[Formation mechanism of by-product PCBs in the p-DCB production].

A typical p-DCB production process was selected in this study. A series of p-DCB product samples, 1 Japanese sample and 1 chlorobenzene sample were collected and analyzed for by-product polychlorinated biphenyls (PCBs). It is a common phenomenon that byproduct PCBs exists in the p-DCB production process. The PCBs levels in the p-DCB samples were 62-781 ng/g and the highest WHO-TEQ in the process was 0.24 ng/g, while the PCBs level in the Japanese sample reached 881 ng/g. PCB31 was the dominate PCB congener in all the p-DCB samples with the maximum 98.5% of the total PCBs. Maximum content of PCBs was TrCBs in the p-DCB samples with the next TeCBs, DiCBs and PeCBs, while MoCBs were the highest in the chlorobenzene sample. Furthermore, a formation mechanism of PCBs in the production process was proposed and proved by the analysis result. It suggested that the formation of PCBs form the condensation of polychlorobenzenes had a relation with the concentration of polychlorobenzenes and the chlorine position in the benzene ring.