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Isobaric phase equilibria of the system 1-butanol + water containing penicillin G potassium salt at low pressures
Fluid Phase Equilibria 214 (2003) 137–149
Isobaric phase equilibria of the system 1-butanol + water containing penicillin G potassium salt at low pressures Zhenghong Gao a,∗ , Siping Wang a , Qingchi Sun b , Fengcai Zhang a b
a Department of Chemistry, Institute of Science, Tianjin University, Tianjin 300072, PR China Department of Inorganic Nonmetallic Materials, Institute of Materials, Tianjin University, Tianjin, PR China
Received 22 January 2002; received in revised form 16 June 2003; accepted 17 June 2003
Abstract The salt effect on the partially miscible system 1-butanol and water containing penicillin G potassium salt was investigated at low pressures using the ebulliometric method. The mean evaporation coefficient, f¯ , of the small ebulliometer used was determined, and the reliability of the ebulliometric method was examined. Phase equilibrium data for the partially miscible system 1-butanol + water without salt and with different salt concentrations at 8.00, 5.33, and 2.67 kPa were measured with the ebulliometer. These data were used to calculate vapor–liquid equilibrium (VLE) compositions using the NRTL model and the modified NRTL model, respectively. vapor–liquid–liquid equilibrium (VLLE) compositions at certain pressure for the binary system without salt and with the salt were also calculated using the obtained NRTL parameters. Some of the results of the calculation were verified by experiments with a glass equilibrium still and gas chromatography analysis and showed good agreement. It was found that the salt effect of the penicillin G potassium salt on the 1-butanol + water binary system at low pressures causes the azeotropic temperature to rise slightly and increases the mutual solubility of the two components. When the penicillin G potassium salt concentration reached 10 wt.%, the 1-butanol + water system becomes completely miscible. © 2003 Elsevier B.V. All rights reserved. Keywords: 1-Butanol; Water; Penicillin G potassium salt; Salt effect; Vapor–liquid equilibrium data; Vapor–liquid–liquid equilibrium data
1. Introduction Penicillin G potassium salt is a very useful medicine. Its purification has to be carried out by vacuum evaporative crystallization [1] because it easily degrades at temperature 323.15 K. The design and optimization of its purification process require phase equilibrium data of the system 1-butanol + water ∗
Corresponding author. Tel.: +86-22-27407728; fax: +86-22-27403475. E-mail address: zh [email protected] (Z. Gao). 0378-3812/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0378-3812(03)00349-2
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containing this salt at subatmospheric conditions. However, these data are not available in literature. To obtain these data using a direct method [2], will encounter difficulties in analyzing the equilibrium vapor and liquid compositions because the 1-butanol + water system is partially miscible and the experiments will require very low pressures. Therefore, in this work, an ebulliometric method, which belongs to the indirect methods, was adopted to determine the phase equilibrium data of the binary system without salt and with penicillin G potassium salt at subatmospheric conditions. This method is based on our previous study [3] on the determination of vapor–liquid equilibrium (VLE) data of the systems benzene–dimethylformamide and toluene–dimethylformamide. In present work, this method was extended to a binary system containing salt. In past decades, many studies on the salt effect of some inorganic salts and some small molecular organic salts on VLE and liquid–liquid equilibrium (LLE) were performed, whereas studies on complex large molecular organic salts of interest for biological pharmacy were rare. To meet the requirement of data needed for the purification of penicillin G potassium salt and to expand the range of the study of the salt effect on phase equilibrium, VLE data and vapor–liquid–liquid equilibrium (VLLE) data for the binary system 1-butanol + water without salt and with penicillin G potassium salt at 7.999, 5.333 and 2.666 kPa were determined by the ebulliometric method using the NRTL model and the modified NRTL model, respectively. In addition, the salt effect of the penicillin G potassium salt on the phase equilibria of the binary system is investigated and discussed on the basis of the phase equilibrium data obtained in this work and the structure and chemical composition of the penicillin G potassium salt. 2. Experimental 2.1. Chemicals Pure grade anhydrous ethanol and benzene and analytical grade 1-butanol, supplied by the Tianjin Second Reagent factory in China, were dehydrated over 5 Å activated molecular sieves. Water was prepared from distilled water purified by ion-exchange resins. The above materials were analyzed by gas chromatography, their purity was found to be better than 99.5 wt.%. Table 1 lists the refractive indices of these components. Penicillin G potassium salt is supplied by the Chemical Engineering academy of Tianjin University in China, and its purity is 99.6 wt.%. 2.2. Apparatus A small ebulliometer described in detail in the literature [3] was used to measure the equilibrium temperatures and pressures for the binary system without salt and with the salt at different concentrations. A standard Hg thermometer with a reading precision of 0.03 ◦ C was employed to measure the equilibrium Table 1 Refractive index n20 D of the chemicals used
Determined Reference [4]
Ethanol
Benzene
1-Butanol
Water
1.3612 1.3611
1.5011 1.5011
1.3970 1.3969
1.3330 1.3330
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temperature of the system. A refractometer made in Germany was used to determine the equilibrium compositions of the liquid phase for binary system. A glass equilibrium still [5] with a conditioning thermostatic bath, controlled to better than 0.1 K, is used to determine the equilibrium compositions of the liquid and vapor phase for the binary system without salt and with the salt. Samples of the equilibrium phases were analyzed by GC analysis. 2.3. Procedure About 20 cm3 of a liquid mixture of known composition obtained by weighing (on a balance with a resolution of 10−4 g) was put into the small ebulliometer. The ebulliometer was connected to a vacuum system and sealed. After the pressure of the system was adjusted slowly using a vacuum system until the desired pressure was reached, the ebulliometer was heated. The amount of reflux drops per minute, controlled with the heating voltage, was within 50–70 drops/min. The equilibrium temperature and pressure of the system were kept constant within ±0.03 K and ±6.6 Pa for about 5 min using a big buffer bottle in the vacuum system. The feed composition, temperature and pressure of system were recorded.
3. Result and discussion 3.1. Determination of the mean evaporation coefficient The method of determining the mean evaporation coefficient, f¯ , of the ebulliometer was described in detail in the literature [3]. The system ethanol + benzene, for which vapor–liquid equilibrium data at the different pressures are published in the literature [6], was selected to determine the evaporation coefficient of the ebulliometer. The feed compositions, qi , and equilibrium temperature, te , for the binary system at 101.325, 93.326 and 50.662 kPa were measured with the ebulliometer. The equilibrium liquid phase compositions, xi , were determined by withdrawing the equilibrium liquid from the liquid sampling valve of the ebulliometer and analyzing its refractive index with a refractometer. The equilibrium vapor compositions were calculated using the NRTL model with parameters obtained from literature [6]. The evaporation coefficient, f, is calculated using Eq. (1) f =
qi − xi yi − qi
(1)
Eq. (1) is obtained from the definition: f = V/L, and the material balance equation: (V +L)qi = Vyi +Lxi [3]. The calculated values of the evaporation coefficient, f¯ , are given in Table 2. Based on the values in Table 2, the value of f¯ of the ebulliometer was set to 0.0472 for this study. Table 2 Calculated values of the evaporation coefficient, f¯ , for the ebulliometer used f¯ Standard deviation, σ
101.33 kPa
93.33 kPa
50.66 kPa
0.0477 0.00444
0.0463 0.00370
0.0476 0.00309
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3.2. Examination of the ebulliometric method and the value of f¯ To verify the ebulliometeric method and the chosen value off¯ , the q–T data of the system 1-butanol + water in the completely miscible region at 101.325 kPa were measured with the ebulliometer. Then, the equilibrium compositions of the liquid and vapor phase were calculated from these experimental data by using the NRTL model and f¯ = 0.0472. The calculated vapor compositions and the experimental temperatures were compared with the data from the literature [7]. The compared results are as follows: y = 0.0061,
T exp = 0.17 K
y stands for the mean absolute deviation between the present and published vapor compositions; T exp stands for the mean absolute deviation between the present and published temperature. The verified results are satisfactory. 3.3. Measurement for the saturation vapor pressure of the single solvent containing salt To calculate the vapor–liquid equilibrium compositions of the system 1-butanol + water containing salt according to the modified NRTL model [8], the saturation vapor pressures of water containing different salt concentrations (1, 5 and 10 wt.%) and 1-butanol saturated with salt in the range of 20–50 ◦ C were measured with the small ebulliometer. These data were regressed by Eq. (2). The regression coefficients are listed in Table 3. B (2) log10 P = A + T where P is the saturation vapor pressure (kPa), T is the bubble point temperature (K), and A and B are the regression coefficients. 3.4. Phase equilibrium data for 1-butanol + water binary system The T and qi data for the binary system 1-butanol + water in completely miscible region at 2.67, 5.33 and 8.00 kPa were measured with the ebulliometer and were used to calculate the equilibrium liquid and vapor compositions for this binary system at these three pressures using the NRTL model and the determined value of f¯ . The experimental and calculated results are listed in Table 4. The iteration method employed in calculating x1,calc had been described in our previous study [3]. The iteration equation is. qi (1 + f¯ ) j+1 (3) xi,calc = j 1 + (yi,calc f¯ /xi,calc ) Table 3 Constants of the vapor pressure equation for solvent + salt mixtures System
A
B
Relative coefficient
Water + salt (1 wt.%) Water + salt (5 wt.%) Water + salt (10 wt.%) 1-Butanol + saturated salt
10.0002 10.1175 10.0417 10.4951
−2312.3 −2349.6 −2328.2 −2598.4
0.9995 0.9999 0.9991 0.9996
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Table 4 VLE data of the binary system 1-butanol (1) + water (2) at low pressures Pressure (kPa)
q1
T (K)
x1,calc
y1,calc
Pcalc (kPa)
|Pcalc − Pexp | (kPa)
8.00
0.0159 0.0196 0.5460 0.6007 0.6584 0.6975 0.7424 0.8198 0.8594 0.9002 0.9201 0.9698
313.2 313.0 312.1 312.5 313.0 313.5 314.5 317.1 319.5 322.1 324.1 328.4
0.0129 0.0159 0.5775 0.6187 0.6784 0.7187 0.7647 0.8423 0.8809 0.9193 0.9375 0.9724
0.0840 0.0976 0.2078 0.2168 0.2341 0.2500 0.2748 0.3431 0.4016 0.4904 0.5523 0.7348
7.96 7.97 8.10 8.09 7.99 7.92 7.93 7.91 8.05 7.98 8.08 8.03
0.04 0.03 0.01 0.09 0.01 0.08 0.07 0.09 0.05 0.02 0.08 0.03
5.33
0.0159 0.0196 0.5460 0.6007 0.6584 0.6975 0.7424 0.8198 0.8594 0.9002 0.9201
304.4 304.2 304.3 304.7 305.0 305.8 306.8 309.1 311.7 314.1 315.8
0.0099 0.0128 0.5786 0.6198 0.6795 0.7198 0.7659 0.8438 0.8826 0.9214 0.9394
0.1477 0.1703 0.1858 0.1949 0.2110 0.2263 0.2490 0.3105 0.3660 0.4518 0.5125
5.29 5.37 5.40 5.41 5.28 5.32 5.33 5.24 5.45 5.32 5.28
0.04 0.04 0.07 0.08 0.05 0.01 0.00 0.09 0.11 0.01 0.05
2.67
0.0159 0.0196 0.5460 0.6007 0.6584 0.6975 0.7424 0.8198 0.8594 0.9002 0.9201 0.9698
293.8 293.2 294.2 294.7 295.2 296.1 296.8 299.7 301.5 305.3 306.2 311.1
0.0120 0.0152 0.5791 0.6202 0.6797 0.7199 0.7655 0.8432 0.8818 0.9202 0.9382 0.9720
0.0997 0.1139 0.1762 0.1878 0.2081 0.2264 0.2520 0.3236 0.3822 0.4770 0.5371 0.7210
2.67 2.61 2.64 2.65 2.60 2.62 2.56 2.62 2.61 2.82 2.70 2.86
0.00 0.06 0.03 0.02 0.07 0.05 0.11 0.05 0.06 0.15 0.03 0.20
In the calculation of x1,calc and y1,calc , the NRTL parameters were obtained for the binary system at three different pressures. These values are summarized in Table 5 in which the correlation accuracy of the NRTL model was also included. The objective function in the correlation is. n F= (Pi,exp − Pi,calc )2
(4)
i
Based on the values of x1,calc in Table 4, the partially miscible binary solutions were prepared and their azeotropic temperatures, T, at three different pressures were measured with the ebulliometer. The results
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Table 5 NRTL parameters for the binary system 1-butanol (1) + water (2) at different pressures P (kPa)
8.00 5.33 2.67
NRTL model’s parameters g12 –g22 (J/mol)
g21 –g11 (J/mol)
α12
2045.239 2530.668 2074.141
7021.199 9418.433 8164.832
0.4061 0.4061 0.4602
P (kPa)
p/p (%)
0.057 0.047 0.068
0.71 0.89 2.56
are listed in Table 6. Then, the compositions of two liquid phases and vapor phase, at the experimental azeotropic temperatures of the system at three different pressures were calculated using the NRTL parameters in Table 5, by controlling the absolute deviation between the two vapor compositions corresponding to the compositions of the two liquid phases better than 0.01. Table 6 shows the calculated results and the results of the comparison between the calculated liquid phase compositions and the experimental LLE compositions obtained using the glass equilibrium still with GC analysis for the system. 3.5. Phase equilibrium data for the binary system with the salt The T and qi data for the binary system containing 1, 5 and 10 wt.% penicillin G potassium salt at 2.67, 5.33 and 8.00 kPa were measured with the ebulliometer. Then, these data were used to calculate the equilibrium liquid and vapor compositions using the modified NRTL model [8] (assuming that the salt was not present in the vapor phase). The experimental and calculated results are given in Tables 7–9. The modified NRTL model used in the calculation is in brief: ln γ1s = ln γ10 + τ1s
(5)
ln γ2s = ln γ20 + τ2s π s ln γis = τis = ln Pi0 Tis ,Ns
(6) (7)
where γis and γi0 are, respectively, the activity coefficient of component i in the binary system with salt and without salt at total pressure π. γi0 was calculated with the NRTL parameters presented in Table 5. γiss is the activity coefficient of single solvent i with salt concentration Ns at pressure π. Pi0 is the saturated vapor pressure of solvent i without salt at temperature Tis which expresses the boiling point of solvent, i, Table 6 Comparison of calculated VLLE data with the experimental VLLE data for the 1-butanol (1) + water (2) system Pressure (kPa)
8.00 5.33 2.67
T (K)
310.2 303.2 292.5
Organic phase
Water phase
y1,calc
x1,calc
x1,exp
x1
x1,calc
x1,exp
x1
0.4744 0.4761 0.4796
0.4821 0.4839 0.4857
0.0077 0.0078 0.0069
0.0351 0.0129 0.0331
0.0194 0.0128 0.0193
0.0157 0.0001 0.0138
0.1844 0.1718 0.1517
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Table 7 VLE data of the system 1-butanol (1) + water (2) containing 10 wt.% salt at low pressures Pressure (kPa)
q1
T (K)
x1,calc a
y1,calc
Pcalc (kPa)
|Pcalc − Pexp | (kPa)
y1,exp
2.67
0.0952 0.2106 0.2450 0.2950 0.4405 0.4934 0.5902 0.6517 0.6912 0.7402 0.7914 0.8338 0.8757
293.9 293.2 293.3 293.3 293.4 293.7 294.6 295.7 296.1 296.9 299.5 300.5 303.7
0.0953 0.2125 0.2481 0.3004 0.4520 0.5069 0.6070 0.6703 0.7108 0.7608 0.8122 0.8542 0.8945
0.1243 0.1694 0.1788 0.1798 0.1963 0.2071 0.2337 0.2577 0.2762 0.3045 0.3504 0.4017 0.4774
2.82 2.71 2.69 2.70 2.64 2.65 2.66 2.70 2.67 2.54 2.71 2.74 2.83
0.15 0.04 0.02 0.04 0.02 0.02 0.00 0.04 0.00 0.13 0.04 0.08 0.16
0.2392
0.0055
0.2645
−0.0117
0.0952 0.2106 0.2450 0.2950 0.4405 0.4934 0.5902 0.6517 0.6912 0.7402 0.7914 0.8338 0.8757
305.0 304.1 304.2 304.3 304.6 305.0 306.1 307.2 307.6 308.3 310.2 312.3 314.9
0.0923 0.2116 0.2467 0.2992 0.4512 0.5063 0.6066 0.6702 0.7108 0.7612 0.8128 0.8550 0.8957
0.1505 0.2002 0.201 0.2051 0.2111 0.2186 0.2392 0.2587 0.2739 0.2989 0.3378 0.3845 0.4531
5.61 5.57 5.55 5.65 5.72 5.66 5.65 5.67 5.72 5.63 5.69 5.72 5.63
0.28 0.23 0.21 0.31 0.39 0.32 0.32 0.34 0.39 0.29 0.35 0.38 0.29
0.2434
0.0042
0.2692
−0.0047
0.0952 0.2106 0.2450 0.2950 0.4405 0.4934 0.5902 0.6517 0.6912 0.7402 0.7914 0.8338 0.8757
311.9 311.3 311.2 311.3 311.6 312.1 313.2 314.4 314.7 315.6 317.3 319.6 321.9
0.0905 0.2104 0.2456 0.2980 0.4504 0.5053 0.6057 0.6692 0.7098 0.7601 0.8116 0.8536 0.8942
0.2024 0.2163 0.2231 0.2304 0.2330 0.2392 0.2586 0.2787 0.2946 0.3219 0.3633 0.4138 0.4846
8.31 8.05 8.01 8.06 8.17 8.30 8.55 8.54 8.66 8.60 8.59 8.62 8.55
0.31 0.05 0.01 0.06 0.17 0.30 0.56 0.54 0.66 0.60 0.60 0.62 0.55
0.2629
0.0043
0.2986
0.004
5.33
8.00
a
y
x1,calc stands for solute-free mol fraction.
containing salt concentration Ns at pressure π. Tis is calculated using Eq. (2) and the regression coefficients from Table 3. Then, the azeotropic temperatures were measured with the ebulliometer, and the VLLE compositions at the experimental azeotropic temperature for the partially miscible binary system with 1 and 5 wt.%
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Table 8 VLE data of the system 1-butanol (1) + water (2) containing 5 wt.% salt at low pressures Pressure (kPa)
q1
T (K)
x1,calc a
y1,calc
Pcalc (kPa)
|Pcalc − Pexp | (kPa)
2.67
0.0102 0.0186 0.4754 0.5442 0.5899 0.6453 0.6883 0.7393 0.7889 0.8277 0.8886
294.5 293.2 293.1 293.5 293.7 294.6 295.8 296.4 297.8 299.7 304.0
0.0069 0.0137 0.4892 0.5605 0.6077 0.6648 0.7089 0.7608 0.8108 0.8492 0.9075
0.0808 0.1256 0.1810 0.1974 0.2105 0.2315 0.2531 0.2829 0.3245 0.3711 0.4849
2.57 2.65 2.52 2.64 2.57 2.56 2.55 2.57 2.58 2.90 2.66
0.10 0.02 0.14 0.03 0.10 0.11 0.12 0.10 0.09 0.23 0.01
0.0102 0.0186 0.4754 0.5442 0.5899 0.6453 0.6883 0.7393 0.7889 0.8277 0.8886
305.6 304.4 304.3 305.0 305.8 306.2 307.3 308.3 309.8 311.4 315.8
0.0055 0.0114 0.4886 0.5601 0.6074 0.6647 0.7090 0.7613 0.8114 0.8501 0.9087
0.1123 0.1791 0.1927 0.2050 0.2164 0.2325 0.2500 0.2761 0.3126 0.3533 0.4592
5.44 5.56 5.55 5.56 5.46 5.44 5.36 5.55 5.26 5.41 5.56
0.11 0.23 0.22 0.23 0.12 0.10 0.02 0.22 0.07 0.08 0.22
0.0102 0.0186 0.4754 0.5442 0.5899 0.6453 0.6883 0.7393 0.7889 0.8277 0.8886
313.1 312.1 311.5 312.1 313.4 313.5 314.5 315.2 317.0 318.0 322.2
0.0078 0.0147 0.4876 0.5591 0.6065 0.6638 0.7081 0.7603 0.8102 0.8488 0.9073
0.0632 0.1021 0.2131 0.2241 0.2360 0.2517 0.2699 0.2975 0.3373 0.3795 0.4893
7.80 7.66 7.87 7.96 8.23 8.17 8.36 8.31 8.18 8.36 8.17
0.20 0.34 0.13 0.04 0.24 0.17 0.36 0.31 0.18 0.36 0.17
5.33
8.00
a
y1,exp
y
0.1908
−0.0066
0.2533
0.0002
0.2026
−0.0024
0.2419
−0.0081
0.2307
0.0066
0.2733
0.0034
x1,calc stands for solute-free mol fraction.
salt at three different pressures were calculated using the modified NRTL model. These results are shown in Table 10. Since the binary system with 10 wt.% salt is completely miscible, no calculation of VLLE compositions for this mixture was performed. Furthermore, in order to examine the calculated VLE and VLLE compositions, some experimental VLE and VLLE data using the glass equilibrium still [5] with GC analysis were compared with the calculated VLE and VLLE data, as shown in Tables 7–10. The results of this comparison are satisfactory except that the absolute deviations of the liquid compositions in the water phase in Table 10 are larger than 0.02.
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Table 9 VLE data of the system 1-butanol (1) + water (2) containing 1 wt.% salt at low pressures Pressure (kPa)
q1
T (K)
x1,calc a
y1,calc
Pcalc (kPa)
|Pcalc − Pexp | (kPa)
2.67
0.0103 0.0191 0.4966 0.5493 0.5914 0.6331 0.6850 0.7448 0.7905 0.8329 0.8749
294.1 292.9 292.9 293.0 293.5 293.9 294.9 296.8 298.8 300.5 303.7
0.0070 0.0142 0.5113 0.5660 0.6095 0.6525 0.7058 0.7666 0.8125 0.8545 0.8948
0.0803 0.1257 0.1820 0.1943 0.2071 0.2217 0.2455 0.2837 0.3245 0.3755 0.4511
2.64 2.56 2.57 2.51 2.52 2.50 2.53 2.65 2.76 2.87 2.79
0.03 0.11 0.10 0.16 0.14 0.17 0.14 0.02 0.09 0.20 0.12
0.0103 0.0191 0.4966 0.5493 0.5914 0.6331 0.6850 0.7448 0.7905 0.8329 0.8749
305.3 304.4 303.9 304.4 304.9 305.4 306.5 308.3 310.2 312.3 314.9
0.0056 0.0116 0.5107 0.5655 0.6091 0.6523 0.7058 0.7670 0.8130 0.8552 0.8959
0.1127 0.1797 0.1934 0.2034 0.2135 0.2255 0.2453 0.2776 0.3130 0.3595 0.4279
5.40 5.62 5.55 5.51 5.55 5.52 5.52 5.54 5.50 5.52 5.52
0.07 0.29 0.22 0.18 0.22 0.19 0.18 0.21 0.17 0.19 0.19
0.0103 0.0191 0.4966 0.5493 0.5914 0.6331 0.6850 0.7448 0.7905 0.8329 0.8749
312.3 312.0 311.0 311.5 312.0 312.6 313.7 315.4 317.3 319.6 321.9
0.0079 0.0151 0.5097 0.5645 0.6082 0.6513 0.7048 0.7659 0.8118 0.8538 0.8944
0.0635 0.1039 0.2141 0.2233 0.2330 0.2455 0.2662 0.3008 0.3389 0.3892 0.4600
7.62 7.65 7.61 7.70 7.76 7.86 8.03 8.37 8.20 8.01 8.22
0.38 0.35 0.39 0.30 0.24 0.14 0.03 0.37 0.20 0.01 0.22
5.33
8.00
a
y1,exp
y
0.2009
−0.0062
0.2777
−0.006
0.2062
−0.0073
0.2728
−0.0048
0.2283
−0.0047
0.3148
0.014
x1,calc stands for solute-free mol fraction.
3.6. The salt effect of penicillin G potassium salt on the binary system 1-butanol + water To investigate the salt effect of the binary system, T–x–y data for the binary system without salt and with 1, 5 and 10 wt.% salt at 5.33 kPa are displayed in Figs. 1 and 2. The salt effect at 2.67 and 8.00 kPa is basically identical with that at 5.33 kPa. From Figs. 1 and 2, it is found that the addition of 1 and 5 wt.% salt to the 1-butanol + water system increases the azeotropic temperature slightly. The mutual solubility of 1-butanol and water increases, and when the salt concentration reaches 10 wt.%, the system becomes
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Table 10 Comparison of the calculated VLLE data with the experimental VLLE data for the 1-butanol (1) + water (2) system containing salt Salt concentration
Pressure T (K) (kPa)
Organic phase
Water phase
Vapor phase
x1,calc
x1,exp
x1
x1,calc
x1,exp
x1
y1,calc
y1,exp
y1
5 wt.%
8.00 5.33 2.67
311.1 303.8 293.0
0.4342 0.4291 0.4408
0.4413 0.4334 0.4481
0.0071 0.0043 0.0073
0.0605 0.0134 0.0345
0.0421 0.0129 0.0131
0.0184 0.0055 0.0214
0.2064 0.1901 0.1762
0.1971 0.1932 0.1824
0.0093 0.0031 0.0062
1 wt.%
8.00 5.33 2.67
310.6 303.6 292.7
0.4562 0.4491 0.4608
0.4510 0.4587 0.4677
0.0052 0.0096 0.0069
0.0555 0.0131 0.0335
0.0343 0.0130 0.0122
0.0212 0.0001 0.0213
0.2042 0.1889 0.1739
0.1953 0.1910 0.1795
0.0089 0.0012 0.0056
completely miscible. The boiling temperature of water containing the salt rises slightly, whereas that of 1-butanol containing the salt decreases. These results demonstrate that the salt effect of the penicillin G potassium salt on the phase equilibrium of the binary system is complicated and different from that of inorganic salts and small molecular organic salts. It had been reported in the literature [9] that the salt effect of NaBr on LLE for the 1-butanol + water binary system results in a reduction of the mutual solubility of the two components because, as is well known, the affinity of NaBr for water is strong whereas that for 1-butanol is weak. But the salt effect of the penicillin G potassium salt leads to an increase in the mutual solubility of 1-butanol and water, even though there is also a stronger affinity of the penicillin G potassium salt for water than for 1-butanol, which is confirmed by the large solubility of the penicillin G potassium salt in water and the small solubility of the salt in 1-butanol. The difference in salt effect of
Fig. 1. The T–x–y curve for the system 1-butanol (1) + water (2) containing different salt concentrations at 5.33 kPa (x1 : solute-free mole fractions of 1-butanol).
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147
Fig. 2. The T–x–y curve for the system 1-butanol (1) + water (2) containing 10 wt.% at 5.33 kPa (x1 : solute-free mole fractions of 1-butanol).
inorganic salts and large molecular organic salts can be explained from the complicated structure of the penicillin G potassium salt:
This structural formula shows that penicillin G potassium salt is not only a high molecular weight compound but also contains various polar and nonpolar chemical groups. So the interaction of penicillin G potassium salt molecules with water and 1-butanol molecules is quite complicated and the size effect of the large penicillin G potassium salt molecules in the binary system has to be considered too, which causes the penicillin G potassium salt to have a special salt effect, different from simple inorganic salts. In a word, it is thought that the special salt effect of penicillin G potassium salt on the phase equilibria of 1-butanol + water, causing the mutual solubility of the two components to increase, is due to various interaction of the salt with water and 1-butanol, respectively and the size effect of the salt molecules. 4. Conclusion The ebulliometric method was used to determine isobaric phase equilibrium data for the binary system 1-butanol + water without salt and with the penicillin G potassium salt at 2.67, 5.33 and 8.00 kPa. qi and T data for the binary system without the salt and with the salt at three different pressures were measured with a small ebulliometer. These data were used to calculate VLE compositions by using the NRTL model and modified NRTL model, respectively. The VLLE compositions at the azeotropic temperature
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for the binary system without salt and with the salt at three different pressures were also calculated using the NRTL parameters obtained in calculating VLE compositions and using a modified NRTL model, respectively. Some of the calculated results were confirmed by experiments with an equilibrium still and GC analysis. In addition, the salt effect of penicillin G potassium salt on the phase equilibrium of the binary system was found to increase the mutual solubility of the two components and to raise slightly the azeotropic temperature. This is different from the salt effect of the inorganic salt reported in literature [9]. The special salt effect of penicillin G potassium salt was considered to be due to its complicated molecule structure, containing various polar and nonpolar chemical groups and its large molecular volume. List of symbols f¯ F g12 –g22 , g21 –g11 L P q T V x y
mean evaporation coefficient objective function interaction parameters in NRTL model liquid stream (mol/h) pressure (kPa) feed composition (mol fraction) temperature (K) vapor stream (mol/h) liquid composition (mol fraction) vapor composition (mol fraction)
Greek letters α12 γ
nonrandomness factor in NRTL model activity coefficient
Superscripts 0 j s
no salt iteration number containing salt
Subscripts calc exp i
calculation experimental component i
Acknowledgements This research was funded by State Key Laboratory of Chemical Engineering in China and by 985 project of Tianjin University in China. References [1] J.K. Wang, M.J. Zhang, T. Wan, Z.C. Ping, G.A. Han, J. Chem. Ind. Eng. (China) 47 (1996) 100–104.
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E. Hala, J. Pick, V. Fried, O. Vilim, Vapor–liquid Equilibrium, second ed., Pergamon Press, Oxford, 1967. Z.H. Gao, Z.L. Ma, L. Chen, Q. Wu, Fluid Phase Equilib. 173 (2000) 253–262. C.W. Robert, CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, 1977. Z.H. Gao, Z.Y. Cui, Y.S. Gan, J.Q. Li, Fluid Phase Equilib. 126 (1996) 135–144. J. Gmehling, V. Onken, W. Arlt, Vapor–liquid Equilibrium Data Collection, Dechema Chemistry Data Series, vol. 1, Part 2a, Dechema, 1977, pp. 380–398. [7] J. Gmehling, V. Onken, W. Arlt, Vapor–liquid Equilibrium Data Collection, Dechema Chemistry Data Series, vol. 1, Part 2a, Dechema, 1977, pp. 178–181. [8] T.C. Tan, Chem. Eng. Res. Des. 68 (A1) (1990) 93–103. [9] A.T. Al-Sahhaf, E. Kapetanovic, J. Chem. Eng. Data 42 (1997) 74–77.
Isobaric phase equilibria of the system 1-butanol + water containing penicillin G potassium salt at low pressures Zhenghong Gao a,∗ , Siping Wang a , Qingchi Sun b , Fengcai Zhang a b
a Department of Chemistry, Institute of Science, Tianjin University, Tianjin 300072, PR China Department of Inorganic Nonmetallic Materials, Institute of Materials, Tianjin University, Tianjin, PR China
Received 22 January 2002; received in revised form 16 June 2003; accepted 17 June 2003
Abstract The salt effect on the partially miscible system 1-butanol and water containing penicillin G potassium salt was investigated at low pressures using the ebulliometric method. The mean evaporation coefficient, f¯ , of the small ebulliometer used was determined, and the reliability of the ebulliometric method was examined. Phase equilibrium data for the partially miscible system 1-butanol + water without salt and with different salt concentrations at 8.00, 5.33, and 2.67 kPa were measured with the ebulliometer. These data were used to calculate vapor–liquid equilibrium (VLE) compositions using the NRTL model and the modified NRTL model, respectively. vapor–liquid–liquid equilibrium (VLLE) compositions at certain pressure for the binary system without salt and with the salt were also calculated using the obtained NRTL parameters. Some of the results of the calculation were verified by experiments with a glass equilibrium still and gas chromatography analysis and showed good agreement. It was found that the salt effect of the penicillin G potassium salt on the 1-butanol + water binary system at low pressures causes the azeotropic temperature to rise slightly and increases the mutual solubility of the two components. When the penicillin G potassium salt concentration reached 10 wt.%, the 1-butanol + water system becomes completely miscible. © 2003 Elsevier B.V. All rights reserved. Keywords: 1-Butanol; Water; Penicillin G potassium salt; Salt effect; Vapor–liquid equilibrium data; Vapor–liquid–liquid equilibrium data
1. Introduction Penicillin G potassium salt is a very useful medicine. Its purification has to be carried out by vacuum evaporative crystallization [1] because it easily degrades at temperature 323.15 K. The design and optimization of its purification process require phase equilibrium data of the system 1-butanol + water ∗
Corresponding author. Tel.: +86-22-27407728; fax: +86-22-27403475. E-mail address: zh [email protected] (Z. Gao). 0378-3812/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0378-3812(03)00349-2
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containing this salt at subatmospheric conditions. However, these data are not available in literature. To obtain these data using a direct method [2], will encounter difficulties in analyzing the equilibrium vapor and liquid compositions because the 1-butanol + water system is partially miscible and the experiments will require very low pressures. Therefore, in this work, an ebulliometric method, which belongs to the indirect methods, was adopted to determine the phase equilibrium data of the binary system without salt and with penicillin G potassium salt at subatmospheric conditions. This method is based on our previous study [3] on the determination of vapor–liquid equilibrium (VLE) data of the systems benzene–dimethylformamide and toluene–dimethylformamide. In present work, this method was extended to a binary system containing salt. In past decades, many studies on the salt effect of some inorganic salts and some small molecular organic salts on VLE and liquid–liquid equilibrium (LLE) were performed, whereas studies on complex large molecular organic salts of interest for biological pharmacy were rare. To meet the requirement of data needed for the purification of penicillin G potassium salt and to expand the range of the study of the salt effect on phase equilibrium, VLE data and vapor–liquid–liquid equilibrium (VLLE) data for the binary system 1-butanol + water without salt and with penicillin G potassium salt at 7.999, 5.333 and 2.666 kPa were determined by the ebulliometric method using the NRTL model and the modified NRTL model, respectively. In addition, the salt effect of the penicillin G potassium salt on the phase equilibria of the binary system is investigated and discussed on the basis of the phase equilibrium data obtained in this work and the structure and chemical composition of the penicillin G potassium salt. 2. Experimental 2.1. Chemicals Pure grade anhydrous ethanol and benzene and analytical grade 1-butanol, supplied by the Tianjin Second Reagent factory in China, were dehydrated over 5 Å activated molecular sieves. Water was prepared from distilled water purified by ion-exchange resins. The above materials were analyzed by gas chromatography, their purity was found to be better than 99.5 wt.%. Table 1 lists the refractive indices of these components. Penicillin G potassium salt is supplied by the Chemical Engineering academy of Tianjin University in China, and its purity is 99.6 wt.%. 2.2. Apparatus A small ebulliometer described in detail in the literature [3] was used to measure the equilibrium temperatures and pressures for the binary system without salt and with the salt at different concentrations. A standard Hg thermometer with a reading precision of 0.03 ◦ C was employed to measure the equilibrium Table 1 Refractive index n20 D of the chemicals used
Determined Reference [4]
Ethanol
Benzene
1-Butanol
Water
1.3612 1.3611
1.5011 1.5011
1.3970 1.3969
1.3330 1.3330
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temperature of the system. A refractometer made in Germany was used to determine the equilibrium compositions of the liquid phase for binary system. A glass equilibrium still [5] with a conditioning thermostatic bath, controlled to better than 0.1 K, is used to determine the equilibrium compositions of the liquid and vapor phase for the binary system without salt and with the salt. Samples of the equilibrium phases were analyzed by GC analysis. 2.3. Procedure About 20 cm3 of a liquid mixture of known composition obtained by weighing (on a balance with a resolution of 10−4 g) was put into the small ebulliometer. The ebulliometer was connected to a vacuum system and sealed. After the pressure of the system was adjusted slowly using a vacuum system until the desired pressure was reached, the ebulliometer was heated. The amount of reflux drops per minute, controlled with the heating voltage, was within 50–70 drops/min. The equilibrium temperature and pressure of the system were kept constant within ±0.03 K and ±6.6 Pa for about 5 min using a big buffer bottle in the vacuum system. The feed composition, temperature and pressure of system were recorded.
3. Result and discussion 3.1. Determination of the mean evaporation coefficient The method of determining the mean evaporation coefficient, f¯ , of the ebulliometer was described in detail in the literature [3]. The system ethanol + benzene, for which vapor–liquid equilibrium data at the different pressures are published in the literature [6], was selected to determine the evaporation coefficient of the ebulliometer. The feed compositions, qi , and equilibrium temperature, te , for the binary system at 101.325, 93.326 and 50.662 kPa were measured with the ebulliometer. The equilibrium liquid phase compositions, xi , were determined by withdrawing the equilibrium liquid from the liquid sampling valve of the ebulliometer and analyzing its refractive index with a refractometer. The equilibrium vapor compositions were calculated using the NRTL model with parameters obtained from literature [6]. The evaporation coefficient, f, is calculated using Eq. (1) f =
qi − xi yi − qi
(1)
Eq. (1) is obtained from the definition: f = V/L, and the material balance equation: (V +L)qi = Vyi +Lxi [3]. The calculated values of the evaporation coefficient, f¯ , are given in Table 2. Based on the values in Table 2, the value of f¯ of the ebulliometer was set to 0.0472 for this study. Table 2 Calculated values of the evaporation coefficient, f¯ , for the ebulliometer used f¯ Standard deviation, σ
101.33 kPa
93.33 kPa
50.66 kPa
0.0477 0.00444
0.0463 0.00370
0.0476 0.00309
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3.2. Examination of the ebulliometric method and the value of f¯ To verify the ebulliometeric method and the chosen value off¯ , the q–T data of the system 1-butanol + water in the completely miscible region at 101.325 kPa were measured with the ebulliometer. Then, the equilibrium compositions of the liquid and vapor phase were calculated from these experimental data by using the NRTL model and f¯ = 0.0472. The calculated vapor compositions and the experimental temperatures were compared with the data from the literature [7]. The compared results are as follows: y = 0.0061,
T exp = 0.17 K
y stands for the mean absolute deviation between the present and published vapor compositions; T exp stands for the mean absolute deviation between the present and published temperature. The verified results are satisfactory. 3.3. Measurement for the saturation vapor pressure of the single solvent containing salt To calculate the vapor–liquid equilibrium compositions of the system 1-butanol + water containing salt according to the modified NRTL model [8], the saturation vapor pressures of water containing different salt concentrations (1, 5 and 10 wt.%) and 1-butanol saturated with salt in the range of 20–50 ◦ C were measured with the small ebulliometer. These data were regressed by Eq. (2). The regression coefficients are listed in Table 3. B (2) log10 P = A + T where P is the saturation vapor pressure (kPa), T is the bubble point temperature (K), and A and B are the regression coefficients. 3.4. Phase equilibrium data for 1-butanol + water binary system The T and qi data for the binary system 1-butanol + water in completely miscible region at 2.67, 5.33 and 8.00 kPa were measured with the ebulliometer and were used to calculate the equilibrium liquid and vapor compositions for this binary system at these three pressures using the NRTL model and the determined value of f¯ . The experimental and calculated results are listed in Table 4. The iteration method employed in calculating x1,calc had been described in our previous study [3]. The iteration equation is. qi (1 + f¯ ) j+1 (3) xi,calc = j 1 + (yi,calc f¯ /xi,calc ) Table 3 Constants of the vapor pressure equation for solvent + salt mixtures System
A
B
Relative coefficient
Water + salt (1 wt.%) Water + salt (5 wt.%) Water + salt (10 wt.%) 1-Butanol + saturated salt
10.0002 10.1175 10.0417 10.4951
−2312.3 −2349.6 −2328.2 −2598.4
0.9995 0.9999 0.9991 0.9996
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Table 4 VLE data of the binary system 1-butanol (1) + water (2) at low pressures Pressure (kPa)
q1
T (K)
x1,calc
y1,calc
Pcalc (kPa)
|Pcalc − Pexp | (kPa)
8.00
0.0159 0.0196 0.5460 0.6007 0.6584 0.6975 0.7424 0.8198 0.8594 0.9002 0.9201 0.9698
313.2 313.0 312.1 312.5 313.0 313.5 314.5 317.1 319.5 322.1 324.1 328.4
0.0129 0.0159 0.5775 0.6187 0.6784 0.7187 0.7647 0.8423 0.8809 0.9193 0.9375 0.9724
0.0840 0.0976 0.2078 0.2168 0.2341 0.2500 0.2748 0.3431 0.4016 0.4904 0.5523 0.7348
7.96 7.97 8.10 8.09 7.99 7.92 7.93 7.91 8.05 7.98 8.08 8.03
0.04 0.03 0.01 0.09 0.01 0.08 0.07 0.09 0.05 0.02 0.08 0.03
5.33
0.0159 0.0196 0.5460 0.6007 0.6584 0.6975 0.7424 0.8198 0.8594 0.9002 0.9201
304.4 304.2 304.3 304.7 305.0 305.8 306.8 309.1 311.7 314.1 315.8
0.0099 0.0128 0.5786 0.6198 0.6795 0.7198 0.7659 0.8438 0.8826 0.9214 0.9394
0.1477 0.1703 0.1858 0.1949 0.2110 0.2263 0.2490 0.3105 0.3660 0.4518 0.5125
5.29 5.37 5.40 5.41 5.28 5.32 5.33 5.24 5.45 5.32 5.28
0.04 0.04 0.07 0.08 0.05 0.01 0.00 0.09 0.11 0.01 0.05
2.67
0.0159 0.0196 0.5460 0.6007 0.6584 0.6975 0.7424 0.8198 0.8594 0.9002 0.9201 0.9698
293.8 293.2 294.2 294.7 295.2 296.1 296.8 299.7 301.5 305.3 306.2 311.1
0.0120 0.0152 0.5791 0.6202 0.6797 0.7199 0.7655 0.8432 0.8818 0.9202 0.9382 0.9720
0.0997 0.1139 0.1762 0.1878 0.2081 0.2264 0.2520 0.3236 0.3822 0.4770 0.5371 0.7210
2.67 2.61 2.64 2.65 2.60 2.62 2.56 2.62 2.61 2.82 2.70 2.86
0.00 0.06 0.03 0.02 0.07 0.05 0.11 0.05 0.06 0.15 0.03 0.20
In the calculation of x1,calc and y1,calc , the NRTL parameters were obtained for the binary system at three different pressures. These values are summarized in Table 5 in which the correlation accuracy of the NRTL model was also included. The objective function in the correlation is. n F= (Pi,exp − Pi,calc )2
(4)
i
Based on the values of x1,calc in Table 4, the partially miscible binary solutions were prepared and their azeotropic temperatures, T, at three different pressures were measured with the ebulliometer. The results
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Table 5 NRTL parameters for the binary system 1-butanol (1) + water (2) at different pressures P (kPa)
8.00 5.33 2.67
NRTL model’s parameters g12 –g22 (J/mol)
g21 –g11 (J/mol)
α12
2045.239 2530.668 2074.141
7021.199 9418.433 8164.832
0.4061 0.4061 0.4602
P (kPa)
p/p (%)
0.057 0.047 0.068
0.71 0.89 2.56
are listed in Table 6. Then, the compositions of two liquid phases and vapor phase, at the experimental azeotropic temperatures of the system at three different pressures were calculated using the NRTL parameters in Table 5, by controlling the absolute deviation between the two vapor compositions corresponding to the compositions of the two liquid phases better than 0.01. Table 6 shows the calculated results and the results of the comparison between the calculated liquid phase compositions and the experimental LLE compositions obtained using the glass equilibrium still with GC analysis for the system. 3.5. Phase equilibrium data for the binary system with the salt The T and qi data for the binary system containing 1, 5 and 10 wt.% penicillin G potassium salt at 2.67, 5.33 and 8.00 kPa were measured with the ebulliometer. Then, these data were used to calculate the equilibrium liquid and vapor compositions using the modified NRTL model [8] (assuming that the salt was not present in the vapor phase). The experimental and calculated results are given in Tables 7–9. The modified NRTL model used in the calculation is in brief: ln γ1s = ln γ10 + τ1s
(5)
ln γ2s = ln γ20 + τ2s π s ln γis = τis = ln Pi0 Tis ,Ns
(6) (7)
where γis and γi0 are, respectively, the activity coefficient of component i in the binary system with salt and without salt at total pressure π. γi0 was calculated with the NRTL parameters presented in Table 5. γiss is the activity coefficient of single solvent i with salt concentration Ns at pressure π. Pi0 is the saturated vapor pressure of solvent i without salt at temperature Tis which expresses the boiling point of solvent, i, Table 6 Comparison of calculated VLLE data with the experimental VLLE data for the 1-butanol (1) + water (2) system Pressure (kPa)
8.00 5.33 2.67
T (K)
310.2 303.2 292.5
Organic phase
Water phase
y1,calc
x1,calc
x1,exp
x1
x1,calc
x1,exp
x1
0.4744 0.4761 0.4796
0.4821 0.4839 0.4857
0.0077 0.0078 0.0069
0.0351 0.0129 0.0331
0.0194 0.0128 0.0193
0.0157 0.0001 0.0138
0.1844 0.1718 0.1517
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Table 7 VLE data of the system 1-butanol (1) + water (2) containing 10 wt.% salt at low pressures Pressure (kPa)
q1
T (K)
x1,calc a
y1,calc
Pcalc (kPa)
|Pcalc − Pexp | (kPa)
y1,exp
2.67
0.0952 0.2106 0.2450 0.2950 0.4405 0.4934 0.5902 0.6517 0.6912 0.7402 0.7914 0.8338 0.8757
293.9 293.2 293.3 293.3 293.4 293.7 294.6 295.7 296.1 296.9 299.5 300.5 303.7
0.0953 0.2125 0.2481 0.3004 0.4520 0.5069 0.6070 0.6703 0.7108 0.7608 0.8122 0.8542 0.8945
0.1243 0.1694 0.1788 0.1798 0.1963 0.2071 0.2337 0.2577 0.2762 0.3045 0.3504 0.4017 0.4774
2.82 2.71 2.69 2.70 2.64 2.65 2.66 2.70 2.67 2.54 2.71 2.74 2.83
0.15 0.04 0.02 0.04 0.02 0.02 0.00 0.04 0.00 0.13 0.04 0.08 0.16
0.2392
0.0055
0.2645
−0.0117
0.0952 0.2106 0.2450 0.2950 0.4405 0.4934 0.5902 0.6517 0.6912 0.7402 0.7914 0.8338 0.8757
305.0 304.1 304.2 304.3 304.6 305.0 306.1 307.2 307.6 308.3 310.2 312.3 314.9
0.0923 0.2116 0.2467 0.2992 0.4512 0.5063 0.6066 0.6702 0.7108 0.7612 0.8128 0.8550 0.8957
0.1505 0.2002 0.201 0.2051 0.2111 0.2186 0.2392 0.2587 0.2739 0.2989 0.3378 0.3845 0.4531
5.61 5.57 5.55 5.65 5.72 5.66 5.65 5.67 5.72 5.63 5.69 5.72 5.63
0.28 0.23 0.21 0.31 0.39 0.32 0.32 0.34 0.39 0.29 0.35 0.38 0.29
0.2434
0.0042
0.2692
−0.0047
0.0952 0.2106 0.2450 0.2950 0.4405 0.4934 0.5902 0.6517 0.6912 0.7402 0.7914 0.8338 0.8757
311.9 311.3 311.2 311.3 311.6 312.1 313.2 314.4 314.7 315.6 317.3 319.6 321.9
0.0905 0.2104 0.2456 0.2980 0.4504 0.5053 0.6057 0.6692 0.7098 0.7601 0.8116 0.8536 0.8942
0.2024 0.2163 0.2231 0.2304 0.2330 0.2392 0.2586 0.2787 0.2946 0.3219 0.3633 0.4138 0.4846
8.31 8.05 8.01 8.06 8.17 8.30 8.55 8.54 8.66 8.60 8.59 8.62 8.55
0.31 0.05 0.01 0.06 0.17 0.30 0.56 0.54 0.66 0.60 0.60 0.62 0.55
0.2629
0.0043
0.2986
0.004
5.33
8.00
a
y
x1,calc stands for solute-free mol fraction.
containing salt concentration Ns at pressure π. Tis is calculated using Eq. (2) and the regression coefficients from Table 3. Then, the azeotropic temperatures were measured with the ebulliometer, and the VLLE compositions at the experimental azeotropic temperature for the partially miscible binary system with 1 and 5 wt.%
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Table 8 VLE data of the system 1-butanol (1) + water (2) containing 5 wt.% salt at low pressures Pressure (kPa)
q1
T (K)
x1,calc a
y1,calc
Pcalc (kPa)
|Pcalc − Pexp | (kPa)
2.67
0.0102 0.0186 0.4754 0.5442 0.5899 0.6453 0.6883 0.7393 0.7889 0.8277 0.8886
294.5 293.2 293.1 293.5 293.7 294.6 295.8 296.4 297.8 299.7 304.0
0.0069 0.0137 0.4892 0.5605 0.6077 0.6648 0.7089 0.7608 0.8108 0.8492 0.9075
0.0808 0.1256 0.1810 0.1974 0.2105 0.2315 0.2531 0.2829 0.3245 0.3711 0.4849
2.57 2.65 2.52 2.64 2.57 2.56 2.55 2.57 2.58 2.90 2.66
0.10 0.02 0.14 0.03 0.10 0.11 0.12 0.10 0.09 0.23 0.01
0.0102 0.0186 0.4754 0.5442 0.5899 0.6453 0.6883 0.7393 0.7889 0.8277 0.8886
305.6 304.4 304.3 305.0 305.8 306.2 307.3 308.3 309.8 311.4 315.8
0.0055 0.0114 0.4886 0.5601 0.6074 0.6647 0.7090 0.7613 0.8114 0.8501 0.9087
0.1123 0.1791 0.1927 0.2050 0.2164 0.2325 0.2500 0.2761 0.3126 0.3533 0.4592
5.44 5.56 5.55 5.56 5.46 5.44 5.36 5.55 5.26 5.41 5.56
0.11 0.23 0.22 0.23 0.12 0.10 0.02 0.22 0.07 0.08 0.22
0.0102 0.0186 0.4754 0.5442 0.5899 0.6453 0.6883 0.7393 0.7889 0.8277 0.8886
313.1 312.1 311.5 312.1 313.4 313.5 314.5 315.2 317.0 318.0 322.2
0.0078 0.0147 0.4876 0.5591 0.6065 0.6638 0.7081 0.7603 0.8102 0.8488 0.9073
0.0632 0.1021 0.2131 0.2241 0.2360 0.2517 0.2699 0.2975 0.3373 0.3795 0.4893
7.80 7.66 7.87 7.96 8.23 8.17 8.36 8.31 8.18 8.36 8.17
0.20 0.34 0.13 0.04 0.24 0.17 0.36 0.31 0.18 0.36 0.17
5.33
8.00
a
y1,exp
y
0.1908
−0.0066
0.2533
0.0002
0.2026
−0.0024
0.2419
−0.0081
0.2307
0.0066
0.2733
0.0034
x1,calc stands for solute-free mol fraction.
salt at three different pressures were calculated using the modified NRTL model. These results are shown in Table 10. Since the binary system with 10 wt.% salt is completely miscible, no calculation of VLLE compositions for this mixture was performed. Furthermore, in order to examine the calculated VLE and VLLE compositions, some experimental VLE and VLLE data using the glass equilibrium still [5] with GC analysis were compared with the calculated VLE and VLLE data, as shown in Tables 7–10. The results of this comparison are satisfactory except that the absolute deviations of the liquid compositions in the water phase in Table 10 are larger than 0.02.
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Table 9 VLE data of the system 1-butanol (1) + water (2) containing 1 wt.% salt at low pressures Pressure (kPa)
q1
T (K)
x1,calc a
y1,calc
Pcalc (kPa)
|Pcalc − Pexp | (kPa)
2.67
0.0103 0.0191 0.4966 0.5493 0.5914 0.6331 0.6850 0.7448 0.7905 0.8329 0.8749
294.1 292.9 292.9 293.0 293.5 293.9 294.9 296.8 298.8 300.5 303.7
0.0070 0.0142 0.5113 0.5660 0.6095 0.6525 0.7058 0.7666 0.8125 0.8545 0.8948
0.0803 0.1257 0.1820 0.1943 0.2071 0.2217 0.2455 0.2837 0.3245 0.3755 0.4511
2.64 2.56 2.57 2.51 2.52 2.50 2.53 2.65 2.76 2.87 2.79
0.03 0.11 0.10 0.16 0.14 0.17 0.14 0.02 0.09 0.20 0.12
0.0103 0.0191 0.4966 0.5493 0.5914 0.6331 0.6850 0.7448 0.7905 0.8329 0.8749
305.3 304.4 303.9 304.4 304.9 305.4 306.5 308.3 310.2 312.3 314.9
0.0056 0.0116 0.5107 0.5655 0.6091 0.6523 0.7058 0.7670 0.8130 0.8552 0.8959
0.1127 0.1797 0.1934 0.2034 0.2135 0.2255 0.2453 0.2776 0.3130 0.3595 0.4279
5.40 5.62 5.55 5.51 5.55 5.52 5.52 5.54 5.50 5.52 5.52
0.07 0.29 0.22 0.18 0.22 0.19 0.18 0.21 0.17 0.19 0.19
0.0103 0.0191 0.4966 0.5493 0.5914 0.6331 0.6850 0.7448 0.7905 0.8329 0.8749
312.3 312.0 311.0 311.5 312.0 312.6 313.7 315.4 317.3 319.6 321.9
0.0079 0.0151 0.5097 0.5645 0.6082 0.6513 0.7048 0.7659 0.8118 0.8538 0.8944
0.0635 0.1039 0.2141 0.2233 0.2330 0.2455 0.2662 0.3008 0.3389 0.3892 0.4600
7.62 7.65 7.61 7.70 7.76 7.86 8.03 8.37 8.20 8.01 8.22
0.38 0.35 0.39 0.30 0.24 0.14 0.03 0.37 0.20 0.01 0.22
5.33
8.00
a
y1,exp
y
0.2009
−0.0062
0.2777
−0.006
0.2062
−0.0073
0.2728
−0.0048
0.2283
−0.0047
0.3148
0.014
x1,calc stands for solute-free mol fraction.
3.6. The salt effect of penicillin G potassium salt on the binary system 1-butanol + water To investigate the salt effect of the binary system, T–x–y data for the binary system without salt and with 1, 5 and 10 wt.% salt at 5.33 kPa are displayed in Figs. 1 and 2. The salt effect at 2.67 and 8.00 kPa is basically identical with that at 5.33 kPa. From Figs. 1 and 2, it is found that the addition of 1 and 5 wt.% salt to the 1-butanol + water system increases the azeotropic temperature slightly. The mutual solubility of 1-butanol and water increases, and when the salt concentration reaches 10 wt.%, the system becomes
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Table 10 Comparison of the calculated VLLE data with the experimental VLLE data for the 1-butanol (1) + water (2) system containing salt Salt concentration
Pressure T (K) (kPa)
Organic phase
Water phase
Vapor phase
x1,calc
x1,exp
x1
x1,calc
x1,exp
x1
y1,calc
y1,exp
y1
5 wt.%
8.00 5.33 2.67
311.1 303.8 293.0
0.4342 0.4291 0.4408
0.4413 0.4334 0.4481
0.0071 0.0043 0.0073
0.0605 0.0134 0.0345
0.0421 0.0129 0.0131
0.0184 0.0055 0.0214
0.2064 0.1901 0.1762
0.1971 0.1932 0.1824
0.0093 0.0031 0.0062
1 wt.%
8.00 5.33 2.67
310.6 303.6 292.7
0.4562 0.4491 0.4608
0.4510 0.4587 0.4677
0.0052 0.0096 0.0069
0.0555 0.0131 0.0335
0.0343 0.0130 0.0122
0.0212 0.0001 0.0213
0.2042 0.1889 0.1739
0.1953 0.1910 0.1795
0.0089 0.0012 0.0056
completely miscible. The boiling temperature of water containing the salt rises slightly, whereas that of 1-butanol containing the salt decreases. These results demonstrate that the salt effect of the penicillin G potassium salt on the phase equilibrium of the binary system is complicated and different from that of inorganic salts and small molecular organic salts. It had been reported in the literature [9] that the salt effect of NaBr on LLE for the 1-butanol + water binary system results in a reduction of the mutual solubility of the two components because, as is well known, the affinity of NaBr for water is strong whereas that for 1-butanol is weak. But the salt effect of the penicillin G potassium salt leads to an increase in the mutual solubility of 1-butanol and water, even though there is also a stronger affinity of the penicillin G potassium salt for water than for 1-butanol, which is confirmed by the large solubility of the penicillin G potassium salt in water and the small solubility of the salt in 1-butanol. The difference in salt effect of
Fig. 1. The T–x–y curve for the system 1-butanol (1) + water (2) containing different salt concentrations at 5.33 kPa (x1 : solute-free mole fractions of 1-butanol).
Z. Gao et al. / Fluid Phase Equilibria 214 (2003) 137–149
147
Fig. 2. The T–x–y curve for the system 1-butanol (1) + water (2) containing 10 wt.% at 5.33 kPa (x1 : solute-free mole fractions of 1-butanol).
inorganic salts and large molecular organic salts can be explained from the complicated structure of the penicillin G potassium salt:
This structural formula shows that penicillin G potassium salt is not only a high molecular weight compound but also contains various polar and nonpolar chemical groups. So the interaction of penicillin G potassium salt molecules with water and 1-butanol molecules is quite complicated and the size effect of the large penicillin G potassium salt molecules in the binary system has to be considered too, which causes the penicillin G potassium salt to have a special salt effect, different from simple inorganic salts. In a word, it is thought that the special salt effect of penicillin G potassium salt on the phase equilibria of 1-butanol + water, causing the mutual solubility of the two components to increase, is due to various interaction of the salt with water and 1-butanol, respectively and the size effect of the salt molecules. 4. Conclusion The ebulliometric method was used to determine isobaric phase equilibrium data for the binary system 1-butanol + water without salt and with the penicillin G potassium salt at 2.67, 5.33 and 8.00 kPa. qi and T data for the binary system without the salt and with the salt at three different pressures were measured with a small ebulliometer. These data were used to calculate VLE compositions by using the NRTL model and modified NRTL model, respectively. The VLLE compositions at the azeotropic temperature
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for the binary system without salt and with the salt at three different pressures were also calculated using the NRTL parameters obtained in calculating VLE compositions and using a modified NRTL model, respectively. Some of the calculated results were confirmed by experiments with an equilibrium still and GC analysis. In addition, the salt effect of penicillin G potassium salt on the phase equilibrium of the binary system was found to increase the mutual solubility of the two components and to raise slightly the azeotropic temperature. This is different from the salt effect of the inorganic salt reported in literature [9]. The special salt effect of penicillin G potassium salt was considered to be due to its complicated molecule structure, containing various polar and nonpolar chemical groups and its large molecular volume. List of symbols f¯ F g12 –g22 , g21 –g11 L P q T V x y
mean evaporation coefficient objective function interaction parameters in NRTL model liquid stream (mol/h) pressure (kPa) feed composition (mol fraction) temperature (K) vapor stream (mol/h) liquid composition (mol fraction) vapor composition (mol fraction)
Greek letters α12 γ
nonrandomness factor in NRTL model activity coefficient
Superscripts 0 j s
no salt iteration number containing salt
Subscripts calc exp i
calculation experimental component i
Acknowledgements This research was funded by State Key Laboratory of Chemical Engineering in China and by 985 project of Tianjin University in China. References [1] J.K. Wang, M.J. Zhang, T. Wan, Z.C. Ping, G.A. Han, J. Chem. Ind. Eng. (China) 47 (1996) 100–104.
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