Article pubs.acs.org/jced
Liquid−Liquid Equilibria of Water + Acetic Acid + Cyclopentyl Methyl Ether (CPME) System at Different Temperatures Hongxun Zhang,* Guangyu Liu, Chen Li, and Lei Zhang School of Chemistry and Chemical Engineering, Henan University of Technology, Zhengzhou, Henan 450001, China
ABSTRACT: Tie-line data of the ternary system water + acetic acid + cyclopentyl methyl ether (CPME) at (293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K are reported. The reliability of the tie-line data was confirmed by using Othmer−Tobias and Hand equations. Distribution coefficients and separation factors were evaluated from the liquid−liquid equilibria (LLE) data. Moreover, the solvent capability of CPME and methyl tert-butyl ether was compared.
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INTRODUCTION The separation of acetic acid from water, as an important industrial problem, has raised public concern for many years, because the recovery of acetic acid has a major influence on the economy of products and important meanings for environmental protection and resource utilization. Commonly known methods for removing water from acetic acid are conventional distillation, azeotropic distillation, extraction, adsorption, and so forth. Liquid−liquid extraction followed by heteroazeotropic distillation is considered to be one of the best energy-saving processes.1−7 This method is a typical solvent-based separation process, of which the most important variable in the design is the choice of solvent. From an energy-saving point of view, Kürüm and Fonyo6 evaluated more than 30 types of possible solvents for acetic acid purification by using extraction followed by azeotropic distillation method and concluded that methyl tert-butyl ether (MTBE) is a promising entrainer. However, recent studies found that MTBE is recalcitrant to biodegradation.8 Therefore, MTBE is a potential pollutant of water in aquifers contaminated. As a new kind of hydrophobic ether solvent, CPME has unique excellent properties and is a possible alternative to tetrahydrofuran (THF), MTBE, dioxane, and other existing ether solvents. The advantageous features of CPME are: (1) high hydrophobicity and thus very easy to dry, (2) suppressed formation of peroxide byproducts, (3) relatively stable under acidic and basic conditions, (4) low vaporization energy, and (5) narrow explosion range. All of these characteristics highlight CPME as an optional process solvent for future investigations.9−13 In this study, we measured the liquid−liquid equilibrium (LLE) data of the system water + acetic acid + CPME at © 2012 American Chemical Society
(293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K and compared it with our previous work.14 Distribution coefficients and separation factors were calculated from the tie-line data to evaluate the capability of CPME to separate acetic acid from water.
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EXPERIMENTAL SECTION Chemicals. Double-distilled water prepared in our laboratory was used throughout the experiment. Acetic acid (CAS Registry No. 64-19-7) with a mass fraction purity of 0.995 was supplied by the Sinopharm Chemical Reagent Co., Ltd. CPME (CAS Registry No. 5614-37-9) was purchased from Alfa Aesar Inc. with a purity of 0.999. All of the chemicals used in this study were checked during the experiments by gas chromatography and used without further purification. Their purities are given in Table 1. Apparatus and Procedure. The apparatus and procedure of this study are similar to those in our previous work.15,16 Table 1. Purity of Chemicals Used in This Work chemical name
source
water made in our lab acetic acid Sinopharm CPME Alfa Aesar a
initial mass fraction purification puritya method 0.995 0.999
none none none
final mass fraction analysis purity method 0.9995 0.9957 0.9995
GCb GCb GCb
Stated by supplier. bGas chromatography.
Received: April 6, 2012 Accepted: September 27, 2012 Published: October 5, 2012 2942
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Table 2. Experimental Tie-Line Data (Mass Fraction w), Distribution Ratio (D1, D2), and Separation Factor (S) for the Water (1) + Acetic Acid (2) + CPME (3) System at (293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K and Atmospheric Pressurea solvent-rich phase T/K
wI2
wII1
wII2
293.15
0.0045 0.0101 0.0197 0.0284 0.0456 0.0676 0.0892 0.1028 0.1205 0.0059 0.0164 0.0307 0.0494 0.0745 0.1086 0.1554 0.1698 0.0091 0.0159 0.0257 0.0392 0.0531 0.0683 0.0929 0.1137 0.1513 0.0070 0.0186 0.0339 0.0537 0.0799 0.1147 0.1630 0.1739 0.0161 0.0228 0.0364 0.0537 0.0728 0.0938 0.1153 0.1418 0.1652 0.0229 0.0461 0.0653 0.0965 0.1241 0.1618 0.1882 0.2141
0.0000 0.0449 0.0976 0.1525 0.2157 0.2825 0.3256 0.3523 0.3802 0.0000 0.0859 0.1581 0.2235 0.2837 0.3375 0.3815 0.3904 0.0000 0.0347 0.0854 0.1425 0.1951 0.2375 0.2821 0.3198 0.3564 0.0000 0.0816 0.1514 0.2139 0.2707 0.3206 0.3615 0.3676 0.0000 0.0354 0.0827 0.1382 0.1870 0.2267 0.2696 0.3095 0.3293 0.0000 0.0598 0.1202 0.1930 0.2354 0.2913 0.3307 0.3420
0.9815 0.9081 0.8482 0.7753 0.7122 0.6334 0.5758 0.5287 0.4793 0.9748 0.8372 0.7562 0.6750 0.5892 0.4997 0.4069 0.3834 0.9703 0.8832 0.7956 0.7196 0.6706 0.6194 0.5747 0.5227 0.4698 0.9599 0.7940 0.7008 0.6150 0.5290 0.4423 0.3537 0.3372 0.9561 0.8581 0.7821 0.7169 0.6559 0.5955 0.5383 0.5032 0.4716 0.9407 0.7840 0.7054 0.6271 0.5499 0.4779 0.4296 0.4032
0.0000 0.0643 0.1133 0.1696 0.2161 0.2733 0.3153 0.3402 0.3706 0.0000 0.1156 0.1792 0.2388 0.2958 0.3470 0.3881 0.3961 0.0000 0.0692 0.1353 0.1907 0.2266 0.2629 0.2930 0.3255 0.3509 0.0000 0.1332 0.2013 0.2583 0.3087 0.3503 0.3797 0.3834 0.0000 0.0718 0.1251 0.1692 0.2103 0.2492 0.2853 0.3071 0.3273 0.0000 0.1054 0.1599 0.2141 0.2611 0.3029 0.3352 0.3449
298.15
303.15
308.15
313.15
318.15
a
water-rich phase
wI1
D1
D2
S
0.0111 0.0232 0.0366 0.064 0.1067 0.1549 0.1944 0.2514
0.6983 0.8614 0.8992 0.9981 1.0337 1.0327 1.0356 1.0259 avg 0.7431 0.8823 0.9361 0.9591 0.9727 0.9831 0.9857 avg 0.5014 0.6312 0.7472 0.8610 0.9034 0.9628 0.9825 1.0157 avg 0.6128 0.7520 0.8279 0.8770 0.9154 0.9519 0.9589 avg 0.4930 0.6611 0.8168 0.8892 0.9097 0.9450 1.0078 1.0061 avg 0.5674 0.7517 0.9014 0.9016 0.9617 0.9866 0.9916 avg
62.7838 37.0896 24.5468 15.5895 9.6852 6.666 5.3259 4.0806 20.7209 37.9333 21.7316 12.7917 7.5850 4.4772 2.5746 2.2260 12.7599 27.8539 19.5399 13.7173 10.8734 8.1926 5.9561 4.5167 3.1538 11.7255 26.1967 15.5449 9.4750 5.8079 3.5301 2.0660 1.8592 9.2114 18.5559 14.2039 10.9042 8.0114 5.7754 4.4118 3.5764 2.8722 8.5389 9.6489 8.1204 5.8580 3.9950 2.8405 2.2520 1.8674 4.9403
0.0196 0.0406 0.0732 0.1264 0.2173 0.3818 0.4428 0.0180 0.0323 0.0545 0.0792 0.1103 0.1616 0.2175 0.3221 0.0234 0.0484 0.0874 0.1510 0.2593 0.4607 0.5157 0.0266 0.0465 0.0749 0.1110 0.1575 0.2142 0.2818 0.3503 0.0588 0.0926 0.1539 0.2257 0.3386 0.4381 0.5310
Standard uncertainties u are u(T) = 0.05 K, u(p) = 2.0 kPa, and u(w) = 0.005.
thermostatically controlled bath with an accuracy of ± 0.05 K to keep the temperature of the LLE cell constant. The mixtures (about 40 cm3) including water, acetic acid, and CPME were
The experimental LLE apparatus includes an approximately 50 cm3 jacketed glass cell, a magnetic agitator, and a thermostatically controlled bath. Water was circulated by using a 501-A 2943
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calibration, we estimated the uncertainty in the mass fraction of the tie-line data to be within ± 0.005.
introduced into the cell by known mass fraction. At each temperature, the heterogeneous mixtures in the cell were stirred by a magnetic agitator for at least 2 h and left to settle for a minimum of 4 h to reach phase equilibrium. Then, the heterogeneous mixtures separated into two phases with a well-defined interface. After that, samples (about 4 cm3) of organic and aqueous phases were sampled from upper and lower layers in the cell by using different syringes simultaneously. Samples of both phases were put in a thermotank to keep them transparent prior to analysis. Sample Analysis. The weights of all components used in this study were determined on an AUY220 electronic balance with a standard uncertainty of 0.0001 g. The components of the samples were analyzed by using a gas chromatograph (GC-122) equipped with a thermal conductivity detector (TCD). A 2 m × 2 mm inner diameter (i.d.) stainless steel column was packed with Porapak Q-S (80/100). The temperatures of the oven, injector, and detector were set at (473.15, 483.15, and 493.15) K, respectively. The carrier gas of the separation column was hydrogen, and its flow rate was kept at 0.8 cm3·s−1. The injection volume was 0.2 mm3. The bridge current of the TCD was 150 mA. Under the given chromatographic conditions, the peak shape of each compound was symmetrical, and the separation was very good. All measurements were carried out in triplicate and made to obtain their mean values. Considering the repeatability and reproducibility of GC and the uncertainty in
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RESULTS AND DISCUSSION Experimental LLE Data. Table 2 lists the experimental tieline data of the ternary system water (1) + acetic acid (2) + CPME (3) at (293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K. All concentrations are expressed in mass fraction. The LLE data of different temperatures were compared and shown in Figure 1. From Figure 1, it can be seen that the immiscibility gap of the investigated system becomes smaller when the temperature increases. Distribution coefficients of water (D1) and acetic acid (D2) and the separation factor of CPME (S) were calculated to evaluate the capability of CPME to separate acetic acid from water as follows: wiI
Di =
S=
wiII
(1)
D2 D1
(2)
where w is mass fraction; the superscript I represents the solvent-rich phase and II the water-rich phase.15 The values of D1, D2, and S and the tie-line data at different temperatures are listed in Table 2. The reliability of the experimental tie-line data at each temperature was determined by using the Othmer−Tobias16 and Hand17 correlation equations, respectively, for the ternary system in this study: ⎛ 1 − wI ⎞ ⎛ 1 − w II ⎞ 3 1 ⎟ ⎟ ⎜ a b = + ln⎜ ln I II ⎝ w1 ⎠ ⎝ w3 ⎠
(3)
⎛ wI ⎞ ⎛ w II ⎞ ln⎜ 2I ⎟ = m + n ln⎜ 2II ⎟ ⎝ w1 ⎠ ⎝ w3 ⎠
(4)
wI3
where is the mass fraction of CPME in the solvent-rich phase; wII1 is the mass fraction of water in the water-rich phase; a, b, m, and n are the fitting parameters of the Othmer−Tobias equation and the Hand equation, respectively.18 Table 3 lists the parameters of the Othmer−Tobias equation and the Hand equation. All of the correlation coefficients (R2) are not less than 0.9907. The standard deviations (SDs) are not more than 0.1764. Comparative Study of Solvents. To study the capability of CPME to separate acetic acid from water solution by using a method of extraction followed by heteroazeotropic distillation, we compared CPME with MTBE in terms of physical properties
Figure 1. Ternary LLE phase diagram of the water (1) + acetic acid (2) + CPME (3) system at different temperatures: ★, T = 293.15 K; ☆, T = 298.15 K; ■, T = 303.15 K; □, T = 308.15 K; ▲, T = 313.15 K; △, T = 318.15 K.
Table 3. Constants of the Othmer−Tobias and Hand Equations Othmer−Tobias
Hand
T/K
a
b
R2 a
SDb
m
n
R2a
SDb
293.15 298.15 303.15 308.15 313.15 318.15
0.0756 −0.1891 −0.1789 −0.5447 −0.2398 −0.3107
1.3287 1.2957 1.3225 1.3228 1.3047 1.2787
0.9937 0.9914 0.9978 0.9907 0.9944 0.9961
0.1456 0.1764 0.0764 0.1757 0.1067 0.0908
0.0990 −0.1092 0.0728 −0.3178 0.0799 −0.0284
1.1647 1.0894 1.3398 1.1235 1.3339 1.2947
0.9974 0.9956 0.9990 0.9955 0.9974 0.9952
0.0539 0.05875 0.0334 0.0583 0.0532 0.0675
a 2
R is the linear correlation coefficient. bSD is the standard deviation. 2944
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Table 4. Physical Properties of CPME and MTBE12 property −3
density (293.15 K) [kg·m ] vapor specific gravity (air = 1) boiling point [K] viscosity (293.15 K) [mPa·s] vaporization energy (bp) [kJ·kg−1] dielectric constant (298.15 K) azeotropic point with water [K] solubility in water [g/100 g] solubility of water in the solvent [g/100 g]
CPMEa
MTBEa
860 3.45 379.15 0.55 289.66 4.76 356.15b 1.1 (296.15 K) 0.3 (296.15 K)
740 3.1 328.15 0.35 341.98 2.6 326.05c 4.8(293.15 K) 1.4(293.15 K)
(Table 4), LLE phase diagrams at 293.15 K (Figure 2), and selectivity (Figure 3). As shown in Table 4, CPME has a higher hydrophobicity and lower vaporization energy than those of MTBE. Higher hydrophobicity means less solvent loss, and lower vaporization energy means more energy-saving. It can be gathered from Figure 2 that the immiscibility gap of water + acetic acid + CPME system is larger than that of the water + acetic acid + MTBE system. As can be seen from Figure 3, the S values of CPME are larger than those of MTBE, at 293.15 K. From the viewpoint of a green sustainable solvent, these are obvious advantages of CPME in the extraction followed by heteroazeotropic distillation process.
a
Azeotrope (mass fraction). bComposition = CPME: 0.8370, H2O: 0.1630. cComposition = MTBE: 0.9650, H2O: 0.0350.
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CONCLUSIONS LLE data of the water + acetic acid + CPME system at (293.15, 298.15, 303.15, 308.15, 313.15, and 318.15) K under atmospheric pressure were determined, and the distribution ratio and separation factor of the investigated system were calculated. The consistency of the experimental tie-line data was checked through the Othmer−Tobias and Hand correlation equations. CPME was compared with MTBE in terms of physical properties, selectivity, and LLE phase diagram. It is concluded that CPME would be a good substitute for conventional organic solvents to separate acetic acid from water by the method of liquid−liquid extraction followed by heteroazeotropic distillation.
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AUTHOR INFORMATION
Corresponding Author
*Phone: +86 371 67756725. Fax: +86 371 67756718. E-mail:
[email protected]. Funding
The authors acknowledge the Education Department of Henan Province (Grant No. 12B530001) and Henan University of Technology for their financial assistance in this project.
Figure 2. Ternary LLE phase diagram at 293.15 K: ☆, water (1) + acetic acid (2) + CPME (3) system; ○, water (1) + acetic acid (2) + MTBE (3) system.14
Notes
The authors declare no competing financial interest.
Figure 3. Separation factor (S) for ☆, water + acetic acid + CPME system and ○, water + acetic acid + MTBE system at T = 293.15 K.14 2945
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