MICROEMULSIONS AS MEDIA FOR DESTRUCTION OF ORGANOHALIDE POLLUTANTS BYELECTROLYSIS

This paper reviews recent work on the dehalogenation of organohalide p ollutants by electrochemical catalysis in bicontinuous microemulsions of didodecyldimethylammonium bromide (DDAB)-water-dodecane. Compared w ith alternative toxic, expensive organic solvents, the catalytic effic iency for the dehalogenations was enhanced for nonpolar organohalides in DDAB microemulsions. Using metal phthalocyanine tetrasulfonates as catalysts, the catalytic efficiencies for the reactions of 1,2,dibromo butane and 1,2-dibromocyclohexane were much larger in a microemulsion than in a homogeneous solvent. The reverse was found for trichloroacet ic acid. Since DDAB and the catalysts adsorb on the carbon cathode, re sults suggest that a DDAB layer on the cathode preconcentrates non-pol ar dibromides but not the polar trichloroacetic acid. For complex mixt ures of polychlorinated biphenyls, DDAB microemulsions performed bette r in bench-scale catalytic dechlorinations than aqueous DDAB dispersio ns, which performed better than aqueous CTAB micelles. Complete conver sion of 100 mg of a 60% chlorine industrial PCB mixture in a 20 ml mic roemulsion could be carried out overnight using an activated lead cath ode, zinc phthalocyanine as catalyst, and ultrasonic mass transport. F inally, the dechlorination of DDT (1,1-bis(4-chlorophenyl)-2,2,2-trich loroethane), which has both aliphatic and aromatic chlorines, was also explored in the microemulsions. Preliminary results suggest that oxyg en may be an effective catalyst for the dechlorination of DDT in DDAB microemulsions to 1,1-diphenylethane using a carbon cathode.