Article pubs.acs.org/jced
Solubility of o-Nitrobenzoic Acid in Modified Supercritical Carbon Dioxide at (308 to 328) K Jun-su Jin,† Zi-ming Dou,† Hong-hai Liu,‡ Hao Wu,*,† and Ze-ting Zhang† †
College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029, China Lanzhou Petrochemical Corporation of CNPC, Gansu, 730060, China
‡
ABSTRACT: The equilibrium solubility of o-nitrobenzoic acid in supercritical carbon dioxide with cosolvents was determined with the dynamic method at temperatures of (308, 318, and 328) K and pressures in the range of (10.0 to 21.0) MPa. Ethanol and ethyl acetate were chosen as the cosolvents with a mole fraction of 3.5 %. The equilibrium solubility of onitrobenzoic acid can be enhanced by the presence of both cosolvents. The enhancement effects of ethanol and ethyl acetate were compared at 318 K; ethyl acetate showed a better cosolvent effect. The experimental data were correlated by the modified Méndez-Santiago and Teja model and the modified Sovova model. The results showed that the two models were able to reasonably correlate the experimental solubility data.
■
INTRODUCTION In the past years, widespread attention has been paid to supercritical fluids (SCFs), due to their potential application in many industrial processes, such as pharmaceuticals, food processing, separation processes, and polymer processing.1−4 Carbon dioxide (CO2) is the most used SCF, since it is nontoxic, inflammable, and inexpensive and it has moderate critical constants (Tc = 304.15 K, Pc = 7.38 MPa). While supercritical carbon dioxide (SCCO2) has many desirable properties, sometimes the solubility of certain compounds in SCCO2 is low as a result of its lack of polarity. People have come to know that adding a small amount of polar cosolvent to SCCO2 often leads to an enhancement in the solubility of a solute.5−7 High-pressure equilibrium solubility data of compounds in SCCO2 are among the most important thermophysical properties that are essential to the SCF process design. Though a number of solid solubility data in SCCO2 have been reported previously,8,9 the available solubility data for solid solute in SCCO2, especially in the system involving cosolvents, are scare. Compounds with various functional groups usually have great variations in the magnitude of solubility in SCCO2. Our laboratory has been studying the solid solubilities of benzoic acid with different positions and classes of functional groups from the 1990s.10−13 o-Nitrobenzoic acid is extensively used as intermediate for the synthesis of pharmaceuticals and dyes. To the best of our knowledge, no solid solubility data regarding this compound have yet been reported before. In our previous work, the solubility data of o-nitrobenzoic acid in pure SCCO2 were measured and correlated.14 As part of our overall research, we have measured the solubility of o-nitrobenzoic acid in SCCO2 with cosolvents at (308, 318, and 328) K from (10.0 to 21.0) MPa in this study. Ethanol and ethyl acetate were chosen as the cosolvent, respectively. Two density-based models, the modified Méndez-Santiago and Teja15 and the modified Sovova11 models, © 2012 American Chemical Society
were employed to correlate the solubility data. The present work is a part of our long-term objective to predict the solubility behavior of solutes in SCFs by analyzing the contribution of functional groups.
■
EXPERIMENTAL SECTION Materials. High-purity CO2 (more than 99.9 % mass fraction) was supplied by Beijing Praxair Industrial Gas Co., Ltd. o-Nitrobenzoic acid (C7H5NO4, a mass purity of more than 99.0 %) was purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd. The melting point of o-nitrobenzoic acid retrieved from the website of Chem YQ is in the range of (420.15 to 421.15) K. Ethanol (with a minimum mass purity of more than 99.7 %) and ethyl acetate (with a minimum mass purity of more than 99.5 %) were obtained from Beijing Chemical Reagent Factory. All of the chemicals were used without further purification. Apparatus and Procedure. The solubility of o-nitrobenzoic acid in modified SCCO2 was measured using a flow-type apparatus as shown schematically in Figure 1. A detailed description of the apparatus and operating procedure had been given in detail in our previous work.10,11 Liquid CO2 was first compressed to the desired operating pressure by a high-pressure syringe pump, while the cosolvent was compressed by a highpressure pump. The concentration of the cosolvent was controlled by regulating the high-pressure gauge pump, accurate to ± 0.01 mL·min−1. After the CO2 and cosolvents were mixed sufficiently in the preheating and mixing cell, they were introduced into a high-pressure equilibrium cell with an available volume of 150 mL, which was loaded with about (40 or 50) g of solute. The equilibrium cell was immersed into a constantReceived: February 1, 2012 Accepted: June 21, 2012 Published: July 17, 2012 2217
dx.doi.org/10.1021/je300023v | J. Chem. Eng. Data 2012, 57, 2217−2220
Journal of Chemical & Engineering Data
Article
at a fixed wavelength of 268 nm. The solute in the U-shape tubes was dissolved in water. In this work, each reported datum was an average of at least five replicated sample measurements. The solubility data obtained were found to be reproducible within ± 5 %.
■
THEORETICAL SECTION
Equation of state (EOS) based models and semiempirical models are used to correlate the solubility data frequently. However, EOS based models require the physical chemistry properties of the solute. These data are normally not available for many complex compounds. Thus, semiempirical models are more suitable to correlate the solubility. The modified MendezSantiago and Teja model and the modified Sovova model are two frequently used semiempirical models, which could correlate the solubility of solutes in modified SCF. Sauceau et al.15 proposed a modified Mendez-Santiago and Teja equation (denoted as modified MST) for ternary cosolvent system. The correlation equation is given in eq 1:
Figure 1. Schematic diagram of the experimental apparatus: 1, CO2 cylinder; 2, high-pressure syringe pump; 3, surge flask; 4, pressure regulating valve; 5, preheating and mixing cell; 6, preheating coil; 7, high-pressure equilibrium cell; 8, pressure gauge; 9, thermometer; 10, decompression sampling valve; 11, heating coil; 12, U-shape tube; 13, rotated flow meter; 14, wet gas flow meter;15, cosolvent vessel; 16, highpressure pump; 17, cosolvent regulating valve; 18, constant-temperature stirred water bath.
temperature stirred water bath, and the temperature was maintained constant within ± 0.5 K by a temperature controller. The temperature and pressure in the cell were measured by a calibrated internal platinum resistance thermometer and a calibrated pressure gauge, respectively. The accuracy of the temperature measurement is ± 0.1 K, and that for the pressure is ± 0.05 MPa. After achievement of phase equilibrium in the cell, the saturated fluid was vented from the top of the cell and then expanded from the decompression sampling valve into a twoconnected U-type tube. The solute finally was separated and collected in the tube in turn. The overall volume of CO2 exited from the tube was measured by the calibrated wet gas flow meter with an uncertainty of ± 0.01 L at room temperature and atmospheric pressure. A model 2100 Unico UV−vis spectrophotometer was used to determine the amount of o-nitrobenzoic acid in the U-shape tube
T ln
y2 ′P Pstd.
= b0 + b1ρf + b2y3 + b3T
(1)
where y2′ is the mole fraction solubility of o-nitrobenzoic acid in SCF with cosolvents; y3 is the mole fraction of cosolvent; Pstd. is the standard pressure (atmospheric pressure equal to 101.325 Pa); T (K) and P (KPa) are the operating temperature and pressure; b0, b1, b2, and b3 are adjustable parameters; ρf (kg·m−3) is the density of CO2 and cosolvent complex. In our work, the densities of SCF mixtures were assumed as the same values of pure SCCO2 because that the concentrations of solute and cosolvent in the SCF phase are relatively dilute. By means of the linear regression analysis of the experimental data, we found that when the mole fraction y3 of colsolvent is kept constant, eq 1 can also be written as:
Table 1. Mole Fraction Solubility of o-Nitrobenzoic Acid in Pure (y2) and Modified (y2′) SCCO2 and Solubility Enhancement Factor cosolvent
a b
T/K
ethanol
308
ethanol
318
ethanol
328
ethyl acetate
318
P/MPa 10.0 12.0 15.0 18.0 21.0 10.0 12.0 15.0 18.0 21.0 10.0 12.0 15.0 18.0 21.0 10.0 12.0 15.0 18.0 21.0
ρa/kg·m−3
106 y214
714.84 768.42 816.06 848.87 874.40 502.57 659.73 743.17 790.18 823.71 326.40 506.85 654.94 724.13 768.74 502.57 659.73 743.17 790.18 823.71
3.74 ± 0.02 5.13 ± 0.02 6.20 ± 0.05 7.72 ± 0.06 8.34 ± 0.08 2.20 ± 0.03 6.67 ± 0.03 11.28 ± 0.05 14.27 ± 0.07 18.42 ± 0.09 1.52 ± 0.02 6.96 ± 0.03 17.00 ± 0.06 27.01 ± 0.08 35.61 ± 0.15 2.20 ± 0.03 6.67 ± 0.03 11.28 ± 0.05 14.27 ± 0.07 18.42 ± 0.09 b
105 y2′
e
1.13 ± 0.03b 1.59 ± 0.05 3.82 ± 0.06 6.67 ± 0.08 9.18 ± 0.09 0.27 ± 0.01 1.87 ± 0.07 8.79 ± 0.07 20.04 ± 0.09 27.35 ± 0.12 0.21 ± 0.01 2.11 ± 0.08 15.57 ± 0.10 35.24 ± 0.11 61.91 ± 0.14 0.57 ± 0.03 4.67 ± 0.06 14.30 ± 0.09 23.57 ± 0.13 34.20 ± 0.17
3.02 3.10 6.16 8.64 11.01 1.23 2.80 7.79 14.04 14.85 1.38 3.03 9.16 13.05 17.39 2.59 7.00 12.68 16.52 18.57
ρ is the density of pure CO2 at different experimental pressures and temperatures, which is obtained from the NIST fluid property database. Standard uncertainties for the measured quantities. 2218
dx.doi.org/10.1021/je300023v | J. Chem. Eng. Data 2012, 57, 2217−2220
Journal of Chemical & Engineering Data T ln
y2 ′P Pstd.
= b4 + b1ρ + b3T
Article
(2)
−3
where b4 = b0 + b2y3; ρ (kg·m ) is the density of pure SCCO2, and it was recommended by the National Institute of Standards and Technology website as shown in Table 1. Moreover, when the mole fraction y3 of colsolvent and the temperature T are kept constant in the meantime, another simplified equation can be written as: T ln
y2 ′P Pstd.
= b5 + b1ρ
(3)
where b5 = b0 + b2y3 + b3T. Recently, a modified Sovova model11 has been proposed by Tang et al., which can be used to correlate the solubility of solids in modified SCCO2 in the form of eq 4: c ln(y2 ′ − y2 ) = ln c0 + c1 ln y3 + c 2 ln y2 + 3 (4) T
Figure 2. Mole fraction solubility (y2′) of o-nitrobenzoic acid in SCCO2 with ethanol in a mole fraction of 0.035 as a function of pressure: ■, 308 K; ▲, 318 K; ▼, 328 K.
in which y′2, y3 have the same meaning as those in eq 1; y2 is the mole fraction solubility of o-nitrobenzoic acid in pure SCCO2 as shown in Table 1; c0, c1, c2, and c3 are the equation parameters. Similarly, two new parameters, c4 and c5, are defined, respectively: c4 = ln c0 + c1 ln y3 (at constant y3); c5 = ln c0 + c1 ln y3 + c3/T (at constant y3 and T). As a result, eq 4 transforms into eq 5 or eq 6, respectively. c ln(y2 ′ − y2 ) = c4 + c 2 ln y2 + 3 (5) T
■
ln(y2 ′ − y2 ) = c5 + c 2 ln y2
obviously seen that the influence of pressure on the equilibrium solubility follows the expected trends that the solubility increases with an increase in pressure at a constant temperature. However, the effect of temperature on the equilibrium solubility is more complicated, and a crossover pressure region at pressures around (10.5 to 11.5) MPa has been observed in Figure 2. The crossover phenomena could be attributed to the competitions between solute's vapor pressure and solvent's density, whose temperature dependences are in opposite directions. At the crossover region, these two competitive factors affect balance. Such retrograde behavior has also been reported before.17,18 Model Correlation. In this work, the modified MST and the modified Sovova models were used to correlate the solubility data of o-nitrobenzoic acid in modified SCCO2. In this case, eqs 2 and 5 were used to correlate the solubility of o-nitrobenzoic acid in SCCO2 with ethanol. For the system (SCCO2 + onitrobenzoic acid + ethyl acetate), eqs 3 and 6 were adopted. The quality of the correlation is expressed in terms of the average absolute relative deviation (AARD) between experimental and calculated values of solubility as follows:
(6)
RESULTS AND DISCUSSION Equilibrium Solubility of o-Nitrobenzoic Acid in Modified SCCO2. In this study, we selected ethanol and ethyl acetate as the cosolvents, and the solubility of o-nitrobenzoic acid in the presence of them was determined with same mole fraction 0.035 at 318 K over a pressure range of (10.0 to 21.0) MPa. The solubility values are listed in Table 1. To reveal the cosolvent enhancement effect more clearly, the solubility enhancement factor e is defined as the ratio of the solubility obtained with cosolvents, y2′ (P, T, y3 = 0.035), to that obtained without cosolvents, y2 (P, T, y3 = 0); the expression is given in eq 7: e=
AARD(%) =
y2 ′(P , T , y3 = 0.035) y2 (P , T , y3 = 0)
(7)
100 N
N
∑ 1
|ycal − yexp | yexp
(8)
where N is the number of data points and the subscripts cal and exp represent the calculated and experimental data, respectively. The software of Microsoft Office Excel 2007 was used to fit the experimental data. The values of parameters and AARDs are presented in Table 2. The correlation results indicate that the models can reasonably fit the experimental data. However, the solubility data with ethanol are not well-correlated with neither of the two models. One reason may be that the strong selfassociations of ethanol moleculars cannot be well reflected. Besides, the density of pure SCCO2 has been employed for the correlation process, instead of the density of the (SCCO2 + ethanol) mixture, and the difference between them may also lead to the high deviation. However, the solubility data with ethanol are not well-correlated. According to eq 2, the experimental solubility data are considered consistently good, if all isotherms collapse to a single straight line on a graph which plotting T ln(y′2P/Pstd) − b3T
From Table 1, it is clear that the solubility of o-nitrobenzoic acid has been dramatically enhanced by the presence of both the cosolvents at 318 K and the enhancement effect induced by ethyl acetate is obviously greater than that by ethanol according to the average values of e. The reason may be interpreted on the basis of the polarity of different cosolvents. The value of dipole is used to indicate the polarity. The dipole of ethyl acetate and ethanol is (1.70 and 1.68) D,16 respectively. Moreover, under the experimental conditions, ethanol with a hydroxyl is easier to associate itself than ethyl acetate, which results to the decrease of molecular interaction between ethanol and o-nitrobenzoic acid. We can find that the order on dipole of the two cosolvents is the same as the enhancement factor. We also measured the solubility of o-nitrobenzoic acid in SCCO2 with ethanol at (308, 318, and 328) K, and the solubility data are presented in Table 1 and plotted in Figure 2. It can be 2219
dx.doi.org/10.1021/je300023v | J. Chem. Eng. Data 2012, 57, 2217−2220
Journal of Chemical & Engineering Data
Article
Table 2. Correlation Parameters for the Solubility of oNitrobenzoic Acid in Modified SCCO2 and AARD (%) of Different Models cosolvent ethanol
ethyl acetate
correlation parameters
N
AARD/%
b1 = 5.0426; b3 = 58.941; b4 = −23856 c2 = 2.4947; c3 = 5030.2; c4 = 3.0491 b1 = 4.7982; b5 = −4795.0
15
16.35
15
18.82
5
2.46
5
4.89
models modified MST modified Sovova modified MST modified Sovova
c2 = 2.1691; c5 = 15.718
PetroChina Company Limited through the Applied Research ProProject (No. 2008D-5006-04-05). Notes
The authors declare no competing financial interest.
■
(1) Fages, J.; Lochard, H.; Letourneau, J. J.; Sauceau, M.; Rodier, E. Particle Generation for Pharmaceutical Applications Using Supercritical Fluid Technology. Powder Technol. 2004, 141, 219−226. (2) Brunner, G. Supercritical Fluids: Technology and Application to Food Processing. J. Food Eng. 2005, 67, 21−33. (3) Sarrade, S.; Guizard, C.; Rios, G. M. New Applications of Supercritical Fluids and Supercritical Fluids Processes in Separation. Sep. Purif. Technol. 2003, 32, 57−63. (4) Kikic, I.; Vecchione, F. Supercritical Impregnation of Polymers. Curr. Opin. Solid State Mater. Sci. 2003, 7, 399−405. (5) Foster, N. R.; Singh, H.; Yun, S. L. J.; Tomasko, D. L.; Macnaughton, S. J. Polar and Nonpolar Cosolvent Effects on the Solubility of Cholesterol in Supercritical Fluids. Ind. Eng. Chem. Res. 1993, 32, 2849−2853. (6) Guan, B.; Liu, Z. M.; Han, B. X.; Yan, H. Solubility of Behenic Acid in Supercritical Carbon Dioxide with Ethanol. J. Supercrit. Fluids 1999, 14, 213−218. (7) Koga, Y.; Iwai, Y.; Hata, Y.; Yamamoto, M.; Arai, Y. Influence of Cosolvent on Solubilities of Fatty Acids and Higher Alcohols in Supercritical Carbon Dioxide. Fluid Phase Equilib. 1996, 125, 115−128. (8) Škerget, M.; Knez, Ž .; Knez-Hrnčič, M. Solubility of Solids in Suband Supercritical Fluids: A Review. J. Chem. Eng. Data 2011, 56, 694− 719. (9) Fonseca, J. M. S.; Dohrn, R.; Peper, S. High-pressure Fluid-phase Equilibria: Experimental Methods and Systems Investigated (2005− 2008). Fluid Phase Equilib. 2011, 300, 1−69. (10) Tian, G. H.; Jin, J. S.; Li, Q. S.; Zhang, Z. T. Solubility of pNitrobenzoic Acid in Supercritical Carbon Dioxide with and without Cosolvents. J. Chem. Eng. Data 2006, 51, 430−433. (11) Tang, Z.; Jin, J. S.; Yu, X. Y.; Zhang, Z. T.; Xu, J. N. Solubility of 3,5-Dinitrobenzoic Acid in Supercritical Carbon Dioxide with Cosolvent at Temperatures from (308 to 328) K and Pressures from (10.0 to 21.0) MPa. J. Chem. Eng. Data 2010, 55, 3834−3841. (12) Tang, Z.; Jin, J. S.; Zhang, Z. T.; Yu, X. Y.; Liu, H. T. Equilibrium Solubility of Pure and Mixed 3,5-Dinitrobenzoic Acid and 3-Nitrobenzoic Acid in Supercritical Carbon Dioxide. Thermochim. Acta 2011, 517, 105−114. (13) Tian, G. H.; Jin, J. S.; Guo, J. J.; Zhang, Z. T. Mixed Solubilities of 5-Sulfosalicylic Acid and p-Aminobenzoic Acid in Supercritical Carbon Dioxide. J. Chem. Eng. Data 2007, 52, 1800−1802. (14) Tang, Z.; Jin, J. S.; Zhang, Z. T.; Liu, H. T. New Experimental Data and Modeling of the Solubility of Compounds in Supercritical Carbon Dioxide. Ind. Eng. Chem. Res. 2012, 51, 5515−5526. (15) Sauceau, M.; Letourneau, J. J.; Richon, D.; Fages, J. Enhanced Density-based Models for Solid Compound Solubilities in Supercritical Carbon Dioxide with Cosolvents. Fluid Phase Equilib. 2003, 208, 99− 113. (16) Smallwood, I. M. Handbook of Organic Solvent Properties; Amold: London, 1996. (17) Gurdial, G. S.; Foster, N. R.; Yun, S. L. J.; Tilly, K. D. Phase Behavior of Supercritical Fluid-entrainer Systems. J. Am. Chem. Soc. 1993, 115, 34−45. (18) Demessie, E. S.; Pillai, U. R.; Junsophonsri, S.; Levien, K. L. Solubility of Organic Biocides in Supercritical CO2 and CO2 + Cosolvent Mixtures. J. Chem. Eng. Data 2003, 48, 541−547.
versus ρ. Figure 3 shows that all of the experimental data follow the predominant trend of linearity.
Figure 3. Comparison of experimental solubility of o-nitrobenzoic acid in SCCO2 with ethanol and the calculated results using the modified MST model. Experimental results: ●, (308, 318, and 328) K. , calculated using the modified MST model.
■
CONCLUSIONS The experimental solubility data of o-nitrobenzoic acid in SCCO2 in the presence of ethanol and ethyl acetate at temperatures from (308 to 328) K and pressures from (10.0 to 21.0) MPa were measured. The mole fraction of cosolvent was 0.035. Ethyl acetate showed a better cosolvent enhancement effect than ethanol, and the maximum value of enhancement factor e for ethyl acetate was close to 19. The crossover pressure region for the ternary system (SCCO2 + o-nitrobenzoic acid + ethanol) was from (10.5 to 11.5) MPa. The modified MST and the modified Sovova models were used to correlate the solubility of o-nitrobenzoic acid in modified SCCO2, and satisfactory results were obtained.
■
REFERENCES
AUTHOR INFORMATION
Corresponding Author
*Tel.: +86-10-64434788. Fax: +86-10-64436781. E-mail:
[email protected];
[email protected]. Funding
This research was financially supported by the funds awarded by National Natural Science Foundation of China (No. 21176012), the support from Science and Technology Bureau of Changzhou City (No. CJ20110013), the Fundamental Research Funds for the Central Universities (No. ZZ1103), and the support from 2220
dx.doi.org/10.1021/je300023v | J. Chem. Eng. Data 2012, 57, 2217−2220
