Conversion Pathways of DDT and Its Derivatives during Catalytic Hydrodechlorination

Di-1,1-chlorophenyl-2,2,2-trichloroethane (DDT) and its derivatives di-1,1-chlorophenyl-2,2-dichloroethane (DDD), di-1,1-chlorophenyl-2,2-dichloroethene (DDE), and di-1,1-chlorophenyl-2-chloroethene (DDMU) were dechlorinated in heptane solution over a sulphide Ni-Mo/C catalyst in a batch reactor. The process was carried out at 150-260 degrees C and hydrogen pressure of 3 MPa. For DDT, fast elimination of chlorine was observed from the aliphatic position, yielding mainly DDD at 150 degrees C. At around 200 degrees C, the aromatic chlorine atoms started to be removed. The complete dechlorination of the DDT derivatives was observed at 260 degrees C, yielding predominantly 1,1-diphenylethane (DPE) and 1,2-diphenylethane (BB). The conversion of DDT to BB was found to proceed via DDD. BB was presumably formed via carbenoid rearrangement of geminal dichlorides. Small amounts of diphenylmethane (DPM) were also found in the final product. Based on the GC-MS and GC-FID analyses of reaction products, the pathways of DDT derivative degradations during hydrodechlorination (HDCl) were proposed.