Article pubs.acs.org/jced
Solubilities of Adipic Acid in Acetic Acid + Water Mixtures and Acetic Acid + Cyclohexane Mixtures Binwei Shen,† Qinbo Wang,*,† Yufang Wang,‡ Xiang Ye,§ Fuqiong Lei,† and Xing Gong† †
Department of Chemical Engineering, Hunan University, Changsha, 410082 Hunan, P. R. China Department of Mathematics and Physics, Jingchu University of Technology, Jingmen, 448000 Hubei, P. R. China § Zhejiang Shuyang Chemical Co. Ltd., Quzhou, 31000 Zhejiang, P. R. China ‡
ABSTRACT: The solubilities of adipic acid in acetic acid + water mixtures at (303.2 to 333.2) K and acetic acid + cyclohexane mixtures at (303.2 to 343.2) K are measured. The measured solubility of adipic acid in acetic acid + cyclohexane mixtures with the mass fraction of acetic acid in the solvent mixtures at (0.1 to 1.0) decreases with increasing mass fraction of cyclohexane at constant temperature. However, for the solubility of adipic acid in acetic acid + water with the mass fraction of acetic acid in the solvent mixtures at (0 to 1.0), acetic acid with a mass fraction of 50 % has the best dissolving capacity for adipic acid at constant temperature. The experimental data was correlated by the nonrandom two-liquid (NRTL) activity coefficient model, and the values of the solubilities calculated using the model showed good agreement with the experimental observations.
1. INTRODUCTION Currently, adipic acid (AA) is the main feedstocks for product nylon-66, which plays an important role in our modern life.1 At present, it is commercially manufactured by the two-step oxidation of cyclohexane. The first step involves oxidation of cyclohexane to cyclohexanone and cyclohexanol at around 433 K and (1 to 2) MPa pressure using either a soluble cobalt catalyst or no catalyst, in the liquid phase, in which the total cyclohexane conversion is less than 4 %. Under such low conversion the selectivity toward cyclohexanol and cyclohexanone (KA oil) can be optimized at (70 to 85) % without much overoxidation of the products. The second step involves oxidation of the KA oil to adipic acid via the use of nitric acid as a mild oxidant. The side product produced from this step includes nitrous oxide (N2O), which shows a global warming effect of 300 times higher than carbon dioxide. Finding a one-step method for manufacturing adipic acid from cyclohexane without producing NOx is the most urgent issue from the viewpoint of green chemistry. Usually in the onestep method, after being oxidized by air in an oxidation reactor, cyclohexane is conversed into adipic acid, which is called crude adipic acid. During the oxidization process, usually the solvent is acetic acid (HOAc). Water (H2O) and AA are the main products. Sequentially, crude adipic acid must be purified to produce pure adipic acid. Usually, crystallization is used to obtain products with a high purity.2 Solubilities of AA in acetic acid + water solvent mixtures and acetic acid + cyclohexane solvent mixtures become a crucial factor in designing separation equipment, as well as in controlling relevant operation conditions. Although it is useful for the aforementioned reasons, very few data are available on the solubility of AA in the aforementioned © 2013 American Chemical Society
solvent mixtures. The solubility of AA was investigated by Mao in six pure solvents.3 Fan measured the solubilites of AA in the mixtures of cyclohexanone and cyclohexanol.1,4 In this work, the solubilities of AA in acetic acid + water mixtures and acetic acid + cyclohexane mixtures are measured at (293.15 to 333.15) K. The experimental solubility data are correlated by the nonrandom two liquid (NRTL) activity coefficient model.5
2. EXPERIMENTAL SECTION 2.1. Materials. Adipic acid, pimelic acid, acetic acid, and cyclohexane were obtained with mass fraction >0.990 from Aladdin Chemistry Co. and had a declared purity of 99.0 wt %. Methanol and acetonitrile were obtained from USA Tedia Company and had a declared purity of 99.9 wt %. Purified water manufactured by Hangzhou Wahaha Group Co. was obtained from the supermarket (596 mL each bottle). All of the other chemicals used were of analytical purity and obtained from Sinopharm Chemical Reagent Co., Ltd. 2.2. Solubility Measurements. The experimental apparatus and sampling methods used in this work were described in detail by Wang et al.6 Briefly, in each experiment, an excess amount of solute AA was added to 80 ± 5 mL of solvent in a 100 mL glass bottle, and then the bottle was heated to the desired temperature within ± 0.1 K by putting it in a thermostatic water bath. The bottle was sealed by a rubber stopper to prevent the evaporation of solvent. The mixture was stirred to accelerate the dissolution of solute AA. About 3 h Received: November 9, 2012 Accepted: March 14, 2013 Published: March 25, 2013 938
dx.doi.org/10.1021/je301202v | J. Chem. Eng. Data 2013, 58, 938−942
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phase constituted of two eluents (i.e., acetonitrile + water), and the following two-component elution program was adopted: from (0 to 10) min, 16 mass % acetonitrile and 84 mass % water. The internal standard method was used to determination the concentration of AA in the solution, and pimelic acid was used as the internal standard. Similar as the method described in the work of Wang et al,6 the instrument constant for AA is determined to be 1.0920 by linear regression, and the linearity was 0.9999. To verify the reliability and reproducibility of the analysis method, five AA solutions of known concentration were analyzed. The five solutions were measured at least five times, and the repeatability was evaluated with a mean relative deviation of less than 1 %. The estimated associated uncertainty of the measured solubility values based on error analysis and repeated observations was within 4 %.
later the stirring was stopped, and the mixture would be left undisturbed in the following several hours. Fifteen min later, two phases would appear in the bottle, i.e., the liquid phase in the upper and the solid phase in the bottle bottom. To verify the attainment of solid−liquid equilibrium, the clear upper liquid phase would be sampled once an hour, and the concentration of AA would be determined. It was found that 2 h after stopping stirring was enough for solute AA in solvent to reach equilibrium, because repetitive measurements during the following several hours indicated the results were reproducible with ± 3 %. For assurance, after stopping stirring at each temperature, the solution was kept isothermal and undisturbed for at least 12 h to ensure that the solution had been saturated. In each measurement, 2 mL of the saturated solution was sampled and then analyzed using the method introduced in Section 2.3. Some of the solubility experiments were conducted two or three times to check the repeatability. The uncertainty in temperature was ± 0.1 K. To verify the reliability of the experimental apparatus and method, the solubility of AA in water and acetic acid was measured and compared with literature data.1,3 As shown in Figures 1 and 2, our results agreed well with the data in literature, with an average deviation of 2 %.
3. RESULTS AND DISCUSSION 3.1. Solubility Data. Solubility of AA in Acetic Acid + Water Mixtures. The measured solubility of AA in acetic acid + water mixtures are summarized in Table 1, where w2 was defined as the mass fraction of acetic acid in binary acetic acid + water solvent mixtures. To verify the reliability of the experimental apparatus, the measured solubility of AA in water and acetic acid were compared with the literature reported data in Figures 1 and 2. From Figures 1 and 2, it can be seen that the solubility data of AA in acetic acid and water reported in this work are in agreement with the data from the literature. The averaged relative deviation calculated between the solubility of the literature and the measured solubility in this work is less than 2 %. It indicates that the measured solubility in this work is reliable. By comparison of all of the solubilities of AA in aqueous acetic acid, an interesting result comes up as shown in Figure 3. At each measured temperature, acetic acid with mass fraction of 50 % has the best dissolving capacity for AA. It indicates that the higher or the lower the mass fraction of water, the less the solubility. In other words, within this mass fraction of water range, there is a slope presenting the change of solubility influenced by solvent concentrations at each measured temperature. This maximumsolubility effect has also been noticed by Chen and Ma for the solubility of terephthalic acid in the mixture of acetic acid and water7 and Wang et al. for the solubility of phthalic acid in the mixture of acetic acid and water.6 Solubility of AA in Acetic Acid + Cyclohexane Mixtures. The measured solubilities of AA in acetic acid + cylcohexane are summarized in Table 2, where w2 was defined as the mass fraction of acetic acid in binary acetic acid + cyclohexane solvent mixtures. From Table 2, it can be seen that, within the temperature range of the measurements, the solubility of AA in all of the mixtures shows an increasing trend as the temperature increases. The solubility of AA in pure acetic acid shows the highest, and it decreases with an increasing concentration of cyclohexane in the mixed acetic acid + cyclohexane system at constant temperature. 3.2. Correlation of Experimental Data. Generally, solid− liquid equilibrium can be approximated by eq 1 that involves such properties of pure solute as enthalpy of fusion, melting point, and so forth.6−8
Figure 1. Determined solubilities and literature data of AA in acetic acid (2): ▲, experimental data (w2 = 1.0); ∗, literature data (w2 = 1.0) from Fan;1,4 −, solubility curve calculated from NRTL model eqs 1 to 4.
Figure 2. Determined solubilities and literature data of AA in water (2): ▲, experimental data (w2 = 1.0); ∗, literature data (w2 = 1.0) from Mao;3 −, solubility curve calculated from NRTL model eqs 1 to 4.
2.3. Concentration Determination Method. The concentration of AA in the solution was determined using a Shimadzu15C high-performance liquid chromatograph (HPLC) with an Inertsil ODS-3 (250 mm × 4.6 mm, 5 μm) chromatographic column. The column temperature is set to 40 °C. The mobile
ln(γ1x1) = −
ΔfusH ⎛ 1 1 ⎞ ΔtrsH ⎛ 1 1 ⎞ ⎜ − ⎟− ⎜ − ⎟ R ⎝T Tfus ⎠ R ⎝T Ttrs ⎠ (1)
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Table 1. Solubilities S of AA (cr, 1) in Acetic Acid (2) + Water (3) Solvent Mixtures at Temperatures (303.2 to 333.2) K and Pressure p = 101.3 kPaa T/K
S/(g·(100g)−1)
303.2 313.2 323.2 333.2
5.80 8.41 11.89 17.10
303.2 313.2 323.2 333.2
6.58 9.48 13.29 19.48
303.2 313.2 323.2 333.2
7.06 10.64 15.09 21.28
303.2 313.2 323.2 333.2
7.95 11.76 16.71 23.11
303.2 313.2 323.2 333.2
8.19 12.10 17.46 24.00
303.2 313.2 323.2 333.2
8.62 12.49 18.70 24.86
Sc/(g·(100g)−1)
RD/%
w2 = 1.0 5.45 8.18 12.06 17.47
−6.10 −2.72 1.42 2.13
6.16 9.31 13.80 20.09
−6.47 −1.76 3.79 3.13
6.80 10.28 15.23 22.22
−3.67 −3.39 0.88 4.42
7.34 11.05 16.33 23.82
−7.61 −6.02 −2.26 3.05
7.78 11.62 17.06 24.81
−4.94 −3.93 −2.29 3.35
8.06 11.91 17.40 25.23
−6.57 −4.68 −6.93 1.48
8.15 11.81 17.06 24.79
0.55 0.80 −2.80 1.48
7.90 11.13 16.01 23.56
13.08 5.25 −2.97 −0.09
7.02 9.47 13.61 20.88
21.55 8.44 −3.10 −1.53
4.90 6.53 10.41 17.75
11.55 −7.86 −13.19 −4.78
3.08 5.10 7.52 15.46
−5.19 −4.22 −5.76 12.04
w2 = 0.9
Figure 3. Solubilities of AA (1) in acetic acid (2) + water (3) mixtures: □, T = 303.15 K; ●, T = 313.15 K; ∗, T = 323.15 K; ▲, T = 333.15 K; −, solubility curve calculated from NRTL model eqs 1 to 4.
w2 = 0.8
occur, and the last term in eq 1 can be neglected. Therefore, eq 1 becomes
w2 = 0.7
ln(γ1x1) = −
w2 = 0.5
3
ln γi =
w2 = 0.4 8.10 11.72 17.55 24.43
303.2 313.2 323.2 333.2
6.99 10.58 16.50 23.58
303.2 313.2 323.2 333.2
4.39 7.09 11.99 18.64
303.2 313.2 323.2 333.2
3.25 5.33 7.98 13.80
a
+
Gij = exp( −ηijτij), τij ≠ τji ,
∑ j=1
3 ⎛ ∑ xτ G ⎞ ⎜τij − k = 1 k kj kj ⎟ 3 3 ∑k = 1 Gkjxk ⎜⎝ ∑k = 1 Gkjxk ⎟⎠
xjGij
τij = aij +
bij T
,
ηij = ηji ,
τii = 0
(4)
To calculate the solubility, the fusion temperature (Tfus) and molar enthalpy of fusion of solute (ΔfusH) are required. Tfus and ΔfusH used in the calculation are 426.15 K and 34 850 J·mol−1, which can be obtained from the literature.9 Using model eqs 1 to 4, the solubilities were correlated, and the model parameters were optimized. In the optimization process, as Renon and Prausnitz proposed, ηij was chosen as 0.3.5 Table 3 shows the optimized NRTL model parameters in eq 4. The optimum algorithm applied in the parameter estimation program was the Nelder−Mead Simplex approach,10 which had been introduced in detail in the work of Wang et al.6 Function fminsearch in the optimization toolbox of Matlab (Mathwork, MA) uses the Nelder−Mead Simplex approach and can be employed for the minimization of the objective function, which is the averaged relative deviation (ARD) between the experimental and the calculated solubility defined by
w2 = 0.1
w2 = 0.0
3
∑k = 1 Gkixk
3
In eq 3, τij and Gij are NRTL model parameters that need to be experimentally determined by
w2 = 0.2 5.78 8.73 14.05 21.21
∑ j = 1 τjiGjixj
(3)
w2 = 0.3
303.2 313.2 323.2 333.2
(2)
In eqs 1 and 2, ΔfusH is the molar fusion enthalpy of solute, Tfus is the fusion temperature, ΔtrsH is the molar enthalpy of solid−solid phase transition, Ttrs is the transition temperature, T is the absolute temperature, R is the universal gas constant, γ1 is the activity coefficient of solute, and x1 is the real mole fraction of solute in solution. Because the activity coefficient γ1 depends on the solution composition and temperature, eq 2 must be solved iteratively. For the definition of the activity coefficient, the NRTL activity coefficient model was used as
w2 = 0.6
303.2 313.2 323.2 333.2
ΔfusH ⎛ 1 1 ⎞ ⎟ ⎜ − R ⎝T Tfus ⎠
Standard uncertainties u are u(T) = 0.1 K, ur(p) = 0.05, ur(S) = 0.04.
ARD =
For the system of AA + acetic acid + water and AA + acetic acid + cyclohexane, the solid−solid phase transition does not 940
1 n
n
∑ abs(RDi), i=1
RDi =
Sci − Si · 100 Si
(6)
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Table 2. Solubilities S of AA (cr, 1) in Acetic Acid (2) + Cyclohexane (3) Solvent Mixtures at Temperatures (303.2 to 343.2) K and Pressure p = 101.3 kPaa T/K
S/(g·(100g)−1)
Sc/(g·(100g)−1)
T/K
RD/%
S/(g·(100g)−1)
w2 = 1.0 303. 313. 323. 333. 343.
2 2 2 2 2
5.80 8.41 11.89 17.10 23.01
303. 313. 323. 333. 343.
2 2 2 2 2
5.38 7.40 10.96 14.92 20.11
303. 313. 323. 333. 343.
2 2 2 2 2
4.86 6.98 9.80 13.29 18.09
303. 313. 323. 333. 343.
2 2 2 2 2
4.03 5.60 8.28 11.49 15.36
303. 313. 323. 333. 343.
2 2 2 2 2
3.23 4.83 6.61 9.45 12.91
RD/%
w2 = 0.5 5.81 8.36 11.77 16.25 22.17
0.14 −0.67 −1.01 −5.00 −3.64
303. 313. 323. 333. 343.
2 2 2 2 2
2.36 3.64 5.14 7.26 9.96
5.23 7.56 10.64 14.76 20.18
−2.79 2.05 −2.92 −1.05 0.33
303. 313. 323. 333. 343.
2 2 2 2 2
1.84 2.62 3.79 5.25 7.27
4.62 6.67 9.44 13.12 17.95
−4.94 −4.39 −3.67 −1.28 −0.79
303. 313. 323. 333. 343.
2 2 2 2 2
1.05 1.81 2.34 3.36 4.74
3.97 5.76 8.16 11.36 15.59
−1.68 2.86 −1.44 −1.09 1.45
303. 313. 323. 333. 343.
2 2 2 2 2
0.57 0.95 1.18 1.86 2.60
3.27 4.76 6.79 9.48 13.03
1.29 −1.31 2.71 0.23 0.94
303. 313. 323. 333. 343.
2 2 2 2 2
0.23 0.41 0.53 0.75 0.95
w2 = 0.9
2.55 3.73 5.33 7.48 10.32
8.21 2.50 3.81 3.02 3.66
1.82 2.67 3.84 5.42 7.51
−1.15 2.04 1.33 3.25 3.29
1.13 1.67 2.41 3.42 4.77
7.11 −7.82 3.13 1.87 0.75
0.56 0.84 1.22 1.74 2.43
−2.08 −11.48 2.89 −6.77 −6.67
0.25 0.37 0.52 0.74 1.02
8.95 −10.41 −1.97 −1.16 7.54
w2 = 0.4
w2 = 0.8
w2 = 0.3
w2 = 0.7
w2 = 0.2
w2 = 0.6
a
Sc/(g·(100g)−1)
w2 = 0.1
Standard uncertainties u are u(T) = 0.1 K, ur(p) = 0.05, ur(S) = 0.04.
Table 3. NRTL Model Parameters in eq 4 for AA + HOAc + Water and AA + HOAc + Cyclohexane i
j
aij
aji
bij
bji
ηij = ηji
AA AA AA HOAc HOAc
HOAc water cyclohexane water cyclohexane
−1.1210·102 −6.0867 −10.801 −1.9763 −12.149 3.91
2.5976 −41.006 1.4474 3.3293 −24.418
2.0094·103 2.0349·103 −8.9421·102 6.0989·102 1.3236·102
−9.4977·102 1.9303·104 −8.6436·103 −7.2389·102 7.4150·105
0.3
ARD/%
where Sci is the solubility calculated by eqs 1 to 4, and n is the number of experimental points. The model parameters and the averaged relative deviation (ARD) between the experimental and the correlated values of AA are also given in Table 3. These results show that the NRTL activity coefficient model equations can be used to correlate the solubility of AA. The experimental solubility and correlation equations in this work can be used as essential data and models for the synthetic and purification process of AA.
■
Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) Fan, L. H. Measurement and Correlation for Solubility of Adipic Acid in Several Solvents. Chin. J . Chem. Eng. 2007, 15 (1), 110−114. (2) Wynn, N. P. Separate Organics by Melt Crystallization. Chem. Eng. Prog. 1992, 88, 52−60. (3) Mao, Z. B.; Sun, X. B.; Luan, X. H. Measurement and Correlation of Solubilities of Adipic Acid in Different Solvents. Chin. J. Chem. Eng. 2009, 17 (3), 473−477. (4) Fan, L. H. Study on Crystallization Thermodynamics of Adipic Acid. Petrochem. Technol. 2006, 35 (3), 245−249. (5) Renon, H.; Prausnitz, J. M. Estimation of parameters for NRTL equation for excess Gibbs energy of strongly non-ideal liquid mixtures. Ind. Eng. Chem. Process. Des. Dev. 1969, 8, 413−419.
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Funding
The project was granted financial support from Key S&T Special Project of Zhejiang Province (2012C13007-2) and Growth of Young Teachers Program in Hunan University. 941
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(6) Wang, Q. B.; Hou, L. X.; Cheng, Y. W.; Li, X. Solubilities of Benzoic Acid and Phthalic Acid in Acetic Acid + Water Solvent Mixtures. J. Chem. Eng. Data 2007, 52, 936−940. (7) Chen, M. M.; Ma, P. S. Solid-Liquid Equilibria of Several System Containing Acetic Acid. J. Chem. Eng. Data 2004, 49, 756−759. (8) Ma, P. S.; Xia, Q. Determination and Correlation for Solubility of Aromatic Acids in Solvents. Chin. J. Chem. Eng. 2001, 9, 39−44. (9) Dean, J. A. Lange’s Handbook of Chemistry, 15th ed.; McGrawHill, Inc.: New York, 1998. (10) Nelder, J. A.; Mead, R. A. Simplex Method for Function Minimization. Comput. J. 1965, 7, 308−313.
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