Novel Mild Hydrodechlorination of PCDDs, PCDFs, and co-PCBs inside Fly Ash Using a Calcium-Promoted Rhodium Carbon Catalyst in Methanol

Environmental Context. The generic term ‘dioxins’, the family of which includes polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like compounds such as coplanar polychlorinated biphenyls (co-PCBs), is used to describe highly toxic and mutagenic compounds. Many methods that involve high-temperature or high-pressure dry hydrogen conditions to ensure adequate decomposition for persistent chlorinated aromatic pollutants present disadvantages for repeated synthesis or recovery of vaporized dioxins and co-PCBs. We discovered that highly efficient degradation of dioxins in fly ash is accomplished in 24 h using metallic calcium and Rh/C in alcohol in a sealed tube at 25°C at 0.15 MPa.

Abstract. Effective hydrodechlorination of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like compounds such as coplanar polychlorinated biphenyls in fly ash was achieved in 24 h using a simple stirring operation in a sealed tube with metallic calcium and Rh/C catalyst in an alcohol solution at room temperature with 0.15 MPa of increasing internal pressure. The initial 7806 pg dioxin toxic equivalent (TEQ) (g of ash)^–1 of dioxins in fly ash, which had adsorbed inside the solid phase, was finally degraded to 23.6 pg of TEQ (g of ash)^–1, according to estimation using gas chromatography–mass spectrometry analysis.