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

Mengmei Zhang; Takashi Fujimori; Kenji Shiota; Alfons Buekens; Kota Mukai; Yasuhiro Niwa; Xiaodong Li; Masaki Takaoka

doi:10.1016/j.jhazmat.2020.122064

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

J Hazard Mater. 2020 Apr 15:388:122064. doi: 10.1016/j.jhazmat.2020.122064. Epub 2020 Jan 9.

Authors

Mengmei Zhang¹, Takashi Fujimori², Kenji Shiota³, Alfons Buekens⁴, Kota Mukai³, Yasuhiro Niwa⁵, Xiaodong Li⁶, Masaki Takaoka³

Affiliations

¹ Department of Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyoto, 6158510, Japan; State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou, 310027, China.
² Department of Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyoto, 6158510, Japan. Electronic address: fujimori.takashi.3e@kyoto-u.ac.jp.
³ Department of Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyoto, 6158510, Japan.
⁴ State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou, 310027, China.
⁵ Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, 3050801, Japan.
⁶ State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou, 310027, China. Electronic address: lixd@zju.edu.cn.

PMID: 31954297
DOI: 10.1016/j.jhazmat.2020.122064

Abstract

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.

Keywords: Chromium chloride; Formation mechanisms; In situ X-ray Absorption Fine Structure (XAFS); Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF).

Publication types

Research Support, Non-U.S. Gov't