement was observed between the experimental and correlated values by the Bachman equation, and the experimental results basically agree well with the hand equation. Figure 2 shows the experimental tie-line values for the system (water + 1-propanol + b-citronellol) as a function of temperatures. 3.2. Activity-coefficient models To represent the experimental ternary LLE values, we used two activity-coefficient models with binary and ternary parameters; the extended UNIQUAC proposed by Nagata [18] and the modified

TABLE 1 Density d, refractive indices nD, and mass fraction purity at T = 293.15 K and P = 0.1 MPa.a Component

(±)-b-citronellol 1-propanol Acetone Water a b

CAS

106-22-9 71-23-8 67-64-1 7732-18-5

d/(g  cm3)

nD

Mass fraction purity

Exp.

Lit.

Exp.

Lit.

GC analysis

0.85537 0.80385 0.79021 0.99815

0.859 b [14] 0.80361 [15] 0.78998 [15] 0.99821 [15]

1.45683 1.38461 1.35811 1.33299

1.4576 b [14] 1.38556 [15] 1.35868 [15] 1.33299 [15]

P0.980 P0.995 P0.995

Standard uncertainties u are u(d) = 0.00005 g  cm3, u(nD) = 0.00002, u(T) = 0.03 K, and u(P) = 5 kPa. T = 291.15 K.

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H. Li et al. / J. Chem. Thermodynamics 86 (2015) 20–26

TABLE 2 Experimental (liquid + liquid) equilibrium mole fraction x (tie-lines) for the system {water (1) + 1-propanol (2) + b-citronellol (3)} at temperature T = (283.15, 298.15 and 313.15) K and pressure P = 0.1 MPa.a Aqueous phase (I) xI1

a b

0.9998 0.9907 0.9834 0.9724 0.9614 0.9545 0.9338 0.9327 0.8879

b

0.9999 0.9924 0.9855 0.9777 0.9670 0.9599 0.9450 0.9416 0.8827

b

0.9999 0.9934 0.9865 0.9787 0.9722 0.9638 0.9566 0.9433 0.8777

b

TABLE 3 Experimental (liquid + liquid) equilibrium mole fraction x (tie-lines) for the system {water (1) + acetone (2) + b-citronellol (3)} at temperature T = (283.15, 298.15 and 313.15) K and pressure P = 0.1 MPa.a

Organic phase (II)

xI2

xI3

xII1

0.0089 0.0162 0.0272 0.0379 0.0448 0.0654 0.0663 0.1093

T = 283.15 K 0.0002 b 0.1970 0.0004 0.2268 0.0004 0.2336 0.0004 0.2601 0.0007 0.2808 0.0007 0.3124 0.0008 0.4579 0.0010 0.3969 0.0028 0.6932

0.0073 0.0142 0.0220 0.0327 0.0397 0.0545 0.0575 0.1135

T = 298.15 K 0.0001 b 0.2180 0.0003 0.2525 0.0003 0.2572 0.0003 0.2743 0.0003 0.3095 0.0004 0.3441 0.0005 0.4400 0.0009 0.4901 0.0038 0.7232

0.0063 0.0132 0.0208 0.0274 0.0356 0.0428 0.0559 0.1174

T = 313.15 K 0.0001 b 0.2333 0.0003 0.2699 0.0003 0.2745 0.0005 0.2884 0.0004 0.3347 0.0006 0.3702 0.0006 0.4436 0.0008 0.5201 0.0049 0.7544

Aqueous phase (I)

xII2

xII3 b

0.0782 0.1406 0.2239 0.2985 0.3519 0.4122 0.4117 0.2785

0.8030 0.6950 0.6258 0.5160 0.4207 0.3357 0.1299 0.1914 0.0283 0.7820 0.6632 0.5758 0.4858 0.3703 0.3006 0.1583 0.1181 0.0257

b

0.7667 0.6463 0.5627 0.4688 0.3401 0.2791 0.1639 0.1042 0.0201

b

b

b

0.0843 0.1670 0.2399 0.3202 0.3553 0.4017 0.3918 0.2511 b

0.0838 0.1628 0.2428 0.3252 0.3507 0.3925 0.3757 0.2255

xI1

a b

0.9998 0.9702 0.9500 0.9122 0.8780 0.8417 0.8058 0.7822

b

0.9999 0.9859 0.9682 0.9448 0.9267 0.8715 0.8541 0.8260 0.7688

b

0.9999 0.9889 0.9665 0.9488 0.9286 0.8858 0.8249 0.7718

b

Organic phase (II) xII1 I

xI2

xI3

0.0296 0.0492 0.0869 0.1207 0.1556 0.1908 0.2107

T = 283.15 K 0.0002 b 0.1970 0.0002 0.2353 0.0008 0.2659 0.0009 0.2770 0.0013 0.3247 0.0027 0.3387 0.0034 0.3950 0.0071 0.4764

0.0137 0.0314 0.0545 0.0725 0.1277 0.1443 0.1706 0.2225

T = 298.15 K 0.0001 b 0.2180 0.0004 0.2353 0.0004 0.2409 0.0007 0.2678 0.0008 0.2998 0.0008 0.3386 0.0016 0.3751 0.0034 0.4429 0.0087 0.5200

0.0109 0.0333 0.0510 0.0708 0.1133 0.1708 0.2162

T = 313.15 K 0.0001 b 0.2333 0.0002 0.2611 0.0002 0.2628 0.0002 0.2949 0.0006 0.3441 0.0009 0.3952 0.0043 0.4730 0.0120 0.5664

xII2

xII3 0.8030 0.6688 0.5560 0.4708 0.3794 0.2916 0.1900 0.1171

b

0.0959 0.1781 0.2522 0.2959 0.3697 0.4150 0.4065

0.7820 0.7088 0.6313 0.5193 0.4295 0.3300 0.2307 0.1525 0.0922

b

0.0559 0.1278 0.2129 0.2707 0.3314 0.3942 0.4046 0.3878

0.7667 0.6749 0.5959 0.4635 0.3611 0.2481 0.1402 0.0749

b

0.0640 0.1413 0.2416 0.2948 0.3567 0.3868 0.3587

b

b

b

Standard uncertainties u are u(T) = 0.02 K and u(x) = 0.0005, and u(P) = 5 kPa. Mutual solubility for (water + b-citronellol) [13].

Standard uncertainties u are u(T) = 0.02 K and u(x) = 0.0005, and u(P) = 5 kPa. Mutual solubility for (water + b-citronellol) [13]. TABLE 4 Bachman and Hand equations parameters for the ternary LLE systems.

UNIQUAC proposed by Tamura et al. [19]. The excess molar Gibbs energy of the extended UNIQUAC and modified models can be expressed by the sum of the two contributions: the combinatorial term accounts for molecular interactions due to molecular different size and shape, and the residual term for the two-body interaction between unlike binary components and the additional multibody interactions among unlike components. The segment fraction /i, and surface fraction hi of component i are expressed as

xi r i /i ¼ X ; xj r j

xi q hi ¼ X i ; xj qj

j

j

T

Hand

K

k1

283.15 298.15 313.15

1.6842 1.5465 1.5251

283.15 298.15 313.15

1.3303 1.2868 1.2231

Bachman b1

2

R

k2

b2

(Water + 1-propanol + b-citronellol) 5.4163 0.9628 0.9958 0.0098 5.3150 0.9831 0.9971 0.0077 5.4469 0.9858 0.9970 0.0064 (Water + acetone + b-citronellol) 2.6740 0.9647 1.0294 2.8391 0.9826 1.0298 2.9499 0.9866 1.0241

0.0526 0.0428 0.0330

R2 0.9995 0.9998 0.9999 0.9967 0.9982 0.9993

ð3Þ

where ri is the molecular-geometric volume parameter of pure component, qi is the molecular-geometric surface parameter of pure component that can be estimated from the Bondi method [20]. In the two models, the interaction correction factor of pure component q0i was used to improve the phase equilibrium representation. The pure-component molecular parameters, r and q for b-citronellol are calculated according to the Bondi method; and the others are directly taken from Sørensen and Arlt [21]. Pure-component molecular parameters, r and q along with correlation factor q0 fixed in the model are listed in table 5. The modified UNIQUAC model couples with the combinatorial correction term of Gmehling et al. [22], and the residual term of the extended UNIQUAC mode involving a universal value of the third parameter C as derived by Maurer and Prausnitz [23]. In the modified UNIQUAC model, the corrected segment fraction /0i is given by

3=4

xi r /0i ¼ P i 3=4 ; j xj r j

ð4Þ

The adjustable binary parameters sij is defined by the binary energy parameters aij



sij ¼ exp 

aij  ; CT

ð5Þ

where aij can be obtained from binary experimental phase equilibrium data, and C was set to 1 for the extended UNIQUAC and 0.65 for the modified UNIQUAC. The detailed expressions of activity coefficient of the two models can be reviewed from the literature. 3.3. Calculations Values of the the mutual solubility for (water + b-citronellol) at different temperature are listed in tables 2 and 3. A set of the binary energy parameters for the immiscible mixture was obtained

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H. Li et al. / J. Chem. Thermodynamics 86 (2015) 20–26

FIGURE 1. Reliability tests of the experimental tie-line results: (a) Hand plots of the system for (water + 1-propanol + b-citronellol), and (b) Bachman plots of the system for (water + acetone + b-citronellol) at different temperatures: s, 283.15 K; 4, 298.15 K; and h, 313.15 K.

from the mutual solubility by solving equations (5) and (6) with a Newton–Raphson iterative method

ðci xi ÞI ¼ ðci xi ÞII ;

ð6Þ

X X xIi ¼ xIIi ¼ 1;

ð7Þ

i

i

where I and II represent equilibrium phases. Phase equilibrium results for the binary mixtures making up the ternary mixtures are available in the literature as follows, isothermal (vapour + liquid) equilibria for (1-propanol + water) at T = 313.15 K and (acetone + water) at T = 298.15 K [24]. The binary energy parameters aij for the miscible mixtures were obtained from (vapour + liquid) equilibrium data reduction using the following thermodynamic equations

Pyi Ui ¼ xi ci Psi Usi expfV Li ðP  Psi Þ=RTg;

FIGURE 2. (Liquid + liquid) equilibria for the ternary (water + 1-propanol + bcitronellol) system at T = (283.15, 298.15 and 313.15) K: (a) 283.15 K; (b) 298.15 K; and (c) 313.15 K. Experimental tie-line (d--d); correlation A (- - - -), by extended UNIQUAC with binary parameters from tables 6 and 7; correlation B ( ), by extended UNIQUAC with binary and ternary parameters from tables 6 and 7.

TABLE 5 Structural parameters for pure components.

ð8Þ

!

ln Ui ¼

2

X XX yj Bij  yi yj Bij P=RT; j

i

ð9Þ

j

where P, x, y, and c are the total pressure, the liquid-phase mole fraction, the vapour-phase mole fraction, and the activity coefficient. The pure component vapour pressure Ps was calculated by using the Antoine equation with coefficients taken from the literature [24]. The liquid molar volume VL was obtained by a modified Racket equation [25]. The fugacity coefficient, Ui, was

a b c

Component

R

q

q0 a

q0 b

Water 1-Propanol Acetone b-Citronelool

0.920 2.780 2.570 7.266

1.400 2.510 2.340 6.192

0.960 0.890 q0.2 q0.2

1.283 1.318 q0.75 q0.75

c

c

Extended UNIQUAC. Modified UNIQUAC. Calculated from Bondi’s method.

calculated from equation (8) using the pure and cross second virial coefficients Bij estimated by the method of Hayden and O’Connell [26]. An optimum set of the binary energy parameter aij was

rP

i

rT

rx

This work

This work

2 3 2  2  cal 2  cal  cal exp exp exp 2 T cal X6 Pi  Pi i  Ti xi  xexp y  y 7 i i F¼ þ þ þ i 4 5; 2 2 2 2

This work

Reference

obtained using a maximum-likely-hood principle [27] by the following objective function

[24]

H. Li et al. / J. Chem. Thermodynamics 86 (2015) 20–26

[24]

24

ry

ð11Þ

26.4 26.4 10.1 10.4 3.4 3.4 2.4 2.2

313.15 (Water + b-citronelool)

MS

298.15 (Water + b-citronelool)

MS

283.15 (Water + b-citronelool)

MS

298.15 (Water + acetone)

9

313.15 (Water + 1-propanol)

N, number of experimental data points; MS, mutual solubility; r, deviation; I, Extended UNIQUAC; and II, Modified UNIQUAC. a

192.38 201.86 570.78 749.44 604.38 532.35 588.47 448.72 590.69 435.76 256.99 123.51 90.76 137.91 607.88 112.55 795.25 224.67 843.46 245.70 I II I II I II I II I II

a12/K Model Na

TABLE 6 Calculated results for the binary phase equilibrium data reduction.

The ternary systems measured exhibit a type 1 (liquid + liquid) phase diagram according to the classification of Sørensen and Arlt. The ternary LLEs of the (water + 1-propanol or acetone + b-citronellol) systems consist of four miscible systems (water + 1-propanol or acetone), (1-propanol or acetone + b-citronellol), and one immiscible system (water + b-citronellol). To correlate the experimental LLE data using the extended and modified UNIQUAC models, we used the methods of correlation A and B. In correlation A, the binary parameters of the extended and modified UNIQUAC models were determined from the binary phase equilibrium data. However, the binary (vapour + liquid) equilibria for (1-propanol + b-citronellol) and (acetone + b-citronellol) have not been reported in the literatures. In the present work, a set of the binary parameters for miscible pair (1-propanol or acetone + b-citronellol) can be determined from the experimental ternary LLEs of the (water + 1-propanol or acetone + b-citronellol) systems by minimizing the objective function of equation (10) using the binary parameters of (water + 1-propanol or acetone) and (water + b-citronellol) systems given in table 6. Table 7 lists the RMSDs between the experimental and calculated results by the method of the correlation A and the binary parameters (a23, a32) of the binary (1-propanol or acetone + b-citronellol) systems obtained fitting the models to the experimental ternary LLEs. The RMSDs obtained for the all ternary systems measured at T = (283.15, 298.15, and 313.15) K were (1.12 and 1.67)% by the extended and modified UNIQUAC models. The extended UNIQUAC model can reproduce accurately the experimental results in comparison with the modified UNIQUAC model. In a further accurate representation of the ternary LLEs as referred by the correction B, the ternary parameters sijk were used. As the binary parameters of the (water + b-citronellol) and (water + 1-propanol or acetone) system given in table 6 and those of (1-propanol or acetone + b-citronellol) systems given in table 7

a21/K

3.4. Results and discussion

9

r(P)/kPa

where n denotes tie-lines k = 1 to n, phases j = 1 and 2, components i = 1, 2, and 3. The deviation between experimental and calculated values was expressed by the root mean square deviation RMSD (%), which can be defined by equation (10). In the both extended and modified UNIQUAC models, a ternary parameter taken into account three body interactions sijk was used for the further correlation of ternary (liquid + liquid) equilibria.

0.84 0.84 0.15 0.30

j

T/K

i

System (1 + 2)

k

r(T)/K

( , )0:5 n X 3 X 2  2  2 X exp cal cal xexp  x x  x ; 6n ijk ijk ijk ijk

RMSD ¼ 100

103 r(x)

where the superscripts cal and exp represent the calculated values and experimental values, respectively; standard deviations in the measured quantities were set as r(P) = 133.3 Pa for pressure; r(T) = 0.05 K for temperature; r(x) = 0.001 for liquid mole fraction; r(y) = 0.003 for vapour mole fraction. The binary parameters for experimental binary data obtained by the extended and modified UNIQUAC models are listed in table 6. In the computation of the ternary LLE mixtures, the following objective function was used to minimize using the simplex method [28]

0.1 0.1 0 0

103 r(y)

ð10Þ

25

H. Li et al. / J. Chem. Thermodynamics 86 (2015) 20–26 TABLE 7 Calculated results for ternary (liquid + liquid) equilibria at temperature T = (283.15, 298.15 and 313.15) K. Systems (1 + 2 + 3)

T/K

N

Model

Correlation A RMSD (%)

(Water + 1-propanl + citronellol)

(Water + acetone + citronellol)

Mean dev.

283.15

8

298.15

8

313.15

8

283.15

9

298.15

9

313.15

9

Ia II I II I II I II I II I II I II

1.53 1.68 1.92 2.70 1.21 2.18 0.85 0.83 0.62 1.17 0.59 1.44 1.12 1.67

Correlation B Estimated parameters a23/K

a32/K

50.44 1747.30 247.00 117.52 481.62 153.85 67.27 109.46 120.62 147.20 213.85 208.01

501.19 261.02 546.85 1157.40 489.95 1379.00 369.74 482.91 349.55 571.42 371.83 711.70

RMSD (%)

Ternary parameters

s231

s132

s123

0.84 0.61 1.29 1.02 1.19 1.06 0.67 0.80 0.60 0.71 0.57 0.78 0.86 0.83

0.0650 0.0268 0.8031 0.0045 0.0010 0.0005 0.3116 0.0027 0.1176 0.0406 0.0634 0.0179

0.0021 3.2579 1.2188 0.7050 0.0010 1.0345 1.5242 0.1752 0.4098 0.8652 0.1101 0.9843

0.3296 0.5516 0.0002 2.2446 0.1098 1.0242 1.4075 0.2401 0.3170 1.1385 0.0219 1.5093

aij, estimated binary parameter; rms, root mean square deviation (by equation (10)).

sijk, ternary parameter; Correlation A with binary parameters; and Correlation B with binary and ternary parameters. a

I, Extended UNIQUAC; II, Modified UNIQUAC; N, number of experimental data.

were determined, the ternary parameters in the models can be obtained fitting the models to the experimental ternary LLEs by minimizing the objective function defined by equation (10). Table 7 shows the RMSDs between experimental and correlated results along with the ternary parameters for the (water + 1-propanol or acetone + b-citronellol) systems. The mean deviations obtained from the six ternary systems were (0.86 and 0.83)% by the extended and modified UNIQUAC models. The correlated results using the ternary parameters obtained by the two models were improved remarkably. Figure 2 displays the calculated results

(correlation A and B) along with experimental LLE tie-line results at the three temperatures for (water + 1-propanol + b-citronellol) system. Figure 2 illustrates the good agreement of the experimental ternary results with those correlated by including the ternary parameters of the ternary LLE systems. On the other hand, the systems have a very low solubility for b-citronellol in the aqueous phase but a higher solubility for water in organic phase at the three temperatures. Figure 3 shows the temperature dependence of the ternary LLE envelope with experimental tie-lines for (water + 1-propanol + bcitronellol) and (water + acetone + b-citronellol) systems at T = (283.15, 298.15, and 313.15) K, where the immiscible regions mildly decrease as temperature increases, could be represented successfully by the two UNIQUAC models as shown in figure 2. Figure 4 illustrates the comparison of immiscible regions for ternary (water + 1-propanol + b-citronellol) and (water + acetone + b-citronellol) LLEs at T = 283.15 K. It is found that the ternary LLE envelope with tie-lines for (water + 1-propanol + bcitronellol) system is similar to those of (water + acetone + b-citronellol) system at the same temperature. It may be explained by the fact that acetone and 1-propanol are C3 organic solvents containing a hydrophilic group in the molecule. To examine the (liquid + liquid) distribution ratios (extractive properties) of 1-propanol or acetone in the (water + b-citronellol)

FIGURE 3. Comparison of experimental ternary (water + 1-propanol + b-citronellol) and (water + acetone + b-citronellol) (liquid + liquid) equilibria at T = (283.15, 298.15 and 313.15) K: s, 283.15 K; 4, 298.15 K; and h, 313.15 K.

FIGURE 4. Comparison of immiscible region for experimental ternary LLEs for (water + 1-propanol + b-citronellol) and (water + acetone + b-citronellol) at T = 283.15 K: s, 1-propanol and 4, acetone.

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H. Li et al. / J. Chem. Thermodynamics 86 (2015) 20–26

acetone + b-citronellol) at T = (283.15, 298.15, and 313.15) K. The systems have a low solubility for b-citronellol in aqueous phase and a high solubility for water in the organic phase at any of the temperatures studied here. It is concluded that the distribution ratios of 1-propanol or acetone for the systems and the miscible regions increase as temperature increases. The (water + 1-propanol + b-citronellol) system has a higher distribution ratio of 1-propanol than those of acetone for the (water + acetone + bcitronellol) system, where the immiscible region of (water + 1-propanol + b-citronellol) system is similar to those of (water + acetone + b-citronellol) system at the same temperatures. The experimental (liquid + liquid) equilibrium values were well correlated with extended UNIQUAC and modified UNIQUAC with binary and ternary parameters. The RMSDs between the experimental results and those calculated by the extended and modified UNIQUAC models were (0.86 and 0.83)% for the all six ternary systems, respectively. Acknowledgements The authors thank the financial support from the National Natural Science Foundation of China (No. 21106021). References

FIGURE 5. Comparison of experimental and calculated distribution ratios of: propanol for (a): (water + 1-propanol + b-citronellol); acetone for (b): (water + acetone + b-citronellol) systems at T = (283.15, 298.15 and 313.15) K: s, 283.15 K; 4, 298.15 K; and h, 313.15 K; correlation B ( ), by extended UNIQUAC with binary and ternary parameters from tables 6 and 7.

mixture, the distribution ratio of 1-propanol or acetone in the ternary LLE mixtures is defined by

D¼

xII2 : xI2

ð12Þ

Figure 5 compares the trend and difference of experimental distribution ratios of 1-propanol and acetone in the ternary (water + 1-propanol or acetone + b-citronellol) at T = (283.15, 298.15, and 313.15) K. It is observed from figure 5 that the distribution ratios of 1-propanol or acetone increase as the system temperature increases. The distribution ratios of 1-propanol for (water + 1-propanol + b-citronellol) system are approximately twice as large compared to those of acetone for (water + acetone + b-citronellol) mixture at the constant temperature and same concentration xII2 . On the other hand, the distribution ratios of 1propanol or acetone at the system temperature decrease as the concentration xII2 in the mixture increases. The results for the distribution ratios by the extended and modified UNIQUAC models are in a fair agreement with the experimental values.

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4. Conclusions (Liquid + liquid) equilibrium tie-line compositions were presented for the ternary mixtures of (water + 1-propanol or

JCT 14-620