ARTICLE pubs.acs.org/IECR
Determination of Chlorobenzene Solubilities in Subcritical Water in a Fused Silica Capillary Reactor from 173 to 267 °C Zhiyan Pan* and Zhong Dong Department of Environmental Engineering, Zhejiang University of Technology, Hangzhou, 310032, P.R. China
bS Supporting Information ABSTRACT: The solubility of chlorobenzene was measured in subcritical water using a fused silica capillary reactor (FSCR) combined with a microscope recorder system to capture the images and identify the temperature of total dissolution. The solubility of chlorobenzene was found to vary between 43.5 mg g1 in water at 173.3 °C and 71.4 mg g1 in water at 266.9 °C, increasing linearly with temperature. A new approximation model was developed to predict the solubility of chlorobenzene in subcritical water at elevated temperatures. This visualization in the FSCR method does not require sampling and subsequent analysis, and it has a great potential for the solubility determinations of other organic or inorganic materials.
1. INTRODUCTION Supercritical water (SCW) and subcritical water (SBCW)1 are regarded as one of the most promising and interesting solvents for chemical engineering applications: they have been used in synthesis,2,3 extraction,46 separation, and precipitation7,8 processes. The supercritical water oxidation (SCWO) process is environmentally friendly and has been widely used since the 1980s for hazardous waste, such as toxicants and recalcitrant organic wastewater.912 However, due to the extreme conditions of elevated temperature and pressure used in this process, the chemical data at these temperatures are scarce, even though these data are important for the formulation of solubility models and evaluation of promising technologies.13 Several solubilities of chemicals in SBCW have been reported; for example, the solubilities of Na2SO4, Na2CO3, and their mixture were studied in supercritical water using the UBC-NORAM SCWO pilot plant, which was created by the University of British Columbia and NORAM Engineers and Constructors Ltd. It consists of a 160 m long alloy tube, the preheaters, test section, and reactor section, and is electrically heated by running alternating current through the tube walls.14 The solubility of K2SO4 in water was studied under the conditions of 373.5382.2 °C and 25 MPa using the experimental apparatus which had windows for visual observation.15 Likewise, the solubility of K2CO3 in water was studied under the conditions of 111256 °C using a visually accessible apparatus consisting of a platinum cell with sapphire windows and gold seals.16 The high-temperature aqueous solubilities of glucose, maltose, and xylose were measured under the conditions of 20180 °C by a continuous-flow technique in which the sugar was saturated at various temperatures in a stream of flowing hot water.17 Solubilities of MgCl2, CaCl2, MgSO4, CaSO4, Na2HPO4, and NaH2PO4 were also investigated using a continuous flow method in SBCW and SCW.18,19 SBCW has been used as a solvent to dissolve a variety of hydrophobic organic compounds (HOCs).20 In general, organic compounds exhibit higher solubility in SBCW than inorganic compounds.21,22 The solubility of naproxen has been measured r 2011 American Chemical Society
in SBCW between 130 and 170 °C using the solubility vessel, having an internal volume of 6.4 mL, by a dynamic method.23 The solubilities of gallic acid hydrate, protocatechuic acid, and catechin hydrate were measured in water between 25.6 and 142.7 °C using a dynamic flow apparatus;24 also the solubilities of quercetin and its dehydrate were measured at temperatures between 25 and 140 °C using a continuous flow type apparatus.25 Berkant et al. used a homemade system consisting of an empty high-performance liquid chromatography (HPLC) column (7.8 mm I.D, and 300 mm long) as the equilibration cell. The cell was placed in the oven of a gas chromatograph (GC) for precise temperature control and solubility measurements of benzoic acid and salicylic acid in water performed on the temperatures ranging from 25 to 200 °C at a constant pressure of 5 MPa.26 In some cases, predicted solubility values by models are in quite serious disagreement with experimentally derived data27 and it is in case of need to develop advanced experimental methods to provide reliable experimental data. Many different methods are used to measure the solubilities in SBCW, such as continuous-flow methods, visual synthetic methods, analytical isothermal methods, etc. Expressions like “static” or “dynamic” are commonly used in connection with many different methods.28,29 In the static method, it is difficult to keep the bulk composition of a sample unchanged while taking a small portion of the sample out of the equilibrium cells for analyses. On the other hand, in the dynamic method, elaborate analytical procedures are needed in most of cases to ensure that system has reached equilibrium before sampling. In addition, these two methods require thermogravimetric analyses (TGA),30 HPLC,31 gas chromatography/ mass spectrometry (GCMS),32 and Raman33 or X-ray34 for subsequent analyses. In this study, we developed a new method using a fused silica capillary reactor (FSCR),35 in combination with a microscope for visual observation, to study the solubility of Received: April 8, 2011 Accepted: September 12, 2011 Revised: August 25, 2011 Published: September 12, 2011 11724
dx.doi.org/10.1021/ie200754g | Ind. Eng. Chem. Res. 2011, 50, 11724–11727
Industrial & Engineering Chemistry Research chlorobenzene in SBCW at elevated temperatures and vaporsaturated pressures.
2. EXPERIMENTAL SECTION The apparatus includes a fused silica capillary reactor, heating/ cooling stage, microscope, digital camera, and a recording system (Figure 1). To prepare a sample, a section of silica capillary (665 μm O.D, 300 μm I.D, and 2 cm long) was cut, and one end of the tube was sealed in an oxyhydrogen flame. Chlorobenzene was injected into the capillary tube and the mass was measured
Figure 1. A schematic diagram of the experimental apparatus: (1) FSCR, (2) heating/cooling stage, (3) circulating water, (4) digital temperature controller, (5) microscope, (6) digital camera, (7) display and recording unit.
Figure 2. An image of a sample in a fused silica capillary reactor, showing chlorobenzene, water, vapor, and silica rod in the FSCR.
ARTICLE
by the following methods: the length of the injected liquid was measured with a micrometer under a microscope (accurate to (1 μm, Leica, DM2500P, Germany, the mass uncertainty was (8 105 mg). Then water was loaded into the tube immediately, and centrifuged to the enclosed end. The space above the liquid phases was partially filled with a silica rod to reduce evaporation of chlorobenzene and water in the free space. The enclosed end of the capillary was then immersed into liquid nitrogen and the open end of the tube was sealed with an oxyhydrogen flame to form a FSCR (Figure 2). The length of the injected water (the mass uncertainty was (7 105 mg) was also measured with a micrometer at room temperature. Finally the FSCR was loaded in the heating/cooling stage (Instec, INS0908051, USA), and the temperature was adjusted via a digital temperature controller (Instec, Instec, STC200, USA). The images of the sample during heating were observed under a microscope and recorded in a computer through a digital camera (JVC, TK-C1481, Japan), and the dissolution temperature of chlorobenzene was identified for each sample. The experimental details were presented in the Supporting Information.
3. RESULTS AND DISCUSSION In this study, the FSCR was heated to the preset temperature in a heating/cooling stage, and the sample was allowed to equilibrate for a period between 8 and 10 h in the presence of a vapor phase. The images of the sample were observed under a microscope and recorded by using a digital camera and a computer. For example, the images of a sample containing 58.0 mg of C6H5Cl/g of H2O, taken during heating from 30.1 to 222.4 °C, are shown in Figure 3; they show the gradual dissolution of C6H5Cl during heating and its total disappearance at 222.4 °C
Figure 3. Dissolution of chlorobenzene in water during heating. The C6H5Cl is shown at the right end of the FSCR. The images of C6H5Cl and H2O in the capillary under the microscope at 30.1 °C (a), and at temperatures between 100.0 and 220.0 °C (bg) during heating. The C6H5Cl swelled at 150.0 °C (c), and dissolved totally at 222.4 °C (h). 11725
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Table 1. Solubility of C6H5Cl in Pure Water
linear equation. Moreover, we have demonstrated the technique has great potential to be applied for the solubility determination of other organics and also inorganic salt crystals in SBCW/SCW.
M1
M2
T
Sm (mg g1)
Sc (mg g1)
relative
(mg)a
(mg)b
(°C)
in waterc
in waterd
error (%)e
0.02
0.46
173.3
43.5
43.0
1.17
0.05
1.03
190.0
48.5
48.1
0.78
0.05
0.91
215.5
54.9
55.9
1.87
0.04
0.69
222.4
58.0
58.1
0.11
0.04
0.66
235.3
60.6
62.0
2.30
0.06
0.94
242.6
63.8
64.3
0.73
0.06 0.04
0.93 0.61
245.4 247.9
64.5 65.6
65.1 65.9
0.96 0.44
’ AUTHOR INFORMATION
0.06
0.89
248.8
67.4
66.2
1.86
Corresponding Author
0.06
0.87
252.8
69.0
67.4
2.38
0.05
0.72
255.3
69.4
68.2
1.81
*Tel.: 86-571-88320061. Fax: 86-571-88320061. E-mail: panzhiyan@ zjut.edu.cn.
0.06
0.85
265.3
70.6
71.2
0.89
0.03
0.42
266.9
71.4
71.7
0.45
’ ASSOCIATED CONTENT
bS
Supporting Information. Materials and experimental method. This material is available free of charge via the Internet at http://pubs.acs.org.
a
M1 = mass of C6H5Cl. b M2 = mass of H2O. c Sm = measured solubility. d Sc = solubility calculated from eq 1. e relative error (%) = [(Sm Sc)/ Sm] 100.
’ ACKNOWLEDGMENT Financial support of this research was provided by Natural Science Foundation of China (No. 21077092). We would like to thank Dr. I. M. Chou of U.S. Geological Survey for his guidance. ’ REFERENCES
Figure 4. Solubility of C6H5Cl in pure water at temperatures between 173.3 and 266.9 °C: (9) experimental data; (—) least-squares fit of the data.
and about 2.2 MPa (calculated by the saturated vapor pressures of water at 222.4 °C). The solubility data of C6H5Cl are summarized in Table 1, and shown in Figure 4. The results indicate that the solubility of C6H5Cl increases with increasing temperature, and can be represented by the linear equation: S ¼ 0:3069T 10:188
ð1Þ
where S is the solubility in mg g1, and T is temperature in °C. The correlation coefficient (R2) is 0.9886, and the maximum relative error of solubility between experimental data and the values calculated from eq 1 is 2.38% (Table 1).
4. SUMMARY A new method using a FSCR, in combination with a microscope and a video recorder system, has been applied to determine the solubility of chlorobenzene in SBCW. The results indicate that the solubility of chlorobenzene increases from 43.5 to 71.4 mg g1 in water when temperature rises from 173.3 to 266.9 °C, and the temperature effect can be represented by the
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