Microwave-Assisted Base-Catalyzed Decomposition Process for the Degradation of Polychlorinated Biphenyl

Microwave irradiation was adopted to combine with the traditional base-catalyzed decomposition (BCD) process for the degradation of polychlorinated biphenyl, thus formed the so-called microwave-assisted base-catalyzed decomposition (MA-BCD) process. 2, 4, 5-trichlorobiphenyl (PCB29) dissolved in hexane or cetane was used to test the effectiveness of the MA-BCD process, where the solvent acted both as reaction medium and as hydrogen donor. The role of sodium hypophosphite (NaH₂PO₂) as hydrogen donor was also investigated. Granular activated carbon (GAC), zero-valent iron powder, copper powder and Pd/C catalyst were selected as catalysts and microwave absorbents. The results indicated that most of PCB29 could be decomposed in a few minutes by the MA-BCD process, with NaH₂PO₂ as hydrogen donor, any kind of the four catalysts and NaOH added. Microwave output power level was a key factor, and the treatment with a higher microwave power for a short time was more effective than that with a lower microwave power for a long time. Higher degradation efficiencies were obtained when NaOH was added in aqueous solution in stead of particles, as the existence of water was helpful for the release of H₂ from NaH₂PO₂. The degradation of PCB29 by the MA-BCD process was through dechlorination, and biphenyl was detected as the main product.