- Email: [email protected]
Liquid–liquid equilibria for the binary systems of propylene glycol ether + water measured by the phase volume method
Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67
Contents lists available at SciVerse ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Liquid–liquid equilibria for the binary systems of propylene glycol ether + water measured by the phase volume method Shih-Yao Lin, Cheng-Hao Su, Li-Jen Chen * Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 19 January 2013 Received in revised form 15 April 2013 Accepted 19 April 2013 Available online 29 May 2013
Liquid–liquid phase equilibrium for two binary systems: 1-propoxy-2-propanol + water and 1-(1methyl-2-propoxyethoxy)2-propanol + water ranging from their lower critical solution temperatures to 328.15 K under atmospheric pressure were performed by using the phase volume method. The experimental data were further correlated with the UNIQUAC model by fitting the UNIQUAC interaction parameters as a function of temperature. The critical mass fraction and the lower critical solution temperature were determined by fitting the experimental data to the critical scaling law. ß 2013 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Liquid–liquid equilibrium Glycol ethers Phase volume method Lower critical solution temperature UNIQUAC model
1. Introduction Glycol ethers are commonly used as solvents and coupling agents in paints, perfume, varnishes, dyes, and in the production of inks, resins, coatings, liquid soaps, cosmetics, and cleaners. Propylene (or ethylene) glycol ethers are formed from the acidor base-catalyzed reaction of propylene (or ethylene) oxide with aliphatic alcohols. Subsequent reaction with additional propylene (or ethylene) oxide leads to the corresponding di- and tripropylene (or ethylene) glycol ethers. Glycol ethers have attracted a great attention as substitutes of certain conventional solvents due to their low toxicity and biodegradability [1–3]. Thermodynamic properties, such as phase equilibrium and viscosity, are essential in many unit operations of the chemical industry, such as extraction and distillation [4–10]. The experimental data of the liquid–liquid equilibrium are necessary for design of these unit operations for separations. Although the homologous series of propylene glycol ether CH3(CH2)i1(OCH(CH3)CH2)jOH, abbreviated by CiPj hereafter, is extensively used in industrial applications, there is very limited information of its phase behavior in the literature. Recently, the liquid–liquid equilibrium measurements of ternary water + alkane + propylene glycol ether systems have been performed in our laboratory [11–15]. On the other hand, the liquid–liquid equilibrium measurements of binary water + C3P1 and water + C3P2
* Corresponding author. Tel.: +886 233663049. E-mail address: [email protected] (L.-J. Chen).
systems have also been reported in the literature [16,17]. However, there exists some inconsistency between these literature data [16,17]. The purpose of this work is to resolve this discrepancy and to determine the lower critical solution temperatures of binary water + C3P1 and water + C3P2 systems. In this study, the liquid–liquid equilibrium measurements of binary water + C3P1 and water + C3P2 systems ranging from their lower critical temperature to 328.15 K under atmospheric pressure were performed by using the phase volume method [18–20]. Note that the phase volume method is a noninvasive, nondestructive, and powerful method for low-pressure phase studies [19,20]. The UNIQUAC model was used to correlate the experimental data. The experimental results could be well described by the UNIQUAC model except the data near the lower critical solution point. Critical scaling law was applied to these experimental data to determine the lower critical solution temperature and critical mass fraction of these binary water + C3P1 and water + C3P2 systems. The critical scaling equations delineate accurate values of the critical composition and critical temperature, which are usually predicted incorrectly by the classical UNIQUAC model. 2. Experimental 2.1. Materials 1-Propoxy-2-propanol (also known as propylene glycol npropyl ether) and 1-(1-methyl-2-propoxyethoxy)2-propanol (also known as dipropylene glycol n-propyl ether), were purchased from Dow Chemical Co. Both C3P1 and C3P2 were fractionally distilled
1876-1070/$ – see front matter ß 2013 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jtice.2013.04.012
S.-Y. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67
64
Table 1 Comparison of the experimental results and literature data [21,22] of densities, r, and refractive index, nD, of the pure compounds at T = 293.15 and 298.15 K.a
r (g/cm3)
Compound
Water content (ppm)
T (K)
Exp.
Lit.
Exp.
Lit.
C3P1
250.1
293.15
0.88588
0.8886 [21] 0.885 [22]
1.4118
1.413 [21] 1.4110 [22]
298.15
0.88111
b
1.4100
b
0.92007 0.91565
b
1.4225 1.4214
b
C3P2 a b
300.4
293.15 298.15
nD
b
b
3
Standard uncertainties u are u(T) = 0.01 K, u(r) = 0.00005 g/cm and u(nD) = 0.0002. No literature data available.
under reduced pressure. The mass fractions of purified C3P1 and C3P2 determined by gas chromatography (GC-8A, Shimadzu Co., Japan) were higher than 99.5%. The density (DMA 4500M, AntonPaar) and refractive index (NAR-3T, Atago) of purified C3P1 and C3P2, compared with literature [21,22] values are given in Table 1. In addition, the water contents of purified C3P1 and C3P2 were determined by Karl Fischer titrator (MKC-501, Kyoto Electronics Co.) and also reported in Table 1. Water was purified by doubledistillation and then followed by a PURELAB Maxima Series (ELGA Labwater) purification system to confirm that the resistivity is always larger than 18.2 MV cm. The precision of measuring mass of sample (Newclassic MS, Mettler Toledo) is 0.0001 g.
equilibration, the volumes of the upper and lower phases were recorded by reading the graduation on the tubes and denoted by Vu and Vl, respectively. The total volume of each sample is denoted by V (=Vu + Vl). The volume fraction of the upper phase f was then calculated. That is, f = Vu/V. Phase volume method [18–20] is simply based on the mass balance for each component. According to the lever rule, the volume fraction of the upper phase is directly proportional to the mass fraction of C3Pj for binary C3Pj + water systems. The total mass balance for this two-liquid-phase-coexisting system can be described by
2.2. Phase volume method
where du and dl stand for the densities of upper and lower phases, respectively. On the other hand, the mass balance of C3Pj for this two-liquidphase-coexisting system is
More than 20 binary C3Pj + water mixtures with different compositions were prepared gravimetrically in graduated tubes. All the graduated tubes were checked and recalibrated by weighing different volumes of water and the precision was 0.05 ml. The total mass m and total mass fraction of C3Pj w were used to specify each sample. All samples were placed in a homemade computercontrolled water thermostat, whose temperature stability was better than 0.01 K. The system temperature was measured by a quartz thermometer (2804A, Quartz Thermometer, Hewlett-Packard) with a precision of 0.01 K. During the equilibration process, the samples were shaken vigorously at least 3 times to ensure thorough mixing, and then left in the computer-controlled water thermostat at least 1 day for equilibration. After the equilibrium was reached, all liquid phases were transparent and interfaces were sharp and mirror-like. The system would separate into two-liquid-phase coexisting within certain composition window. The upper and lower phases were, respectively, C3Pj-rich and aqueous phases. Following the
m ¼ V fdu þ Vð1 fÞdl
mw ¼ V fdu wu þ Vð1 fÞdl wl
(1)
(2)
where symbols wu and wl stand for the mass fractions of C3Pj in the upper and lower phases, respectively. Substituting Eq. (1) into Eq. (2) yields w wl m f¼ : (3) wu wl Vdu Eq. (3) implies that the phase volume fraction f is a function of total mass fraction of C3Pj w, that is, f = f(w). The extrapolation of f = 0 (i.e., w = wl) and f = 1 (i.e., w = wu and Vdu = m) can be applied to determine the equilibrium compositions of the conjugated phases, as demonstrated in Fig. 1. The experiment was performed at different temperatures to search for the lower critical solution temperature and then the phase diagram could be depicted. 3. Results and discussion
Fig. 1. Illustration of an example (water + C3P2 system at 325.15 K) of variation of the volume fraction as a function of the mass fraction of CiPj. The mass fractions of conjugated phases could be determined by linear relationship between volume fraction (f) and mass fraction of C3P2 (w).
The experimental equilibrium concentrations for binary C3P1 + water and C3P2 + water systems at different temperatures are given in Tables 2 and 3, respectively. The experimental temperature window for the C3P1 + water system was ranging from 304.85 K to 328.15 K and from 286.90 K to 328.09 K for the C3P2 + water system. All the mass fractions of lower and upper phases, wl and wu , at different temperatures were calculated by the linear relationship of volume fraction of upper phase (f) and total mass fraction of C3Pj (w) with the correlation coefficient always better than 0.9995. The phase diagrams of liquid–liquid equilibrium for binary C3P1 + water and C3P2 + water systems reported by Christensen et al. [16] and by Davison et al. [17] are compared with our experimental results, as shown in Figs. 2 and 3. For the C3P1 + water system, our experimental results of mass fractions of the C3P1-rich phase are consistent with the literature data [16,17], but not the case of the aqueous phase. While for the
S.-Y. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67
65
Table 2 Experimental and calculated mass fraction of C3P1 of equilibrium liquid phases for the binary C3P1 + water system at various temperatures. T (K)
304.85 305.16 305.66 306.13 307.14 308.27 309.29 310.31 311.29 312.32 313.35 314.38 315.22 316.24 318.11 320.11 322.14 324.14 326.15 328.15 Average absolute
Experimental results
Calculated results
wl
wu
wl
wu
0.3502 0.3205 0.2925 0.2743 0.2531 0.2324 0.2229 0.2144 0.2066 0.1959 0.1882 0.1830 0.1764 0.1698 0.1663 0.1597 0.1526 0.1483 0.1409 0.1374 deviation
0.4827 0.5166 0.5477 0.5712 0.5967 0.6174 0.6314 0.6437 0.6516 0.6582 0.6659 0.6740 0.6826 0.6858 0.6953 0.7030 0.7112 0.7176 0.7248 0.7307
0.3105 0.2995 0.2875 0.2744 0.2519 0.2327 0.2196 0.2079 0.2001 0.1923 0.1856 0.1798 0.1756 0.1709 0.1636 0.1570 0.1510 0.1458 0.1407 0.1359 0.0105
0.5052 0.5268 0.5554 0.5711 0.5972 0.6187 0.6344 0.6455 0.6572 0.6662 0.6739 0.6805 0.6852 0.6903 0.6982 0.7056 0.7124 0.7193 0.7267 0.7349 0.0069
Fig. 2. The phase diagram for binary C3P1 + water system: experimental results of this work (*), results from gas chromatography ( ), Christensen et al. [16] ( ), Davison et al. [17] ( ), the critical point determined from the critical scaling law () and calculated results by the UNIQUAC model (solid line).
Table 3 Experimental and calculated mass fraction of C3P2 of equilibrium liquid phases for the binary C3P2 + water system at various temperatures. T (K)
286.90 287.19 287.41 287.72 288.01 288.19 289.11 290.36 291.20 292.22 293.16 297.15 301.11 305.25 309.10 313.14 317.10 321.13 325.15 328.09 Average absolute
Experimental results
Calculated results
wl
wu
wl
wu
0.3809 0.3530 0.3372 0.3234 0.3127 0.3074 0.2787 0.2556 0.2426 0.2287 0.2208 0.1834 0.1600 0.1366 0.1167 0.1056 0.0940 0.0830 0.0731 0.0686 deviation
0.5846 0.6084 0.6250 0.6413 0.6530 0.6600 0.6966 0.7147 0.7269 0.7405 0.7491 0.7875 0.7973 0.8123 0.8277 0.8296 0.8361 0.8393 0.8425 0.8458
0.3486 0.3369 0.3295 0.3194 0.3108 0.3059 0.2837 0.2597 0.2448 0.2324 0.2212 0.1846 0.1585 0.1366 0.1193 0.1038 0.0911 0.0807 0.0730 0.0691 0.0086
0.6141 0.6275 0.6365 0.6484 0.6586 0.6643 0.6901 0.7166 0.7264 0.7439 0.7541 0.7822 0.7990 0.8125 0.8232 0.8327 0.8400 0.8448 0.8461 0.8444 0.0091
C3P2 + water system, our experimental results are fairly consistent with the literature data [16,17], except the C3P2-rich phase at temperature higher than 310 K. The origin of this discrepancy is unknown. To further verify the composition determined by the phase volume method, the mass fractions in these systems were double-checked by gas chromatography (GC-8A, Shimadzu Co.,
Fig. 3. Coexistence curve for binary C3P2 + water system: experimental results of this work (*), results from gas chromatography ( ), Christensen et al. [16] ( ), Davison et al. [17] ( ), the critical point determined from the critical scaling law () and calculated results by the UNIQUAC model (solid line).
Japan). The experimental details of the gas chromatography method to determine the mass fractions of the conjugated phase followed closely our previous works [11–15]. The results of gas chromatography are given in Table 4. The mass fractions determined by gas chromatography have an excellent agreement with the results by the phase volume method, as demonstrated in Figs. 2 and 3. It should be noted that the classical predictive models are not able to precisely describe the liquid–liquid equilibrium phase behavior of mixtures containing compound with both hydrophobic and hydrophilic functionality [23]. Thus, the UNIQUAC model was used to correlate experimental data. The volume parameter, r, and surface area parameter, q, of each compound were directly adopted from the commercial simulator Aspen Plus and listed in Table 5. The binary interaction parameter aij is defined by ai j ¼
ui j u ji R
(4)
where uij and uji are the UNIQUAC energy interaction parameters between components i and j, and R is the gas constant. These
Table 4 Experimental mass fractions determined by gas chromatography. System
T (K)
wl
wu
C3P1 + water
308.15 318.15
0.2357 0.1655
0.6139 0.6993
C3P2 + water
288.15 298.15 308.15
0.2992 0.1719 0.1216
0.6560 0.7947 0.8257
Table 5 The volume parameter r and surface area parameter q of the UNIQUAC model adopted from the commercial simulator Aspen Plus. Parameter
Water
C3P1
C3P1
r q
0.92 1.40
5.043 4.368
7.312 6.224
66
S.-Y. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67
Table 6 Estimated UNIQUAC parameters for binary system C3P1 (1) + water (2) and C3P2 (1) + water (2) (a12 = b0 + b1/T + b2 ln T + b3T and a21 = c0 + c1/T + c2 ln T + c3T). Parameter
C3P1 + water
C3P2 + water
b0 b1 b2 b3 c0 c1 c2 c3
1.112 107 3.069 108 1.930 106 3.035 103 7.621 106 2.094 108 1.324 106 2.090 103
4.114 106 1.129 108 7.152 105 1.137 103 3.254 105 8.533 106 5.729 104 9.902 101
Table 7 The critical mass fraction of C3Pj and the lower critical solution temperature of binary C3P1 (1) + water (2) and C3P2 (1) + water (2) systems. System
wc
C3P1 + water C3P2 + water
0.4212 0.4864
Tc (K) Exp.
Lit. [16]
304.61 286.59
305.15 283.15
effective binary interaction parameters a12 and a21 for each temperature were solved exactly and then were further correlated with temperature by the following equations: a12 ¼ b0 þ
b1 þ b2 ln T þ b3 T T
(5)
a21 ¼ c0 þ
c1 þ c2 ln T þ c3 T T
(6)
The results of the correlated parameters are given in Table 6. The phase boundary concentrations calculated from UNIQUAC model with estimated effective binary interaction parameters given by Eqs. (5) and (6) are also shown as black solid curves in Figs. 2 and 3. The calculated curves of these two systems describe the experimental data well except the regions very close to the lower critical solution point, as reported in Tables 2 and 3, on account of the classical limit of UNIQUAC model. The critical scaling law, instead of the classical UNIQUAC model, was applied to determine the critical point. When the system is close to its critical temperature, Tc, according to the renormalization group theory, the phase boundaries wu and wl should obey the scaling law as [24] wu ¼ wc þ Beb þ C ebþD þ De1a
(7)
wl ¼ wc Beb C ebþD þ De1a
(8)
where wc is the critical mass fraction, the coefficients B, C, and D are system-dependent parameters, e is the reduced temperature defined as e ðT T c Þ=T c , and b, D, and a are universal criticalscaling exponents with the value of 0.324 [24–28], 0.5 [24–26], and 0.11 [26–28], respectively. Subtracting Eq. (8) from Eq. (7) yields wu wl ¼ 2Beb þ 2C ebþD When the system temperature temperature, the second term on can be neglected because of (b + D = 0.824 versus b = 0.324). Eq. (9) can be recasted as ðwu wl Þ1=b ¼ B0 ðT T c Þ
(9) is very close to its critical the right-hand side of Eq. (9) the larger exponent value Neglecting the second term,
(10)
On the other hand, adding Eqs. (7) and (8) yields wu þ wl ¼ wc þ De1a 2
(11)
The critical mass fraction wc and the lower critical solution temperature Tc could be determined by fitting our experimental results of the phase boundaries to the critical scaling law, Eqs. (10) and (11) [29]. The estimated critical points for the C3P1 + water and C3P2 + water systems are given in Table 7 and shown as symbol cross in Figs. 2 and 3. Note that the estimated critical point is slightly above, as expected, that of the UNIQUAC model, as shown in Figs. 2 and 3. In addition, the lower critical solution temperatures of Christensen et al. [16] are also listed in Table 7 for comparison. In contrast to the CiEj + water system, the lower critical solution temperature of the C3P1 + water system 304.65 K is higher than that of the C3P2 + water system 286.65 K, which is consistently higher than that of the C3P3 + water system, as pointed out by Christensen et al. [16]. The symbol CiEj is the abbreviation of the ethylene glycol ether CH3(CH2)i1(OCH2CH2)jOH. It is well understood that the lower critical solution temperature of the CiEj + water system is consistently lower than that of the CiEj+1 + water system [29,30]. 4. Conclusions The phase diagrams of liquid–liquid equilibrium for binary C3P1 + water and C3P2 + water systems near their lower critical solution temperatures are determined by the phase volume method. All the results are fitted to the UNIQUAC model and the critical scaling law. The estimated critical temperature for the C3P1 + water is lower than that for C3P2 + water system, thus leading a wider composition range of immiscibility. Acknowledgement This work was supported by the National Science Council of Taiwan. References [1] Gonsior SJ, West RJ. Biodegradation of glycol ethers in soil. Environ Toxicol Chem 1995;14:1273–9. [2] Spencer PJ. New toxicity data for the propylene glycol ethers – a commitment to public health and safety. Toxicol Lett 2005;156:181–8. [3] Staples CA, Boatman RJ, Cano ML. Ethylene glycol ethers: an environmental risk assessment. Chemosphere 1998;36:1585–613. [4] Wu TY, Chen BK, Hao L, Kuo CW, Sun IW. Thermophysical properties of binary mixtures {1-methyl-3-pentylimidazolium tetrafluoroborate + polyethylene glycol methyl ether}. J Taiwan Inst Chem Eng 2012;43:313–21. [5] Chiou DR, Chen LJ. Liquid–liquid equilibria for the ternary system water + diethylene glycol monohexyl ether + 2-methyl-2-butanol. Fluid Phase Equilib 2004;218:229–34. [6] Lin BJ, Chen LJ. Liquid–liquid equilibria for the ternary system water + tetradecane + 2-butyloxyethanol. Fluid Phase Equilib 2004;216:13–20. [7] Lin BJ, Chen LJ. Liquid–liquid equilibria for the ternary system water + dodecane + 2-butyloxyethanol in the temperature range from 25 8C to 65 8C. J Chem Eng Data 2002;47:992–6. [8] Liu YL, Chiou DR, Chen LJ. Liquid–liquid equilibria for the ternary system water + octane + diethylene glycol monobutyl ether. J Chem Eng Data 2002;47:310–2. [9] Hu HS, Chen LJ. Liquid–liquid equilibria for the ternary system water + ntetradecane + 2-(2-n-hexyloxyethoxy)ethanol at 293.15 K and 303.15 K. J Chem Eng Data 2000;45:304–7. [10] Hu HS, Chiu CD, Chen LJ. Liquid–liquid equilibria for the ternary system water + n-dodecane + 2-(2-n-hexyloxyethoxy)ethanol. Fluid Phase Equilib 1999;164:187–94. [11] Su CH, Chen LJ. Liquid–liquid equilibria for the ternary system water plus hexadecane plus propylene glycol n-propyl ether. J Chem Eng Data 2011;56:589–94. [12] Su CH, Chen LJ. Liquid–liquid equilibria for the ternary system water plus tetradecane plus propylene glycol n-propyl ether. J Chem Eng Data 2011;56:2976–9.
S.-Y. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67 [13] Su CH, Chen LJ. Liquid–liquid equilibria for the ternary system water plus dodecane plus 1-(1-methyl-2-propoxyethoxy)-2-propanol. J Chem Eng Data 2012;57:1899–902. [14] Su CH, Lin SY, Chen LJ. (Liquid plus liquid) equilibria for the ternary system (water plus dodecane plus propylene glycol n-propyl ether). J Chem Thermodyn 2012;47:358–61. [15] Su CH, Chen LJ. Liquid–liquid equilibria for the ternary system (water + hexadecane + dipropylene glycol n-propyl ether). Fluid Phase Equilib 2013;346:20–4. [16] Christensen SP, Donate FA, Frank TC, LaTulip RJ, Wilson LC. Mutual solubility and lower critical solution temperature for water plus glycol ether systems. J Chem Eng Data 2005;50:869–77. [17] Davison RR, Smith WH, Hood DW. Mutual solubility of water glycerol and glycol ethers. J Chem Eng Data 1966;11:404. [18] Polyakov VI, Grinberg VY, Tolstoguzov VB. Application of phase-volume-ratio method for determining the phase diagram of water–casein–soybean globulins system. Polym Bull 1980;2:757–60. [19] Kim KY, Lim KH. Fits of scaling and UNIQUAC equations to liquid–liquid equilibrium (LLE) phase compositions of the binary amphiphile 2-butoxyethanol (1) plus water (2) measured by the phase volume method. J Chem Eng Data 2001;46:967–73. [20] Lim KH, Reckley JS, Smith DH. Liquid–liquid phase-equilibrium in binarymixtures of the nonionic amphiphile CH3(CH2)5(OCH2CH2)2OH and water. J Colloid Interface Sci 1993;161:465–70.
67
[21] Lide DR. CRC handbook of chemistry and physics. 89th ed. Boca Raton, FL: CRC Press; 2008. [22] Speight JG. Lange’s handbook of chemistry. 16th ed. New York: McGraw-Hill; 2005. [23] Gerber RP, Soares RP. Assessing the reliability of predictive activity coefficient models for molecules consisting of several functional groups. Braz J Chem Eng 2013;30:1–11. [24] Rowlinson JS, Widom B. Molecular theory of capillarity. Oxford: Clarendon Press; 1982. [25] Baker GA, Nickel BG, Green MS, Meiron DI. Ising-model critical indices in three dimensions from the Callan–Symanzik equation. Phys Rev Lett 1976;36: 1351–4. [26] Baker GA, Nickel BG, Meiron DI. Critical indices from perturbation analysis of Callan–Symanzik equation. Phys Rev B 1978;17:1365–74. [27] Greer SC, Moldover MR. Thermodynamic anomalies at critical points of fluids. Annu Rev Phys Chem 1981;32:233–65. [28] Le Guillou JC, Zinn-Justin J. Critical exponents from field-theory. Phys Rev B 1980;21:3976–98. [29] Lai HH, Chen LJ. Liquid–liquid equilibrium phase diagram and density of three water + nonioinic surfactant CiEj binary system. J Chem Eng Data 1999;44:251–3. [30] Kahlweit M, Busse G, Jen J. Adsorption of amphiphiles at water/air interfaces. J Phys Chem 1991;95:5580–6.
Contents lists available at SciVerse ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Liquid–liquid equilibria for the binary systems of propylene glycol ether + water measured by the phase volume method Shih-Yao Lin, Cheng-Hao Su, Li-Jen Chen * Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
A R T I C L E I N F O
A B S T R A C T
Article history: Received 19 January 2013 Received in revised form 15 April 2013 Accepted 19 April 2013 Available online 29 May 2013
Liquid–liquid phase equilibrium for two binary systems: 1-propoxy-2-propanol + water and 1-(1methyl-2-propoxyethoxy)2-propanol + water ranging from their lower critical solution temperatures to 328.15 K under atmospheric pressure were performed by using the phase volume method. The experimental data were further correlated with the UNIQUAC model by fitting the UNIQUAC interaction parameters as a function of temperature. The critical mass fraction and the lower critical solution temperature were determined by fitting the experimental data to the critical scaling law. ß 2013 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Liquid–liquid equilibrium Glycol ethers Phase volume method Lower critical solution temperature UNIQUAC model
1. Introduction Glycol ethers are commonly used as solvents and coupling agents in paints, perfume, varnishes, dyes, and in the production of inks, resins, coatings, liquid soaps, cosmetics, and cleaners. Propylene (or ethylene) glycol ethers are formed from the acidor base-catalyzed reaction of propylene (or ethylene) oxide with aliphatic alcohols. Subsequent reaction with additional propylene (or ethylene) oxide leads to the corresponding di- and tripropylene (or ethylene) glycol ethers. Glycol ethers have attracted a great attention as substitutes of certain conventional solvents due to their low toxicity and biodegradability [1–3]. Thermodynamic properties, such as phase equilibrium and viscosity, are essential in many unit operations of the chemical industry, such as extraction and distillation [4–10]. The experimental data of the liquid–liquid equilibrium are necessary for design of these unit operations for separations. Although the homologous series of propylene glycol ether CH3(CH2)i1(OCH(CH3)CH2)jOH, abbreviated by CiPj hereafter, is extensively used in industrial applications, there is very limited information of its phase behavior in the literature. Recently, the liquid–liquid equilibrium measurements of ternary water + alkane + propylene glycol ether systems have been performed in our laboratory [11–15]. On the other hand, the liquid–liquid equilibrium measurements of binary water + C3P1 and water + C3P2
* Corresponding author. Tel.: +886 233663049. E-mail address: [email protected] (L.-J. Chen).
systems have also been reported in the literature [16,17]. However, there exists some inconsistency between these literature data [16,17]. The purpose of this work is to resolve this discrepancy and to determine the lower critical solution temperatures of binary water + C3P1 and water + C3P2 systems. In this study, the liquid–liquid equilibrium measurements of binary water + C3P1 and water + C3P2 systems ranging from their lower critical temperature to 328.15 K under atmospheric pressure were performed by using the phase volume method [18–20]. Note that the phase volume method is a noninvasive, nondestructive, and powerful method for low-pressure phase studies [19,20]. The UNIQUAC model was used to correlate the experimental data. The experimental results could be well described by the UNIQUAC model except the data near the lower critical solution point. Critical scaling law was applied to these experimental data to determine the lower critical solution temperature and critical mass fraction of these binary water + C3P1 and water + C3P2 systems. The critical scaling equations delineate accurate values of the critical composition and critical temperature, which are usually predicted incorrectly by the classical UNIQUAC model. 2. Experimental 2.1. Materials 1-Propoxy-2-propanol (also known as propylene glycol npropyl ether) and 1-(1-methyl-2-propoxyethoxy)2-propanol (also known as dipropylene glycol n-propyl ether), were purchased from Dow Chemical Co. Both C3P1 and C3P2 were fractionally distilled
1876-1070/$ – see front matter ß 2013 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jtice.2013.04.012
S.-Y. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67
64
Table 1 Comparison of the experimental results and literature data [21,22] of densities, r, and refractive index, nD, of the pure compounds at T = 293.15 and 298.15 K.a
r (g/cm3)
Compound
Water content (ppm)
T (K)
Exp.
Lit.
Exp.
Lit.
C3P1
250.1
293.15
0.88588
0.8886 [21] 0.885 [22]
1.4118
1.413 [21] 1.4110 [22]
298.15
0.88111
b
1.4100
b
0.92007 0.91565
b
1.4225 1.4214
b
C3P2 a b
300.4
293.15 298.15
nD
b
b
3
Standard uncertainties u are u(T) = 0.01 K, u(r) = 0.00005 g/cm and u(nD) = 0.0002. No literature data available.
under reduced pressure. The mass fractions of purified C3P1 and C3P2 determined by gas chromatography (GC-8A, Shimadzu Co., Japan) were higher than 99.5%. The density (DMA 4500M, AntonPaar) and refractive index (NAR-3T, Atago) of purified C3P1 and C3P2, compared with literature [21,22] values are given in Table 1. In addition, the water contents of purified C3P1 and C3P2 were determined by Karl Fischer titrator (MKC-501, Kyoto Electronics Co.) and also reported in Table 1. Water was purified by doubledistillation and then followed by a PURELAB Maxima Series (ELGA Labwater) purification system to confirm that the resistivity is always larger than 18.2 MV cm. The precision of measuring mass of sample (Newclassic MS, Mettler Toledo) is 0.0001 g.
equilibration, the volumes of the upper and lower phases were recorded by reading the graduation on the tubes and denoted by Vu and Vl, respectively. The total volume of each sample is denoted by V (=Vu + Vl). The volume fraction of the upper phase f was then calculated. That is, f = Vu/V. Phase volume method [18–20] is simply based on the mass balance for each component. According to the lever rule, the volume fraction of the upper phase is directly proportional to the mass fraction of C3Pj for binary C3Pj + water systems. The total mass balance for this two-liquid-phase-coexisting system can be described by
2.2. Phase volume method
where du and dl stand for the densities of upper and lower phases, respectively. On the other hand, the mass balance of C3Pj for this two-liquidphase-coexisting system is
More than 20 binary C3Pj + water mixtures with different compositions were prepared gravimetrically in graduated tubes. All the graduated tubes were checked and recalibrated by weighing different volumes of water and the precision was 0.05 ml. The total mass m and total mass fraction of C3Pj w were used to specify each sample. All samples were placed in a homemade computercontrolled water thermostat, whose temperature stability was better than 0.01 K. The system temperature was measured by a quartz thermometer (2804A, Quartz Thermometer, Hewlett-Packard) with a precision of 0.01 K. During the equilibration process, the samples were shaken vigorously at least 3 times to ensure thorough mixing, and then left in the computer-controlled water thermostat at least 1 day for equilibration. After the equilibrium was reached, all liquid phases were transparent and interfaces were sharp and mirror-like. The system would separate into two-liquid-phase coexisting within certain composition window. The upper and lower phases were, respectively, C3Pj-rich and aqueous phases. Following the
m ¼ V fdu þ Vð1 fÞdl
mw ¼ V fdu wu þ Vð1 fÞdl wl
(1)
(2)
where symbols wu and wl stand for the mass fractions of C3Pj in the upper and lower phases, respectively. Substituting Eq. (1) into Eq. (2) yields w wl m f¼ : (3) wu wl Vdu Eq. (3) implies that the phase volume fraction f is a function of total mass fraction of C3Pj w, that is, f = f(w). The extrapolation of f = 0 (i.e., w = wl) and f = 1 (i.e., w = wu and Vdu = m) can be applied to determine the equilibrium compositions of the conjugated phases, as demonstrated in Fig. 1. The experiment was performed at different temperatures to search for the lower critical solution temperature and then the phase diagram could be depicted. 3. Results and discussion
Fig. 1. Illustration of an example (water + C3P2 system at 325.15 K) of variation of the volume fraction as a function of the mass fraction of CiPj. The mass fractions of conjugated phases could be determined by linear relationship between volume fraction (f) and mass fraction of C3P2 (w).
The experimental equilibrium concentrations for binary C3P1 + water and C3P2 + water systems at different temperatures are given in Tables 2 and 3, respectively. The experimental temperature window for the C3P1 + water system was ranging from 304.85 K to 328.15 K and from 286.90 K to 328.09 K for the C3P2 + water system. All the mass fractions of lower and upper phases, wl and wu , at different temperatures were calculated by the linear relationship of volume fraction of upper phase (f) and total mass fraction of C3Pj (w) with the correlation coefficient always better than 0.9995. The phase diagrams of liquid–liquid equilibrium for binary C3P1 + water and C3P2 + water systems reported by Christensen et al. [16] and by Davison et al. [17] are compared with our experimental results, as shown in Figs. 2 and 3. For the C3P1 + water system, our experimental results of mass fractions of the C3P1-rich phase are consistent with the literature data [16,17], but not the case of the aqueous phase. While for the
S.-Y. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67
65
Table 2 Experimental and calculated mass fraction of C3P1 of equilibrium liquid phases for the binary C3P1 + water system at various temperatures. T (K)
304.85 305.16 305.66 306.13 307.14 308.27 309.29 310.31 311.29 312.32 313.35 314.38 315.22 316.24 318.11 320.11 322.14 324.14 326.15 328.15 Average absolute
Experimental results
Calculated results
wl
wu
wl
wu
0.3502 0.3205 0.2925 0.2743 0.2531 0.2324 0.2229 0.2144 0.2066 0.1959 0.1882 0.1830 0.1764 0.1698 0.1663 0.1597 0.1526 0.1483 0.1409 0.1374 deviation
0.4827 0.5166 0.5477 0.5712 0.5967 0.6174 0.6314 0.6437 0.6516 0.6582 0.6659 0.6740 0.6826 0.6858 0.6953 0.7030 0.7112 0.7176 0.7248 0.7307
0.3105 0.2995 0.2875 0.2744 0.2519 0.2327 0.2196 0.2079 0.2001 0.1923 0.1856 0.1798 0.1756 0.1709 0.1636 0.1570 0.1510 0.1458 0.1407 0.1359 0.0105
0.5052 0.5268 0.5554 0.5711 0.5972 0.6187 0.6344 0.6455 0.6572 0.6662 0.6739 0.6805 0.6852 0.6903 0.6982 0.7056 0.7124 0.7193 0.7267 0.7349 0.0069
Fig. 2. The phase diagram for binary C3P1 + water system: experimental results of this work (*), results from gas chromatography ( ), Christensen et al. [16] ( ), Davison et al. [17] ( ), the critical point determined from the critical scaling law () and calculated results by the UNIQUAC model (solid line).
Table 3 Experimental and calculated mass fraction of C3P2 of equilibrium liquid phases for the binary C3P2 + water system at various temperatures. T (K)
286.90 287.19 287.41 287.72 288.01 288.19 289.11 290.36 291.20 292.22 293.16 297.15 301.11 305.25 309.10 313.14 317.10 321.13 325.15 328.09 Average absolute
Experimental results
Calculated results
wl
wu
wl
wu
0.3809 0.3530 0.3372 0.3234 0.3127 0.3074 0.2787 0.2556 0.2426 0.2287 0.2208 0.1834 0.1600 0.1366 0.1167 0.1056 0.0940 0.0830 0.0731 0.0686 deviation
0.5846 0.6084 0.6250 0.6413 0.6530 0.6600 0.6966 0.7147 0.7269 0.7405 0.7491 0.7875 0.7973 0.8123 0.8277 0.8296 0.8361 0.8393 0.8425 0.8458
0.3486 0.3369 0.3295 0.3194 0.3108 0.3059 0.2837 0.2597 0.2448 0.2324 0.2212 0.1846 0.1585 0.1366 0.1193 0.1038 0.0911 0.0807 0.0730 0.0691 0.0086
0.6141 0.6275 0.6365 0.6484 0.6586 0.6643 0.6901 0.7166 0.7264 0.7439 0.7541 0.7822 0.7990 0.8125 0.8232 0.8327 0.8400 0.8448 0.8461 0.8444 0.0091
C3P2 + water system, our experimental results are fairly consistent with the literature data [16,17], except the C3P2-rich phase at temperature higher than 310 K. The origin of this discrepancy is unknown. To further verify the composition determined by the phase volume method, the mass fractions in these systems were double-checked by gas chromatography (GC-8A, Shimadzu Co.,
Fig. 3. Coexistence curve for binary C3P2 + water system: experimental results of this work (*), results from gas chromatography ( ), Christensen et al. [16] ( ), Davison et al. [17] ( ), the critical point determined from the critical scaling law () and calculated results by the UNIQUAC model (solid line).
Japan). The experimental details of the gas chromatography method to determine the mass fractions of the conjugated phase followed closely our previous works [11–15]. The results of gas chromatography are given in Table 4. The mass fractions determined by gas chromatography have an excellent agreement with the results by the phase volume method, as demonstrated in Figs. 2 and 3. It should be noted that the classical predictive models are not able to precisely describe the liquid–liquid equilibrium phase behavior of mixtures containing compound with both hydrophobic and hydrophilic functionality [23]. Thus, the UNIQUAC model was used to correlate experimental data. The volume parameter, r, and surface area parameter, q, of each compound were directly adopted from the commercial simulator Aspen Plus and listed in Table 5. The binary interaction parameter aij is defined by ai j ¼
ui j u ji R
(4)
where uij and uji are the UNIQUAC energy interaction parameters between components i and j, and R is the gas constant. These
Table 4 Experimental mass fractions determined by gas chromatography. System
T (K)
wl
wu
C3P1 + water
308.15 318.15
0.2357 0.1655
0.6139 0.6993
C3P2 + water
288.15 298.15 308.15
0.2992 0.1719 0.1216
0.6560 0.7947 0.8257
Table 5 The volume parameter r and surface area parameter q of the UNIQUAC model adopted from the commercial simulator Aspen Plus. Parameter
Water
C3P1
C3P1
r q
0.92 1.40
5.043 4.368
7.312 6.224
66
S.-Y. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67
Table 6 Estimated UNIQUAC parameters for binary system C3P1 (1) + water (2) and C3P2 (1) + water (2) (a12 = b0 + b1/T + b2 ln T + b3T and a21 = c0 + c1/T + c2 ln T + c3T). Parameter
C3P1 + water
C3P2 + water
b0 b1 b2 b3 c0 c1 c2 c3
1.112 107 3.069 108 1.930 106 3.035 103 7.621 106 2.094 108 1.324 106 2.090 103
4.114 106 1.129 108 7.152 105 1.137 103 3.254 105 8.533 106 5.729 104 9.902 101
Table 7 The critical mass fraction of C3Pj and the lower critical solution temperature of binary C3P1 (1) + water (2) and C3P2 (1) + water (2) systems. System
wc
C3P1 + water C3P2 + water
0.4212 0.4864
Tc (K) Exp.
Lit. [16]
304.61 286.59
305.15 283.15
effective binary interaction parameters a12 and a21 for each temperature were solved exactly and then were further correlated with temperature by the following equations: a12 ¼ b0 þ
b1 þ b2 ln T þ b3 T T
(5)
a21 ¼ c0 þ
c1 þ c2 ln T þ c3 T T
(6)
The results of the correlated parameters are given in Table 6. The phase boundary concentrations calculated from UNIQUAC model with estimated effective binary interaction parameters given by Eqs. (5) and (6) are also shown as black solid curves in Figs. 2 and 3. The calculated curves of these two systems describe the experimental data well except the regions very close to the lower critical solution point, as reported in Tables 2 and 3, on account of the classical limit of UNIQUAC model. The critical scaling law, instead of the classical UNIQUAC model, was applied to determine the critical point. When the system is close to its critical temperature, Tc, according to the renormalization group theory, the phase boundaries wu and wl should obey the scaling law as [24] wu ¼ wc þ Beb þ C ebþD þ De1a
(7)
wl ¼ wc Beb C ebþD þ De1a
(8)
where wc is the critical mass fraction, the coefficients B, C, and D are system-dependent parameters, e is the reduced temperature defined as e ðT T c Þ=T c , and b, D, and a are universal criticalscaling exponents with the value of 0.324 [24–28], 0.5 [24–26], and 0.11 [26–28], respectively. Subtracting Eq. (8) from Eq. (7) yields wu wl ¼ 2Beb þ 2C ebþD When the system temperature temperature, the second term on can be neglected because of (b + D = 0.824 versus b = 0.324). Eq. (9) can be recasted as ðwu wl Þ1=b ¼ B0 ðT T c Þ
(9) is very close to its critical the right-hand side of Eq. (9) the larger exponent value Neglecting the second term,
(10)
On the other hand, adding Eqs. (7) and (8) yields wu þ wl ¼ wc þ De1a 2
(11)
The critical mass fraction wc and the lower critical solution temperature Tc could be determined by fitting our experimental results of the phase boundaries to the critical scaling law, Eqs. (10) and (11) [29]. The estimated critical points for the C3P1 + water and C3P2 + water systems are given in Table 7 and shown as symbol cross in Figs. 2 and 3. Note that the estimated critical point is slightly above, as expected, that of the UNIQUAC model, as shown in Figs. 2 and 3. In addition, the lower critical solution temperatures of Christensen et al. [16] are also listed in Table 7 for comparison. In contrast to the CiEj + water system, the lower critical solution temperature of the C3P1 + water system 304.65 K is higher than that of the C3P2 + water system 286.65 K, which is consistently higher than that of the C3P3 + water system, as pointed out by Christensen et al. [16]. The symbol CiEj is the abbreviation of the ethylene glycol ether CH3(CH2)i1(OCH2CH2)jOH. It is well understood that the lower critical solution temperature of the CiEj + water system is consistently lower than that of the CiEj+1 + water system [29,30]. 4. Conclusions The phase diagrams of liquid–liquid equilibrium for binary C3P1 + water and C3P2 + water systems near their lower critical solution temperatures are determined by the phase volume method. All the results are fitted to the UNIQUAC model and the critical scaling law. The estimated critical temperature for the C3P1 + water is lower than that for C3P2 + water system, thus leading a wider composition range of immiscibility. Acknowledgement This work was supported by the National Science Council of Taiwan. References [1] Gonsior SJ, West RJ. Biodegradation of glycol ethers in soil. Environ Toxicol Chem 1995;14:1273–9. [2] Spencer PJ. New toxicity data for the propylene glycol ethers – a commitment to public health and safety. Toxicol Lett 2005;156:181–8. [3] Staples CA, Boatman RJ, Cano ML. Ethylene glycol ethers: an environmental risk assessment. Chemosphere 1998;36:1585–613. [4] Wu TY, Chen BK, Hao L, Kuo CW, Sun IW. Thermophysical properties of binary mixtures {1-methyl-3-pentylimidazolium tetrafluoroborate + polyethylene glycol methyl ether}. J Taiwan Inst Chem Eng 2012;43:313–21. [5] Chiou DR, Chen LJ. Liquid–liquid equilibria for the ternary system water + diethylene glycol monohexyl ether + 2-methyl-2-butanol. Fluid Phase Equilib 2004;218:229–34. [6] Lin BJ, Chen LJ. Liquid–liquid equilibria for the ternary system water + tetradecane + 2-butyloxyethanol. Fluid Phase Equilib 2004;216:13–20. [7] Lin BJ, Chen LJ. Liquid–liquid equilibria for the ternary system water + dodecane + 2-butyloxyethanol in the temperature range from 25 8C to 65 8C. J Chem Eng Data 2002;47:992–6. [8] Liu YL, Chiou DR, Chen LJ. Liquid–liquid equilibria for the ternary system water + octane + diethylene glycol monobutyl ether. J Chem Eng Data 2002;47:310–2. [9] Hu HS, Chen LJ. Liquid–liquid equilibria for the ternary system water + ntetradecane + 2-(2-n-hexyloxyethoxy)ethanol at 293.15 K and 303.15 K. J Chem Eng Data 2000;45:304–7. [10] Hu HS, Chiu CD, Chen LJ. Liquid–liquid equilibria for the ternary system water + n-dodecane + 2-(2-n-hexyloxyethoxy)ethanol. Fluid Phase Equilib 1999;164:187–94. [11] Su CH, Chen LJ. Liquid–liquid equilibria for the ternary system water plus hexadecane plus propylene glycol n-propyl ether. J Chem Eng Data 2011;56:589–94. [12] Su CH, Chen LJ. Liquid–liquid equilibria for the ternary system water plus tetradecane plus propylene glycol n-propyl ether. J Chem Eng Data 2011;56:2976–9.
S.-Y. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 45 (2014) 63–67 [13] Su CH, Chen LJ. Liquid–liquid equilibria for the ternary system water plus dodecane plus 1-(1-methyl-2-propoxyethoxy)-2-propanol. J Chem Eng Data 2012;57:1899–902. [14] Su CH, Lin SY, Chen LJ. (Liquid plus liquid) equilibria for the ternary system (water plus dodecane plus propylene glycol n-propyl ether). J Chem Thermodyn 2012;47:358–61. [15] Su CH, Chen LJ. Liquid–liquid equilibria for the ternary system (water + hexadecane + dipropylene glycol n-propyl ether). Fluid Phase Equilib 2013;346:20–4. [16] Christensen SP, Donate FA, Frank TC, LaTulip RJ, Wilson LC. Mutual solubility and lower critical solution temperature for water plus glycol ether systems. J Chem Eng Data 2005;50:869–77. [17] Davison RR, Smith WH, Hood DW. Mutual solubility of water glycerol and glycol ethers. J Chem Eng Data 1966;11:404. [18] Polyakov VI, Grinberg VY, Tolstoguzov VB. Application of phase-volume-ratio method for determining the phase diagram of water–casein–soybean globulins system. Polym Bull 1980;2:757–60. [19] Kim KY, Lim KH. Fits of scaling and UNIQUAC equations to liquid–liquid equilibrium (LLE) phase compositions of the binary amphiphile 2-butoxyethanol (1) plus water (2) measured by the phase volume method. J Chem Eng Data 2001;46:967–73. [20] Lim KH, Reckley JS, Smith DH. Liquid–liquid phase-equilibrium in binarymixtures of the nonionic amphiphile CH3(CH2)5(OCH2CH2)2OH and water. J Colloid Interface Sci 1993;161:465–70.
67
[21] Lide DR. CRC handbook of chemistry and physics. 89th ed. Boca Raton, FL: CRC Press; 2008. [22] Speight JG. Lange’s handbook of chemistry. 16th ed. New York: McGraw-Hill; 2005. [23] Gerber RP, Soares RP. Assessing the reliability of predictive activity coefficient models for molecules consisting of several functional groups. Braz J Chem Eng 2013;30:1–11. [24] Rowlinson JS, Widom B. Molecular theory of capillarity. Oxford: Clarendon Press; 1982. [25] Baker GA, Nickel BG, Green MS, Meiron DI. Ising-model critical indices in three dimensions from the Callan–Symanzik equation. Phys Rev Lett 1976;36: 1351–4. [26] Baker GA, Nickel BG, Meiron DI. Critical indices from perturbation analysis of Callan–Symanzik equation. Phys Rev B 1978;17:1365–74. [27] Greer SC, Moldover MR. Thermodynamic anomalies at critical points of fluids. Annu Rev Phys Chem 1981;32:233–65. [28] Le Guillou JC, Zinn-Justin J. Critical exponents from field-theory. Phys Rev B 1980;21:3976–98. [29] Lai HH, Chen LJ. Liquid–liquid equilibrium phase diagram and density of three water + nonioinic surfactant CiEj binary system. J Chem Eng Data 1999;44:251–3. [30] Kahlweit M, Busse G, Jen J. Adsorption of amphiphiles at water/air interfaces. J Phys Chem 1991;95:5580–6.