Development of thermochemical destruction method of perfluorocarbons (PFCs)

Abstract

Abatement of green house gas (GHG) emission is a critical environmental issue. Among the six GHGs specified in Kyoto protocol, perfluorocarbons (PFCs) is the most potent. We investigated the thermal reductive destruction of PFCs using solid reagents. The complete destruction of PFCs (CF4, C2F6, C3F8 and SF6) was successfully achieved by flowing the gas through a heated reagent bed (300-800degreesC) that contained powder mixtures of alkali halides (AX), CaO, and Si. To make this treatment process more economical, using blast furnace slag and Si-containing sludge as reagents instead of pure CaO and Si powder was also investigated. Comparable reactivities for destructing PFCs were obtained between the pure AX/CaO/Si and the AX/Slag/Si-sludge systems. Among various ternary mixture systems, the CsF-containing reagent showed the highest activity for the PFCs destruction. The thermal reductive destruction efficiency increased in the order of CF4 < C2F6 < C3F8 < SF6. The pure pyrolysis of SF6 Was observed at as low as 600degreesC. The destruction of SF6 in the ternary AX/CaO/Si system was more efficient than in the CaO or MgO-only system. The X-ray diffraction analysis of the powder products showed that fluoride-containing materials were generated as a result of the reaction between PFCs and the heated reagents, indicating that the hot solid mixtures can effectively trap the harmful fluorines within the solid products. No toxic HF and SiF4 formation was observed in the exhaust gas stream.