Chlorination Mechanism of Carbon during Dioxin Formation Using Cl-K Near-edge X-ray-absorption Fine Structure

Abstract

Many environmental organic chemicals have chloride in their structure. Thus, researching the chlorination mechanism of carbon is of interest. Dioxins are typically concentrated in fly ash collected from the post-combustion zone during the operation of municipal solid waste incinerators. In this study, we report the application of Cl-K near-edge X-rayabsorption fine structure (NEXAFS) in determining the chlorination mechanism of carbon in fly ash. The separation of a chloride-carbon (C-Cl) bond was readily recognizable as a peak in the Cl-K NEXAFS spectrum. Chlorination effects could be estimated using Cl K-edge NEXAFS with no dependence on metal species. Analysis of Cl K-edge NEXAFS spectra showed the reduction of copper(II) chloride at 300 C and oxidation of iron(III) chloride at 400 C in connection with the chlorination of carbon.

Contrasting Effects of Sulfur Dioxide on Cupric Oxide and Chloride during Thermochemical Formation of Chlorinated Aromatics

“…From our results, the contrasting effects of SO 2 gas were strongly dependent on the oxide/chloride ratio of Cu in the fly ash. In “real” MSWI fly ash, Cu exists as the oxide and chloride. ,, A high S/Cl ratio resulted in no inhibition of PCDD/Fs with coal cofiring in MFA . In this case, we suggest one possible reason is the low fraction of CuCl 2 in the MFA.…”

“…In a previous study, we reported catalytic and direct chlorination of a C matrix by CuCl 2 . , The C matrix was chlorinated in the case of MFA–CuO in the presence of SO 2 gas because reactions and progressed. “Real” MSWI fly ash contained trace Cu, and some part of the Cu exists as the oxide. ,, The major fraction of Cl in real MSWI fly ash was bonded with K (i.e., KCl). , Thus, reactions and may occur practically in real incinerators. Increasing PCDD/Fs with injected SO 2 gas into MFAs has been reported previously, , which was likely at least partly caused by this mechanism, related to the interaction between SO 2 gas and the solid-phase CuO + KCl system.…”

“…According to previous studies, , we selected SiO 2 as a representative base material to measure the amount of aromatic-Cls. BN was used in X-ray absorption spectroscopic experiments because we needed to make a disk shape to measure in situ Cu K-edge XANES , and to avoid interference by Si K-edge absorption in the case of S K-edge NEXAFS measurements . Previously, we reported that no significant difference existed in the formed content of aromatic-Cls between the use of BN and SiO 2 .…”

“…Previous studies have discussed reactions between gas-phase Cl species (Cl 2 or HCl) and SO 2 gas. MSWI fly ash generally contains percentage-order Cl combined with alkaline (earth) metals such as potassium (K), sodium, and calcium. , Although the main Cl species [i.e., potassium chloride (KCl), sodium chloride (NaCl), and CaCl 2 ] in the solid phase have small promoting effects in generating PCDD/Fs, , PCBs, , and CBzs , in MSWI fly ash, dramatic increases in such aromatic-Cls were found by adding trace amounts of cupric oxide (CuO) , and chloride (CuCl 2 ). ,, In fact, Cu in “real” MSWI fly ash exists mainly in chloride and oxide forms. ,, Such cupric compounds exhibit catalyst-like behaviors using solid-phase Cl species as a Cl sink. Thus, interactions among solid-phase Cl species, cupric compounds, and SO 2 gas remain unstudied in terms of their role and involvement in the mechanism with SO 2 gas in the thermochemical formation of aromatic-Cls.…”

Quantitative Speciation of Insoluble Chlorine in Environmental Solid Samples

“…These were consistent with previous reports. 8,10,34,43 As shown in Figure 2A, differences in the shape of the spectra between 2815 and 2830 eV were large enough to distinguish between aromatic-Cl, aliphatic-Cl, and different species of inorganic Cl.…”