An integrated two-stage process for effective dechlorination of polychlorinated biphenyls in subcritical water in the presence of hydrogen donors

Abstract: In this study, a novel two-stage process, i.e. first stage for hydrogen species generation at 150°C and second stage for PCB dechlorination at 330°C, was developed for efficient PCB degradation in subcritical water with nanoscale Ni/Fe particles. The obtained results showed that over 92% of PCBs was completely converted into 1-alkyl-benzenes during this process. The addition of hydrogen donors could greatly enhance PCB dechlorination in descending order: oxalic acid≈HAc>NaH2PO4 ≈KH2PO4. The anion introduced along with H+ played the crucial role in overall dechlorination process due to the undesired reaction between anion and reactive nanoscale Ni/Fe. Oxalic acid was quite effective for the generation of hydrogen species by supply more available H+ without undesired side reaction. In contrast, phosphate could react with Ni/Fe rapidly to form complex precipitates on particle surface and thereby block the reactive sites of particle following suspension of dechlorination. In addition, low 150°C at first stage as compared to 330°C at second stage favored the dissolution and adsorption of hydrogen on Ni surface for catalyzing to form more reactive hydrogen species used for rapid dechlorination. [Copyright &y& Elsevier]