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 > NaH 2 PO 4 % KH 2 PO 4 . 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.

Application of Subcritical Water to Dechlorinate Polyvinyl Chloride Electric Wires

“…Subcritical or supercritical fluids have been successfully applied as a simpler and environmental friendly methods for decomposition of various polymer materials [8][9][10][11][12].…”

Application of Supercritical Water To Decompose Brominated Epoxy Resin and Environmental Friendly Recovery of Metals from Waste Memory Module

“…All the problems above should be solved properly. In recent years, supercritical water (SCW, T ≥ 374 °C, P ≥ 22.1 MPa) is introduced as an environmentally friendly method to decompose organic polymers due to its extraordinary properties, such as low viscosities, high mass transport coefficient, high diffusivity, and high solubility for organics. − Utilization of green solvents in chemical reactions is quite significant. As one of the nontoxic and nonflammable solvents, water has been considered to be an ideal solvent in chemical reactions compare with traditional organic solvents. − Water in SCW conditions can act not only as a solvent but also as a reactant, catalyst, or product due to the different properties, which are mainly dependent on temperature and pressure.…”

Degradation of brominated epoxy resin and metal recovery from waste printed circuit boards through batch sub/supercritical water treatments

“…In recent years, supercritical water (SCW, T P 374°C, P P 22.1 MPa) is introduced as an environment-friendly method to recycle organic polymers due to its extraordinary properties, such as low viscosities, high mass transport coefficient, high diffusivity and high solubility for organics [9][10][11]. In our previous works [12], supercritical fluids were employed for debromination and recovery of oil from waste plastic containing brominated flame retardant in computer housing, where the retardant was in additive type [13].…”