Article pubs.acs.org/jced
Experimental Determination and Correlation of Liquid−Liquid Equilibria for Water + Cyclohexanone + Solvents (Toluene or p‑Xylene) Ternary Systems at 303.15 and 323.15 K under 101.3 kPa Hai Liu, Peng Cui, Kun Xin, Lanyi Sun, Yunfang Wang, and Qingsong Li* The State Key Lab of Heavy Oil Processing and College of Chemical Engineering, China University of Petroleum (East China), Qingdao, 266580 Shandong, People’s Republic of China ABSTRACT: Liquid−liquid equilibria (LLE) data for the water + cyclohexanone + solvents (toluene or p-xylene) ternary systems were reported at 303.15 and 323.15 K under 101.3 kPa. The distribution coefficient (D) and separation factors (S) were calculated to evaluate the separating efficiency of the selected solvents. Besides, both the Hand and the Bachman correlation equations were used to ascertain the reliability and consistency of the obtained LLE data. The nonrandom two-liquid (NRTL) and the universal quasi-chemical activity coefficient (UNIQUAC) models were both applied to correlate the experimental results for the studied ternary systems with the RMSD% values of these two models as low as 0.16. Also, the binary interaction parameters were obtained for these two correlation models.
1. INTRODUCTION Cyclohexanone is one of the key reactants for the manufacture of adipic acid and ε-caprolactam, which will be further manufactured as nylon-6 and nylon-66 fibers, respectively, and is also a widely used solvent.1 It is mainly manufactured by catalytic oxidation cyclohexane in industry in the presence of cobalt-based catalysts, resulting in the mixture of cyclohexanol and cyclohexanone (KA oil). Apart from this method, it can also be manufactured by the process of hydrogenation of phenol in the presence of noble metal catalysts.2,3 Therefore, all the preparation methods will produce a large number of industrial wastewater containing cyclohexanone, causing great harm to the environment.4−6 In order to meet environmental regulations, some necessary treatments have been applied prior to their discharge into receiving waters, such as activated carbon adsorption, incineration, as well as solvent extraction.7 The activated carbon adsorption method is limited to its low efficiency and difficult to realize large scale industrialization. Incinerations have been found to be serious drawbacks including air pollution and high cost. In comparison, liquid−liquid extraction becomes a convenient energy saving and environmental friendly choice, which could not only effectively solve water discharge, but also recover some useful chemicals. Thus, recovering cyclohexanone by solvent extraction from aqueous solutions is of great environmental and economic interest. However, there are few studies on separating cyclohexanone from wastewater using extraction method. In the open literature, Vozin8,9 et al. reported several solvents such as cyclohexane and benzene have been used to recover cyclohexanone from wastewater. Pei10 et al. studied the distribution of cyclohexanone between water and cyclohexane at 303.2−333.2K. However, © 2017 American Chemical Society
there is no liquid−liquid equilibrium (LLE) data for ternary systems of water + cyclohexanone + toluene or water + cyclohexanone + p-xylene. Thus, in order to design, simulate, and optimize a proper extraction process, it is essential to obtain reliable ternary LLE data.11 In this work, the experimental LLE results were measured for the ternary systems water + cyclohexanone + solvents (toluene or p-xylene) at 303.15 and 323.15 K under 101.3 kPa. Taking into account the practical application, only low concentration (1−20 wt %) of cyclohexanone aqueous solution was studied. As far as we know, all these LLE data have not been reported by others up to now. In addition, the distribution coefficients (D) and separation factors (S) were also used to investigate the separation efficiency. Moreover, the reliability and consistency of the obtained experimental tie-line data were ascertained by Bachman equation12 and Hand equation.13 Besides, both the NRTL14 and UNIQUAC15 activity coefficient models were adopted to correlate the experimental results and binary energy interaction parameters were obtained.
2. EXPERIMENTAL SECTION 2.1. Chemicals. The main information on the chemicals employed in this work were listed in Table 1. Cyclohexanone, p-xylene, and toluene were obtained from Sinopharm Chemical Reagent. Co. Distilled water was self-made in our laboratory and used throughout all experiments. The purities of the materials were higher than 0.99 and were tested by gas-chromatography. Received: March 16, 2017 Accepted: June 29, 2017 Published: July 17, 2017 2367
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both maintained at 523.15 K. In each analysis, we first kept the initial temperature of the column at 393.15 K for 1.5 min, increased to 523.15 K at a rate of 20 K·min−1, and then held at this temperature for the other 1 min. We measured each sample at least three times and reported the mean value with the resulting standard deviation less than 0.08%. Moreover, the GUM standard19 was used to calculate the uncertainty of the two liquid layers compositions. 2.3. Standard Uncertainty Calculation. Standard uncertainty was employed to calculate the uncertainty according to the GUM standard.19 These calculation equations are shown as follows
Table 1. Materials Main Description of the Chemicals component
CAS
supplier
reported GC purity (mass %)
GC purity (mass %)
water cyclohexanone p-xylene toluene
7732-18-5 98-01-1 106-42-3 108-88-3
self-made Sinopharm Sinopharm Sinopharm
⩾99.5 ⩾99.0 ⩾99.5
99.92 99.66 99.53 99.91
Table 2. UNIQUAC Structural Parameters (r and q) component
r
q
water cyclohexanone p-xylene toluene
0.9200 4.1140 4.6579 3.9228
1.3997 3.3400 3.5360 2.9700
n 2
s (qk ) =
∑
(qj − q ̅ )2
j=1
All the chemical regents in this work were used without further purification. 2.2. Procedure. The experimental results for the ternary system water + cyclohexanone + solvents (toluene or p-xylene) were obtained at desired temperature and at 101.3 kPa. The experimental apparatus and procedure employed in this work have been presented in detail in our recent work16 and other typical LLE studies.17,18 In this work, the liquid mixture was stirred vigorously for 2 h and left undisturbed to reach phase equilibrium and splitting in the following 4 h. After the mixture was formed into two liquid phases, the samples from two layers were taken by a long needle syringe carefully. By changing the compositions or the temperatures of the mixture, a series of LLE tie-line data were obtained with the uncertainty of ±0.1 K for all experimental operations. The internal standard method was adopted to determine the composition for the two liquids, where isopropanol was chosen as the internal standard substance. The samples collected from two layers were measured by a gas chromatograph (GC6820, Agilent Technologies) equipped with a thermal conductivity detector (TCD) and Porapak N column (3 mm × 3 m). In GC analysis, the carrier gas was high purity hydrogen, whose flow rate is 1.0 mL/s. The injector and the detector temperatures were
s 2 (q ̅ ) =
(n − 1)
(1)
s 2(qk ) (2)
n
u(x i) = s(X̅ i )
(3)
where (s(qk)) is the experimental standard deviation, (qk) denotes the observed value, Xi is an input quantity, and u(xi) represents the standard uncertainty.
3. RESULTS AND DISCUSSION 3.1. Experimental LLE Data. The LLE results for the ternary systems water + cyclohexanone + solvents (toluene as well as p-xylene) at 303.15 and 323.15 K under 101.3 kPa are shown in Table 3 and Table 4 with all concentrations presented in mole fraction. The triangle phase diagrams of the studied ternary systems at desired temperatures were plotted and shown in Figures 1−4. The feed compositions for different systems were also presented in these figures. As can be observed, the feed composition points agree with tie-line accurately, which is in line with the rules of lever and indicates that mass balance is satisfied in all the experimental process.20 To estimate the ability of toluene as well as p-xylene to extract cyclohexanone from wastewater, the distribution coefficient (D)
Table 3. Experimental LLE Data (Mole Fraction) for Water (1) + Cyclohexanone (2) + Solvents (3) System at 303.15 K under 101.3 kPaa organic phase x1
x2
x3
x1
x2
x3
D
S
toluene
0.0065 0.0095 0.0114 0.0094 0.0111 0.0134 0.0122 0.0138 0.0064 0.0089 0.0105 0.0090 0.0108 0.0133 0.0131 0.0166
0.0084 0.0356 0.0530 0.0728 0.0996 0.1412 0.1638 0.1849 0.0093 0.0385 0.0590 0.0810 0.1111 0.1427 0.1762 0.2082
0.9851 0.9549 0.9356 0.9178 0.8894 0.8454 0.8240 0.8013 0.9843 0.9525 0.9305 0.9099 0.8781 0.8441 0.8107 0.7752
0.9995 0.9991 0.9988 0.9985 0.9982 0.9976 0.9973 0.9971 0.9995 0.9990 0.9987 0.9983 0.9979 0.9976 0.9966 0.9968
0.0001 0.0005 0.0007 0.0010 0.0013 0.0019 0.0022 0.0025 0.0001 0.0006 0.0009 0.0013 0.0017 0.0021 0.0028 0.0030
0.0003 0.0004 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0004 0.0004 0.0004 0.0004 0.0004 0.0003 0.0006 0.0003
58.81 74.47 73.86 73.84 74.61 74.18 74.11 74.24 76.77 62.59 63.71 64.26 64.93 68.02 71.59 70.29
9116 7821 6470 7857 6722 5531 6054 5370 9960 7005 6055 7095 5989 5110 5435 4220
p-xylene
a
aqueous phase
solvent
Standard uncertainties u are u(T) = 0.1 K, u(p) = 0.3 kPa, and u(x) = 0.0036. 2368
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Table 4. Experimental LLE Data (Mole Fraction) for Water (1) + Cyclohexanone (2) + Solvents (3) System at 323.15 K under 101.3 kPaa organic phase x1
x2
x3
x1
x2
x3
D
S
toluene
0.0084 0.0100 0.0111 0.0126 0.0134 0.0141 0.0145 0.0167 0.0083 0.0093 0.0116 0.0124 0.0128 0.0148 0.0165 0.0214
0.0082 0.0373 0.0565 0.0782 0.1007 0.1298 0.1605 0.1900 0.0099 0.0395 0.0537 0.0812 0.1133 0.1459 0.1778 0.2084
0.9835 0.9527 0.9325 0.9092 0.8859 0.8561 0.8251 0.7934 0.9818 0.9512 0.9347 0.9065 0.8739 0.8394 0.8057 0.7703
0.9994 0.9989 0.9988 0.9986 0.9983 0.9979 0.9976 0.9972 0.9996 0.9991 0.9988 0.9981 0.9975 0.9977 0.9969 0.9951
0.0001 0.0005 0.0007 0.0009 0.0012 0.0015 0.0019 0.0022 0.0001 0.0005 0.0008 0.0011 0.0016 0.0019 0.0024 0.0030
0.0005 0.0006 0.0005 0.0005 0.0005 0.0006 0.0005 0.0006 0.0003 0.0004 0.0004 0.0007 0.0009 0.0007 0.0008 0.0009
100.6 79.22 84.60 85.00 83.92 84.12 86.42 86.35 88.15 74.37 65.64 71.15 72.09 76.93 75.18 68.79
9045 7903 7650 6764 6236 5957 5962 5162 9605 7996 5641 5730 5617 5202 4551 3202
p-xylene
a
aqueous phase
solvent
Standard uncertainties u are u(T) = 0.1 K, u(p) = 0.3 kPa, and u(x) = 0.0038.
Figure 1. Ternary phase diagram for water + cyclohexanone + toluene system at 303.15 K. (a) Integrated ternary phase diagram. (b) Zoomed-in view of the phase points in toluene phase. (c) Zoomed-in view of the feed spots. (d) Zoomed-in view of the phase points in aqueous phase (☆) feed composition; (*) experimental data; (□) NRTL model; (○) UNIQUAC model.
phase, respectively. The values of D and S at each temperature calculated are also shown in Tables 3 and 4, which indicates toluene as well as p-xylene are excellent solvents for removal of cyclohexanone from aqueous solution. Besides, as can be seen from Tables 3 and 4, higher D and S values were obtained in the ternary system containing toluene than that of ternary system containing p-xylene at the same temperature, demonstrating that toluene is more appropriate for extraction. It could also be found that temperature has an insignificant effect on the extraction performance of the selected solvents and 303.15 K is better for extraction process. The separation factors (S) versus cyclohexanone mole
and separation factor (S) were adopted, which were defined as the following equations x 2β D= x 2α (4) x 2β
S=
x1β x 2α x1α
(5)
where x2α and x1α represent the mole fractions of cyclohexanone and water in the water-rich phase, respectively. x2β and x1β denote the mole fractions of cyclohexanone and water in the solvents-rich 2369
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Figure 2. Ternary phase diagram for water + cyclohexanone + toluene system at 323.15 K. (a) Integrated ternary phase diagram. (b) Zoomed-in view of the phase points in toluene phase. (c) Zoomed-in view of the feed spots. (d) Zoomed-in view of the phase points in aqueous phase (☆) feed composition; (*) experimental data; (□) NRTL model; (○) UNIQUAC model.
Figure 3. Ternary phase diagram for water + cyclohexanone + p-xylene system at 303.15 K. (a) Integrated ternary phase diagram. (b) Zoomed-in view of the phase points in p-xylene phase. (c) Zoomed-in view of the feed spots. (d) Zoomed-in view of the phase points in aqueous phase (☆) feed composition; (*) experimental data; (□) NRTL model; (○) UNIQUAC model.
To assess the reliability and consistency of the obtained experimental tie-line data, both the Hand and Bachman correlation equations were employed, which are listed as follows
concentraction in the solvents-rich phase at desired temperatures (303.15 and 323.15K) are presented in Figure 5. As can be observed from the figure, the values of separation factors (S) decrease as the concentration of cyclohexanone in the organic phase increases, which indicates that separating capability of solvents decreases and low concentration is suitable for extraction operation.
⎛ x 2β ⎞ ⎛x ⎞ ln⎜⎜ ⎟⎟ = a + b ln⎜ 2α ⎟ ⎝ x1α ⎠ ⎝ x 3β ⎠ 2370
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Figure 4. Ternary phase diagram for water + cyclohexanone + p-xylene system at 323.15 K. (a) Integrated ternary phase diagram. (b) Zoomed-in view of the phase points in p-xylene phase. (c) Zoomed-in view of the feed spots. (d) Zoomed-in view of the phase points in aqueous phase (☆) feed composition; (*) experimental data; (□) NRTL model; (○) UNIQUAC model.
Figure 5. Experimental separation factor (S) versus the cyclohexanone mole fraction (x2β) in the solvent phase for the ternary system water (1) + cyclohexanone (2) + solvents (3).
⎛ x 3β ⎞ x3β = m + n⎜ ⎟ ⎝ x1α ⎠
Figure 6. Hand plots of the system water + cyclohexanone + solvents (toluene + p-xylene) at 303.15 and 323.15 K.
correlate the experimental LLE data for water + cyclohexanone + solvents (toluene or p-xylene) ternary systems by using Aspen 8.4 software. For the NRTL model, the corresponding equations are14
(7)
where a, b and m, n represent the constants of the Hand and Bachman equations, x2α and x1α denote the mole contents of cyclohexanone and water in the aqueous phase, respectively. x3β and x2β are the mole contents of solvents and cyclohexanone in the organic phase, respectively. The Hand plots and Bachman plots for the studied ternary systems are shown in Figures 6 and 7. Table 5 presents the fitting parameters together with corresponding linear regression coefficients R2. All the values of R2 are close to 1, which demonstrates the reliability and a satisfactory quality of the experimental LLE data. 3.2. Correlation of Experimental Data. Both the NRTL and UNIQUAC activity coefficients models were adopted to
gij − gjj = RTτij ,
gji − gii = RTτji ,
τij = aij +
bij T
(8)
where aij and bij are the binary interaction parameters simulated by NRTL model, and gij − gjj and gji − gii represent the calculated NRTL binary energy interaction parameters. For the UNIQUAC simulation, the employed equations are15 uij − ujj = RTτij ,
uji − uii = RTτji ,
⎛ bij ⎞ τij = ⎜ −aij − ⎟ T⎠ ⎝ (9)
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where xexp and xcal represent the experimental and calculated mole fraction, respectively. n denotes the number of tie lines. The subscripts i, j, and k are the components, the phases and the tie lines, respectively. Moreover, the root-mean-square deviation (RMSD) values were applied to assess the quality of correlation from NRTL and UNIQUAC models, which is given by the following form 1/2 ⎧ n 2 3 (x exp − x cal)2 ⎫ ⎪ ⎪ ijk ijk ⎬ RMSD = ⎨∑ ∑ ∑ ⎪ ⎪ 6n ⎩k=1 j=1 i=1 ⎭
the corresponding n, xexp, xcal, k, j, i are the same with those in the OF equations. The RMSD% values are presented in Table 6 and all of them are less than 0.53, which indicate all the experimental tie-line data could be correlated well by these two models. In addition, the fitted LLE data at different temperature by using both the NRTL and UNIQUAC model are also shown in Figures 1−4. As can be observed, the calculated data coincides well with the experimental data, demonstrating that these two models are suitable for simulating cyclohexanone extraction.
Figure 7. Bachman plots of the system water + cyclohexanone + solvents (toluene + p-xylene) at 303.15 and 323.15 K.
where aij and bij denote the binary interaction parameters simulated by UNIQUAC model, and uij − ujj and uji − uii are the calculated UNIQUAC binary energy interaction parameters. For the UNIQUAC correlation, the volume parameter r and area parameter q are derived from literature21,22 and shown in Table 2. The obtained binary interaction parameters (aij and aji, bij and bji) of UNIQUAC and NRTL models were presented in Table 6. The NRTL nonrandomness parameters αij were fixed at 0.2 or 0.3 and the values were also listed in Table 6. The binary interaction parameters of these two models for these studied ternary systems were obtained by minimizing the objective function (OF), which is given as follows n
OF =
2
4. CONCLUSIONS The liquid−liquid equilibria (LLE) for water + cyclohexanone + toluene as well as water + cyclohexanone + p-xylene ternary systems were investigated at 303.15 and 323.15 K under 101.3 kPa. The reliability and consistency of the obtained LLE data were checked by using both the Hand and Bachman equations. The calculated distribution coefficients and separation factors indicate that toluene as well as p-xylene has a good performance on the extraction of cyclohexanone from wastewater. Moreover, the experimental LLE results were fitted well with both the NRTL and the UNIQUAC models and the
3
∑ ∑ ∑ (xijkexp − xijkcal)2 (10)
i=1 j=1 k=1
(11)
Table 5. Parameters of the Hand and Bachman Equations for Water (1) + Cyclohexanone (2) + Solvents (3) System at Desired Temperature Hand T/K
a
b
toluene 303.15 K toluene 323.15 K p-xylene 303.15 K p-xylene 323.15 K
5.361 4.6982 4.5589 4.5362
1.1396 1.0180 1.0348 1.0159
Bachman 2a
R
0.9993 0.9941 0.9922 0.9919
m
n
R2 a
−0.0107 −0.0090 −0.0109 −0.0143
1.0103 1.0084 1.0104 1.0141
0.9999 0.9999 0.9999 0.9999
a 2
R is the linear correlation coefficient.
Table 6. Binary Interaction Parameters of NRTL and UNIQUAC Models for the System Water (1) + Cyclohexanone (2) + Solvents (3) at the Temperatures T = 303.15 and 323.15 K and p = 101.3 kPa model NRTL
UNIQUAC
NRTL
UNIQUAC
i-j
aij
1-2 1-3 2-3 1-2 1-3 2-3
82.52 627.81 −20.88 −3.75 −2.22 0.05
1-2 1-3 2-3 1-2 1-3 2-3
59.59 157.14 5.95 0.16 −5.42 −0.32
aji
bij
Water (1) + Cyclohexanone (2) + Toluene (3) 58.94 −10000.00 −241.05 −27892.07 6.58 7653.36 −12.44 64.05 −1.71 −281.55 1.47 −245.65 Water (1) + Cyclohexanone (2) + p-Xylene (3) 95.14 −2686.23 −0.17 −5118.99 −4.67 −900.64 −1.18 48.59 5.77 1744.33 0.34 −96.84 2372
bji
α
RMSD/%
9092.94 12443.23 −2739.15 −2794.17 −281.48 −201.56
0.2 0.2 0.3
0.23
−2698.23 851.94 823.32 −356.37 −2635.64 104.60
0.2 0.2 0.3
0.16
0.53
0.50
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(21) Xin, K.; Song, Y. H.; Dai, F. F. Liquid−liquid equilibria for the extraction of furfural from aqueous solution using different solvents. Fluid Phase Equilib. 2016, 425, 393−401. (22) Lei, F.; Wang, Q.; Gong, X. Liquid−liquid equilibria for ternary system water + acetic acid + cyclohexanone at (293.2−323.2) K. Fluid Phase Equilib. 2014, 382, 65−69.
corresponding optimum interaction parameters of these two models were obtained. All the RMSD% values are below 0.53, indicating a satisfactory correlation quality for both two models.
■
AUTHOR INFORMATION
ORCID
Qingsong Li: 0000-0003-1425-8822 Notes
The authors declare no competing financial interest.
■
REFERENCES
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