PCDD/Fs formation catalyzed by the copper chloride in the fly ash

Abstract

The secondary formation of dibenzo-p-dioxin and dibenzofurans (PCDD/Fs) in the flue gas and ash from the municipal solid waste incinerator (MSWI) systems has attracted considerable public concern. The objective of our research was thus to examine reactions in fly ash from an MSWI operated with different precursors with similar chemical compositions, such as dibenzofurans (DFs), and metal chlorides, such as copper chloride (CuCl₂). We observed that the concentrations of PCDD/Fs in CuCl₂ and in a mixture of CuCl₂ and DFs were 369.5 and 5307.8 ng/g, respectively, and thus significantly higher in the latter. Due to the catalytic effect of copper ions and the similar structure of dibenzofurans for PCDFs, the effect of the additive in forming PCDD/Fs were obvious. The concentrations of PCDD/Fs in CuCl₂ and copper oxide (CuO) were 369.5 and 97.05 ng/g, respectively. The results also show that the PCDD/Fs concentration when copper chloride was added was four times higher than when copper oxide was added. In addition, the level of activity of the chlorine atoms is greater than that of the oxygen atoms during the formation of PCDD/Fs. This study suggests that the use of metal-containing substances (such as Cu, Cl, Zn) or chlorination precursors (such as DF, chlorobenzene) should be avoided in the combustion process.

Keywords:

• Fly ash
• PCDD/Fs
• synergetic effect
• metal chloride
• catalysis

Acknowledgments

The authors would like to thank the Super Micro Mass Research and Technology Center, Cheng Shiu University, for sampling and analysis.