Measurement and Correlation for the Solubility of Sodium p

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Cite This: J. Chem. Eng. Data 2018, 63, 1556−1567

Measurement and Correlation for the Solubility of Sodium p‑Toluenesulfonate, Sodium Sulfite, and Sodium p‑Methylphenoxide in Aqueous Sodium Hydroxide Solutions and Sodium Sulfite in Aqueous Ethanol Solutions Kang-Kang Pei, Rui-Xiong Zhao, Guo-Liang Zhang, Qing Xia,* and Feng-Bao Zhang*

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School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P.R. China S Supporting Information *

ABSTRACT: The solubilities of sodium p-toluenesulfonate (NaPTS), sodium sulfite (Na2SO3), and sodium p-methylphenoxide (NaCRS) in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions were investigated using a dynamic method over the temperature range from 277 to 341 K at atmospheric pressure. The experimental results showed that the solubilities of NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions decreased distinctly with the solutefree mass fraction of NaOH (w04) and ethanol (w05). Further, there were obvious transition points in the solubility−temperature curves of NaPTS and Na2SO3 in aqueous NaOH solutions, and the transition points shifted to lower temperature as w04 rose. The forming of transition point was due to the different equilibrium solid phase, which was revealed by characterization of the equilibrium solid phase. But the transition points in the solubility−temperature curves of Na2SO3 in aqueous ethanol solutions remained constant at different w05 values. As the temperature rose, the solubilities of NaPTS and NaCRS in aqueous NaOH solutions increased, while the solubilities of Na2SO3 increased at first and then decreased after the transition points in both aqueous NaOH and ethanol solutions. The experimental data were correlated with the electrolyte nonrandom two-liquid (E-NRTL) model, and model parameters were determined simultaneously. On the basis of the solubility difference between Na2SO3 and NaCRS, a new process for reusing the NaOH in the alkali fusion reaction residue was proposed theoretically. solution is evaporated and filtrated to get the solid NaPTS.4 The solid NaPTS reacts with excess NaOH (molar ratio, NaPTS:NaOH = 1:2.4);5,6 then, sodium p-methylphenoxide (C7H7ONa, NaCRS, CAS No. 1121-70-6) and Na2SO3 are produced in the alkali fusion step. However, because of the low reaction yield (70%), there is a lot of NaOH (about 0.125 mass fraction) in the reaction residue.7 Water is added to dissolve the NaCRS, and then the insoluble Na2SO3 is filtrated and reused in the neutralization 1 step, whereas the filtrate, the NaCRS solution with a large amount of unreacted NaOH, is acidified by the sulfur dioxide, leading to the waste of NaOH and sulfur dioxide.4 Considering the shortcomings above, if we can separate NaCRS out of the aqueous NaOH solution and recycle the unreacted NaOH, which can be used in neutralization 2 step, then the consumption of sulfur dioxide and NaOH can be reduced. After the acidification, the obtained p-cresol and Na2SO3 are separated to gain both main product p-cresol and byproduct Na2SO3. However, there is a little NaOH in the Na2SO3 gained from filtration. As Na2SO3 is almost insoluble in

1. INTRODUCTION p-Cresol (C7H8O, CAS No. 106-44-5), an important organic intermediate, is extremely valuable for the production of pesticides, medicines, spices, dyes, and cosmetics.1 Recently, the demand for p-cresol is increasing each year all over the world, especially in the developing countries. Although there are some other processes to produce p-cresol, the main industrial process to produce p-cresol is sulfonation−alkali fusion process,2 which is shown in Figure 1. It includes four steps:3 sulfonation, neutralization, alkali fusion, and acidification, which has already been investigated intensively. Although the process above seems perfect, there are a few defects in the actual industrial process. The actual flowsheet is shown in Figure 2. In the neutralization 1 step, most of the ptoluenesulfonic acid (C7H8O3S, PTSA, CAS No. 104-15-4) is neutralized by sodium sulfite (Na2SO3, CAS No. 7757-83-7) to obtain sodium p-toluenesulfonate (C7H7O3SNa, NaPTS, CAS No. 657-84-1). Then, NaOH is added in the neutralization 2 step, on the one hand to react with the remaining PTSA and keep the solution alkaline, on the other hand to separate NaPTS out easily as the solubility of NaPTS in aqueous NaOH solutions is lower than that in water. To confirm the proper concentration of aqueous NaOH solution, the solubility of NaPTS in aqueous NaOH solutions is needed. Afterward, the © 2018 American Chemical Society

Received: December 15, 2017 Accepted: March 6, 2018 Published: March 13, 2018 1556

DOI: 10.1021/acs.jced.7b01089 J. Chem. Eng. Data 2018, 63, 1556−1567

Journal of Chemical & Engineering Data

Article

Figure 1. Sulfonation−alkali fusion process for the p-cresol production.

Figure 2. Actual industrial process in the production of p-cresol.

Table 1. Source and Mass Fraction Purity of the Chemicals Used in the Experiment chemical name

CAS no.

source

NaPTSa

657-84-1

Na2SO3

7757-83-7

NaOH p-cresol NaH THFa n-hexane NaCRSa

1310-73-2 106-44-5 7646-69-7 109-99-9 110-54-3 1121-70-6

Heowns Biochemical Technology Co., Ltd., Tianjin, China Tianjin Hengshan Chemical Reagents Co., Tianjin, China Guangfu Chemical Reagents Co., Tianjin, China Adamas Reagent Co., Ltd., Shanghai, China Yuanli Chemical Reagents Co., Tianjin, China Yuanli Chemical Reagents Co., Tianjin, China Yuanli Chemical Reagents Co., Tianjin, China synthesized in our laboratory

Deionized water ethanol

7732-18-5

Nankai Chemical Reagents Co., Tianjin, China

64-17-5

Yuanli Chemical Reagents Co., Tianjin, China

a b

initial mass fraction purity

purification method

final mass fraction purity

0.980

recrystallization

0.990

HPLCb

0.990

0.990

HPLCb

>0.98 0.990 0.60 0.998 0.990 0.990

>0.98 0.990 0.60 0.998 0.990 0.990

0.998

0.998

analysis method

GCc GCc GCc HPLCb and ICPd

GCc

NaPTS, NaCRS, and THF are the abbreviations of sodium p-toluenesulfonate, sodium p-methylphenoxide, and tetrahydrofuran, respectively. High-performance liquid chromatography. cGas chromatograph. dInductively coupled plasma emission spectrometer.

correlating the experimental data. The NaOH recycling process was discussed theoretically.

ethanol but NaOH is soluble in ethanol, ethanol maybe a suitable solvent for the purification of Na2SO3. To improve the process above, solubilities of NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions are needed. However, it should be noted that very little literature has been reported on them. Therefore, the solubilities of NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions were measured by a dynamic method over the temperature range from 277 to 341 K at atmospheric pressure in this work. The new electrolyte nonrandom two-liquid (ENRTL) model,8,9 which has been applied to correlate the solubility data in many electrolyte systems,10,11 was used for

2. EXPERIMENTAL SECTION 2.1. Materials Preparation. NaCRS was synthesized by reacting p-cresol with sodium hydride (NaH) in tetrahydrofuran (THF) as the published work reported.12,13 NaH was suspended in purified THF with stirring. Then, the solution of p-cresol in THF was added drop by drop with stirring. After the addition was complete, the mixture was stirred overnight at room temperature. Excess NaH was removed by filtration under nitrogen, and the product was precipitated by adding the filtrate to enough of n-hexane. The precipitate was filtered under nitrogen, washed with n-hexane, and dried to constant 1557



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Table 2. Molality Solubility Data of NaPTS (m1) in Aqueous NaOH Solutions at Temperature Texp and Pressure 0.1 MPa for the System of {NaPTS (1) + NaOH (4) + Water (6)}a m1/(mol·kg−1)

Texp/K

Tcal/K

ESP

m1/(mol·kg−1)

Texp/K

Tcal/K

ESP

3.938 4.158 4.407 4.656 4.891 5.124 5.350 5.607

303.67 308.63 314.39 320.10 325.42 330.21 334.76 339.45

303.62 308.94 314.70 320.24 325.26 330.05 334.52 339.39

NaPTS NaPTS NaPTS NaPTS NaPTS NaPTS NaPTS NaPTS

w04

w04

w04

w04

w04

w04

w04

1.346 1.715 2.133 2.620 3.103 3.354 3.477 3.550 3.735 = 0.0301 9.389 × 10−1 1.226 1.615 2.118 2.394 2.657 2.740 2.868 = 0.0600 5.216 × 10−1 7.060 × 10−1 9.274 × 10−1 1.134 1.347 1.587 1.812 1.954 2.119 = 0.0904 3.076 × 10−1 3.660 × 10−1 4.354 × 10−1 5.183 × 10−1 6.296 × 10−1 7.965 × 10−1 9.484 × 10−1 1.101 1.282 = 0.1200 1.518 × 10−1 2.283 × 10−1 3.413 × 10−1 4.513 × 10−1 5.392 × 10−1 6.385 × 10−1 7.425 × 10−1 8.854 × 10−1 = 0.1500 3.538 × 10−2 7.379 × 10−2 1.228 × 10−1 1.448 × 10−1 1.647 × 10−1 1.820 × 10−1 2.067 × 10−1 2.355 × 10−1 = 0.2000 2.868 × 10−3 6.272 × 10−3

277.13 281.54 285.00 288.48 290.45 291.49 292.17 293.80 298.78

277.35 281.59 285.13 288.20 290.50 291.49 291.93 293.86 298.59

= 0.0000 NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS NaPTS

277.73 281.52 285.11 288.50 289.96 291.27 292.55 296.19

277.79 281.68 285.54 288.83 290.05 290.99 293.18 296.38

NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS NaPTS

3.043 3.239 3.458 3.703 3.959 4.251 4.531 4.850

300.57 305.20 310.71 315.98 321.59 327.42 332.57 338.31

300.67 305.33 310.40 315.86 321.34 327.36 332.87 338.87


277.59 281.38 284.27 286.19 287.87 289.16 292.02 294.56 298.77

277.09 280.49 283.73 286.02 287.73 289.16 291.11 294.69 298.73

NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS NaPTS NaPTS

2.290 2.498 2.726 2.938 3.182 3.441 3.722 3.992

302.93 307.51 312.94 317.50 322.49 327.72 333.16 338.28

302.79 307.57 312.65 317.21 322.26 327.43 332.83 337.83


277.56 279.62 281.23 283.14 285.09 286.88 288.57 292.62 298.39

278.23 279.87 281.64 283.44 285.28 287.24 289.71 294.37 299.43

NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS·2H2O NaPTS NaPTS NaPTS

1.448 1.625 1.808 1.999 2.237 2.487 2.732 2.969

303.30 308.21 312.97 317.38 322.64 327.79 333.10 338.21

303.78 308.17 312.50 316.82 321.95 327.11 331.98 336.51


278.56 282.58 286.25 292.69 296.91 301.17 305.28 309.66

278.49 282.02 284.38 292.10 296.74 301.12 305.09 309.89

NaPTS·2H2O NaPTS·2H2O NaPTS NaPTS NaPTS NaPTS NaPTS NaPTS

1.042 1.217 1.422 1.633 1.834 2.038 2.241

314.24 318.45 323.43 328.22 332.57 336.44 340.35

314.57 319.33 324.44 329.35 333.76 338.05 342.13

NaPTS NaPTS NaPTS NaPTS NaPTS NaPTS NaPTS

277.29 280.98 285.55 290.22 295.53 297.93 302.29 306.54

277.40 280.85 284.75 292.40 296.56 299.34 302.55 305.59

NaPTS·2H2O NaPTS·2H2O NaPTS NaPTS NaPTS NaPTS NaPTS NaPTS

2.691 3.207 4.035 5.193 6.402 7.769 9.159 1.057

10−1 10−1 10−1 10−1 10−1 10−1 10−1

310.75 314.20 317.97 322.66 327.08 331.43 335.54 339.70

308.52 312.24 317.02 322.33 326.94 331.45 335.55 339.37


NaPTS NaPTS

4.230 × 10−2 5.036 × 10−2

313.84 317.77

278.12 282.85

1558

× × × × × × ×

NaPTS NaPTS DOI: 10.1021/acs.jced.7b01089 J. Chem. Eng. Data 2018, 63, 1556−1567


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Table 2. continued w04

m1/(mol·kg−1)

Texp/K

= 0.2000 1.011 × 10−2 1.476 × 10−2 1.925 × 10−2 2.458 × 10−2 2.944 × 10−2 3.536 × 10−2

287.18 291.93 296.66 301.55 305.19 309.30

Tcal/K

ESP NaPTS NaPTS NaPTS NaPTS NaPTS NaPTS

m1/(mol·kg−1)

Texp/K

10−2 10−2 10−2 10−1 10−1

321.51 325.58 329.85 334.03 338.19

6.036 7.129 8.434 1.045 1.300

× × × × ×

Tcal/K

ESP NaPTS NaPTS NaPTS NaPTS NaPTS

a ESP represents the equilibrium solid phase. The w04 represents the solute-free mass fraction of NaOH. Standard uncertainties u are u(Texp) = 0.2 K, ur(m) = 0.02, ur(p) = 0.05, u(w04) = 0.0001.

3. THERMODYNAMIC MODELING BASIS 3.1. Solubility Equations Description. The solubility product constant (Ks) is used for describing the SLE in electrolyte systems, which exists in saturated solutions between the salt and its respective dissociated ions. It associates the activity coefficients with mole fraction of ions. The following formula can be used for aqueous solutions and applied to both single-component and multicomponent systems.17

weight in vacuum at 333.15 K before experiment. The mass fraction purity of NaCRS used in the experiment was analyzed by high-performance liquid chromatography (HPLC, Hitachi L-7100, Japan) combined with inductively coupled plasma emission spectrometry (ICP). Before the measurement, purchased NaPTS was recrystallized 3 times from deionized water (electrical conductivity less than 5 μs·cm−1) and dried to constant weight at 333.15 K. Because Na2SO3 is oxidized easily in air, it was dried in vacuum to constant weight at 333.15 K. The deionized water used in the solubility measurement was deoxygenated in the ultrasonic sonicator for half an hour before the experiment. The mass fraction purity of NaPTS and Na2SO3 was analyzed by HPLC.14 The HPLC results are presented in Figures S1, S2, and S3 (Supporting Information). Other chemical reagents were analytical grade and used without further purification. The Na2SO3 crystals were analyzed by X-ray diffraction (XRD) before and after the dissolution to ensure that Na2SO3 was not oxidized in the experiment, and the result is presented in Figure S4 (Supporting Information). The detailed information on the chemicals used in the experiment is listed in Table 1. 2.2. Apparatus and Procedure of Solubility Measurement. The measurement of solubility was conducted by the dynamic method. The laser monitoring system (JS2-1009016, Beijing, China) was used to observe the dissolution process and determine the solid−liquid equilibrium (SLE) temperature of the mixture. The intensity of the laser beam could reach a maximum value and then keep stable when the last crystal disappeared, and then we could record the corresponding temperature as the SLE temperature. The apparatus and procedure of the experiment were already described in detail previously.15,16 A certain amount of solute and solvent were weighed accurately using an analytical balance (Gibertini, Crystal 200, Italy, with an accuracy of ±0.0001 g) and transferred into a jacketed glass vessel. Afterward, the mixture was stirred continuously and heated slowly at a heating rate less than 0.2K·h−1. The temperature of the mixture was controlled by a refrigerated/heating circulator (Julabo FP45HE, Germany, temperature stability ±0.01 K) and measured by a platinum resistance thermometer Pt-100 (calibrated with an accuracy of 0.01 K), which was immersed in the inner chamber. To prevent volatilization of the solvent, a cold-water condenser tube was connected with the vessel. Nitrogen was introduced into the vessel to prevent oxidation of the solute when measuring the solubilities of NaCRS and Na2SO3. Repeated experiments were conducted for each mixture composition to ensure the accuracy of the solubility data in this work. In addition, the standard uncertainties of the measurement, which were calculated from the repeated experimental measurements, are reported in Tables 2−5.

K s = a+ν+a−ν− = (γ+x+)ν+ (γ−x−)ν−

(1)

where ν, a, γ, and x denote the number of the dissociated ion, the ion activity, the ion activity coefficient, and the mole fraction solubility of the dissociated ion, respectively. The subscripts (+) and (−) refer to cation and anion, respectively. In the SLE of NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions, the temperature dependence of Ks can be represented by the Van’t Hoff equation as follows:18 ln K s = A +

B T

(2)

where T is absolute temperature in Kelvin, and A and B are constants gained by solubility data modeling and denote the thermal parameters of the pure salts shown in Table 6. However, in the system of Na2SO3 in aqueous ethanol solutions, eq 2 needs to be modified. This is because in this system, Ks is not only the function of temperature and solute but also the solvent. Therefore, the following linear function is introduced to describe the effect of solvent composition, which has been successfully used in solubility data regression for a mixed-solvent electrolyte system.19 ln K s = Cx 0 + D(1 − x 0) +

[Ex 0 + F(1 − x 0)] T

(3)

where x0 denotes the solute-free mole fraction of ethanol in aqueous ethanol solutions, and C, D, E, and F are constants obtained through solubility data modeling shown in Table 7. 3.2. E-NRTL Thermodynamic Model Description. The ion activity coefficient γ is calculated by the E-NRTL model in this work. The activity coefficients of measured solutes are denoted as unsymmetric activity coefficients because of their strong polarity. Applied in the multicomponent electrolyte system, the E-NRTL model is based on two fundamental assumptions about the lattice structure of electrolyte system: like-ion repulsion assumption and local electroneutrality assumption.20 The E-NRTL thermodynamic model is described by the following expression. ln γi* = ln γi*PHD + ln γi*lc 1559

(4) DOI: 10.1021/acs.jced.7b01089 J. Chem. Eng. Data 2018, 63, 1556−1567


Article

Table 3. Molality Solubility Data of Na2SO3 (m2) in Aqueous NaOH Solutions at Temperature Texp and Pressure 0.1 MPa for the System of {Na2SO3 (2) + NaOH (4) + Water (6)}a m2/(mol·kg−1)

Texp/K

Tcal/K

ESP

m2/(mol·kg−1)

Texp/K

Tcal/K

ESP

2.880 2.790 2.715 2.638 2.583 2.527 2.471 2.402

308.09 313.02 317.46 321.57 325.38 329.61 333.92 339.49

308.68 313.28 317.38 321.95 325.42 329.23 333.21 338.50

Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3

w04

w04

w04

w04

w04

w04

1.264 1.483 1.707 1.995 2.261 2.589 2.889 2.956 2.908 = 0.0300 9.558 × 10−1 1.156 1.364 1.607 1.868 2.146 2.388 2.475 2.496 = 0.0600 7.087 × 10−1 8.778 × 10−1 1.067 1.299 1.529 1.802 1.972 2.045 2.024 = 0.0901 5.361 × 10−1 6.787 × 10−1 8.447 × 10−1 1.055 1.274 1.493 1.584 1.567 = 0.1202 4.219 × 10−1 5.211 × 10−1 6.635 × 10−1 8.258 × 10−1 1.008 1.089 1.182 1.217 1.176 = 0.1500 3.673 × 10−1 4.534 × 10−1 5.826 × 10−1 7.219 × 10−1 7.782 × 10−1 8.394 × 10−1 8.531 × 10−1 8.050 × 10−1 7.557 × 10−1

277.89 282.30 286.28 291.01 295.47 299.46 303.28 304.80 306.55

277.23 282.47 287.00 291.91 295.75 299.77 302.92 305.12 307.32

= 0.0000 Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3 Na2SO3

277.90 282.24 286.36 290.35 294.59 298.63 301.80 302.77 303.66

278.98 283.12 286.65 290.37 294.34 298.49 301.82 302.93 303.29

Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3

2.480 2.401 2.321 2.244 2.142 2.071 2.034 1.998 1.955

304.83 308.98 313.10 317.74 323.61 327.82 331.57 335.73 339.98

304.06 308.12 312.58 317.27 324.06 329.35 332.33 335.37 339.24

Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3

277.47 281.92 286.00 290.49 294.27 298.53 300.78 301.73 302.64

277.03 281.71 285.72 289.74 293.44 298.08 301.11 301.55 302.67

Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3 Na2SO3

1.996 1.921 1.855 1.798 1.740 1.686 1.617 1.567 1.525

303.86 308.00 311.75 315.71 320.26 324.67 331.12 335.58 339.89

304.19 308.48 312.62 316.55 320.78 325.10 331.25 336.22 340.88


277.28 281.65 285.87 290.53 294.61 298.19 299.91 301.83

276.49 281.29 285.53 289.75 293.64 297.87 299.90 302.13

Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3 Na2SO3

1.509 1.450 1.392 1.338 1.288 1.239 1.190 1.139

305.87 310.05 314.60 319.26 323.77 328.30 333.49 339.84

305.80 309.88 314.17 318.62 323.21 328.11 333.69 340.19


277.44 281.22 285.43 289.65 293.20 295.01 296.52 297.39 300.23

277.59 281.36 285.63 289.46 293.16 294.80 296.85 296.53 299.21

Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3 Na2SO3

1.118 1.062 1.017 9.754 9.313 8.921 8.590 8.276 7.974

× × × × × ×

10−1 10−1 10−1 10−1 10−1 10−1

304.35 308.68 313.06 317.37 322.32 326.68 330.83 335.32 340.04

303.41 307.91 311.89 315.88 320.64 325.36 329.80 334.44 339.37


278.94 282.59 286.56 290.67 291.73 293.00 294.35 298.52 302.46

279.80 283.23 287.36 290.96 292.28 293.68 294.53 298.65 303.41

Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3 Na2SO3 Na2SO3

7.057 6.695 6.433 6.179 5.943 5.705 5.474 5.252

× × × × × × × ×

10−1 10−1 10−1 10−1 10−1 10−1 10−1 10−1

307.51 312.14 316.10 320.48 325.09 329.66 334.27 339.60

309.04 313.66 317.40 321.41 325.50 330.08 334.99 340.20


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Table 3. continued m2/(mol·kg−1)

m2/(mol·kg−1)

Texp/K

Tcal/K

ESP

× × × × × × × ×

10−1 10−1 10−1 10−1 10−1 10−1 10−1 10−1

308.11 312.02 316.80 321.36 325.88 331.17 336.21 340.59

308.64 312.22 316.34 320.74 325.12 330.08 335.95 341.71


× × × × × × ×

10−2 10−2 10−2 10−2 10−2 10−2 10−2

310.93 315.37 319.88 325.01 330.92 335.69 339.76

Texp/K

Tcal/K

ESP

278.90 282.63 285.97 286.27 286.73 290.24 294.46 298.99 303.85

278.87 282.48 284.76 285.89 286.19 290.23 294.91 299.40 304.51

Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3

3.124 3.031 2.934 2.839 2.752 2.663 2.566 2.479

Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3

3.307 3.266 3.229 3.196 3.154 3.115 3.082

w04

= 0.2000 2.773 × 10−1 3.470 × 10−1 3.981 × 10−1 4.015 × 10−1 3.998 × 10−1 3.788 × 10−1 3.580 × 10−1 3.409 × 10−1 3.242 × 10−1 0 w4 = 0.3000 4.381 × 10−2 4.086 × 10−2 3.803 × 10−2 3.644 × 10−2 3.525 × 10−2 3.426 × 10−2 3.359 × 10−2

280.04 284.68 289.39 293.27 297.42 301.96 305.95


a

ESP represents the equilibrium solid phase. The w04 represents the solute-free mass fraction of NaOH. Standard uncertainties u are u(Texp) = 0.2K, ur(m) = 0.02, ur(p) = 0.05, u(w04) = 0.0001.

ln γi*lc = ln γilc − ln γilc, ∞

determined by Nelder Mead Simplex Method22 combined with Matlab (Mathwork, MA). The optimization process is designed to minimize the objective function below.

(5)

where i = c,a and c,a refer to the cation and anion, respectively. lnγi*PHD and lnγi*lc are ion i unsymmetric activity coefficients introduced by the Pitzer−Debye−Hückel resulting from the long-range ion−ion interaction and the NRTL model from the short-range interaction, respectively. lnγlc,∞ is the activity i coefficient at the infinite dilution mixed-solvent solutions. The superscript * denotes the unsymmetric reference state and the activity coefficients of cation and anion are normalized to the unsymmetric activity coefficients by eq 5. The detailed expressions of lnγi*PHD and lnγlci are given in the paper of Chen et al.9,21 The expressions of lnγlc,∞ in this work are described as i ln γilc , ∞ = zi(Gimτim + τmi)

⎡N ⎤0.5 exp 2 σ = ⎢∑ (T − T ) /(N − 1)⎥ ⎢⎣ i = 1 ⎦⎥

where T represents the experimental equilibrium temperature, and when σ is minimized, the T is recorded as the calculated temperature Tcal. The molality solubility data, Texp and Tcal, are shown in Tables 2−5, and the σ given in Table 9 denotes the root-mean-square deviation between Texp and Tcal. N is the number of total experimental points. Because of the difficulty of correlation for the whole systems, all experimental data are used for objective function minimization except for some solubility data (w04 = 0.2000 for NaPTS, w04 = 0.3000 for Na2SO3, some points in w04 = 0.2503 and w04 = 0.3001 for NaCRS).

(6)

where zi represents the charge number of cation and anion. G and τ are the E-NRTL model parameters which are expressed as the function of temperature to describe phase behavior over a large temperature range. Subscript i, m refer to the ions and solvent, respectively. Gim,τim are the function of Gnj, τnj (n ≠ j), respectively, and the relationships between Gim and Gnj, τim, τmi and τnj are shown in the work.20 Gnj = exp( −ατnj), (n ≠ j)

4. RESULTS AND DISCUSSION 4.1. Solubilities of NaPTS, Na2SO3, and NaCRS in Aqueous NaOH Solutions and Na2SO3 in Aqueous Ethanol Solutions. The investigated solubility data of NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions are listed in Tables 2−5 respectively, in which w04 is the solute-free mass fraction of NaOH in solvent, w05 is the solute-free mass fraction of ethanol in solvent. m1, m2, and m3 denote the molality solubility of NaPTS, Na2SO3, and NaCRS in the unit of mole solute per kilogram aqueous NaOH or ethanol solution, respectively. ESP represents the equilibrium solid phase of each data point. The solubility−temperature curves of three solutes at different values of w04 and w05 are shown in Figures 3−6, respectively. As can be seen from Figures 3−6, the solubilities of NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions decrease with the solute-free mass fraction of NaOH (w40) and ethanol (w50). Besides, the solubilities of NaPTS and NaCRS rise with temperature in all concentration ranges. However, there are obvious transition

(7)

where α represents the symmetric nonrandomness factor parameter given in Table 8. For salt−water and organic solvent−water, nonrandomness factors α are fixed as 0.2 and 0.3, respectively. Besides, the salt−organic solvent nonrandomness factor α is regressed in this work. Subscripts n and j denote the solutes or solvent, which are NaPTS, Na2SO3, NaCRS, NaOH, water, and ethanol in this work. The format of τ is expressed as follows: τnj = anj +

bnj T

, ( n ≠ j)

(9)

exp

(8)

where anj and bnj are correlated parameters given in Table 8 and represent the temperature dependence of τnj. 3.3. Correlation of Experimental Data. The E-NRTL model parameters (include parameters A−F in eqs 2 and 3) are 1561



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Table 4. Molality Solubility Data of NaCRS (m3) in Aqueous NaOH Solutions at Temperature Texp and Pressure 0.1 MPa for the System of {NaCRS (3) + NaOH (4) + Water (6)}a m3/(mol·kg−1)

Texp/K

Tcal/K

m3/(mol·kg−1) w04

6.272 6.454 6.586 6.908 7.301

278.67 281.84 284.35 288.84 292.99

280.65 282.79 284.31 287.86 291.95

3.069 3.411 3.839 4.218 4.601 5.094

277.07 281.53 286.94 291.61 295.95 300.24

277.96 282.17 287.08 291.12 294.95 299.55

3.647 × 10−1 5.379 × 10−1 7.735 × 10−1 1.115 1.505 1.991

279.28 283.62 287.75 291.74 295.99 300.80

280.29 283.46 287.03 291.44 295.81 300.63

4.783 5.461 6.728 8.563 1.102 2.028 3.709

× × × × × × ×

10−2 10−2 10−2 10−2 10−1 10−1 10−1

277.36 282.58 287.84 292.07 296.25 299.80 302.31

1.270 1.511 1.808 2.275 2.790 3.472 4.163 5.146 7.146

× × × × × × × × ×

10−2 10−2 10−2 10−2 10−2 10−2 10−2 10−2 10−2

280.16 285.38 289.57 294.50 299.23 302.94 305.21 307.82 310.23

294.06 295.40 298.55 301.69

306.95 308.86

Texp/K

Tcal/K

ESP

= 0.0000 7.738 8.394 8.962 9.912

297.37 302.95 307.21 311.66

296.20 302.04 306.64 313.52

NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O

= 0.1001 5.629 6.186 6.783 7.418 8.075

304.66 309.08 313.23 317.45 321.17

304.15 308.57 312.93 317.18 321.21

NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O

ESP NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O w04 NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O w04 NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O w04 NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O w04 NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O

= 0.2000 2.475 3.125 3.774 4.528 5.386 6.120 = 0.2503 7.473 × 10−1 1.315 2.064 2.957 3.723 4.547

305.06 309.31 313.32 317.45 322.74 326.83

304.91 310.03 314.59 319.33 324.15 327.85

NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O

306.43 310.56 315.08 320.94 325.77 329.89

305.88 310.51 315.63 320.90 324.88 328.73

NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O

= 0.3001 1.427 2.861 5.499 9.272 1.546 2.279 3.149 3.641

312.26 314.58 317.40 320.77 324.66 328.49 331.88 333.64

312.63 316.07 319.00 321.44 324.49 327.65 331.06 332.86

NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O NaCRS·H2O

× × × ×

10−1 10−1 10−1 10−1

a

ESP represents the equilibrium solid phase. The w04 represents the solute-free mass fraction of NaOH. Standard uncertainties u are u(Texp) = 0.3K, ur(m) = 0.02, ur(p) = 0.05, u(w04) = 0.0001.

the transition temperature, saturated NaPTS aqueous solutions were prepared at 290 and 335 K, respectively. The purchased NaPTS is sample 1. The solution (290 K) was cooled to 277 K to get crystal sample 2, and the solution (335 K) was cooled to 295 K to obtain crystal sample 3. The samples were analyzed by thermogravimetric analysis (TGA), and the results are shown in Figure S5 (Supporting Information). TGA result of sample 2 gives 15.79% weight loss of hydrate, which is nearly the same as the theoretical value (the weight of H2O in NaPTS·2H2O molecule is 15.65%). It is proved that the SLE is between NaPTS·2H2O and water at the temperature lower than the transition temperature. The work of Shikata23 suggests that 2 to 3.5 water molecules are tightly hydrated to PTS− in aqueous solution, which is consistent with the result of our work. Moreover, the results of sample 1 and sample 3 do not show obvious weight loss of hydrate, which proves that the SLE is between NaPTS and water at the temperature higher than the transition temperature.

points in the solubility−temperature curves of Na2SO3 in both aqueous NaOH and ethanol solutions. The solubilities of Na2SO3 in aqueous NaOH solutions increase at first and then decrease after the transition points. Similarly, there are transition points in the solubility−temperature curves of NaPTS as well, but the slopes of solubility−temperature curves are dramatically different before and after the transition points. Besides, the transition points in the solubility−temperature curves of both Na2SO3 and NaPTS shift to lower temperature as w04 rises. Ultimately, the transition point disappears when the mass fraction of NaOH is 0.20 in NaPTS and 0.30 in Na2SO3, but the condition is different for Na2SO3 in aqueous ethanol solutions. The transition points remain constant at aqueous ethanol solutions of different w05. The existence of transition points in the solubility− temperature curves of NaPTS may be due to the formation of the hydrate of NaPTS. To confirm the forms of NaPTS salts which precipitated at the temperature lower and higher than 1562



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Table 5. Molality Solubility Data of Na2SO3 (m2) in Aqueous Ethanol Solutions at Temperature Texp and Pressure 0.1 MPa for the System of {Na2SO3 (2) + Ethanol (5) + Water (6)}a m2/(mol·kg−1)

Texp/K

Tcal/K

m2/(mol·kg−1)

ESP w05

5.513 × 10−1 6.960 × 10−1 8.238 × 10−1 1.013 1.152 1.303 1.466 1.656 1.725

278.73 283.16 286.84 291.09 293.85 296.28 299.16 302.14 303.20

278.77 283.29 286.72 291.07 293.87 296.58 299.22 301.96 302.90

2.255 3.073 3.915 4.679 5.546 6.720 7.836

× × × × × × ×

10−1 10−1 10−1 10−1 10−1 10−1 10−1

279.91 285.38 289.49 292.34 294.97 298.18 300.87

280.42 284.80 288.63 291.67 294.75 298.42 301.50

9.005 1.349 1.680 2.024 2.425 3.191 3.648

× × × × × × ×

10−2 10−1 10−1 10−1 10−1 10−1 10−1

279.10 284.89 289.18 292.26 295.14 298.92 300.99

280.85 285.47 288.41 291.16 294.05 298.85 301.38

1.587 2.740 4.328 5.918 8.288 1.036 1.262

× × × × × × ×

10−2 10−2 10−2 10−2 10−2 10−1 10−1

278.25 280.79 284.11 286.66 290.59 294.44 299.50

277.40 280.54 284.26 287.50 291.72 294.98 298.18

= 0.0998 1.682 1.643 1.587 1.531 1.481 1.439 1.405 1.372

Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O Na2SO3·7H2O w05 = 0.1999 Na2SO3·7H2O 8.942 Na2SO3·7H2O 8.678 Na2SO3·7H2O 8.424 Na2SO3·7H2O 8.165 Na2SO3·7H2O 7.919 Na2SO3·7H2O 7.662 Na2SO3·7H2O 7.419 w05 = 0.2999 Na2SO3·7H2O 3.964 Na2SO3·7H2O 3.890 Na2SO3·7H2O 3.796 Na2SO3·7H2O 3.689 Na2SO3·7H2O 3.593 Na2SO3·7H2O 3.517 Na2SO3·7H2O 3.434 w05 = 0.3998 Na2SO3·7H2O 1.391 Na2SO3·7H2O 1.386 Na2SO3·7H2O 1.378 Na2SO3·7H2O 1.355 Na2SO3·7H2O 1.339 Na2SO3·7H2O 1.302 Na2SO3·7H2O

Texp/K

Tcal/K

307.18 310.93 316.52 321.94 326.75 330.89 333.95 336.97

308.06 311.07 315.80 320.84 325.80 330.37 334.31 338.32


ESP

× × × × × × ×

10−1 10−1 10−1 10−1 10−1 10−1 10−1

302.84 307.61 313.83 320.12 325.15 330.10 335.61

304.25 309.11 313.91 319.16 324.53 330.53 336.53

Na2SO3·7H2O Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3

× × × × × × ×

10−1 10−1 10−1 10−1 10−1 10−1 10−1

303.36 309.38 315.54 322.45 328.02 332.87 337.33

302.97 308.99 314.94 321.76 327.90 332.58 337.44


× × × × × ×

10−1 10−1 10−1 10−1 10−1 10−1

304.32 309.78 313.64 319.66 323.23 330.49

304.87 309.00 313.12 320.38 323.86 329.91

Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3 Na2SO3

a

ESP represents the equilibrium solid phase. The w05 represents the solute-free mass fraction of ethanol. Standard uncertainties uare u(Texp) = 0.3K, ur(m) = 0.02, ur(p) = 0.05, u(w04) = 0.0001.

oxidized during the measurement of solubility, the purchased Na2SO3 and the crystals precipitated are analyzed by X-ray diffraction (XRD). The results are shown in Figure S4 (Supporting Information). All peaks of the XRD pattern can be readily ascribed to Na2SO3, and no impurity is detected. The shift of transition points to lower temperature as w04 rises in the solubility−temperature curves of both Na2SO3 and NaPTS may be explained as follows. The transition point means the SLE shifts from Na2SO3·7H2O-NaOH-H2O (or NaPTS·2H 2 O-NaOH-H 2 O) to Na 2 SO 3 -NaOH-H 2 O (or NaPTS-NaOH-H2O). We can consider there are two kinds of water in the solution. One is solvent water used for dissolving solute, and other is crystal water which is tightly hydrated to solute molecule. When the solvent water needed

Table 6. Parameters of Solubility Product Equation Defined by Eq 2 for NaPTS, Na2SO3, and NaCRS in Aqueous NaOH Solutions

a

solute

solvent

NaPTS

NaOH-H2O

Na2SO3

NaOH-H2O

NaCRS

NaOH-H2O

1a 2b 1a 2b

A

B/K

34.804 47.720 500.42 160.20 −313.92

−10 858 −21 898 −1.5901 × 105 −50 913 42 555

Before the transition points. bAfter the transition points.

As for Na2SO3, the existence of the transition points is due to the transformation of Na2SO3·7H2O to Na2SO3 according to the work of Lynn and Kobe.24,25 To confirm Na2SO3 is not

Table 7. Parameters of Solubility Product Equation Defined by Eq 3 for Na2SO3 in Aqueous Ethanol Solutions

a

solute

solvent

Na2SO3

ethanol-H2O

1a 2b

C

D

E/K

F/K

−3740.0 −3410.4

1857.8 −188.00

−6.2950 × 105 −1.6915 × 105

−5.5941 × 105 18 768

Before the transition points. bAfter the transition points. 1563



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Table 8. E-NRTL Model Parameters α Defined by Eq 7 and anj, bnj Defined by Eq 8 for NaPTS + NaOH + Water, Na2SO3 + NaOH + Water, NaCRS + NaOH + Water, and Na2SO3 + Ethanol + Water Systems

a

n

j

NaOH

NaPTS

NaPTS

water

NaOH

Na2SO3

Na2SO3

water

ethanol

Na2SO3

ethanol NaOH NaCRS NaOH

water NaCRS water water

1a 2b 1a 2b 1a 2b 1a 2b 1a 2b

anj

ajn

bnj/K

bjn/K

αnj = αjn

−525.05 −12.739 2.4753 −14.104 −56.413 −41.878 0.41560 −13.371 −826.04 53.896 −57.818 4.8274 −6.2152 −12.987

16.570 23.090 253.49 224.77 152.05 −13.609 −230.20 84.410 433.17 30.506 15.927 −187.04 201.87 150.59

1.5011 × 105 1158.8 −4125.9 809.07 19 633 13 196 −3606.0 571.75 2.4071 × 105 −32 640 21452 258.79 −456.82 358.43

−65 31.4 −8208.0 −46 144 −37108 −49 496 2929.3 1.0195 × 105 5538.6 −2.1987 × 105 −36 124 −5963.8 29 049 −26 417 −10 469

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 7.3105 × 10−3 2.9529 × 10−2 0.3 0.2 0.2 0.2

Before the transition points. bAfter the transition points.

Table 9. Root-Mean-Square Deviations σ Described by the E-NRTL Model for NaPTS, Na2SO3, and NaCRS in Binary NaOH (w04) + Water (1 − w04) Solvent Mixtures and Na2SO3 in Binary Ethanol (w05) + Water (1 − w05) Solvent Mixturesa solute NaPTS

Na2SO3

NaCRS

Na2SO3

solvent system

σ/K

w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w04 w05 w05 w05 w05

0.19 0.31 0.42 0.87 1.02 1.14

= = = = = = = = = = = = = = = = = = = = = = = =

0.0000 0.0301 0.0600 0.00904 0.1200 0.1500 0.2000 0.0000 0.0300 0.0600 0.0901 0.1202 0.1500 0.2000 0.3000 0.0000 0.1001 0.2000 0.2503 0.3001 0.0998 0.1999 0.2999 0.3998

0.56 0.68 0.57 0.50 0.91 0.87 0.65

Figure 3. Plot of molality solubility of NaPTS (m1) vs temperature (T) at different solute-free NaOH mass fraction (w40): points, experimental values, (□) w04 = 0.0000; (○) w04 = 0.0301; (△) w04 = 0.0600; (◊) w04 = 0.0904; (☆) w04 = 0.1200; (+) w04 = 0.1500; (×) w04 = 0.2000; , calculated from the E-NRTL model.

1.27 0.60 0.97 1.02 1.06 0.61 0.82 0.77 0.78

in Table 8 also confirms this, where α between ethanol and Na2SO3 is close to zero. There are also some features about the solubility−temperature curves of NaCRS. The solubility difference at low temperature is less obvious in comparison with its behavior at high temperature. When w04 = 0.25, the solubility of NaCRS grows slowly at temperature lower than 300 K. Nevertheless, the solubility rises rapidly at temperature higher than 300 K. Similarly, when w04 = 0.30, the quickly changed temperature is about 312 K, which indicates that the quickly changed temperature rises with w04. To confirm the forms of synthetic NaCRS and the precipitated NaCRS salts, the two samples were also analyzed by thermogravimetric analysis (TGA), and the results are shown in Figure S6 (Supporting Information). TGA result of synthetic NaCRS (sample 4) does not show obvious weight loss of hydrate, but the result of precipitated NaCRS (sample 5) gives 12.59% weight loss of hydrate, which is nearly the same

a Defined by eq 9). The w04 and w05 represent the solute-free mass fraction of NaOH and ethanol, respectively.

increases, the crystal water would be taken away. As w04 rises, more and more water is used for dissolving the NaOH, and more crystalline water in the molecule is taken away earlier. Therefore, transition points shift to lower temperature as w04 rises. But the transition points in the solubility−temperature curves of Na2SO3 in aqueous ethanol solutions remain constant at different w05. This is because there is hardly no interaction between ethanol and Na2SO3, causing the addition of ethanol to have no influence on the SLE shift. Nonrandomness factor α 1564



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Figure 4. Plot of molality solubility of Na2SO3 (m2) vs temperature (T) at different solute-free NaOH mass fraction (w40): points, experimental values, (□) w04 = 0.0000; (○) w04 = 0.0300; (△) w04 = 0.0600; (◊) w04 = 0.0901; (☆) w04 = 0.1202; (+) w04 = 0.1500; (×) w04 = 0.2000; (◁)w04 = 0.3000; , calculated from the E-NRTL model.

Figure 6. Plot of molality solubility of Na2SO3 (m2) vs temperature (T) at different solute-free ethanol mass fraction (w05) of aqueous ethanol solutions: points, experimental values, (□) w05 = 0.0000 ; (○) w05 = 0.0998; (Δ) w05 = 0.1999; (◊) w05 = 0.2999; (☆) w05 = 0.3998; , calculated from the E-NRTL model.

Figure 7. Plot of molality solubility m2 of Na2SO3 in pure water: (●) this work; (△) Kobe and Hellwig;25 (◊) Lewis and David;26 (□) Foerster et al.27

Figure 5. Plot of molality solubility of NaCRS (m3) vs temperature (T) at different solute-free NaOH mass fraction (w40): points, experimental values, (□) w04 = 0.0000; (○) w04 = 0.1001; (Δ) w04 = 0.2000; (◊) w04 = 0.2503; (☆) w04 = 0.03001; , calculated from the ENRTL model.

4.3. The Parameters of the E-NRTL Model. The parameters of the solubility product for NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions, which are defined by eq 2, are given in Table 6. Those for Na2SO3 in aqueous ethanol solutions, which are defined by eq 3, are given in Table 7. The interaction parameters of the E-NRTL model are listed in Table 8. Table 9 shows the root-mean-square deviations of SLE temperature of NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions described by the E-NRTL model. Because some solubility− temperature curves are quite different with others, it is difficult to correlate all of the determined data together, and some solubility data (w04 = 0.2000 for NaPTS, w04 = 0.3000 for Na2SO3, three points in w04 = 0.2503, and seven points in w04 = 0.3001 for NaCRS) are not used for correlation. The rootmean-square deviations of the SLE temperature of NaPTS,

as the theoretical value (the weight of H2O in NaCRS·H2O molecule is 12.16%). It is proved that the SLE is between NaCRS·H2O and water in all NaOH concentration ranges. 4.2. Comparison with the Literature Data. The experimental solubility data of Na2SO3 and NaPTS in pure water are compared with the literature data in Figures 7 and 8, respectively. It can be observed that the present results of Na2SO3 show good agreement with the results of Kobe and Hellwig25 and Lewis and David,26 though the solubility is lower than the data reported by Foerster27 when the temperature is higher than 304 K. Further, the solubility of NaPTS in our work is similar to the results of Zhao3 but higher than the results of Renich and Taft.28 1565



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residue to form a slurry. The slurry mixture is filtrated at 363.15 K (filtration 1) because solubility difference between Na2SO3 and NaCRS is larger at higher temperature. The filter cake 1, mainly Na2SO3, can be reused in the neutralization 1 step. The filtrate 1, which is the aqueous NaCRS solution containing 15% NaOH, is concentrated, cooled to room temperature (303.15 K) and filtrated twice (filtration 2 and 3). After filtration twice, almost all NaCRS can be obtained in the cakes (cakes 2 and 3), which are mainly NaCRS containing little NaOH and Na2SO3. The cakes are acidified by the sulfur dioxide to obtain the main product p-cresol. The filtrate 3, which is mainly 25% NaOH solution containing little NaCRS, could be recycled to the neutralization 2 step.

5. CONCLUSIONS The solubilities of NaPTS, Na2SO3, and NaCRS in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions were measured over the temperature range from 277 to 341 K at atmospheric pressure using a dynamic method. The solubilities of NaPTS and NaCRS increase with temperature, while the solubilities of Na2SO3 increase at first and then decrease after the transition points in both aqueous NaOH and ethanol solutions. Solubilities of all the systems decrease evidently with solute-free mass fraction of NaOH (w04) and ethanol (w05). The solubility of NaPTS is very small when w04 = 0.20. Therefore, the suitable mass fraction of NaOH to separate NaPTS out is 0.2 or larger than 0.2. An enormous difference between the solubilities of Na2SO3 and NaCRS is observed. This feature can be used to separate them after alkali fusion. The E-NRTL model is used in the correlation of the experimental solubility data, and model parameters are reported. The root-mean-square deviations of SLE temperature range from 0.19 to 1.27 K. According to the determined data, a new strategy for recycling the NaOH in the alkali fusion reaction residue is proposed theoretically.

Figure 8. Plot of molality solubility m1 of NaPTS in pure water: (●) this work; (△) Zhao et al.;3 (□) Renich and Taft.28

Na2SO3, and NaCRS in aqueous NaOH solutions and Na2SO3 in aqueous ethanol solutions vary from (0.19 −1.14), (0.50− 0.91), (0.60−1.27), and (0.61−0.82) K, respectively. 4.4. Application of the Solubility Data in the Recycle of NaOH. As can be seen from the solubility data, the solubility of NaPTS (m1) in 0.20 mass fraction aqueous NaOH solution (w04 = 0.20) is very small. At the temperature of 298 K, m1 is about 0.02 mol·kg−1. Therefore, in the neutralization 2 step, the suitable mass fraction of NaOH to separate NaPTS out is 0.2 or larger than 0.2. According to the determined solubility data, the solubility of Na2SO3 (m2) in aqueous NaOH solutions is much lower than the solubility of NaCRS (m3) . For instance, at around 326 K, m3 is over 20 times higher than m2 (m2 = 2.752 × 10−1 mol· kg−1, m3 = 6.120 mol·kg−1) when w04 = 0.20, and at around 331 K, m3 is over one hundred times higher than m2(m2 = 3.154 × 10−2 mol·kg−1, m3 = 3.149 mol·kg−1) when w04 = 0.30. Further, this difference will be much larger as the temperature rises because m3 increases with temperature but m2 decreases with temperature. Therefore, a new strategy which is based on the solubility difference is designed to separate Na2SO3 and NaCRS out of the reaction residue. The new strategy is shown in Figure 9. After alkali fusion reaction, a certain amount of water is added to the reaction

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b01089. HPLC analysis results of NaPTS, Na2SO3, and NaCRS (Figures S1−S3), XRD patterns of Na2SO3 (Figure S4), and thermal degradation patterns of NaPTS and NaCRS (Figures S5 and S6) (PDF)

Figure 9. Flowsheet of the new strategy. 1566



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AUTHOR INFORMATION

Corresponding Authors

*Tel.: 86-22-27408778; E-mail: [email protected]. *Tel.: 86-22-27408778; E-mail: [email protected]. ORCID

Qing Xia: 0000-0003-0941-8852 Notes

The authors declare no competing financial interest.

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REFERENCES

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Measurement and Correlation for the Solubility of Sodium p

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