Microemulsions as media for destruction of organohalide pollutants by electrolysis

Abstract

This paper reviews recent work on the dehalogenation of organohalide pollutants by electrochemical catalysis in bicontinuous microemulsions of didodecyldimethylammonium bromide (DDAB)—water—dodecane. Compared with alternative toxic, expensive organic solvents, the catalytic efficiency for the dehalogenations was enhanced for non-polar organohalides in DDAB microemulsions. Using metal phthalocyanine tetrasulfonates as catalysts, the catalytic efficiencies for the reactions of 1,2-dibromobutane and 1,2-dibromocyclohexane were much larger in a microemulsion than in a homogeneous solvent. The reverse was found for trichloroacetic acid. Since DDAB and the catalysts adsorb on the carbon cathode, results suggest that a DDAB layer on the cathode preconcentrates non-polar dibromides but not the polar trichloroacetic acid.

For complex mixtures of polychlorinated biphenyls, DDAB microemulsions performed better in bench-scale catalytic dechlorinations than aqueous DDAB dispersions, which performed better than aqueous CTAB micelles. Complete conversion of 100 mg of a 60% chlorine industrial PCB mixture in a 20 ml microemulsion could be carried out overnight using an activated lead cathode, zinc phthalocyanine as catalyst, and ultrasonic mass transport. Finally, the dechlorination of DDT (1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane), which has both aliphatic and aromatic chlorines, was also explored in the microemulsions. Preliminary results suggest that oxygen may be an effective catalyst for the dechlorination of DDT in DDAB microemulsions to 1,1-diphenylethane using a carbon cathode.