Article pubs.acs.org/jced
Solubility of 2,3,5,6-Tetrachloropyridine in Supercritical CO2: Measurement and Correlation Hongyou Cui,*,† Shaosong Qian,‡ Fei Qin,† and Chuanbo Wang† †
School of Chemical Engineering and ‡School of Life Science, Shandong University of Technology, Zhangzhou Road 12, Zibo, Shandong 255049, China ABSTRACT: 2,3,5,6-Tetrachloropyridine (TCP) is an important chemical and intermediate for synthesis of pesticides and pharmaceuticals. The solubility of TCP in supercritical carbon dioxide was measured using a static analytical method at temperatures of 313 K, 323 K, and 333 K and pressures in the range of 10.0 MPa to 24.0 MPa. The result showed that TCP solubility increased with the increase of pressure at isothermal conditions, while it decreased with increasing temperature at isobaric conditions. The experimental data were correlated using four density-based models (Chrastil, Mendez-Santiago and Teja, Bartle, and Kumar and Johnston), respectively. The calculated results show good agreement with the experimental data.
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INTRODUCTION 2,3,5,6-Tetrachloropyridine (TCP) is white to light yellow crystalline solid in pure state. Its formula is C5HCl4N with a molecular weight of 216.88, a melting point of 363.7 K, and a boiling point of 524.8 K. It is almost insoluble in water but soluble in organic solvents like methanol, toluene, methyl cyanide, and so forth. Its solubility in water at 25 °C is only 52 mg/L.1 TCP is industrially manufactured by the chlorination of pyridine.2 It also can be obtained as a byproduct from the production process of 3,5,6-trichloropyridin-2-ol using trichloroacetyl chloride and acrylonitrile as the raw materials.3 TCP is mainly used for the production of chlorpyrifos, one of the most widely used organophosphate insecticides with moderately toxic to humans. Although it has been banned for home uses since 2001 in the USA, it remains widely used in agriculture. TCP is also can be used to prepare herbicides, for example, triclopyr.4 At present, China has become the largest production base of chlorpyrifos in the world in terms of capacity and output. However, the disposal of process wastewater, which contains TCP, 3,5,6-trichlorpyridin-2-ol, and other known and unknown compounds, causes serious concerns since these compound are very hard to degradation or decomposition.2 Supercritical carbon dioxide extraction has been shown highly effective in mixture separation due to its mild operation conditions and nontoxicity. By supercritical CO2 extraction, TCP is expected to be recycled and thus to some extent reduce the toxicity of the wastewater.5 However, very little information on the thermodynamic properties of TCP is available until now. Qin et al. had measured the solubility of TCP in methanol, ethanol, and 2-propanol.6 There has been no report as to the solubility data of PCP and TECP in supercritical CO2. © 2014 American Chemical Society
In this work, the solubility of TCP in supercritical carbon dioxide is measured and correlated with four semiempirical models.
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EXPERIMENTAL SECTION
Materials. Carbon dioxide (purity 99.9 %) was supplied by Shandong Basan Factory (Shandong Province, China). Naphthalene was purchased from Sigma (purity 99 %). TCP with a purity of 99 % was obtained from Jinguan Chemicals, Jiangsu Province. All of these chemicals were used without further purification. Apparatus and Procedures. The solubility of TCP was experimentally determined in an apparatus as illustrated in Figure 1. It is mainly composed of a high-pressure cell, a sampling tube, and an ethanol trapping vessel. The highpressure cell was made of a piece of stainless steel tube with an inner diameter of 10 mm and 150 mm long. The sampling tube was a stainless steel tube (2 mm in inner diameter and 100 mm long) connected with three valves. To ensure the temperature constant, both the high pressure cell and the sampling tube were subjected to immersion in the water bath with a temperature control accuracy of ± 0.1 K. For the CO2 delivery, CO2 gas from a cylinder was first condensed via ice bathing and then pressurized by a syringe pump. The pressure of CO2 was adjusted by a CO2 buffer tank and a back-pressure regulator with an accuracy of ± 0.1 MPa. The system pressure was measured by a pressure transducer (± 0.01 MPa). Received: May 13, 2013 Accepted: December 30, 2013 Published: January 6, 2014 269
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Figure 1. Schematic diagram of the experimental apparatus for TCP solubility measurement in supercritical CO2.
Table 1. Comparison of the Solubility Data of Naphthalene in Supercritical CO2 this work T/K
p/MPa
308.15 308.15 308.15 308.15 308.15 308.15 318.15 318.15 318.15 318.15 318.15
8.0 10.0 14.0 16.0 20.0 24.0 8.50 10.0 14.0 20.0 25.0
ref 16 3
ref 17
ref 15
p/MPa
10 y
p/MPa
10 y
p/MPa
10 y
p/MPa
103 y
± ± ± ± ± ± ± ± ± ± ±
8.80 10.40 13.80 15.20 16.80 20.10 8.50 10.30 13.70 19.90 25.00
7.8 11.2 13.9 15.3 16.7 16.6 1.1 8.2 16.5 23.8 25.8
8.05 13.52 15.05 20.03 24.82 29.92 8.49 9.83 15.06 19.77 24.98
4.4 13.9 14.7 16.1 19.6 17.5 1.1 6.0 20.8 23.7 25.0
10.70 13.80 16.80 20.40
11.6 15.0 16.3 17.5
9.7 13.10 16.70 19.70 25.20
10.1 13.6 16.6 18.0 17.8
0.3 0.4 0.6 0.6 0.7 0.8 0.3 0.5 0.6 0.8 0.9
3
ref 18
10 y 4.8 10.3 14.1 15.4 17.3 19.0 1.2 6.7 17.4 24.0 25.3
3
3
absorption cell, the calibration curve of TCP in ethanol at 290 nm was determined as C = (A − 0.005)/0.02838(μg/mL) with a correlation coefficient of 0.9996. A is the absorbance, and C is the concentration of TCP in ethanol in unit of μg/mL. The solubility of TCP in supercritical is calculated by n TCP y= n TCP + nCO2
When performing the experiment, 10 g of TCP was loaded in the high-pressure cell after blending with glass balls (0.2 mm in diameter). At each end of the cell was packed with glass wool and filter paper to avoid channeling and physical entrapment. Then the high-pressure cell was pressurized with high-pressure CO2 to desired pressure and maintained at least 30 min to reach equilibrium. When sampling, valves 2 and 3 were closed, and valve 1 was slowly opened until reaching to a pressure balance between the sampling tube and the high pressure cell. After that, valve 1 was turned off, and valve 3 was slightly opened, allowing to slowly depressurizing CO2 and dissolving the released TCP in the ethanol trapping vessel in a bubbling manner. The released CO2 flowed through the next vessel full of water. By water discharging, the CO2 volume was measured. The precipitated TCP during depressurizing was washed by ethanol, which was delivered continuously by a high-performance liquid chromatography (HPLC) pump. The effluent ethanol was merged into the trapping ethanol solution. After ethanol washing, CO2 was used to flush the tube and the pipelines. The reliability of the instrument was cross-checked against binary solubility data in the literature for naphthalene. Naphthalene trapped in hexane was diluted to a convenient volume and measured at 265 nm using UV−vis spectrophotometer (UV757CRT, Shanghai Precision Instrument Co.). The concentration of naphthalene was calculated based on a calibration curve from UV analysis of naphthalene standard solution. The amount of TCP was determined by ultraviolet spectrophotometric method at 290 nm.7 Using a 1 cm
n TCP = nCO2 =
Cmn 216.88 pVCO2 RT
where nTCP and nCO2 refer to the mole number of TCP and CO2; m is the total volume of ethanol used in the trapping and washing; n is the dilution times when determining the absorbance by UV−vis spectrophotometer. 216.88 is the molecular weight of TCP. The solubility data reported were the average of triplicate measurements. The relative deviation of measurements was generally less than 10 %.
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RESULTS AND DISCUSSION To validate the reliability of the experimental apparatus and procedures, naphthalene solubility in supercritical carbon dioxide at 308 K and 318 K was first measured and compared with the literature data. The measured solubility and the literature data of naphthalene in terms of the mole fraction, y, in supercritical carbon dioxide summarize in Table 1. For 270
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comparison, the solubility data as a function of pressure at isothermal condition is also illustrated in Figure 2. One can see
Figure 3. Solubility of 2,3,5,6-tetrachloropyridine in the tested range of pressure and temperature: ■, 313.15 K; red ●, 323.15 K; blue ▲, 333.15 K. Figure 2. Comparison of naphthalene solubility data in supercritical carbon dioxide at different pressures (8 MPa to 25 MPa) and temperature at 308.15 K: pink ★, this work; green ▼, ref 16; ■, ref 17; red ●, ref 15; blue ▲, ref 18; and temperature at 318.15 K: pink ☆, this work; blue ▽, ref 16; □, ref 17.
absolute difference of the triplicate measurements at each measurement condition, which was calculated by yerr =
that there is good agreement between various measurements either at 308.15 K or at 318.15 K, indicating the reliability and accuracy of the experimental apparatus and procedures. The solubility of TCP and the measurement standard deviation in supercritical carbon dioxide along with temperature, pressure, and density of CO2 related to each measurement is listed in Table 2 and also illustrated in Figure 3 and Figure 4 as a function of pressure (MPa) and CO2 density (kg· m−3), respectively. y is the experimental value of the TCP solubility in terms of the mole fraction. yErr is the average
1 3
3
∑ |yi − yi ̅ | i=1
yi is the measured value, and yi̅ is the average value at each measurement condition. The solubility of TCP is about 10 times smaller compared to naphthalene. This is expected since TCP is slightly higher than naphthalene in polarity, and more soluble in polar solvents. The TCP solubilities in methanol, ethanol, and 2-propanol at 313.15 K were reported to be 0.014, 0.042, and 0.056 (mole fraction).6 Carbon dioxide is a compound that has no dipole moment but only a small quadrupole moment, low polarizability, and low
Table 2. Experimental Solubility Data of 2,3,5,6-Tetrachloropyridine in Supercritical Carbon Dioxidea T
P
d
103 y
103 yErr
103yChrastil
103 yMST
103 yBartle
103 yKJ
K
MPa
kg·m−3
mol·mol−1
mol·mol−1
mol·mol−1
mol·mol−1
mol·mol−1
mol·mol−1
313.15
10.0 12.0 14.0 16.0 18.0 20.0 24.0 10.0 12.0 14.0 16.0 18.0 20.0 24.0 10.0 12.0 14.0 16.0 18.0 20.0 24.0
628.61 717.76 763.27 794.90 819.51 839.81 872.48 384.33 590.89 672.17 722.09 757.12 784.29 825.62 289.95 434.43 561.37 637.50 687.25 723.68 776.07
3.51 5.41 7.06 7.95 8.95 9.98 10.88 0.65 2.30 3.59 4.83 5.69 6.13 7.28 0.35 0.88 1.67 2.51 3.22 3.77 4.82
0.18 0.18 0.17 0.17 0.24 0.17 0.14 0.09 0.16 0.19 0.26 0.21 0.22 0.23 0.03 0.08 0.10 0.14 0.16 0.14 0.14
3.65 5.69 6.99 8.01 8.87 9.63 10.95 0.57 2.40 3.69 4.69 5.50 6.19 7.36 0.18 0.70 1.65 2.53 3.26 3.87 4.89
3.32 5.83 7.32 8.35 9.12 9.73 10.66 0.48 2.13 3.53 4.63 5.48 6.14 7.16 0.25 0.65 1.52 2.43 3.19 3.83 4.82
3.34 5.85 7.32 8.33 9.09 9.68 10.59 0.45 2.07 3.50 4.64 5.51 6.22 7.31 0.21 0.57 1.41 2.33 3.14 3.83 4.93
3.60 5.48 6.78 7.86 8.83 9.71 11.32 0.94 2.48 3.63 4.58 5.40 6.14 7.45 0.50 0.98 1.79 2.56 3.23 3.83 4.90
323.15
333.15
a
Standard uncertainties u are u(T) = 0.1 K, ur(P) = 0.025, and ur(y) = 0.012. 271
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where k, a, and b are adjustable parameters that can be estimated from the experimental solubility data. In the assumption of the Chrastil model, k reflects the association number of the molecules of a gas B with one molecule of solute A to form a solvated complex ABk. b is related to the enthalpy change (ΔH) as b = ΔH/R. ΔH is a sum of the salvation heat and the sublimation heat of the solid solute, and R is the universal gas constant. The Kumar and Johnston model is a correlation about the logarithm of the mole fraction of the solute in supercritical CO2, ln y, CO2 density (kmol·m−3), and the temperature. The model expression is given as ln y = kρ(kmol ·m−3) + a + b/T (K)
where k, a, and b are adjustable parameters. k and b have similar meanings as in the Chrastil model. The Bartle model is defined as the following
Figure 4. Solubility isotherms of 2,3,5,6-tetrachloropyridine in supercritical carbon dioxide as a function of CO2 density: ■, 313.15 K; red ▲, 323.15 K; blue ★, 333.15 K.
⎛ yp ⎞ ln⎜⎜ ⎟⎟ = k(ρ(kg·m−3) − ρref (kg·m−3)) + a + b/T (K) ⎝ pref ⎠
Here k, a, and b are adjustable parameters. Compared to the KJ model, reduced pressure P/Pref and reduced density ρref are introduced. Here we assume that Pref is the critical pressure of CO2, Pref = Pc = 4.38 MPa and ρref equals the critical density of CO2, ρref = ρc = 467.5 kg·m−3. Another density-based model was proposed by MendezSantiago and Teja in 1999. This model originated from the linear relationship between T ln(E) and ρ, which was derived from the theory of dilute solutions.
relative dielectric constant. Although these properties vary with temperature and pressure under supercritical conditions, its polarity corresponds largely to cyclohexane. As shown in Figure 3, the solubility of TCP increased with the increase of pressure at a constant temperature. This is predictable because an increase in pressure at isothermal conditions will increase the density of carbon dioxide and thus increase the specific interaction between TCP and carbon dioxide molecules. Furthermore, the increase in carbon dioxide density also could lead to an increase in the polarity of carbon dioxide. In the range of pressure tested, the solubility of TCP decreased with elevating temperature. The effects of elevating temperature on the solubility at isobaric conditions usually can be attributed to two aspects: (1) enhancing the solute vapor pressure or (2) decreasing carbon dioxide density and further changing the intermolecular interaction between molecules of solute and solvent. From the experimental results, obviously, the enhancement effect of temperature via vapor pressure on TCP solubility is hard to compensate for the negative effect on the CO2 density. Figure 4 clearly shows a noticeable effect of CO2 density on TCP solubility, especially at a high CO2 density zone. The tendency that TCP solubility decreased with temperature in the tested range at constant CO2 density might be ascribable to the “solvation cage effect”. Since TCP is a weak Lewis base while CO2 is a weak Lewis acid, the stronger interaction of TCP with CO2 molecules could exist than common organic molecules. When increasing temperature, the chemical interaction between TCP and CO2 becomes weak, as a result, the clustered CO2 around a TCP molecule will decrease, and the solubility declines. Four semiempirical density-based models, namely, the Chrastil model,8 Kumar−Johnston (KJ), 9 Bartle,10 and Mendez-Santiago and Teja (MST) models,11 were usually used to correlate the solubility of a solute in pure and modified supercritical CO2. If the solubility is not very high, satisfactory correlation results could be obtained.12−14 The Chrastil model relates the solute solubility (S, kg/m3) in supercritical CO2, the supercritical CO2 density (ρ, kg/m3), and temperature (T, K) as
⎛ P ⎞ T ln(E) = T ln⎜y2 ⎟ = kρ(kg·m−3) + a + bT (K) ⎝ Psub ⎠
where E is the enhancement factor. It is necessary to predetermine the sublimation pressures Psub. Since the sublimation pressure of a solid solute is not often available, a modified MST equation was proposed by Sauceau et al.,15 in which Psub is substituted by the standard pressure, Pref = 1 bar. ⎛ P ⎞ T ln⎜y2 ⎟ = kρ(kg·m−3) + a + bT (K) ⎝ Pref ⎠
To obtain the model parameters by fitting the experimental solubility data, Matlab 7.0 (Mathworks, USA) was used to minimize the objective function using the lsqcurvefit.m, which is a Matlab function used to solve the nonlinear least-squares problems. The objective function is defined as N
OBJ =
∑ (yical
− yiexp )2
for KJ, Bartle, and MST models
i N
OBJ =
∑ (Sical − Siexp)2
for the Chrastil model
i
where i is the experimental point. N is the total data number. exp ycal are the calculated solubility by the model and the i and yi experimental solubility data, respectively, in units of mol·mol−1. exp Scal are the calculated solubility by the models and the i and Si experimental solubility data, respectively, in units of kg·m−3. AARD is the average absolute relative deviation, defined by
ln S(kg· m−3) = k ln ρ(kg·m−3) + a + b/T (K) 272
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Table 3. Fitted Model Parameters of TCP Solubility Data in Supercritical Carbon Dioxide model
equation
k
a
b
AARD%
Chrastil KJ Bartle MST
ln S = k ln ρ(kg·m−3) + a + b/T(K) ln y = kρ(kmol·m−3) + a + b/T(K) ln(yp/pref) = k[ρ(kg·m−3) − ρref(kg·m−3)] + a + b/T(K) T ln[y2(P/Pref)] = kρ(kg·m−3) + a + b/T(K)
2.355·10−3 0.206 8.321·10−3 2.621
−2.549·10−2 −14.975 −6.105 −2103.19
2.150 2.004·103 −198.280 −3.948
5.73 7.20 8.82 6.70
Figure 5. Self-consistency tests using four different models: (a) Chrastil model; (b) KJ model; (c) Bartle model; and (d) MST model. Isotherms at: ■, 313.15 K; red ●, 323.15 K; blue ▲, 333.15 K. The continuous lines reveal the linearity of the used models.
AARD% =
100 N
N
∑ i=1
|yi ,cal − yi ,exp |
density zone, these models gave very good agreement with the experimental solubility data. However, at the low CO2 density zone, the predicted errors were relatively bigger. The calculated solubility data of TCP by Chrastil model, the Bartle model, and the MST model were lower than the experimental data, while the calculated data by the KJ model were higher than the experimental data. These results suggest that all of these four density-based models are not very satisfactory at a low density zone. A similar result occurred when fitting other compounds.13
yi ,exp
The correlated solubility data of TCP in supercritical carbon dioxide are presented in Table 2. Table 3 summarizes the adjustable parameters and average absolute relative deviation (AARD) of four models. From Table 3, one can see that the four density-based models gave similar deviations. The AARD data for Chrastil, KJ, Bartle, and MST were 5.73 %, 7.20 %, 8.82 %, and 6.70 %, respectively. Figure 5a−d shows the comparisons between the experimental solubility data and the calculated data by the Chrastil, the KJ model, the Bartle, and the MST model, respectively. It can be seen that all of these four CO2 density-based models correlated very well, with AARD less than 10 %. At a high
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CONCLUSION The solubility of 2,3,5,6-tetrachloropyridine in supercritical carbon dioxide was measured in the temperature range of 313.15K to 333.15 K and in the pressure range of 10.0 MPa to 24.0 MPa. In the tested range of temperature and pressure, the solubility of 2,3,5,6-tetrachloropyridine increased with the 273
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(18) Stassi, A.; Bettini, R.; Gazzaniga, A.; Giordano, F.; Schiraldi, A. Assessment of solubility of ketoprofen and vanillic acid in scCO2 under dynamic conditions. J. Chem. Eng. Data 2000, 45, 161−165.
increase in pressure at isothermal conditions but decreased with the temperature at isobaric conditions. Four semi-empirical density-based models (Chrastil, KJ, Bartle, and MST) were used to correlate the solubility of TCP in supercritical carbon dioxide. Compared to the experimental data, the AARD of the calculated solubility data of 2,3,5,6-tetrachlorpyridine using the fitting parameters of these correlations were 5.73 %, 7.20 %, 8.82 %, and 6.70 % for Chrastil, KJ, Bartle, and MST models, respectively.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Walker, J. D. Applications of QSARs in toxicology: a US Government perspective. J. Mol. Struct.: THEOCHEM 2003, 622, 167−184. (2) Liu, N.; Cui, H.; Yao, D. Decomposition and oxidation of sodium 3,5,6-trichloropyridin-2-ol in sub- and supercritical water. Proc. Saf. Environ. Prot. 2009, 87, 387−394. (3) Martin, P. Process for producing 2,3,5,6-tetrachloropyridine and 3,5,6-trichloropyridin-2-ol. US4327216, 1982. (4) Shroff, D. K.; Shroff, A. C.; Dave, S. P. Preparation of triclopyr, its intermediate and butoxyethyl ester. WO/2010/023679 2010. (5) Yu, J.-J. Removal of organophosphate pesticides from wastewater by supercritical carbon dioxide extraction. Water Res. 2002, 36, 1095− 1101. (6) Qin, J.; Zeng, Z.; Xue, W. Experimental Measurement and Correlation of solubility of pentachloropyridine and tetrachloropyridine in methanol, ethanol, and 2-propanol. J. Chem. Eng. Data 2006, 51, 145−147. (7) Liu, N. C. H.; Yao, D. Determination of 2,3,5,6-Tetrachloropyridine by Ultraviolet Spectrophotometry (in Chinese). Agrochemicals 2008, 47, 190−191. (8) Chrastil, J. Solubility of solids and liquids in supercritical gases. J. Phys. Chem. 1982, 86, 3016−3021. (9) Kumar, S.; Johnston, K. P. Modelling the solubility of solids in supercritical fluids with density as the independent variable. J. Supercrit. Fluids 1988, 27, 1551−1553. (10) Bartle, K. D.; Clifford, A. A.; Jafar, S. A.; Shilstone, G. F. Solubility of solids and liquids of low volatility in supercritical carbon dioxide. J. Phys. Chem. Ref. Data 1991, 20, 713−756. (11) Mendez-Santiago, J.; Teja, A. S. The solubility of solids in supercritical fluids. Fluid Phase Equilib. 1999, 158, 501−510. (12) 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. (13) Zeinolabedini Hezave, A.; Esmaeilzadeh, F. Solubility Measurement of Diclofenac Acid in the Supercritical CO2. J. Chem. Eng. Data 2012, 57, 1659−1664. (14) Ren, J.; Zhan, S.; Zhou, J.; Zhang, M. New Equilibrium Autoclave for Determining Solubility and Melting Point of Solid Solute in Supercritical Fluids. 1. Determination of Solubility of Levonorgestrel in Supercritical Carbon Dioxide. Ind. Eng. Chem. Res. 2012, 51, 2451−2455. (15) Sauceau, M.; Fages, J.; Letourneau, J.; Richon, D. A novel apparatus for accurate measurments of solid solubilities in supercritical phases. Ind. Eng. Chem. Res. 2000, 39, 4609−4614. (16) Sahihi, M.; Ghaziaskar, H. S.; Hajebrahimi, M. Solubility of Maleic Acid in Supercritical Carbon Dioxide. J. Chem. Eng. Data 2010, 55, 2596−2599. (17) Fathi, M. R.; Yamini, Y.; Sharghi, H.; Shamsipour, M. Solubilities of some recently synthesized 1,8-dihydroxy-9,10-anthraquinone derivatives in scCO2. Talanta 1999, 48, 951−957. 274
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