Article pubs.acs.org/est
Visual Observations and Raman Spectroscopic Studies of Supercritical Water Oxidation of Chlorobenzene in an Anticorrosive Fused-Silica Capillary Reactor Huicheng Liu and Zhiyan Pan* Department of Environmental Engineering, Zhejiang University of Technology, Hangzhou 310032, P.R. China S Supporting Information *
ABSTRACT: Supercritical water oxidation of chlorobenzene (CB) was studied using an anticorrosive fused-silica capillary reactor (FSCR) combined with a polarization microscope recorder system for visual observations and a Raman spectroscopic system for qualitative and quantitative analyses of the gaseous products. The effects of operating parameters, including the stoichiometric amount of oxidizer, temperature, and reaction time, on oxidation behavior were investigated. Our results show that a 100% conversion yield of CB and 100% CO2 yield were achieved with a 150% stoichiometric amount of H2O2 at 450 °C within 8 and 10 min, respectively. The conversion yield and the CO2 yield both depend strongly on temperature, and the CO2 yield is always less than the CB conversion yield under the same experimental conditions, suggesting that some carbon exists in intermediate products of incomplete oxidation, as confirmed by gas chromatography−mass spectrometry. Global kinetics analysis based on the complete conversion of CB to CO2 showed that the reaction was first order. CB phase-changes in sub- and supercritical H2O−H2O2 system in the FSCR were observed and recorded; CB eventually dissolved completely to form a homogeneous liquid solution above 326.1 °C. This method has great potential for use in the theoretical study of fluids and chemical reactions under elevated pressure−temperature conditions.
■
hydrogen peroxide was studied at a temperature of 400 °C and a pressure of 30 MPa with a flow reactor; the results showed that the decomposition of 3-chlorobiphenyl was higher than 99.9%.20 Chlorobenzene (CB) has been identified by the U.S. Environmental Protection Agency (EPA) as a principal organic hazardous compound because of its low biodegradability and accumulation potential in soil and water, and also because it is a structural unit of complex chloroaromatic compounds. Dechlorination of CB is difficult because of the high strength of the aromatic C−Cl bond, which is around 95 kcal mol−1, compared to more typical values of around 85 kcal mol−1.21 Thus, in this study, we chose CB as a model compound for studying the SCWO process. The SCWO process for wastewater treatment has been extensively studied by many researchers. However, almost all of the previous studies were performed in large-scale stainlesssteel reactors, which were readily corroded at temperatures higher than 500 °C in supercritical water, particularly in the presence of chloride ions.22 One of the greatest problems in the
INTRODUCTION Chlorinated organic compounds, one of the largest groups of anthropogenic materials, are widely used in the chemical and electronics industries. Many of these materials have high stability and tend to accumulate in the environment, so disposal of chlorinated organic compound wastes in order to minimize the environmental hazards has become an urgent issue.1−3 Various methods for the destruction of chlorinated organic compounds have therefore been developed, and biodegradation,4,5 ultrasonic degradation,6,7 ultraviolet irradiation,8,9 plasma treatment,10,11 ozonation,12,13 and incineration14 are successful detoxification methods. However, these methods also have some unfavorable aspects such as low decomposition rates, inefficiency, and unsafe operation. Supercritical water oxidation (SCWO) has proved to be one of the most effective and environmentally friendly methods for the destruction of hazardous organic wastes. The SCWO reaction typically proceeds in a single fluid-phase consisting of organic compounds, an oxidizer, and water. Supercritical water (Tc = 374 °C, Pc = 22.1 MPa) has a weaker hydrogen-bond network and lower dielectric constant than those of ambient water. The reaction system, which has no interphase masstransfer limitations, leads to a fast reaction rate and high oxidation-efficiency. It has been studied and used for a variety of applications.15−19 The SCWO of 3-chlorobiphenyl using © 2012 American Chemical Society
Received: Revised: Accepted: Published: 3384
November 28, 2011 February 7, 2012 February 21, 2012 February 21, 2012 dx.doi.org/10.1021/es204262d | Environ. Sci. Technol. 2012, 46, 3384−3389
Environmental Science & Technology
Article
SCWO of chlorinated organic compounds is that reactor vessels made of metal alloys are readily corroded by HCl generated as an oxidation product. Corrosion has become one of the major problems hindering the development and industrial applications of SCWO technology.23 In most cases, the liquid-phase reactor effluent, but not the gas-phase products, were sampled and analyzed by gas chromatography (GC), high-performance liquid chromatography (HPLC), and ion chromatography (IC), partly due to the difficult of gas sampling. Also, nearly all previous studies have concentrated on the kinetics of reactant disappearance, with only a few works focusing on the kinetics of total organic carbon conversion to CO2 during SCWO. In this study, we analyzed both the liquidand gas-phase products using GC and Raman spectroscopy. The purpose of this work was to experimentally evaluate the complete conversion of CB to CO2, water, and HCl under SCWO conditions, using an optically transparent anticorrosive fused-silica capillary reactor (FSCR) in combination with a polarization microscope recorder system for visual observation of the phase behavior changes and also recording of the magnified images together with reaction temperature and time information, and a Raman spectroscopic system for qualitative and quantitative analyses of the gas-phase products, without sampling, and to present the results of a kinetics study of CO2 formation during the SCWO of CB.
Figure 1. Photomicrograph of fused-silica capillary reactor (665 μm O.D., 300 μm I.D., and 2 cm long) (a), and photograph of fused-silica capillary reactor (4 mm O.D., 2 mm I.D., and 5 cm long) and a ruler (b).
water bath to ambient conditions, ensuring cessation of all reactions in the FSCR. The reaction time was defined as the time between the temperature inside the FSCR reaching 94% of the oven temperature and quenching. After cooling, the gasand liquid-phase products were analyzed using Raman spectroscopy, GC, and GC-mass spectrometry (GC-MS). The experimental details are presented in the Supporting Information. Sample Analysis. Before breaking open the cooled reactors, the gas-phase product, CO2, produced from the SCWO of CB was directly determined by Raman spectroscopy using a JY/Horiba LabRam HR Raman system (Horiba Jobin Yvon, Villeneuve d’Ascq, France); the system was equipped with 531.95-nm (frequency doubled Nd:YAG) laser excitation, a 10× Olympus objective with 0.25 numerical aperture, and a 1800-grooves/mm grating with a spectral resolution of about 1 cm−1. An approximately 50-mW laser light was focused on the sample to acquire spectra in the range 1200−1500 cm−1 (covers the peak of the Fermi diad of CO2). The integration time was 120 s, with three accumulations per spectrum. An Agilent 6890 GC (Agilent, Santa Clara, CA, USA) equipped with a capillary column (HP-5MS, 30 m × 0.25 mm × 0.25 μm) and coupled with a mass-selective detector (MSD) was used to identify unreacted CB and liquid intermediate products. The oven temperature was held at 70 °C for 2 min, followed by 15 °C min−1 ramping to 260 °C, and then holding at 260 °C for 5 min. The GC injector temperature was 250 °C and the MSD injector temperature was 320 °C. The CB conversion yield is defined as follows:
■
EXPERIMENTAL SECTION Materials. All chemicals and reagents were purchased from commercial sources and used as received. CB (CAS 108-90-7, purity >99.0%) was purchased from the Lingfeng Co., Ltd. (Shanghai, China). H2O2 (30 wt %), used as the oxidizer, was purchased from the China National Pharmaceutical Industry Co., Ltd. (Shanghai, China). All other chemicals used for analyses were of analytical reagent grade. The fused-silica capillary tubing (665 μm O.D. and 300 μm I.D., or 4 mm O.D. and 2 mm I.D.) used in this study was purchased from Polymicro Technologies LLC (Phoenix, AZ, USA) and Technical Glass Products, Inc. (Painesville, OH, USA). Experimental Procedure. To prepare a sample, a section of silica capillary tubing (665 μm O.D., 300 μm I.D., and 2 cm long; or 4 mm O.D., 2 mm I.D., and 5 cm long) was cut, and one end of the tube was sealed in an oxyhydrogen flame. CB and H2O2 were injected into the capillary tube using a microsyringe, and then centrifuged to the closed end. The amounts of CB and H2O2 loaded into each reactor varied with the reaction conditions to be used. The closed end of the capillary was then immersed in liquid nitrogen and the open end of the tube was quickly sealed with an oxyhydrogen flame to form an FSCR (Figure 1). The sealing procedure was fast enough (within 5 s) to avoid increasing the temperature of the liquid inside the FSCR, thus preventing vapor loss. The FSCR (665 μm O.D., 300 μm I.D., and 2 cm long) was then inserted into the sample chamber of a heating−cooling stage (INS0908051, INSTEC, Inc., Boulder, CO, USA). Images of the sample during the reaction were observed under a polarization microscope (DM2500P, Leica, Wetzlar, Germany), and recorded continuously in a computer through a digital camera (TK-C1481, JVC, Yokohama, Japan). The experimental details have been described previously.24,25 The larger FSCR (4 mm O.D., 2 mm I.D., and 5 cm long) was placed in a hot-air oven which had been preheated to the desired reaction temperature. After a specified reaction time, the FSCR was removed from the hot-air oven and quenched rapidly in a cold-
CB conversion yield (%) = ((Amount of CB feed − Amount of CB remaining
■
after reaction)/(Amount of CB feed)) × 100%
RESULTS AND DISCUSSION Phase-Behavior Changes of CB in the FSCR. Under ambient conditions, there are three phases (i.e., CB in oil form, an aqueous fluid, and a vapor phase) in the FSCR. However, the mixing state of these phases under the elevated temperature−pressure conditions is unknown. To investigate the phase-behavior changes of CB in H2O−H2O2 system during the heating and cooling processes, the sample was heated to a maximum temperature of 400 °C at a rate of 10 °C min−1. Figure 2a shows the phase changes during the heating process. As the temperature increased, CB gradually dissolved in the H2O−H2O2 system and the green color of the oil phase became lighter. Note that CB finally dissolved completely in the 3385
dx.doi.org/10.1021/es204262d | Environ. Sci. Technol. 2012, 46, 3384−3389
Environmental Science & Technology
Article
The amount of H2O2 varied from 100% to 300%, based on the stoichiometric amounts in the following reaction: C6H5Cl + 14H2O2 → 6CO2 + 16H2O + HCl
It is interesting to note that the effect of the stoichiometric amount of H2O2 on the CB conversion yield increased more slowly in the range 150−300% than it did in the range 100− 150%. The reason may be that in the advanced oxidation processes, a large excess of H2O2 reduces the wastewater treatment efficiency as a result of free-radical scavenging by H2O2, as in the following reaction: H2O2 + •OH → H2O + HO2 •
This may cause dilution by H2O2 of the overall concentration of reactants.26 Consequently, the amount of oxidizer must be larger than the stoichiometric equivalence; an appropriate excess of H2O2 can be introduced as an additional parameter for controlling the oxidation reaction rate to some extent. In the following experiments, therefore, the stoichiometric amount of H2O2 used was 150% in each case. Effects of Temperature and Time on CB Conversion Yield and CO2 Yield. Most hazardous organic compounds can be completely oxidized to CO2 and water in a very short reaction time in supercritical water,27 and the CO2 quantitative is very important because SCWO of complex organic compounds proceeds through a series of steps that produce numerous products of incomplete oxidation; the reactions do not proceed to CO2 in a single step.28 The oxidation efficiency can also be estimated by monitoring the amount of CO2 produced. To show the effects of reaction time on CBoxidation efficiency in supercritical water, before breaking open the cooled FSCR samples which had been reacted at 450 °C for different reaction times (from 0 to 10 min), Raman spectra of the vapor phase were recorded; the results are shown in Figure 4. The Raman spectrum of CO2 consists of an upper band, a lower band, and two hot bands; the upper and lower bands (Fermi diad split by Fermi resonance) are especially pronounced.29 Note that the amount of CO2 dissolved in the aqueous phase under the experimental conditions is less than
Figure 2. Photomicrographs of chlorobenzene in hydrogen peroxide in fused-silica capillary reactor during heating process (a), and cooling process (b).
subcritical H2O−H2O2 system formed a homogeneous liquid solution at 326.1 °C, and there were still two coexisting phases (i.e., a liquid fluid and a vapor phase) in the FSCR. As the temperature increased further, a homogeneous solution formed above 369.3 °C and the green color practically disappeared. The sample was held at 400 °C for 10 min, and then the temperature of the sample was gradually cooled to ambient conditions; the phase changes are shown in Figure 2b. During the cooling process, separation of the oil and aqueous phases occurred at 336.9 °C. The amount of oil increased substantially and suspended oily spheres were observed, but the total amount of oil was significantly less than that before the reaction. From this visualization, we can conclude that some of the CB decomposed during the SCWO process. Effects of the Amount of Oxidizer on CB Conversion Yield. We used an aqueous H2O2 solution as the oxygen source, and the effects of the stoichiometric amount of H2O2 on CB SCWO are shown in Figure 3. The reaction temperature and time were maintained at 375 °C and 5 min, respectively.
Figure 4. Raman spectra of CO2 produced by oxidation of CB in supercritical water with 150% stoichiometric amounts of oxidizer at 450 °C at different reaction times. Raman spectra were calibrated by the peak of monocrystalline silicon (520.7 cm−1), and the spectra were collected under similar conditions; the increase in CO2 signals indicates the progress of the oxidation process.
Figure 3. Effects of stoichiometric amount of H2O2 on CB conversion yield (T = 375 °C, t = 5 min). 3386
dx.doi.org/10.1021/es204262d | Environ. Sci. Technol. 2012, 46, 3384−3389
Environmental Science & Technology
Article
0.28 mol kg−1,30 and can be neglected. Informative spectra of the aqueous phase could not be obtained because of the high fluorescence of the sample. It is known that CO2 pressure (or density) is linearly related to the Raman peak area in a calibrated Raman spectrometer.31 As shown in Figure 5, the peak area increases with reaction
than the CB conversion yield, indicating that the rate of total organic carbon disappearance is always less than the rate of reactant disappearance. For instance, at 400 °C, when the reaction time was increased from 2 to 10 min, the CB conversion yield increased from 23.32% to 67.48%, and the highest CO2 yield did not exceed 28.01%, implying that some carbon is present in intermediate products formed during SCWO of CB at low temperatures and insufficient reaction times. Some of the intermediate byproducts of incomplete oxidation in the liquid phase were identified by GC-MS as benzene, 4-methyl-3-penten-2-one, and 4-hydroxy-4-methyl-2pentanone. Reaction Kinetics Analysis. The main objective of a wastewater treatment technology is to convert organic compounds to CO2 completely. The rate law for CO2 formation is therefore particularly important for evaluating SCWO, and possibly designing SCWO reactors.32,33 In this paper, we therefore present the global rate laws for the conversion of total organic carbon to CO2 during the SCWO of CB. Assuming that complete conversion of CB to CO2 follows pseudo-first-order kinetics, the integrated form of the proposed pseudo-first-order kinetics equation is ln(1 − x) = −kt
Figure 5. Raman peak area of CO2 (scattered symbols) and CO2 yield (lines) vs reaction time with 150% stoichiometric amount of oxidizer at different temperatures.
where k denotes the pseudo-first-order rate constant, t denotes the reaction time, and x denotes the CO2 yield. The linear relationships between ln(1 − x) and t for each temperature are shown in Figure 7; the uncertainties given are the 97%
time in the temperature range 350−450 °C, and levels off (with peak area = S*) at a reaction temperature of 450 °C and reaction time of 10 min, indicating complete conversion of the carbon in CB to CO2, which corresponds to the maximum CO2 yield of 100%. The CO2 yield at time t, having a peak area of S, can therefore be calculated from the following: CO2 yield (%) =
S × 100% S*
The effects of reaction time on the CB conversion yield at different temperatures were calculated based on changes in the amounts of CB before and after reaction; the results are shown in Figure 6. As expected, increasing the reaction time from 2 to 10 min increased the conversion yield at all temperatures. Taken together, the results in Figures 5 and 6 show that the maximum CB conversion yield and a CO2 yield up to 100% were obtained within 8 and 10 min at 450 °C, respectively, using a 150% stoichiometric amount of H2O2. And under comparable reaction conditions, the CO2 yield was always less
Figure 7. Linear relationships between ln(1 − x) and t for CB oxidation in sub- and supercritical water. Note the increase in the slope as the temperature increases, indicating acceleration of the reaction with increasing temperature.
confidence intervals for various reaction times. The straight lines suggest that oxidation of CB in sub- and supercritical water follows first-order kinetics. The global reaction rate constant can be expressed in terms of the Arrhenius frequency factor, A, and the activation energy, Ea ⎛ −E ⎞ k = A exp⎜ a ⎟ ⎝ RT ⎠
where Ea is the apparent activation energy (kJ mol−1), A is the pre-exponential factor (s−1), R is the gas constant (8.314 J mol−1 K−1), and T is the temperature (K).
Figure 6. Effects of reaction time on CB conversion yield with 150% stoichiometric amount of oxidizer at different temperatures. 3387
dx.doi.org/10.1021/es204262d | Environ. Sci. Technol. 2012, 46, 3384−3389
Environmental Science & Technology
Article
acknowledge Dr. I. M. Chou of the U.S. Geological Survey for his guidance, Prof. Chunmian Lin of the Zhejiang University of Technology for his suggestions, and also three anonymous reviewers.
The Arrhenius plot is shown in Figure 8. A straight line was obtained (98% confidence intervals), giving an activation
■
(1) Wei, G. T.; Wei, C. H.; He, F. M.; Wu, C. F. Dechlorination of chlorobenzene in subcritical water with Fe/ZrO(2), Ni/ZrO(2) and Cu/ZrO(2). J. Environ. Monit. 2009, 11 (3), 678−683. (2) Choi, J.; Shin, C. B.; Park, T. J.; Suh, D. J. Characteristics of vanadia-titania aerogel catalysts for oxidative destruction of 1,2dichlorobenzene. Appl. Catal., A 2006, 311, 105−111. (3) Ghaffar, A.; Tabata, M. Dechlorination of chlorobenzene compounds on flyash; effects of metals, aqueous/organic solvents and temperatures. Appl. Catal., B 2009, 86 (3−4), 152−158. (4) Borja, J.; Taleon, D. M.; Auresenia, J.; Gallardo, S. Polychlorinated biphenyls and their biodegradation. Process Biochem. 2005, 40 (6), 1999−2013. (5) Field, J. A.; Sierra-Alvarez, R. Microbial degradation of chlorinated dioxins. Chemosphere 2008, 71 (6), 1005−1018. (6) Chowdhury, P.; Viraraghavan, T. Sonochemical degradation of chlorinated organic compounds, phenolic compounds and organic dyes - A review. Sci. Total Environ. 2009, 407 (8), 2474−2492. (7) Lim, M.; Son, Y.; Khim, J. Frequency effects on the sonochemical degradation of chlorinated compounds. Ultrason. Sonochem. 2011, 18 (1), 460−465. (8) Miao, X. S.; Chu, S. G.; Xu, X. B. Degradation pathways of PCBs upon UV irradiation in hexane. Chemosphere 1999, 39 (10), 1639− 1650. (9) Bhatkhande, D. S.; Sawant, S. B.; Schouten, J. C.; Pangarkar, V. G. Photocatalytic degradation of chlorobenzene using solar and artificial UV radiation. J. Chem. Technol. Biotechnol. 2004, 79 (4), 354− 360. (10) Indarto, A.; Yang, D. R.; Choi, J. W.; Lee, H.; Song, H. K. CCl4 decomposition by gliding arc plasma: Role of C-2 compounds on products distribution. Chem. Eng. Commun. 2007, 194 (8), 1111− 1125. (11) Francke, K. P.; Miessner, H.; Rudolph, R. Cleaning of air streams from organic pollutants by plasma-catalytic oxidation. Plasma Chem. Plasma Process. 2000, 20 (3), 393−403. (12) Poznyak, T.; Vivero, J. Degradation of aqueous phenol and chlorinated phenols by ozone. Ozone-Sci. Eng. 2005, 27 (6), 447−458. (13) Javorska, H.; Tlustos, P.; Komarek, M.; Lestan, D.; Kaliszova, R.; Szakova, J. Effect of ozonation on polychlorinated biphenyl degradation and on soil physico-chemical properties. J. Hazard. Mater. 2009, 161 (2−3), 1202−1207. (14) Cho, C. H.; Ihm, S. K. Development of new vanadium-based oxide catalysts for decomposition of chlorinated aromatic pollutants. Environ. Sci. Technol. 2002, 36 (7), 1600−1606. (15) Lee, S. H.; Park, K. C.; Mahiko, T.; Sekizawa, K.; Izumizaki, Y.; Tomiyasu, H. Supercritical water oxidation of polychlorinated biphenyls based on the redox reactions promoted by nitrate and nitrite salts. J. Supercrit. Fluids 2006, 39 (1), 54−62. (16) Bermejo, M. D.; Cocero, M. J. Supercritical water oxidation: A technical review. AIChE J. 2006, 52 (11), 3933−3951. (17) Savage, P. E. Organic chemical reactions in supercritical water. Chem. Rev. 1999, 99 (2), 603−621. (18) Brunner, G. Near and supercritical water. Part II: Oxidative processes. J. Supercrit. Fluids 2009, 47 (3), 382−390. (19) Ding, Z. Y.; Frisch, M. A.; Li, L. X.; Gloyna, E. F. Catalytic oxidation in supercritical water. Ind. Eng. Chem. Res. 1996, 35 (10), 3257−3279. (20) Hatakeda, K.; Ikushima, Y.; Ito, S.; Saito, N.; Sato, O. Supercritical water oxidation of a PCB of 3-chlorobiphenyl using hydrogen peroxide. Chem. Lett. 1997, 3, 245−246. (21) Morlando, R.; Manahan, S. E.; Larsen, D. W. Iron-catalyzed cocurrent flow destruction and dechlorination of chlorobenzene during gasification. Environ. Sci. Technol. 1997, 31 (2), 409−415.
Figure 8. Arrhenius plot for reaction rate constants.
energy of 142.8 kJ mol−1 and a pre-exponential factor of 22.2 s−1. Significance of This Work. In this study, an optically transparent anticorrosive FSCR instead of the conventional stainless-steel reactor, in combination with a microscope recorder system for visual observation the chemical reaction phase behavior changes under elevated temperature−pressure conditions, and monitored using a Raman spectroscopic method without sampling, was constructed and its applicability for studying CB oxidation in sub- and supercritical water was demonstrated. FSCR-Raman spectroscopy-based method is visually accessible, low in energy and materials consumptions, expeditiousness, absent of undesired catalytic effects of the reactor wall, resistant to corrosion, and could be directly coupled with a Raman spectroscopic system for monitoring the chemical reaction progress in situ. Moreover, due to the small size of the reactor, it minimizes the resistances in mass transfer and heat transfer, such that the observed kinetics approaches to the intrinsic one, and the kinetic results may be applied to optimum reactor design at throughputs in industrial operations. This technology has great potential to be applied for the theoretical study of fluids and chemical reactions under elevated pressure−temperature conditions.
■
ASSOCIATED CONTENT
S Supporting Information *
Experimental apparatus, GC-MS analysis of the liquid phase byproducts results, Raman spectra of gas phase products between 0 and 4000 cm‑1 wavenumbers, and determination of the FSCR heat-transfer. This information is available free of charge via the Internet at http://pubs.acs.org.
■
REFERENCES
AUTHOR INFORMATION
Corresponding Author
*Tel: 86-571-88320061; fax: 86-571-88320061; e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS Financial support for this research was provided by the Natural Science Foundation of China (21077092). We thank and 3388
dx.doi.org/10.1021/es204262d | Environ. Sci. Technol. 2012, 46, 3384−3389
Environmental Science & Technology
Article
(22) Hatakeda, K.; Ikushima, Y.; Sato, O.; Aizawa, T.; Saito, N. Supercritical water oxidation of polychlorinated biphenyls using hydrogen peroxide. Chem. Eng. Sci. 1999, 54 (15−16), 3079−3084. (23) Sun, M. C.; Wu, X. Q.; Zhang, Z. E.; Han, E. H. Oxidation of 316 stainless steel in supercritical water. Corros. Sci. 2009, 51 (5), 1069−1072. (24) Pan, Z. Y.; Chou, I. M.; Burruss, R. C. Hydrolysis of polycarbonate in sub-critical water in fused silica capillary reactor with in situ Raman spectroscopy. Green Chem. 2009, 11 (8), 1105− 1107. (25) Pan, Z. Y.; Dong, Z. Determination of chlorobenzene solubilities in subcritical water in a fused silica capillary reactor from 173 to 267 degrees C. Ind. Eng. Chem. Res. 2011, 50 (20), 11724−11727. (26) Wang, S. Z.; Guo, Y.; Chen, C. M.; Zhang, J.; Gong, Y. M.; Wang, Y. Z. Supercritical water oxidation of landfill leachate. Waste Manage. 2011, 31 (9−10), 2027−2035. (27) Lin, K. S.; Wang, H. P. Supercritical water oxidation of 2chlorophenol catalyzed by Cu2+ cations and copper oxide clusters. Environ. Sci. Technol. 2000, 34 (22), 4849−4854. (28) Martino, C. J.; Savage, P. E. Total organic carbon disappearance kinetics for the supercritical water oxidation of monosubstituted phenols. Environ. Sci. Technol. 1999, 33 (11), 1911−1915. (29) Song, Y. C.; Chou, I. M.; Hu, W. X.; Robert, B.; Lu, W. J. CO(2) Density-Raman shift relation derived from synthetic inclusions in fused silica capillaries and its application. Acta Geol. Sin.-Engl. Ed. 2009, 83 (5), 932−938. (30) Duan, Z. H.; Sun, R. An improved model calculating CO2 solubility in pure water and aqueous NaCl solutions from 273 to 533 K and from 0 to 2000 bar. Chem. Geol. 2003, 193 (3−4), 257−271. (31) Seitz, J. C.; Pasteris, J. D.; Chou, I. M. Raman spectroscopic characterization of gas mixtures 0.2. Quantitative composition and pressure determination of the CO2-CH4 system. Am. J. Sci. 1996, 296 (6), 577−600. (32) Li, R. K.; Thornton, T. D.; Savage, P. E. Kinetics of CO2 formation from the oxidation of phenols in supercritical water. Environ. Sci. Technol. 1992, 26 (12), 2388−2395. (33) Yu, J. L.; Savage, P. E. Kinetics of catalytic supercritical water oxidation of phenol over TiO2. Environ. Sci. Technol. 2000, 34 (15), 3191−3198.
3389
dx.doi.org/10.1021/es204262d | Environ. Sci. Technol. 2012, 46, 3384−3389
