Article pubs.acs.org/jced
Solubility of 3‑Aminobenzoic Acid in Supercritical Carbon Dioxide Modified by Ethanol Ying Li, Yanying Ning, Junsu Jin,* and Zeting Zhang College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China S Supporting Information *
ABSTRACT: The solubilities of 3-aminobenzoic acid with different concentrations of ethanol cosolvent in supercritical carbon dioxide were measured by using flow-type equipment at pressures from 10.0 MPa to 21.0 MPa and temperature 308 K to 328 K. The effects on solubility of 3-aminobenzoic acid in SCCO2 with ethanol mole concentration of 1.0 % were investigated at temperatures of 308 K, 318 K, and 328 K; then, the study was also carried out with ethanol mole concentrations of 2.0 % and 4.0 % at 318 K, respectively. The experimental results revealed that the equilibrium solubility of 3-aminobenzoic acid was effectively increased in the presence of ethanol. The measured solubility data were correlated using the modified Sovova model, the modified Chrastil model, and the modified MST model, and the best agreement was obtained applying the modified Sovova model.
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modified by González et al.13 and the MST model modified by Thakur and Gupta,14 respectively.
INTRODUCTION
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The solubility of a solid solute in supercritical fluid (SCF) varies significantly with solvent density; that makes SCF an attractive solvent for extraction and distillation processes. Now, supercritical carbon dioxide (SCCO2) extraction technology has been widely applied as an environmentally friendly separation method for its economic and social benefits.1−4 The solubility data of a solid in SCF, especially in SCCO2 is indispensable for the design of a SCF technology process. However, the solubility of solute with strong polarity is low in SCCO2 due to its nonpolarity, which limits the application of SCCO2 in supercritical fluid extraction.5,6 The previous studies found that the addition of a small amounts of organic solvents can improve its solvent power.7−10 Therefore, it is important to know the solubility of solid solute in pure SCCO2 and in SCCO2 modified by ethanol cosolvent. 3-Aminobenzoic acid (3-ABA) is a momentous intermediate in organic synthesis, pharmaceuticals, and dyestuffs. Consequently, it is significant to determine the solubility of 3-ABA in environmentally friendly solventSCCO2. In our previous work,11 we found that the solubility of 3-ABA in pure SCCO2 was low. Thus, it is important to study the solubility of 3-ABA in SCCO2 with cosolvents. In this study, the experimental and theoretical investigations of 3-ABA solubility in SCCO2 modified by ethanol were conducted at 308 K to 328 K and 10.0 MPa to 21.0 MPa with the mole concentration of cosolvent from 1.0% to 4.0%. Moreover, the influences of temperature, pressure, and especially cosolvent concentration on the solubility of 3-ABA in SCCO2 were investigated in detail. The experimental solubility data were correlated by the Sovova model modified by Tang et al.,12 the Chrastil model © 2013 American Chemical Society
EXPERIMENTAL SECTION Material. Carbon dioxide (mass purity ≥ 99.9 %) was obtained from Beijing Praxair Industrial Gas Co., Ltd. 3-ABA (C7H7NO2) with a mass purity of 99.0 % was obtained from Beijing Hengye Zhongyuan Chemical Co., Ltd. The chemical structure of 3-ABA was shown in Figure 1, and the melting
Figure 1. Chemical structure of 3-aminobenzoic acid.
point, which is 447.2 K, was retrieved from the Web site of Chem. YQ. Ethanol (mass purity ≥ 99.7 %) was obtained from the Beijing Chemical Reagent Factory. No purification process was carried out on the chemicals before experiment. Apparatus and Procedure. The solubility of 3-ABA in SCCO2 with ethanol was determined upon a flow-type Received: January 25, 2013 Accepted: July 17, 2013 Published: July 30, 2013 2176
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Figure 2. Schematic diagram of the experimental apparatus: 1, CO2 cylinder; 2, compressor; 3, high-pressure surge flask; 4, back pressure valve; 5, pressure regulating valve; 6, cosolvent vessel; 7, high-pressure pump; 8, cosolvent regulating valve; 9, preheating and mixing cell; 10, safety valve; 11, pressure gauge; 12, temperature controller; 13, heater; 14, constant-temperature stirred water bath; 15, high-pressure equilibrium cell; 16, decompression sampling valve; 17, thermometer; 18, heating coils; 19, U-shaped container; 20, rotated flow meter; 21, wet-gas flow meter.
The reliability of the experimental equipment was confirmed in our previous papers via the study about the other benzoic acid derivatives.15,16 In this paper, each data point was measured three times, and the average value was used for the further study. To obtain a low experimental error, the error of each measurement was lower than 5%.
apparatus as shown in Figure 2. In the apparatus, a high pressure equilibrium cell (available volume of 150 mL) was installed in a water bath with stirring (CS-530, Chongqing Yinhe Experimental Instrument Corporation). The temperature in the cell was controlled using a temperature controller (controlling error was ± 0.5 K). The temperature in the cell was also measured using a thermometer (platinum resistancetype, XMT, Beijing Chaoyang Automatic Instrument Factory). The pressure was measured using a pressure meter (Heise, CTUSA). The measurement error was ± 0.1 K for temperature and ± 0.05 MPa for pressure. Before entering into the cell, CO2 was first compressed through a compressor (NOVA, 5542121). The cosolvent, ethanol, was pumped via a high pressure pump (Beijing Satellite Factory, LB-10C). The controlling error of the pump was ± 0.01 mL/min. CO2 and ethanol were blended first. The temperature was controlled using an electricity coil. Then, the mixture of CO2 and ethanol was pumped into the equilibrium cell from bottom at a desired pressure and temperature, in which about 40 g to 50 g of 3-ABA was loaded. The flow rate of CO2 was 0.6 L/min, and the residence time in the cell was no less than 30 min. Then, the saturated CO2 was introduced into the cell via a decompress valve. That valve was also heated using a coiled heater. Then, the stream flowed into two U-type tubes. A calibrated wet-gas flow meter (Changchun Instrument Factory, LML-2) was used to determine the volume of CO2. The measurement error of the flow meter was ± 0.01 L under the experimental temperature and pressure. Analytical Methods and Solubility Measurements. The contents of the chemicals in the U-shaped containers were measured with an UV spectrophotometer (UNICO, UV2100). The reference solution was deionized water. The maximum UV absorption of 3-ABA was 229 nm. A calibration curve of solute concentration was established and the regression coefficient was higher than 0.9995. The mole solubility of solute in SCCO2 was calculated as follows: yt =
St × M1 St × M1 + ρ × M 2
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RESULTS AND DISCUSSION The mole fraction solubility data of 3-ABA in SCCO2 in the presence of ethanol cosolvent, with the concentration of 1.0 %, at temperatures of 308 K, 318 K, and 328 K over the pressures range of 10.0 MPa to 21.0 MPa is listed in Table 1. The density of CO2 was also shown in Table 1. These data were collected from the NIST database, and the solubility values of 3-ABA in pure SCCO2 were also included in Table 1. Moreover, the solubility data of 3-ABA in SCCO2 with ethanol mole fraction of 1.0 %, 2.0 %, and 4.0 % at 318 K are listed in Table 2. Effect of Pressure and Temperature on Solubility. It can be perceived from Table 1 and Figure 3 that the equilibrium solubility of 3-ABA increased with the increase of pressure at the experimental temperatures (308, 318, and 328) K. The solvent density increases and the interactions between the molecules of solute and solvent become stronger with the increase of pressure. This is the reason for the change of solubility. Furthermore, in Figure 3, shows the crossover pressure regions at the range of (11.5 to 12.2) MPa for 3-ABA. The crossover pressure regions should be the result of a competing effect of the vapor pressure of the solute and the solvent density. The dependence of the two variables on the temperature are in opposite directions. The solute solubility mainly increases with the increase of the solute vapor pressure and the solvent density. While, the solute vapor pressure increases and the solvent density decreases with temperature increasing. At the pressure below the crossover pressure region, the solid solute was more soluble at low temperature than high temperature because the solvent density effect on the solute solubility is more sensitive to the solute solubility than the solute vapor pressure. However, at the pressure above the crossover pressure region, the solvent density becomes less sensitive than the solute vapor pressure, therefore, the solid solute solubility increases with increasing temperature. These two competitive factors act equally at the crossover point. To compare the promotion effect of the ethanol on the 3ABA in SCCO2, the solubility enhancement factor (E) was defined as the ratio of the solubility obtained with ethanol to
(1)
where yt is the mole fraction solubility of the solute (mol·mol−1); St is the solubility of solute (g·L−1); M1 is the molecular weight of CO2; and M2 is the molecular weight of 3ABA (g·mol−1); ρ is the density of CO2 (room temperature and atmospheric pressure) (g·L−1). 2177
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Table 1. The Mole Fraction Solubility of 3-ABA in Pure SCCO2 and Modified SCCO2 by Ethanol in Mole Fraction of 1.0 %, and Solubility Enhancement Factor (E) of Ethanol P/MPa
a
ρ/g·L
−1b
binaryc
ternary
6
106yt
E
10 yb
10.0 12.0 15.0 18.0 21.0 average
714.8 768.4 816.1 848.9 874.4
T = 308 K 1.90 1.99 2.45 2.79 2.92
10.0 12.0 15.0 18.0 21.0 average
502.6 659.7 743.2 790.2 823.7
T = 381 K 1.75 2.92 3.50 4.24 4.87
2.61 3.10 3.88 4.32 5.11
± ± ± ± ±
0.10 0.10 0.09 0.15 0.16
1.49 1.06 1.11 1.02 1.05 1.15
10.0 12.0 15.0 18.0 21.0 average
326.4 506.9 654.9 724.1 768.7
T = 328 K 1.79 3.07 4.68 5.65 6.57
2.05 3.25 4.95 5.94 6.93
± ± ± ± ±
0.06 0.06 0.17 0.12 0.26
1.15 1.06 1.06 1.05 1.05 1.07
2.70 3.13 3.38 3.39 3.47
± ± ± ± ±
0.08 0.08 0.13 0.11 0.10
1.42 1.57 1.38 1.22 1.19 1.36
Figure 3. The mole fraction solubility (yt) of 3-ABA in SCCO2 modified by ethanol (1.0 mol %): ●, 308 K; ▲, 318 K; ■, 328 K.
Standard uncertainties u are u(T) = 0.1 K, u(P) = 0.05 MPa. bρ is the density of pure CO2 at different experimental pressures and temperatures. The values are obtained from the NIST fluid property database. cThe solubility data of the binary system is obtained from ref 11. a
that without ethanol at the same pressure and temperature as follows: y E= t yb (2)
Figure 4. The mole fraction solubility (yt) of 3-ABA in SCCO2 modified by ethanol at 318 K: ●, 0.0 %; ▲, 1.0 %; ■, 2.0 %; ⧫, 4.0 %.
where, yt and yb are the mole fraction solubilities of 3-ABA in SCCO2 in ternary (3-ABA + ethanol + SCCO2) and binary (3ABA + SCCO2) systems, respectively. The average of the E values were 1.36 for 308 K, 1.15 for 318 K and 1.07 for 328 K respectively, which were also listed in Table 1. The average of the E value under different pressures decreased with temperature increasing. The results show that when the temperature increases, the enhancement effect of the cosolvent reduced; and the enhancement effect of the cosolvent decreases with the increase of pressure. Effect of Ethanol Concentration on Solubility. It can be perceived from Table 2 and Figure 4 that the addition of
ethanol with the concentration of 1.0 %, 2.0 %, and 4.0 % enhances the solubility of 3-ABA in SCCO2 at temperature of 318 K in the pressure range of 10.0 MPa to 21.0 MPa. The E values were 1.15, 1.23, and 1.66 at ethanol mole concentration of 1.0 %, 2.0 %, and 4.0 %, respectively. Such results could be explained from two aspects. On the one hand, the density of supercritical mixed fluid increases with the increase of cosolvent concentration, leading to the improvement of 3-ABA solubility in SCCO2. On the other hand, the molecular interaction between the cosolvent and the
Table 2. The Mole Fraction Solubility of 3-ABA and Solubility Enhancement Factor (E) in SCCO2 with Ethanol in Mole Fractions of 1.0 %, 2.0 %, and 4.0 % at 318 K 1.0 %
2.0 %
4.0 %
P (MPa)
106yt
E
106yt
E
106yt
E
10.0 12.0 15.0 18.0 21.0
2.61 ± 0.10 3.10 ± 0.10 3.88 ± 0.09 4.32 ± 0.15 5.11 ± 0.16 average
1.49 1.06 1.11 1.02 1.05 1.15
3.03 ± 0.07 3.40 ± 0.06 4.00 ± 0.09 4.49 ± 0.13 5.21 ± 0.11 average
1.73 1.16 1.14 1.06 1.07 1.23
4.47 ± 0.15 4.73 ± 0.14 5.25 ± 0.21 5.71 ± 0.17 6.14 ± 0.22 average
2.55 1.62 1.50 1.35 1.26 1.66
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less than that of temperature, so, better AARD (%) of the modified Sovova model (5.03) and the modified Chrastil model (6.79) were obtained than that of the modified MST model (17.50), whereas the effect of solubility in the pure SCCO2 is only taken into account in the modified Sovova model. From the correlation results, it was found that the effect of the solute solubility in pure SCCO2 cannot be ignored in forecasting the solubility of solid solute in SCCO2 with cosolvent.
solute is enhanced with the increase of cosolvent concentration, promoting the dissolution of solute in SCCO2. Model Correlation. In this study, the equilibrium solubility data of 3-ABA in SCCO2 with ethanol was correlated using the modified Sovova model,12 the modified Chrastil model,13 and the modified MST model.14 The modified Sovova model12 is formulized as yt − yb = a0yca1 yba 2 ea3/T
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(3)
CONCLUSIONS The solubilities of 3-ABA in SCCO2 with ethanol as cosolvent were measured at the three temperatures of 308 K, 318 K, and 328 K and over the pressure of 10.0 MPa to 21.0 MPa. The mole concentration of ethanol was 1.0 %, 2.0 %, and 4.0 % in the experiments. The crossover pressure in the ternary system (3-ABA + ethanol + SCCO2) was 11.5 MPa to 12.2 MPa. The solubility enhancement factor (E) of ethanol as cosolvent increases with the decrease of temperature and the increase of concentration of ethanol in SCCO2. The measured data in the ternary system (3-ABA + ethanol + SCCO2) were correlated using the modified Sovova model, the modified Chrastil model, and the modified MST model, and the total values of AARD (%) were 5.03, 6.79, and 17.50, respectively.
where T is the temperature (K); yc is the mole fraction of cosolvent in SCCO2 (mol·mol−1); a0, a1, a2, and a3 are parameters that are irrelative to temperature and pressure and should be determined by experimental data. The modified Chrastil model13 formula is expressed as ln St = b0 + b1 ln ρ + b2 /T + b3 ln Sc
(4)
−1
where ρ is the density of CO2 (g·L ); St is the solubility of the solute (g·L−1); Sc is the concentration of cosolvent (g·L−1); b0 is parameter relating to the solution enthalpy and vaporization enthalpy of the solute; b2 is parameter relating to the molecular weight and melting point of the solute. Thakur and Gupta14 proposed a modified form of the MST model, which is expressed as T ln(yt P) = c0 + c1ρ + c 2ρyc + c3yc
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(5)
where, ρ, T, and P are the density of CO2 (mol·mL ), temperature (K), and pressure (bar), respectively; c0, c1, c2, and c3 are adjustable parameters. The following formula was used to calculate the average absolute relative deviation (AARD (%)) of the model: AARD /% =
100 N
n
∑
Experimental data summary. This material is available free of charge via the Internet at http://pubs.acs.org.
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yexp
AUTHOR INFORMATION
Corresponding Author
*Tel.: +86-10-64434788. Fax: +86-10-64436781. E-mail: jinjs@ mail.buct.edu.cn.
|ycal − yexp |
i=1
ASSOCIATED CONTENT
S Supporting Information *
−1
(6)
Funding
where, ycal is the calculated value of the mole fraction solubility of solute (mol·mol−1); yexp is the experimental value of the mole fraction solubility of solute (mol·mol−1); and N is the number of data points. In Table 3, it were listed the correlated results and optimal parameters using the three models.
This research was financially supported by the National Natural Science Foundation of China (No. 21176012), the Natural Science Foundation of Jiangsu Province (No. BK2012595), and the financial support from Petrochina Limited Company (No. 2012A-2012-01). The authors are grateful to the support of this research from the Mass Transfer and Separation Laboratory in Beijing University of Chemical Technology.
Table 3. Correlation Parameters and Results of Solubility of 3-ABA in SCCO2 with Ethanol Using the Modified Sovova Model, the Modified Chrastil Model and the Modified MST Model
Notes
models modified Sovova modified Chrastil modified MST
correlation parameters −14
a0 = 4.5367·10 ; a1 = 1.0441; a2 = −0.75599; a3 = 3525.9 b = −7.2807; b1 = 1.9553; b2 = −3415.8; b3 = 0.20750 c0 = −3182.7; c1 = 47356; c2 = −26452; c3 = 3963.5
The authors declare no competing financial interest.
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