Palladium-catalyzed reductive dehalogenation of dissolved chlorinated aliphatics using electrolytically-generated hydrogen

Recent studies have shown that reductive dehalogenation of chlorinated hydrocarbons by hydrogen occurs rapidly in the presence of a palladium catalyst. The speed and completeness of these reactions may offer advantages for groundwater remediation. A practical design challenge arises with the need to expeditiously saturate the aqueous phase with hydrogen. To address this, a two-stage treatment column (hydrogen generator and catalytic reactor) has been developed. The first stage consists of an undivided electrolyzer cell which generates hydrogen by electrolyzing the influent water. The second stage contains a catalyst bed of palladium metal supported on alumina beads. This reactor has been tested with groundwater containing various chlorinated aliphatics. Using a flow rate of 300 ml/min and a current of 4 amps under a potential of 8 volts, removal efficiencies greater than 95% were achieved for PCE, TCE, 1,1-DCE, and carbon tetrachloride with residence times on the order of 2 minutes. Chloroform and 1,2-DCA appear less susceptible to dehalogenation by this process. These results imply that dissolved oxygen present in solution does not completely inhibit reduction of the chlorinated hydrocarbons on the catalyst.