Direct Chlorination of Carbon by Copper Chloride in a Thermal

Feb 25, 2009 - A high concentration of chlorinated organic compounds such as dioxins, PCBs, and chlorobenzenes, etc., has been found in the fly ash of...
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Research Direct Chlorination of Carbon by Copper Chloride in a Thermal Process TAKASHI FUJIMORI* AND MASAKI TAKAOKA Department of Urban and Environmental Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nisikyo-ku, 615-8540, Kyoto, Japan

Received October 24, 2008. Revised manuscript received January 24, 2009. Accepted February 4, 2009.

A high concentration of chlorinated organic compounds such as dioxins, PCBs, and chlorobenzenes, etc., has been found in the fly ash of the postcombustion zone in a thermal process, i.e., waste incineration. The behavior of Cu and Cl in model fly ash was studied by using in situ X-ray absorption finestructureanddiffractiontechniqueusingsynchrotronradiation. Copper chloride changed its chemical state during rising temperature. These chemical states of copper played three types of roles: First, a two-step dechlorination at around 300 °C (the reduction of CuCl2 to CuCl) and 400 °C (the oxidation CuCl to CuO) and chlorination of the carbon matrix occurs. Chlorides from reduced copper chloride directly bonded aromatic or aliphatic carbon at the temperature that most of the chlorinated organic compounds formed. Second, catalyzed by CuO and CuCl, carbon gasification is promoted over 250 °C. Third, the formation of surface oxygen complexes may be catalyzed by CuCl at 300-350 °C. The control of copper may be important to reducing the formation of chlorinated organic compounds.

Introduction Toxic and trace chlorinated organic (organo-Cl) compounds are produced unintentionally by humans and persist in the environment (1, 2). Thermal processes are a major anthropogenic source of organo-Cl compounds (3, 4). Polychlorinated dibenzo-p-dioxins, furans, and biphenyls are known to be emitted from municipal solid waste incinerators (5, 6), and many researchers have suggested the homo- and heterogeneous formation of organo-Cl compounds from macromolecular carbons (7-9). Ash collected from the postcombustion zone, called fly ash, has the highest concentration of organo-Cl compounds, and unburned carbon and chlorine sources in fly ash and surrounding oxygen are known to be essential factors for organo-Cl formation (7, 8). In addition, metal compounds with low concentrations in fly ash promote organo-Cl formation. Copper in particular has a strong potential, and its chlorination mechanism has been proposed (10-14). However, little experimental data to support the predicted behavior of Cu and Cl at the atomic level have been acquired. X-ray absorption spectroscopy has recently been used to monitor the redox change of copper in fly ash upon heating (15, 16) or under the presence of a * Corresponding author e-mail: t012002.mbox.media.kyoto-u.ac.jp. 10.1021/es802996a CCC: $40.75

Published on Web 02/25/2009

takashi.fujimori@

 2009 American Chemical Society

precursor (17). The behavior of chlorine and the atomic environment of copper were not clarified in these studies, however, because the X-ray absorption fine structure (XAFS) was used like a fingerprint of an unknown chemical form of copper. Therefore, little direct evidence exists to clarify the formation mechanism of organo-Cl compounds with copper at the atomic level. The chlorination mechanism can be better described if the behaviors of copper and chlorine atoms are observed at the same time. In the present work, we reveal the behaviors of Cu and Cl in fly ash and provide basic information on the chlorination mechanism of carbon by copper that produces organo-Cl compounds during thermal processes.

Materials and Method Sample Called Model Fly Ash. To determine the behavior of Cu and Cl, we prepared a model fly ash (MFA) that was a mixture of copper(II) chloride dihydrate (CuCl2 · 2H2O), activated carbon (AC), and boron nitride (BN) containing 1.9% Cu, 2.0% Cl, 5.0% AC, and the remaining 91.1% was almost entirely BN. Any organic compounds were removed from the AC by heating at 500 °C for 60 min under a 100% nitrogen stream. The compositions of MFA were based on previous research described in text reference (15). Previously we reported that there was no significant difference of formation content of chlorinated organic compounds between the use of BN and that of fused silica (15). We also measured the following Cl K-edge XANES spectra of two types of MFAs that contained CuCl (3.0%) or CuO (2.5%) + KCl (4.7%) with the Cu/Cl ratios adjusted to 1 mol/2 mol, instead of CuCl2 · 2H2O, i.e., CuCl + AC (5.0%) + BN and CuO + KCl + AC (5.0%) + BN. In Situ Cu K-edge X-ray Absorption Fine Structure and Data Analysis. Using in situ Cu K-edge XAFS, we detected the chemical structure of Cu at the atomic level in the MFA. After the MFA was ground using a mortar and agate mortar for 10 min respectively, 200 mg was pressed into a disk (13 mm in diameter). Cu K-edge XAFS was performed using beamline BL01B1 in SPring-8 (Hyogo, Japan), as a MFA disk was heated in the T-type in situ cell (15), which was constructed of a glass cell, a mantle heater, and a temperature controller. The cell consisted of a tubular part 4.0 cm in diameter, and the T measured 11.5 cm each side. A MFA disk was placed on a glass stand on a sample board and inserted in the cell. The X-rays passed through a window made of Kapton film. A water-cooled tube was coiled outside the Kapton film so that the thermal load did not affect the Kapton film. The temperature of the sample was increased gradually from room temperature to 400 °C, following the profile shown in Figure S1. The 10% O2 (90% N2) gas atmosphere was introduced from the inlet of the T-type cell at 50 mL/min and exhausted from the outlet. The energy area from 8730 to 9820 eV of Cu K-edge extended X-ray absorption fine structure (EXAFS) could be measured in 2.5 min by quick scan mode. EXAFS spectra of a MFA disk were collected in transmission mode with a Si(111) monochromator. The energies were first adjusted using the reference copper foil. The spectra of reference materials, CuCl2 · 2H2O, CuCl2, CuCl, Cu2(OH)3Cl, CuO, Cu2O, and Cu, were measured to compare their spectral shapes and to identify major species because an X-ray absorption near edge structure (XANES) spectrum can be used as fingerprint that reflects the local environment of copper. Species can be distinguished using the linear combination fit technique, in which spectra of known reference species are fitted to the spectrum of the unknown VOL. 43, NO. 7, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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sample. We conducted linear combination fit of the XANES spectrum to determine the major species using REX 2000 ver 2.5.5 software (Rigaku, Japan). The residual value, R value ) Σ(XANESmeasd - XANEScalcd)2/Σ(XANESmeasd)2, was used to evaluate the linear combination fit for the experimental spectra. We also analyzed Cu K-edge EXAFS to obtain details on the local Cu environment. An EXAFS spectrum provides information on the environment surrounding a target atom, i.e., the coordination number and atomic distance (18). Background removal and normalization were performed. REX 2000 was used to fit the Cu-EXAFS function using paths for CuCl2 and CuO as generated by the FEFF (version 8.10) program. The fitting was limited to a k range of 2.7-12.0 Å-1, k3 weighted, with modified Hanning windows, and an R range from 1.0 to 2.2 Å. Cu-Cl path in CuCl2 (2.26 Å) (19) and Cu-O path in CuO (1.95 Å) (20) were used to fit the data. Fitting was performed on the coordination number, the radial distance, the Debye-Waller factor (DW), and the energy shifts (dE) of each shell. The number of independent N for a single spectrum analyzed by Fourier transform can be calculated from N ) 2 + (2∆k∆R)/π where ∆k is the k range over which the Fourier Transform was performed and ∆R is the R range for the same (21). For the ranges used, this expression gives a maximum of 9 variable parameters, which is higher than the actual number of variables we used. We adopted dE e 20 (Å-1) and DW > 0 (Å2) for analytical and physical limitation and confirmed that the DW which means thermal vibration of molecule showed increase upon heating of the MFA (22). Cl K-Edge X-ray Absorption Near Edge Structure. The Cl forms present after MFA was heated were determined by measuring the Cl K-edge XANES. A MFA was ground using a mortar for 10 min. The MFA powder was then inserted on a quartz boat into a quartz tube (120 cm × 4.0 cm in diameter) filled with 10% O2 (90% N2) at 50 mL/min and heated for 30 min in an electric furnace preheated to 200, 250, 300, 350, and 400 °C. After the heating procedure, MFA powder was sealed as quickly as possible and supplied to the measurement of Cl K-edge XANES performed using BL-11B in Photon Factory (Tsukuba, Japan). In situ cell could not be used in Photon Factory because of physical restriction of the device. Powdered MFA samples were mounted on carbon tape and their XANES spectra were collected in total fluorescence yield (TFY) mode in a vacuum. X-ray absorption spectra of Cl in different inorganic and organic reference compounds were collected to assist in the identification of the chemical state of Cl in MFA after heating (Figure 1). The references of copper compounds were CuCl2 · 2H2O, CuCl2, CuCl, and Cu2(OH)3Cl and polyvinyl chloride as aliphatic organic carbon connected to Cl, and their XANES spectra were measured in total electron yield (TEY) mode in a vacuum. We selected Cl references, 1,3,5-, 1,2,4,5-, and pentachlorobenzene and 2,3-, 2,4-, 2,6-, 3,4-, 2,3,6-, and 2,3,4,6-chlorophenol connected to aromatic carbon. Cl K-edge XANES spectra of chlorobenznenes and chlorophenols were measured under atmospheric pressure by conversion electron yield (CEY) method at BL-9A in Photon Factory. All Cl-XANES spectra were calibrated against the intense absorption feature of solid KCl at 2822.8 eV. The absorption peaks of Cl combined with aliphatic and aromatic carbon and copper are below 2820.2 and 2821.1 ((0.1) eV and over 2822.0 eV, respectively (ref. Figure 1). Copper chlorides have pre-edge features (about 2817 eV). Therefore, Cl bound to inorganic, aromatic, or aliphatic carbon can be distinguished by the features of a Cl XANES spectrum (23). Reflected in these spectral features, analyses were performed between 2814 and 2823 eV by a linear combination fit using reference materials of chlorine using REX 2000. In Situ Powdery X-ray Diffraction Using Synchrotron Radiation. The chemical forms in the MFA were determined by in situ powder X-ray diffraction using synchrotron 2242

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FIGURE 1. Cl K-edge XANES of reference Cl materials connected with copper and aromatic and aliphatic carbon, which have different maximum peak positions. CP, CBz, and PVC are chlorophenol, chlorobenzene, and polyvinyl chloride, respectively. radiation (SR-XRD). About 0.6 mg of A MFA was filled in a quartz capillary column (0.5 mm diameter) using a Pasteur pipet and sealed by a burner under air atmosphere. We placed the capillary at Debye-Scherrer camera for measurement SR-XRD using BL02B2 in SPring-8 (Hyogo, Japan). Diffraction X-ray pattern can be detected by imaging plate. The capillary was heated by N2 gas from room temperature to 400 °C and we measured SR-XRD pattern for which crystal information was identified by using MDI Jade 6j software (Rigaku, Japan) contained with ICDD powder diffraction file. Measurement of Total Organic Carbon. The total organic carbon (TOC) of the MFA was measured by a total organic carbon analyzer (TOC-5000A/SSM-5000A: Shimadzu) at 900 °C under 99.9% O2 gas (150 mL/min) and 4-5 kg/cm2G pressure. D-(+) glucose (TOC 40%) was used as a standard substance.

Results and Discussion Chlorination Effect by Copper(II) Chloride. Dynamic changes in the forms of Cu and Cl in the MFA were clearly observed by X-ray absorption and diffraction using synchrotron radiation (Cu: Figures 2A, 3A, and 4; and Cl: Figure 5A). Cu K-edge spectra of room temperature, 300, and 400 °C observed in this study had the same shapes as in our previous research (15). And Cl K-edge XANES was also measured under the CuCl2 · 2H2O (50%) + AC (50%). From room temperature to 400 °C, Cl-K edge spectra in this mixture had the same shapes as in CuCl2 · 2H2O (50%) + AC (50%). Therefore, our data of Cu and Cl K-edge XANES were reproducibile or representative. The MFA was made by mixing in a mortar at room temperature (rt), but the Cu K-edge

FIGURE 2. Cu K-edge XANES (A) spectra of MFA upon heating from room temperature (rt) to about 400 °C at a rate of 5 °C/min under a 10% oxygen gas stream (50 mL/min). The chemical forms of Cu at each temperature were revealed by a linear combination fit of XANES; rt (B) and 400 °C maintained for about 18 min (C) show the goodness of fit (R value ) 0.004 and 0.020). The dotted and bold lines shown in (B) and (C) are the calculated and measured spectra, respectively.

FIGURE 3. Fourier-transformed EXAFS (A) spectra of MFA upon heating from room temperature (rt) to about 400 °C at a rate of 5 °C/min under a 10% oxygen gas stream (50 mL/min). The coordination numbers of the Cu-Cl and Cu-O shells as a function of temperature are shown in (B) as fitted from the EXAFS spectra upon heating. XANES and SR-XRD pattern indicated that this physical procedure did not appreciably affect the form of Cu (Figures 2B and 4). Because Cu-Cl and Cu-O shell patterns are close together, errors with the Fourier transform data were estimated to be larger when copper was maintained in the CuCl2 · 2H2O form below about 100 °C (Figure 3A); thus, the

FIGURE 4. In situ synchrotron powder X-ray diffraction pattern of MFA during heating from room temperature (rt) to 400 °C. The main acute peak pattern (no symbol) was derived from boron nitride, and the halo peak before and after 14° was derived by activated carbon. coordination number is not shown in Figure 3B. CuCl2 · 2H2O dehydrates around 100 °C (Figure 4), and the chemical form of copper is then CuCl2, which has a coordination number and atomic distance for Cu-Cl of 3.3 ( 0.5 and 2.26 ( 0.01 Å, respectively, according to analysis of Cu K-edge EXAFS (Figure 3B). The environment surrounding Cl was hardly changed by the dehydration of CuCl2 · 2H2O, because the Cl K-edge XANES spectra below 200 °C had the same prepeak intensity at 2817 eV, which was derived from copper(II) chloride (Figures 5B and 1). Hydrated and nonhydrated copper(II) chloride with a carbon matrix were thought to show the same behavior over dehydration temperature around 100 °C (Figure 4). On the other hand, at 400 °C copper(II) oxide was the dominant form of Cu based on XANES and SR-XRD (Figures 2C and 4), and the atomic distance and coordination number of Cu-O were 1.92 ( 0.01 Å and 8.7 ( 1.4, respectively, according to analysis of EXAFS (Figure 3B). In contrast, the major chemical form of Cl was CuCl at 400 °C (Figure 5C). Compared with CuCl, CuO was the dominant form of copper at 400 °C. According to the temperature profile of the in situ XAFS measurement (Figure S1), the appearance of CuO occurred over about 150 min from the starting point when kept at 400 °C for about 10 min, based on analysis of the XANES region. In contrast, the form of Cu changed little when kept at 200 (ca. 60-80 min) and 300 °C (ca. 100-120 min) for about 20 min. Therefore, the rate of oxidation at 400 °C is more rapid than that at 200 and 300 °C. Here, we reported a characteristic chemical state of copper between CuCl2 at around 100 °C and CuO at 400 °C, as shown in the orange region in Figures 2A and 3A. This Cu form was caused by the reduction of copper near 300 °C and maintenance of its chemical form even around 350 °C as follows: The energy point of the first maximum in the derivative of the Cu K-edge XANES spectrum (called the “edge”) can provide information on the redox state of copper (Figure S2) (16). The edge position changed to 8981.0 eV around 300 °C, and the valence of copper was shown to be lower than that of Cu(II) by comparing the edges of reference copper compounds. Therefore, Cu was reduced from Cu(II) VOL. 43, NO. 7, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 5. Cl K-edge XANES spectra (A) after MFA was heated for 30 min under a 10% oxygen gas stream (50 mL/min) at constant temperatures up to 400 °C. Linear combination fit using reference materials of chlorine shown in (B). The calculated spectral fits (dotted line) and measurement spectra (bold line) at each temperature were good (R value ) 0.016-0.035). The percentage of Cl-species as a function of temperature is shown in (C). The “aromatic-Cl” represents the sum of the ratio of chlorophenols and chlorobenzenes based on the spectral analyses, and “aliphatic-Cl” is the ratio of the C-Cl bond derived from polyvinyl chloride. to Cu(I) or Cu(0). The coordination number of the first shell of Cu-Cl decreased 1.5 ( 0.3 between 310 and 350 °C by half of the CuCl2 form at 100 °C, and the atomic distance was shortened 2.19 ( 0.02 Å more than CuCl2 at 100 °C according to analysis of the EXAFS spectra (Figure 3B). Based on the SR-XRD pattern, CuCl was best identified from 275 to 350 °C (Figure 4). A reduction process from CuCl2 to CuCl at temperatures around 300 °C was also revealed by analyses of Cl K-edge XANES (Figure 5C). Consequently, the most stable reduction state of copper was CuCl. We conclude that the majority of CuCl2 within the carbon matrix dechlorinated to CuCl around 300 °C and kept this state to about 350 °C. Some of the CuCl was gradually oxidized to CuO by the surrounding oxygen gas at temperatures above 360 °C, and drastic oxidation to CuO started to occur at 400 °C (Figure 3B). Thus, a dechlorination process occurred at that time. From 370 to 390 °C, two-shell fitting of the Fourier transform data for Cu-O and Cu-Cl showed large errors, and the results of the analyses are not shown in Figure 3B. However, the coordination numbers of Cu-Cl and Cu-O are thought to gradually decrease and increase, respectively, because of the continuous change in the XANES and Fourier-transform EXAFS spectra upon heating (the black spectra between the orange and red described in Figures 3A and 4A). When the dechlorination reaction of Cu occurred, we found strong evidence of the C-Cl bond. The Cl K-edge XANES spectrum of the MFA at 300 °C, the first dechlorination of copper, had the lowest energy position of the absorption maximum at 2821.1 eV (Figure 5A). According to Figure 1, copper chlorides have a larger energy position at 2822.0 eV 2244

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than the MFA at 300 °C. The absorption maximum of the MFA at 300 °C is the same energy as Cl connected to an aromatic carbon (Figure 1). The ratio of Cl connected to aromatic and aliphatic carbons was the maximum at 300 °C based on analyses of Cl K-edge XANES spectra (Figure 5B and C). The C-Cl bond was derived from the dechlorination of copper because the only chlorination source in MFA was copper(II) chloride, i.e., the direct chlorination of carbon by copper occurred. A direct chlorination mechanism by copper(II) chloride was proposed by Weber et al. (13) as follows: 2CuCl2 + R-H f2CuCl + R-Cl + HCl, where R is organic carbon. CuCl2 reduction can be described by the following reaction: 2CuCl2 f2CuCl + Cl2, which has a negative Gibbs free energy change (∆G) over 224 °C at the thermodynamic equilibrium state. Cl2 mainly occurred in the substitution reaction with R-H (24). We almost confirmed this mechanism at the atomic level by analyzing the Cu and Cl forms using XAFS and the SR-XRD pattern. Organo-Cl compounds are known to be generated at the maximum rate in/on fly ash around 300 °C (25). The results of the temperature profile of aromatic- and aliphatic-Cl (Figure 5C) coincided well with that of organo-Cl and showed that the direct chlorination by copper started around 250 °C. This may be a key formation mechanism for chlorinated organic compounds in fly ash in thermal processes. Based on the way that dechlorination occurred at about 400 °C by the oxidation of copper (ref. Figures 2C, 3B, and 4) and because the ratio of aromaticand aliphatic-Cl was then smaller than at 300 °C (Figure 5C), the content of organo-Cl compounds has roots in the balance between chlorination and the destruction of the carbon matrix (ref. Figure 7). Other Copper Compounds: Copper(I) Chloride and Copper(II) Oxide. The Cl K-edge XANES spectra of two types of MFAs, CuCl (3%) + AC (5.0%) + BN or CuO (2.5%) + KCl (4.7%) + AC (5.0%) + BN, were also measured. Each XANES spectrum did not change its features from room temperature to 400 °C, and Cl kept bonding to copper in the MFA with CuCl (Figures 1 and S3A) or to potassium in the MFA with CuO + KCl (Figure S3B). Because CuCl is hardly reduced compared to CuCl2 at temperatures around 300 °C, the chlorinating force of copper(I) chloride is thought to be weaker than that of copper(II) chloride. When CuO coexisted with an inorganic chlorine source (KCl) in the solid phase, the Cl form maintained the same XANES spectrum of reference for KCl (Figure S3B). The chlorination effect of KCl is much weaker than that of copper(II) chloride (14), and its effect is thought to be less than that of direct chlorination by CuCl2, although catalytic chlorination called the Deacon reaction by CuO has been reported (11). The results suggesting that the chlorination of the carbon matrix by the reduction of Cu(II)-Cl, not Cu(I)-Cl or Cu-O mixed with inorganic chloride, started at around 250 °C are important for understandingthechlorinationmechanismoforgano-Clcompounds. Consumption of Carbon. The consumption of carbon by copper(II) chloride and the appearance of surface organic compounds (SOCs) in an MFA were evaluated to discuss the interaction between copper and carbon. The organic carbon content was measured by a TOC analyzer. In the case involving only activated carbon, the organic carbon content did not change after 30 min of heating at temperatures up to 400 °C under a 10% oxygen stream. With the addition of copper(II) chloride, organic carbon started to be consumed below 300 °C (Figure 6A). At 300 °C, copper(II) chloride is reduced by carbon and the Cu form resembles CuCl, as previously noted (ref. Figures 3B and 4). A spill-over effect has been suggested for the interaction of oxygen, CuCl, and the carbon matrix via the surface (26). The CuCl may catalyze the spill-over effect to carbon gasification at 300 °C. At 400 °C, the Cu form was clearly CuO (ref. Figures 2C and 4). Carbon gasification is catalyzed by CuO (27), and this

FIGURE 6. Thermal behavior of carbon in MFA. Organic carbon was consumed by copper chloride(II) at temperatures over 200 °C compared with the activated carbon (AC)-only sample (A). Absorption bands of the FT-IR with peaks around 1720 cm-1 (O) and 1570 cm-1 (0) indicated surface oxygen complexes (SOCs) such as lactone and diketone (26) on the carbon matrix and changed with increasing temperature (B). gasification process, i.e., the destruction of the carbon matrix, implies that the content of destructive organic-Cl compounds increases as the temperature rises above 300 °C. More evidence of the oxidation of the carbon surface was provided by Fourier transform infrared (FT-IR) spectroscopy of a disk of MFA, which contained a mixture of copper chloride(II) dehydrate and activated carbon (1:1 weight) that was heated for 30 min under a 10% oxygen gas stream and 99.5% KBr. The absorbance of SOC bands (26) at 1720 and 1570 cm-1 increased from 300 °C, which showed the maximum SOC content (Figure 6B), but this tendency was not shown using only AC. SOCs may increase by the spill-over effect attributed to CuCl at 300 °C and decrease by carbon gasification derived from the CuO at 400 °C. Formation Mechanism of Organo-Cl Compounds. X-ray absorption and diffraction spectroscopy have enabled us to understand the behavior of Cu and Cl at the atomic level. We conclude that copper chloride is key to the formation of organo-Cl compounds in thermal processes and plays three types of roles: First, chlorination of the carbon matrix occurs by a two-step dechlorination process at around 300 °C (the reduction of CuCl2 to CuCl) and 400 °C (the oxidation CuCl to CuO). Second, carbon gasification begins at temperatures over 250 °C with copper changing to CuO and CuCl. Third, the formation of surface oxygen complexes may be catalyzed by CuCl existing in a stable state at 300-350 °C. The formation mechanisms of organo-Cl compounds derived from copper can be outlined as shown in Figure 7. The strongest form of copper for chlorination is the Cu(II)-Cl state, not Cu(I)-Cl or Cu-O with an inorganic chlorine source as described above. In the first role, a part of CuCl may react with chlorine and/or oxygen to form a catalytic cycle with CuCl2 or oxychloride in order to produce organo-Cl compounds (15). Trace copper(II) chloride in real fly ash may perform each role, and the organo-Cl content reaches a maximum at around 300 °C when the chlorination and SOC formation are superior to the gasification process (Figure 7). The temperature range of 250-400 °C, especially around 300 °C, is clearly dangerous in thermal processes for the organic-Cl profile, as shown in Figure 5C. In the case of municipal solid waste incinerators, this dangerous temperature zone inevitably exists in the postcombustion zone due to the architectural structure of such facilities. Therefore, increasing the temperature gradient in this zone, e.g., by quenching, can be effective (28). As the components of organo-Cl compounds, i.e., carbon, chlorine, and oxygen, are widespread and abundant on Earth, control of these elements will be difficult.

FIGURE 7. Formation mechanism of organo-Cl compounds by copper(II) chloride in the thermal process. Oxygen (29) can be controlled in the dangerous temperature zone in thermal processes, but this requires sophisticated facilities and is expensive. One solution to this difficulty may be to control the trace element copper. Eliminating the inflow of copper to thermal facilities or chemically inhibiting copper at the atomic level might decrease the creation of organo-Cl compounds by thermal processes and thereby have beneficial effects on the environment and human health.

Acknowledgments We thank N. Takeda, K. Oshita, K. Shiota, S. Morisawa, and T. Yamamoto for supporting this study; H. Tanida and T. Uruga (BL01B1) (Proposal 2005B0439) and K. Kato (BL02B2) (2006A1093) for helping with Cu XAFS and SR-XRD measurement at SPring-8; Y. Kitajima (BL-11B) and Y. Inada (BL9A) for helping with Cl XANES measurement at Photon Factory (Proposal 2007G069). And we greatly acknowledge the financial support by a Grand-in-Aid for Young Sciencetist (A) from JSPS (17681008).

Supporting Information Available Three supporting figures. This material is available free of charge via the Internet at http://pubs.acs.org.

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