The Catalytic Hydrodechlorination Of Chlorophenols And Chlorinated Dioxins Over Palladium Catalyst In Aqueous Solutions

Chlorinated organic compounds exhibit high toxicity and form a class ofenvironmentally undesirable compounds that are associated with a broad range ofindustrial processes. In recent years, the catalytic hydrodechlorination has receivedattention as one of the simplest methods and the most promising innovativetechnologies for the disposal of toxic waste streams containing chlorinated organiccompounds, converting the toxic organic chlorides into the correspondinghydrocarbons under mild conditions.In this study, using H2 as a hydrogen donor, aromatic chlorides,chlorophenols, triclosan (2,4,4'-trichloro-2'-hydroxydiphenylether, dioxinprecursor) and 2,4,8-trichlorodibenzofuran (2,4,8-TCDF) were catalyticallyhydrodechlorinated in liquid phase under mild conditions over a commercialpalladium on carbon catalyst.In aqueous solutions, the effects of the presence of organic solvents, basesand ions were discussed on the reaction rates and the catalyst activity in detail. Thefunction of water, which led the catalyst to the high activity and high stability, wasdeeply investigated in the hydrodechlorination of chlorinated organic compounds.The effects of the organic solvents on the dechlorination and the catalyst activitywere also described. The selective hydrodechlorination of polychlorinated phenols,triclosan and 2,4,8-trichlorodibenzofuran, which contains the C-O bond, wasinvestigated in liquid phase with Pd/C and H2. It was found that the C-Cl bond inthe para-position of C-O bond was easier to be hydrogenated than those in theortho-positions of C-O bond. This method ―the catalytic hydrodechlorinationmight be expected as a useful technology to eliminate and reduce the toxicity ofpolychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, especiallyfor higher chlorinated 2,3,7,8-substiuted dioxins. Additional, the mechanism of thehydrogenation of 4-CP was investigated and discussed in this paper.