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Measurement and correlation for the solubility of 2-chloro-5-nitrotoluene-4-sulfonic acid and 2-amino-5-chloro-4-methylbenzenesulfonic acid in aqueous sulfuric acid solutions
Fluid Phase Equilibria 406 (2015) 142–146
Contents lists available at ScienceDirect
Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid
Measurement and correlation for the solubility of 2-chloro-5-nitrotoluene-4-sulfonic acid and 2-amino-5-chloro-4-methylbenzenesulfonic acid in aqueous sulfuric acid solutions Hai-Ming Li, Shi-Liang Liu, Guang Han, Yuan-Xiao Li, Feng-Bao Zhang, Guo-Liang Zhang, Qing Xia ∗ School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China
a r t i c l e
i n f o
Article history: Received 29 May 2015 Received in revised form 21 July 2015 Accepted 22 July 2015 Available online 26 July 2015 Keywords: 2-chloro-5-nitrotoluene-4-sulfonic acid 2-amino-5-chloro-4methylbenzenesulfonic acid Solubility Sulfuric acid Modified Apelblat model
a b s t r a c t The solubility of 2-chloro-5-nitrotoluene-4-sulfonic acid (CNT acid) and 2-amino-5-chloro-4methylbenzenesulfonic acid (CLT acid) in aqueous sulfuric acid solutions was measured over the temperatures range from 276.91 to 345.42 K at atmospheric pressure by a dynamic method. The solubility of CNT acid and CLT acid in aqueous sulfuric acid solutions increased with temperature. In the experiment, the highest solubility of CNT acid and CLT acid was both obtained in pure water, and the lowest solubility was exhibited at solute-free mass fraction of aqueous sulfuric acid solutions w30 = 0.50 and w30 = 0.20, respectively. The experimental data were correlated with the modified Apelblat model, and the root-mean-square deviations ranged from 0.76 to 1.28 K. According to the solubility data, the improvement of separation process of CNT acid and CLT acid was recommended. © 2015 Elsevier B.V. All rights reserved.
1. Introduction 2-amino-5-chloro-4-methylbenzenesulfonic acid (C7 H8 ClNO3 S, CLT acid, CAS No. 88-53-9) is a significant intermediate in the production of red organic pigments, which is widely used in the synthesis such as paint, rubber, color inks, et al. [1–5]. CLT acid is indispensable intermediate in the high-grade red organic pigments. In recent years, the demand for CLT acid is rising rapidly. And now China has become the largest producer [6]. The synthetic routes of CLT acid vary from the difference of the raw materials [7–12]. Toluene sulfonation process is widely used industrially in China [13], which is illustrated in Fig. 1 [14]. Firstly, toluene is sulfonated by excess amount of concentrated sulfuric acid at 378.15 to 383.15 K. Secondly, chlorine gas is introduced to the residue of sulfonation reaction and reacts with p-toluenesulfuric acid at 323.15 K. Thirdly, nitration reaction is processed by dropwise adding concentrated nitric acid at 303.15 K, the produced 2-chloro-5-nitrotoluene-4-sulfonic acid
∗ Corresponding author. Tel.: +86 22 27400292; fax: +86 22 27408778. E-mail address: [email protected] (Q. Xia). http://dx.doi.org/10.1016/j.fluid.2015.07.041 0378-3812/© 2015 Elsevier B.V. All rights reserved.
(C7 H6 ClNO5 S, CNT acid, CAS NO. 6973-13-3) is salted out by saturated brine. Thus, large amount of saline sulfuric acid aqueous solution is come out as process wastewater and is difficult to be treated. Finally, CNT acid solution, which is pretreated by introducing alkaline solution to modify the pH value ranging between 6 and 7, is reduced by iron powder, and CLT acid can be obtained after neutralization, filtration to remove iron sludge and acidification by hydrochloric acid or sulfuric acid [14]. Although the above process has been a mature method of CLT acid production and can optimize the cost, it is mainly restricted by bad performance of separation processes and environmental impacts. Therefore, further improvement in the process is needed indeed. In this work, the solubility of CNT acid and CLT acid in aqueous sulfuric acid solutions has been measured by a dynamic method over temperatures range from 276.91 to 345.42 K and concentrations of aqueous sulfuric acid solutions range from 0.00 to 0.80 (solute-free mass fraction) at atmospheric pressure. These data are useful to improve the separation processes of CNT acid and CLT acid, and not available in the published literature. The modified Apelblat model, which has been applied to correlate the solubility data in many previous jobs [15–17], was used to correlate the obtained
H.-M. Li et al. / Fluid Phase Equilibria 406 (2015) 142–146
143
Fig. 1. The synthetic route of CLT acid.
data. The separation process improvement was discussed and the optimized process parameters were suggested.
3. Results and discussion 3.1. Experimental solubility data of CNT acid and CLT acid
2. Experimental 2.1. Experimental materials CNT acid was purified by recrystallizing twice from deionized water and dried to constant weight in vacuum at 338.15 K for 48 hours. Their purities were measured by HPLC (Hitachi L-7100, Japan). The CNT acid and CLT acid crystals of prior to dissolution and dissolution equilibrium were analyzed by X-ray diffraction (XRD) to ensure that the crystals has not changed in the process of dissolution. The exact mass fraction of concentrated sulfuric acid was calibrated with sodium hydroxide and phenolphthalein indicator before it was used for preparing a certain concentration aqueous sulfuric acid solution. The pH value of each aqueous sulfuric acid solution was measured by a pH meter before the sample was dissolved. Other materials were purchased and used without further purification. The detailed information of the materials used in the experiment is listed in Table 1. 2.2. Experimental apparatus and procedure Predetermined solvent and solute were weighed using an electronic analytical balance (Gibertini, Crystal 200, Italy, accuracy of ± 0.0001 g) and transferred into a jacketed glass vessel. The mixtures were stirred continuously and heated slowly with a heating rate less than 0.08 K h−1 . A refrigerated/heating circulator (Julabo FP45-HE, Germany, temperature stability ± 0.01 K) was used to control the temperature of the solution by circulating water. And the temperature was measured by a platinum resistance thermometer (PT-100, calibrated with an accuracy of ± 0.01 K). The solubility experiment was determined by the dynamic method [18,19] at atmospheric pressure. The laser monitoring system (JS2-1009016, Beijing, China) was used to observe the course of dissolution and determine the solid-liquid equilibrium (SLE) temperature. In the experiment, the degree of dissolution of solute can be represented by the intensity of laser beam. When the last crystal disappeared, the intensity of the laser beam reached a maximum value and kept steady, the solubility equilibrium was considered to be reached. The temperature was taken as the SLE temperature. In addition, the uncertainties of the measurement are reported in Tables 2 and 3.
The solubility data of CNT acid and CLT acid in aqueous sulfuric acid solutions are listed in Tables 2 and 3, in which Texp is the measured absolute temperature, m1 and m2 are molality solubility of CNT acid and CLT acid in aqueous sulfuric acid solutions, respectively, w30 is the solute-free mass fraction of sulfuric acid in the mixture solvents, and pH is the starting value of aqueous sulfuric acid solutions. Figs. 2 and 3 (0.40≤ w30 ≤0.80) present the solubility curves of CNT acid at different values of w30 . It is shown that the solubility of CNT acid in aqueous sulfuric acid solutions enhances with temperature. As shown in Fig. 3, when temperature is less than 310 K, the differences of the solubility is relatively small between w30 = 0.40 and w30 = 0.80, and the analogous conclusions can be reached when w30 = 0.50 and w30 = 0.60. The solubility of CNT acid decreases firstly and increases subsequently with w30 at constant temperature. Especially within w30 = 0.50 to 0.60, the solubility of CNT acid is significantly lower than that in other concentrations. The highest and the lowest solubility of CNT acid in aqueous sulfuric acid solutions are obtained in pure water (w30 = 0.00) and w30 = 0.50 aqueous sulfuric acid solutions, respectively. In order to catch the suitable pH value of acidification after reduction reaction, the solubility of CLT acid in different pH water was determined and presented in Fig. 4. As it can be seen from Fig. 4, the solubility of CLT acid increases with the enhancement of temperature. The solubility of CLT acid declines with w30 in solvent mixtures. When temperature is less than 310 K, the distinction of the solubility is relatively small in pH = 0.51 to 5.09. And the solubility of CLT acid at (w30 = 0.20) is a little lower than that at (pH = 0.51).
Table 1 Source and mass fraction purity of the materials used in the experiment. Materials
Mass fraction purity
Sources
CNT acid CLT acid Concentrated Sulfuric acid Deionized water
0.995 0.992 0.968
Prepared in laboratory TCI Reagent Co. Ltd, Shanghai, China Yuanli Chemical Reagents Co. Ltd. Tianjin, China Nankai Chemical Reagents Co. Tianjin, China
CNT acid and CLT acid are the abbreviations of 2-chloro-5-nitrotoluene-4-sulfonic acid and 2-amino-5-chloro-4-methylbenzenesulfonic acid, respectively.
Fig. 2. Plot of molality solubility of CNT acid (m1 ) vs. temperature (T) in different solute-free mass fraction of aqueous sulfuric acid solutions (w30 ): () w30 = 0.00; () w30 = 0.20; (䊐) w30 = 0.40; (䊏) w30 = 0.50; () w30 = 0.60; (䊉) w30 = 0.80;–, calculated from the modified Apelblat equation.
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Table 2 The molality solubility data of CNT acid (m1 ) in different solute-free mass fraction of sulfuric acid w30 for the system of {CNT acid (1) + sulfuric acid (3) + water (4)} at temperature Texp and pressure 0.1 MPa. m1 (mol kg−1 )
Texp (K)
m1 (mol kg−1 )
Texp (K)
m1 (mol kg−1 )
Texp (K)
300.85 304.36 309.53 313.97 317.61
13.05 14.98 17.01 19.83 24.14
322.55 327.74 332.17 337.46 342.36
300.70 305.59 310.18 314.87 318.91
5.678 6.708 7.786 8.487 10.13
323.29 328.66 334.57 337.60 342.96
304.97 309.26 313.63 318.93 321.49 325.33
0.3701 0.5851 0.8576 1.306
329.85 334.32 338.28 342.87
302.89 307.46 311.77 316.04 319.36 323.96
1.571 × 10−2 1.839 × 10−2 2.310 × 10−2 2.909 × 10−2 3.286 × 10−2
329.24 332.65 336.63 341.57 344.62
304.87 308.73 312.35 316.02 320.05 323.89 327.77
3.095 × 10−2 3.519 × 10−2 4.088 × 10−2 4.722 × 10−2 5.433 × 10−2
331.25 334.65 338.02 341.51 345.12
305.21 310.37 314.57 318.43 322.26 326.09
0.6527 0.9231 1.438 2.317
330.34 334.77 339.25 343.32
w30
3.343 3.726 4.139 4.737 5.481
278.04 282.37 286.29 291.63 295.86
0.8306 1.044 1.371 1.779 2.246
277.23 280.91 285.87 290.82 295.94
5.037 × 10−3 5.585 × 10−3 6.462 × 10−3 8.281 × 10−3 1.158 × 10−2 1.669 × 10−2
277.28 282.36 286.83 291.29 296.34 300.95
0.3289 × 10−3 0.5849 × 10−3 1.033 × 10−3 1.577 × 10−3 2.137 × 10−3 2.904 × 10−3
277.52 281.45 285.96 290.65 295.35 298.67
0.4352 × 10−3 0.7177 × 10−3 1.250 × 10−3 1.896 × 10−3 2.731 × 10−3 3.835 × 10−3 5.261 × 10−3
277.63 279.85 284.01 288.08 292.55 297.05 301.26
6.413 × 10−3 7.037 × 10−3 7.829 × 10−3 9.542 × 10−3 1.501 × 10−2 2.039 × 10−2
277.31 280.26 284.94 290.44 296.05 300.68
= 0.00 6.265 7.241 8.336 9.827 11.33 w30 = 0.20 2.688 3.177 3.696 4.269 4.798 w30 = 0.40 2.324 × 10−2 4.097 × 10−2 6.258 × 10−2 0.1135 0.1713 0.2524 w30 = 0.50 3.882 × 10−3 4.889 × 10−3 6.128 × 10−3 7.563 × 10−3 9.353 × 10−3 1.165 × 10−2 w30 = 0.60 6.969 × 10−3 9.033 × 10−3 1.148 × 10−2 1.429 × 10−2 1.742 × 10−2 2.205 × 10−2 2.624 × 10−2 w30 = 0.80 2.866 × 10−2 4.845 × 10−2 9.092 × 10−2 0.1763 0.2924 0.4509
Standard uncertainties u are u (Texp ) = ± 0.3 K, u(m) = ± 2 × 10−5 mol kg−1 , u(P) = ± 0.001 MPa.
Fig. 3. Plot of molality solubility of CNT acid (m1 ) vs. temperature (T) in different solute-free mass fraction of aqueous sulfuric acid solutions (w30 ): (䊐) w30 = 0.40 (277.28 K≤T≤309.26 K); (䊏) w30 = 0.50; () w30 = 0.60; (䊉) w30 = 0.80 (277.31 K≤T≤310.37 K);–, calculated from the modified Apelblat equation.
Fig. 4. Plot of molality solubility of CLT acid (m2 ) vs. temperature (T) in different solute-free mass fraction of aqueous sulfuric acid solutions (w30 ): (䊉) w30 = 0.00 (pH = 7); () pH = 5.09; (䊐) pH = 3.71; () pH = 1.38; () pH = 0.51; (䊏) w30 = 0.20 (pH = −0.366);–, calculated from the modified Apelblat equation.
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Table 3 The molality solubility data of CLT acid (m2 ) in different initial pH of sulfuric acid solutions pH value for the system of {CLT acid (2) + sulfuric acid (3) + water (4)} at temperature Texp and pressure 0.1 MPa. m2 × 103 (mol kg−1 )
Texp (K)
m2 × 103 (mol kg−1 )
Texp (K)
m2 × 103 (mol kg−1 )
Texp (K)
295.45 299.15 303.64 306.18 308.99 313.45 316.13
12.22 13.49 14.19 14.82 15.16 15.34
322.15 326.45 329.42 333.15 337.01 341.26
w30
0.3534 0.4051 0.5738 1.004 1.511 2.043 2.495
276.84 279.13 280.17 283.14 286.76 289.75 292.66
0.1198 0.2059 0.3822 0.5165 0.6636 0.8271
276.91 281.06 286.64 290.41 294.53 298.51
0.09413 0.1847 0.2705 0.3948 0.5451 0.7363
277.39 281.46 284.32 288.30 292.93 298.07
0.06334 0.1755 0.2857 0.4102 0.5383
278.09 283.48 288.78 293.63 298.56
0.07669 0.1733 0.2316 0.3075 0.3983 0.5102
279.24 284.36 287.96 292.47 296.65 300.90
0.06751 0.1301 0.1926 0.2239 0.2783 0.3392 0.4051
279.43 283.62 289.16 292.66 296.17 299.15 302.42
= 0.00 (pH = 7) 3.289 4.307 5.775 6.893 8.043 9.257 10.39 pH = 5.09 1.047 1.396 1.921 2.439 3.043 3.941 pH = 3.71 0.9514 1.242 1.733 2.126 2.707 3.328 pH = 1.38 0.7291 0.9941 1.532 1.917 2.407 pH = 0.51 0.6557 0.8234 1.107 1.409 1.775 2.308 w30 = 0.20 (pH = −0.366) 0.4890 0.5845 0.6965 0.8282 0.9714 1.128 1.332
302.86 307.71 312.22 317.49 322.43 327.47
4.878 6.121 7.906 8.755
331.81 336.63 341.34 343.72
302.27 307.05 311.91 316.96 321.86 326.79
3.819 4.576 5.518 6.353
330.72 335.75 341.18 343.97
303.44 307.74 313.07 317.67 322.68
2.893 3.376 4.085 4.912
328.07 333.52 338.49 344.11
305.51 309.93 315.28 319.05 323.32 328.89
2.796 3.246 3.862 4.418
333.73 337.97 342.08 345.42
305.55 308.68 311.34 313.47 316.14 318.65 320.95
1.581 1.864 2.177 2.532 2.911 3.331 3.612
324.38 327.89 330.91 334.15 338.24 342.25 345.25
Standard uncertainties u are u(Texp ) = ± 0.3 K, u(m) = ± 5 × 10−5 mol kg−1 , u(P) = ± 0.001 MPa.
The highest and the lowest solubility of CLT acid in aqueous sulfuric acid solutions are obtained in pure water (w30 = 0.00) and w30 = 0.20 aqueous sulfuric acid solutions, respectively. 3.2. Correlation of experimental data The modified Apelblat equation has been used as an empirical equation in many previously published studies of SLE data in sulfuric acid system [20,21]. Therefore in this study, the modified Apelblat equation was used to correlate the experimental data. The modified Apelblat equation is expressed as follows: ln m = a + b/T + c ln T
() =
N i=1
1/2 ((T
exp
3.3. Application of the experimental data in the improvement of CNT acid and CLT acid separation process
(1)
where m is the molality solubility of CNT acid or CLT acid; T is the calculated equilibrium temperature; a, b and c are the model parameters. The root-mean-square deviation between the experimental equilibrium temperature Texp and the calculated equilibrium temperature T is taken as the objective function which is defined as
where N is the number of experimental data points. The nonlinear minimization function in Matlab is used for minimizing and estimating parameters a, b and c. The three model parameters and for determined systems are listed in Table 4. The root-mean-square deviations range from 0.76 to 1.28 K. The calculated results show good agreement with the experimental data. It is clear that the modified Apelblat model can describe well the solubility for the aqueous sulfuric acid solution systems measured.
2
) − (T )) /(N − 1)
(2)
According to the experiment, the solubility of CNT acid reaches the minimized value when w30 = 0.50. Hence, after the nitration reaction, the sulfuric acid concentration in this solution is around 0.90 mass fraction, which can be diluted to 0.5 to generate the most amount of CNT acid. Thus, in the separation process, salinity wastewater can be avoided, and of course, the treatment and reuse of 0.5 mass fraction aqueous sulfuric acid solutions should be considered. After the reduction reaction, the mixture is aqueous CLTNa solution which sulfuric acid is added to obtain the desired product CLT acid. In order to achieve separation process as much as possible,
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H.-M. Li et al. / Fluid Phase Equilibria 406 (2015) 142–146
Table 4 Parameters of the modified Apelblat model and root-mean-square deviations for CNT acid and CLT acid in binary sulfuric acid (w30 ) + water (1 − w30 ) solvent mixtures (defined by Eqs. (1) and (2)). Solute
Solvent
a
b
c
(K)
CNT acid
w30 = 0.00 w30 = 0.20 w30 = 0.40 w30 = 0.50 w30 = 0.60 w30 = 0.80 w30 = 0.00 (pH = 7) pH = 5.09 pH = 3.71 pH = 1.38 pH = 0.51 w30 = 0.20 (pH = −0.366)
−174.08 128.54 −1466.4 319.79 509.75 −1726.6 1048.6 229.79 445.91 611.29 288.86 235.73
5503.8 −8789.9 59792 −19825 −28773 71290 −52113 −15378 −25119 −33028 −17990 −15751
27.621 −17.237 222.63 −44.296 −72.282 261.57 −153.12 −31.323 −63.534 −87.955 −40.260 −32.299
0.99 0.81 1.26 1.22 0.76 1.19 1.22 1.22 1.23 1.28 1.14 1.06
CLT acid
more acid should be introduced into the solution. However, the present determined data exhibit that solubility differences of CLT acid between w30 = 0.20 and pH = 0.51 and pH = 1.38 aqueous sulfuric acid solutions are tiny. For example, the amount difference dissolved of CLT acid per kilogram solvent between w30 = 0.20 and pH = 1.38 aqueous sulfuric acid solutions is 0.04679 grams. Furthermore, CLT acid will be attached with sulfuric acid whose viscosity is relatively high when its w30 = 0.20, which will confine the purity of CLT acid product. Hence the aqueous sulfuric acid solutions whose pH value is 1 to 2 would like to be recommended for aqueous CLTNa solution acidification and separating CLT acid product. In this way, CNT acid and CLT acid can be separated as much as possible, which can obtain high yield of CLT acid. 4. Conclusions The solubility of CNT acid and CLT acid in different aqueous sulfuric acid solutions at a temperature ranging from 276.91 to 345.42 K have been measured by the dynamic method. The solubility data have been correlated by the modified Apelblat model. The results calculated from the model show good agreement with the experimental data and the root-mean-square deviations range from 0.76 to 1.28 K. The solubility of both systems increases with temperature. The highest solubility of CNT acid and CLT acid is both obtained in pure water, and the lowest solubility is exhibited at w30 = 0.50 and w30 = 0.20, respectively. The aqueous sulfuric acid
solutions w30 = 0.50 and pH = 1 to 2 are recommended for CNT acid and CLT acid product separation. References [1] S.L. Bekoe, J.W. Bats, M.U. Schmidt, Crystal Struct. Commun. 68 (2012) 45–50. [2] J.M. Nuss, J.H. Platman, M. Nuss. WO 9302145 (1993). [3] U. Nickel, R. Jung, K. Saitmacher, L. Unverdorben, R. Baur, H. Macholdt, C. Wille. US 20030083410 (2003). [4] S.L. Bekoe, S.D. Thoms, J. Bruening, E. Alig, S.J. Vande, A. Jacco, A. Lakatos, C. Glaubitz, M.U. Schmidt, Crystalline Mater. 225 (2010) 382–387. [5] Y. Hirasawa, A. Mochizuki. US 5286287 (1994). [6] X. Zhang, C.Y. Wu, Z.T. Shi, J. China Environ. Sci. 04 (2012) 630–634. [7] I.D. Lee, S.U. Nam, J.S. Lee. KR 2013117316 (2013). [8] X. Zhuang. CN 103420875 (2013). [9] C.G. Sun, B.B. Liu, S.X. Yu, Dyeing Industry 03 (1990) 29–32. [10] Z. Chen, X. Wang, Q. Xu, W. Zhao, W. Qiu, R. Liu, G. Zou. CN 102964278 (2013). [11] R. Jiang, E. He. CN 101906057 (2010). [12] T.Y. Zhang, H.X. Shi, J. Hu, Q.S. Yang, Trans. Tianjin Univ. 16 (2010) 161–166. [13] Y.M. Cui, S.C. Shao, Y.S. Wang, X.S. Li, Chem. Reaction Eng. Technol. 17 (2001) 94–96. [14] L.L. Zhang, M.F. Zhao, Chem. Intermediate 07 (2004) 20–24. [15] A. Apelblat, E. Manzurola, J. Chem. Thermodyn. 29 (1997) 1527–1533. [16] A. Apelblat, E. Manzurola, J. Chem. Thermodyn. 31 (1999) 1347–1357. [17] E. Manzurola, A. Apelblat, J. Chem. Thermodyn. 34 (2002) 1127–1136. [18] T. Liu, W. Zou, W. Zhao, F.B. Zhang, G.L. Zhang, Q. Xia, Fluid Phase Equilib. 374 (2014) 102–107. [19] Y.H. Hu, X. Chen, W.G. Yang, J. Guan, X.L. Zhao, Fluid Phase Equilib. 288 (2010), 83-86.6. [20] H.K. Zhao, F. Zhang, J. Chem. Eng. Data 55 (2010) 3955–3957. [21] C.Y. Song, H. Wang, H. Ding, J.H. Zhao, J.S. Wang, L.C. Wang, J. Chem. Eng. Data 55 (2010) 2495–2497.
Contents lists available at ScienceDirect
Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid
Measurement and correlation for the solubility of 2-chloro-5-nitrotoluene-4-sulfonic acid and 2-amino-5-chloro-4-methylbenzenesulfonic acid in aqueous sulfuric acid solutions Hai-Ming Li, Shi-Liang Liu, Guang Han, Yuan-Xiao Li, Feng-Bao Zhang, Guo-Liang Zhang, Qing Xia ∗ School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China
a r t i c l e
i n f o
Article history: Received 29 May 2015 Received in revised form 21 July 2015 Accepted 22 July 2015 Available online 26 July 2015 Keywords: 2-chloro-5-nitrotoluene-4-sulfonic acid 2-amino-5-chloro-4methylbenzenesulfonic acid Solubility Sulfuric acid Modified Apelblat model
a b s t r a c t The solubility of 2-chloro-5-nitrotoluene-4-sulfonic acid (CNT acid) and 2-amino-5-chloro-4methylbenzenesulfonic acid (CLT acid) in aqueous sulfuric acid solutions was measured over the temperatures range from 276.91 to 345.42 K at atmospheric pressure by a dynamic method. The solubility of CNT acid and CLT acid in aqueous sulfuric acid solutions increased with temperature. In the experiment, the highest solubility of CNT acid and CLT acid was both obtained in pure water, and the lowest solubility was exhibited at solute-free mass fraction of aqueous sulfuric acid solutions w30 = 0.50 and w30 = 0.20, respectively. The experimental data were correlated with the modified Apelblat model, and the root-mean-square deviations ranged from 0.76 to 1.28 K. According to the solubility data, the improvement of separation process of CNT acid and CLT acid was recommended. © 2015 Elsevier B.V. All rights reserved.
1. Introduction 2-amino-5-chloro-4-methylbenzenesulfonic acid (C7 H8 ClNO3 S, CLT acid, CAS No. 88-53-9) is a significant intermediate in the production of red organic pigments, which is widely used in the synthesis such as paint, rubber, color inks, et al. [1–5]. CLT acid is indispensable intermediate in the high-grade red organic pigments. In recent years, the demand for CLT acid is rising rapidly. And now China has become the largest producer [6]. The synthetic routes of CLT acid vary from the difference of the raw materials [7–12]. Toluene sulfonation process is widely used industrially in China [13], which is illustrated in Fig. 1 [14]. Firstly, toluene is sulfonated by excess amount of concentrated sulfuric acid at 378.15 to 383.15 K. Secondly, chlorine gas is introduced to the residue of sulfonation reaction and reacts with p-toluenesulfuric acid at 323.15 K. Thirdly, nitration reaction is processed by dropwise adding concentrated nitric acid at 303.15 K, the produced 2-chloro-5-nitrotoluene-4-sulfonic acid
∗ Corresponding author. Tel.: +86 22 27400292; fax: +86 22 27408778. E-mail address: [email protected] (Q. Xia). http://dx.doi.org/10.1016/j.fluid.2015.07.041 0378-3812/© 2015 Elsevier B.V. All rights reserved.
(C7 H6 ClNO5 S, CNT acid, CAS NO. 6973-13-3) is salted out by saturated brine. Thus, large amount of saline sulfuric acid aqueous solution is come out as process wastewater and is difficult to be treated. Finally, CNT acid solution, which is pretreated by introducing alkaline solution to modify the pH value ranging between 6 and 7, is reduced by iron powder, and CLT acid can be obtained after neutralization, filtration to remove iron sludge and acidification by hydrochloric acid or sulfuric acid [14]. Although the above process has been a mature method of CLT acid production and can optimize the cost, it is mainly restricted by bad performance of separation processes and environmental impacts. Therefore, further improvement in the process is needed indeed. In this work, the solubility of CNT acid and CLT acid in aqueous sulfuric acid solutions has been measured by a dynamic method over temperatures range from 276.91 to 345.42 K and concentrations of aqueous sulfuric acid solutions range from 0.00 to 0.80 (solute-free mass fraction) at atmospheric pressure. These data are useful to improve the separation processes of CNT acid and CLT acid, and not available in the published literature. The modified Apelblat model, which has been applied to correlate the solubility data in many previous jobs [15–17], was used to correlate the obtained
H.-M. Li et al. / Fluid Phase Equilibria 406 (2015) 142–146
143
Fig. 1. The synthetic route of CLT acid.
data. The separation process improvement was discussed and the optimized process parameters were suggested.
3. Results and discussion 3.1. Experimental solubility data of CNT acid and CLT acid
2. Experimental 2.1. Experimental materials CNT acid was purified by recrystallizing twice from deionized water and dried to constant weight in vacuum at 338.15 K for 48 hours. Their purities were measured by HPLC (Hitachi L-7100, Japan). The CNT acid and CLT acid crystals of prior to dissolution and dissolution equilibrium were analyzed by X-ray diffraction (XRD) to ensure that the crystals has not changed in the process of dissolution. The exact mass fraction of concentrated sulfuric acid was calibrated with sodium hydroxide and phenolphthalein indicator before it was used for preparing a certain concentration aqueous sulfuric acid solution. The pH value of each aqueous sulfuric acid solution was measured by a pH meter before the sample was dissolved. Other materials were purchased and used without further purification. The detailed information of the materials used in the experiment is listed in Table 1. 2.2. Experimental apparatus and procedure Predetermined solvent and solute were weighed using an electronic analytical balance (Gibertini, Crystal 200, Italy, accuracy of ± 0.0001 g) and transferred into a jacketed glass vessel. The mixtures were stirred continuously and heated slowly with a heating rate less than 0.08 K h−1 . A refrigerated/heating circulator (Julabo FP45-HE, Germany, temperature stability ± 0.01 K) was used to control the temperature of the solution by circulating water. And the temperature was measured by a platinum resistance thermometer (PT-100, calibrated with an accuracy of ± 0.01 K). The solubility experiment was determined by the dynamic method [18,19] at atmospheric pressure. The laser monitoring system (JS2-1009016, Beijing, China) was used to observe the course of dissolution and determine the solid-liquid equilibrium (SLE) temperature. In the experiment, the degree of dissolution of solute can be represented by the intensity of laser beam. When the last crystal disappeared, the intensity of the laser beam reached a maximum value and kept steady, the solubility equilibrium was considered to be reached. The temperature was taken as the SLE temperature. In addition, the uncertainties of the measurement are reported in Tables 2 and 3.
The solubility data of CNT acid and CLT acid in aqueous sulfuric acid solutions are listed in Tables 2 and 3, in which Texp is the measured absolute temperature, m1 and m2 are molality solubility of CNT acid and CLT acid in aqueous sulfuric acid solutions, respectively, w30 is the solute-free mass fraction of sulfuric acid in the mixture solvents, and pH is the starting value of aqueous sulfuric acid solutions. Figs. 2 and 3 (0.40≤ w30 ≤0.80) present the solubility curves of CNT acid at different values of w30 . It is shown that the solubility of CNT acid in aqueous sulfuric acid solutions enhances with temperature. As shown in Fig. 3, when temperature is less than 310 K, the differences of the solubility is relatively small between w30 = 0.40 and w30 = 0.80, and the analogous conclusions can be reached when w30 = 0.50 and w30 = 0.60. The solubility of CNT acid decreases firstly and increases subsequently with w30 at constant temperature. Especially within w30 = 0.50 to 0.60, the solubility of CNT acid is significantly lower than that in other concentrations. The highest and the lowest solubility of CNT acid in aqueous sulfuric acid solutions are obtained in pure water (w30 = 0.00) and w30 = 0.50 aqueous sulfuric acid solutions, respectively. In order to catch the suitable pH value of acidification after reduction reaction, the solubility of CLT acid in different pH water was determined and presented in Fig. 4. As it can be seen from Fig. 4, the solubility of CLT acid increases with the enhancement of temperature. The solubility of CLT acid declines with w30 in solvent mixtures. When temperature is less than 310 K, the distinction of the solubility is relatively small in pH = 0.51 to 5.09. And the solubility of CLT acid at (w30 = 0.20) is a little lower than that at (pH = 0.51).
Table 1 Source and mass fraction purity of the materials used in the experiment. Materials
Mass fraction purity
Sources
CNT acid CLT acid Concentrated Sulfuric acid Deionized water
0.995 0.992 0.968
Prepared in laboratory TCI Reagent Co. Ltd, Shanghai, China Yuanli Chemical Reagents Co. Ltd. Tianjin, China Nankai Chemical Reagents Co. Tianjin, China
CNT acid and CLT acid are the abbreviations of 2-chloro-5-nitrotoluene-4-sulfonic acid and 2-amino-5-chloro-4-methylbenzenesulfonic acid, respectively.
Fig. 2. Plot of molality solubility of CNT acid (m1 ) vs. temperature (T) in different solute-free mass fraction of aqueous sulfuric acid solutions (w30 ): () w30 = 0.00; () w30 = 0.20; (䊐) w30 = 0.40; (䊏) w30 = 0.50; () w30 = 0.60; (䊉) w30 = 0.80;–, calculated from the modified Apelblat equation.
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Table 2 The molality solubility data of CNT acid (m1 ) in different solute-free mass fraction of sulfuric acid w30 for the system of {CNT acid (1) + sulfuric acid (3) + water (4)} at temperature Texp and pressure 0.1 MPa. m1 (mol kg−1 )
Texp (K)
m1 (mol kg−1 )
Texp (K)
m1 (mol kg−1 )
Texp (K)
300.85 304.36 309.53 313.97 317.61
13.05 14.98 17.01 19.83 24.14
322.55 327.74 332.17 337.46 342.36
300.70 305.59 310.18 314.87 318.91
5.678 6.708 7.786 8.487 10.13
323.29 328.66 334.57 337.60 342.96
304.97 309.26 313.63 318.93 321.49 325.33
0.3701 0.5851 0.8576 1.306
329.85 334.32 338.28 342.87
302.89 307.46 311.77 316.04 319.36 323.96
1.571 × 10−2 1.839 × 10−2 2.310 × 10−2 2.909 × 10−2 3.286 × 10−2
329.24 332.65 336.63 341.57 344.62
304.87 308.73 312.35 316.02 320.05 323.89 327.77
3.095 × 10−2 3.519 × 10−2 4.088 × 10−2 4.722 × 10−2 5.433 × 10−2
331.25 334.65 338.02 341.51 345.12
305.21 310.37 314.57 318.43 322.26 326.09
0.6527 0.9231 1.438 2.317
330.34 334.77 339.25 343.32
w30
3.343 3.726 4.139 4.737 5.481
278.04 282.37 286.29 291.63 295.86
0.8306 1.044 1.371 1.779 2.246
277.23 280.91 285.87 290.82 295.94
5.037 × 10−3 5.585 × 10−3 6.462 × 10−3 8.281 × 10−3 1.158 × 10−2 1.669 × 10−2
277.28 282.36 286.83 291.29 296.34 300.95
0.3289 × 10−3 0.5849 × 10−3 1.033 × 10−3 1.577 × 10−3 2.137 × 10−3 2.904 × 10−3
277.52 281.45 285.96 290.65 295.35 298.67
0.4352 × 10−3 0.7177 × 10−3 1.250 × 10−3 1.896 × 10−3 2.731 × 10−3 3.835 × 10−3 5.261 × 10−3
277.63 279.85 284.01 288.08 292.55 297.05 301.26
6.413 × 10−3 7.037 × 10−3 7.829 × 10−3 9.542 × 10−3 1.501 × 10−2 2.039 × 10−2
277.31 280.26 284.94 290.44 296.05 300.68
= 0.00 6.265 7.241 8.336 9.827 11.33 w30 = 0.20 2.688 3.177 3.696 4.269 4.798 w30 = 0.40 2.324 × 10−2 4.097 × 10−2 6.258 × 10−2 0.1135 0.1713 0.2524 w30 = 0.50 3.882 × 10−3 4.889 × 10−3 6.128 × 10−3 7.563 × 10−3 9.353 × 10−3 1.165 × 10−2 w30 = 0.60 6.969 × 10−3 9.033 × 10−3 1.148 × 10−2 1.429 × 10−2 1.742 × 10−2 2.205 × 10−2 2.624 × 10−2 w30 = 0.80 2.866 × 10−2 4.845 × 10−2 9.092 × 10−2 0.1763 0.2924 0.4509
Standard uncertainties u are u (Texp ) = ± 0.3 K, u(m) = ± 2 × 10−5 mol kg−1 , u(P) = ± 0.001 MPa.
Fig. 3. Plot of molality solubility of CNT acid (m1 ) vs. temperature (T) in different solute-free mass fraction of aqueous sulfuric acid solutions (w30 ): (䊐) w30 = 0.40 (277.28 K≤T≤309.26 K); (䊏) w30 = 0.50; () w30 = 0.60; (䊉) w30 = 0.80 (277.31 K≤T≤310.37 K);–, calculated from the modified Apelblat equation.
Fig. 4. Plot of molality solubility of CLT acid (m2 ) vs. temperature (T) in different solute-free mass fraction of aqueous sulfuric acid solutions (w30 ): (䊉) w30 = 0.00 (pH = 7); () pH = 5.09; (䊐) pH = 3.71; () pH = 1.38; () pH = 0.51; (䊏) w30 = 0.20 (pH = −0.366);–, calculated from the modified Apelblat equation.
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Table 3 The molality solubility data of CLT acid (m2 ) in different initial pH of sulfuric acid solutions pH value for the system of {CLT acid (2) + sulfuric acid (3) + water (4)} at temperature Texp and pressure 0.1 MPa. m2 × 103 (mol kg−1 )
Texp (K)
m2 × 103 (mol kg−1 )
Texp (K)
m2 × 103 (mol kg−1 )
Texp (K)
295.45 299.15 303.64 306.18 308.99 313.45 316.13
12.22 13.49 14.19 14.82 15.16 15.34
322.15 326.45 329.42 333.15 337.01 341.26
w30
0.3534 0.4051 0.5738 1.004 1.511 2.043 2.495
276.84 279.13 280.17 283.14 286.76 289.75 292.66
0.1198 0.2059 0.3822 0.5165 0.6636 0.8271
276.91 281.06 286.64 290.41 294.53 298.51
0.09413 0.1847 0.2705 0.3948 0.5451 0.7363
277.39 281.46 284.32 288.30 292.93 298.07
0.06334 0.1755 0.2857 0.4102 0.5383
278.09 283.48 288.78 293.63 298.56
0.07669 0.1733 0.2316 0.3075 0.3983 0.5102
279.24 284.36 287.96 292.47 296.65 300.90
0.06751 0.1301 0.1926 0.2239 0.2783 0.3392 0.4051
279.43 283.62 289.16 292.66 296.17 299.15 302.42
= 0.00 (pH = 7) 3.289 4.307 5.775 6.893 8.043 9.257 10.39 pH = 5.09 1.047 1.396 1.921 2.439 3.043 3.941 pH = 3.71 0.9514 1.242 1.733 2.126 2.707 3.328 pH = 1.38 0.7291 0.9941 1.532 1.917 2.407 pH = 0.51 0.6557 0.8234 1.107 1.409 1.775 2.308 w30 = 0.20 (pH = −0.366) 0.4890 0.5845 0.6965 0.8282 0.9714 1.128 1.332
302.86 307.71 312.22 317.49 322.43 327.47
4.878 6.121 7.906 8.755
331.81 336.63 341.34 343.72
302.27 307.05 311.91 316.96 321.86 326.79
3.819 4.576 5.518 6.353
330.72 335.75 341.18 343.97
303.44 307.74 313.07 317.67 322.68
2.893 3.376 4.085 4.912
328.07 333.52 338.49 344.11
305.51 309.93 315.28 319.05 323.32 328.89
2.796 3.246 3.862 4.418
333.73 337.97 342.08 345.42
305.55 308.68 311.34 313.47 316.14 318.65 320.95
1.581 1.864 2.177 2.532 2.911 3.331 3.612
324.38 327.89 330.91 334.15 338.24 342.25 345.25
Standard uncertainties u are u(Texp ) = ± 0.3 K, u(m) = ± 5 × 10−5 mol kg−1 , u(P) = ± 0.001 MPa.
The highest and the lowest solubility of CLT acid in aqueous sulfuric acid solutions are obtained in pure water (w30 = 0.00) and w30 = 0.20 aqueous sulfuric acid solutions, respectively. 3.2. Correlation of experimental data The modified Apelblat equation has been used as an empirical equation in many previously published studies of SLE data in sulfuric acid system [20,21]. Therefore in this study, the modified Apelblat equation was used to correlate the experimental data. The modified Apelblat equation is expressed as follows: ln m = a + b/T + c ln T
() =
N i=1
1/2 ((T
exp
3.3. Application of the experimental data in the improvement of CNT acid and CLT acid separation process
(1)
where m is the molality solubility of CNT acid or CLT acid; T is the calculated equilibrium temperature; a, b and c are the model parameters. The root-mean-square deviation between the experimental equilibrium temperature Texp and the calculated equilibrium temperature T is taken as the objective function which is defined as
where N is the number of experimental data points. The nonlinear minimization function in Matlab is used for minimizing and estimating parameters a, b and c. The three model parameters and for determined systems are listed in Table 4. The root-mean-square deviations range from 0.76 to 1.28 K. The calculated results show good agreement with the experimental data. It is clear that the modified Apelblat model can describe well the solubility for the aqueous sulfuric acid solution systems measured.
2
) − (T )) /(N − 1)
(2)
According to the experiment, the solubility of CNT acid reaches the minimized value when w30 = 0.50. Hence, after the nitration reaction, the sulfuric acid concentration in this solution is around 0.90 mass fraction, which can be diluted to 0.5 to generate the most amount of CNT acid. Thus, in the separation process, salinity wastewater can be avoided, and of course, the treatment and reuse of 0.5 mass fraction aqueous sulfuric acid solutions should be considered. After the reduction reaction, the mixture is aqueous CLTNa solution which sulfuric acid is added to obtain the desired product CLT acid. In order to achieve separation process as much as possible,
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Table 4 Parameters of the modified Apelblat model and root-mean-square deviations for CNT acid and CLT acid in binary sulfuric acid (w30 ) + water (1 − w30 ) solvent mixtures (defined by Eqs. (1) and (2)). Solute
Solvent
a
b
c
(K)
CNT acid
w30 = 0.00 w30 = 0.20 w30 = 0.40 w30 = 0.50 w30 = 0.60 w30 = 0.80 w30 = 0.00 (pH = 7) pH = 5.09 pH = 3.71 pH = 1.38 pH = 0.51 w30 = 0.20 (pH = −0.366)
−174.08 128.54 −1466.4 319.79 509.75 −1726.6 1048.6 229.79 445.91 611.29 288.86 235.73
5503.8 −8789.9 59792 −19825 −28773 71290 −52113 −15378 −25119 −33028 −17990 −15751
27.621 −17.237 222.63 −44.296 −72.282 261.57 −153.12 −31.323 −63.534 −87.955 −40.260 −32.299
0.99 0.81 1.26 1.22 0.76 1.19 1.22 1.22 1.23 1.28 1.14 1.06
CLT acid
more acid should be introduced into the solution. However, the present determined data exhibit that solubility differences of CLT acid between w30 = 0.20 and pH = 0.51 and pH = 1.38 aqueous sulfuric acid solutions are tiny. For example, the amount difference dissolved of CLT acid per kilogram solvent between w30 = 0.20 and pH = 1.38 aqueous sulfuric acid solutions is 0.04679 grams. Furthermore, CLT acid will be attached with sulfuric acid whose viscosity is relatively high when its w30 = 0.20, which will confine the purity of CLT acid product. Hence the aqueous sulfuric acid solutions whose pH value is 1 to 2 would like to be recommended for aqueous CLTNa solution acidification and separating CLT acid product. In this way, CNT acid and CLT acid can be separated as much as possible, which can obtain high yield of CLT acid. 4. Conclusions The solubility of CNT acid and CLT acid in different aqueous sulfuric acid solutions at a temperature ranging from 276.91 to 345.42 K have been measured by the dynamic method. The solubility data have been correlated by the modified Apelblat model. The results calculated from the model show good agreement with the experimental data and the root-mean-square deviations range from 0.76 to 1.28 K. The solubility of both systems increases with temperature. The highest solubility of CNT acid and CLT acid is both obtained in pure water, and the lowest solubility is exhibited at w30 = 0.50 and w30 = 0.20, respectively. The aqueous sulfuric acid
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