Thermochemical formation of dioxins promoted by chromium chloride: In situ Cr- and Cl-XAFS analysis

[Display omitted] •The promoting effect of CrCl3 on the PCDD/F formation is experimentally confirmed.•Behavior of Cr and Cl during PCDD/F formation is monitored by in situ XAFS.•For the first time in situ XAFS is performed successfully on Cl.•The influence of temperature and oxygen content is studie...

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Published in:Journal of hazardous materials 2020-04, Vol.388, p.122064-122064, Article 122064
Main Authors: Zhang, Mengmei, Fujimori, Takashi, Shiota, Kenji, Buekens, Alfons, Mukai, Kota, Niwa, Yasuhiro, Li, Xiaodong, Takaoka, Masaki
Format: Article
Language:English
Subjects:
Chromium chloride
Formation mechanisms
In situ X-ray Absorption Fine Structure (XAFS)
Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF)
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Summary:[Display omitted] •The promoting effect of CrCl3 on the PCDD/F formation is experimentally confirmed.•Behavior of Cr and Cl during PCDD/F formation is monitored by in situ XAFS.•For the first time in situ XAFS is performed successfully on Cl.•The influence of temperature and oxygen content is studied.•Mechanisms of chromium chloride promoted formation of dioxins are revealed. Chromium is commonly found in the flue gases and ashes of Municipal Solid Waste Incineration. It has been reported as an active catalyst for the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) during de novo tests, yet its specific mode of action has remained unclear. This study aims to identify the effects of chromium chloride on the formation of PCDD/F and other chloro-aromatics and to elucidate the underlying reaction mechanisms. A series of de novo tests, conducted over a wide range of temperature (from 250 to 550 °C) and for four different oxygen contents (0, 5, 10, 20 %), confirmed the promoting effect of CrCl3 on the PCDD/F formation. In situ X-ray Absorption Fine Structure (XAFS) spectroscopy was applied to investigate the behavior of CrCl3 during heating, describing the entire picture of CrCl3-promoted formation pathways of dioxins. The effect of oxygen was studied by measuring XAFS spectra on samples heated at different oxygen concentrations. According to these spectra, chromium compounds play two key roles during dioxins formation: (a) chlorinating carbon, using chlorine derived from conversion of CrCl3 into Cr2O3, and further oxidation to Cr(VI), and (b) facilitating oxidative destruction of the carbon matrix, while reducing Cr(VI) to Cr2O3.
ISSN:0304-3894
1873-3336
DOI:10.1016/j.jhazmat.2020.122064