Dechlorination of Polychlorinated Biphenyls in Industrial Transformer Oil by Radiolytic and Photolytic Methods
C G. Jones, Joseph Silverman, M I. Al-Sheikhly, Pedatsur Neta, Dianne L. Poster
Used electrical transformer oils containing low (nearly equal to} 95 g g-1) or high (>800,000 g g-1) concentrations of polychlorinated biphenyls (PCBs) were treated using electron, gamma, and ultraviolet radiation and the efficiency of dechlorination by the various methods is compared. Analysis of the inorganic chloride ions formed by irradiation with different doses shows progressive dechnorination and after high doses complete dechlorination of the PCBs is achieved. Complete dechlorination is confirmed by determining the concentrations of PCBs in the oils using liquid and gas chromatography. Transformer oil containing nearly equal to} 95 g g-1 PCB (nearly equal to} 3.5 mmol L-1 chlorine) is completely dechlorinated by irradiation with 600 kGy after the addition of 10% triethylamine (TEA) (initial radiolytic yield 0.02 mol J-1). Transformer oil containing>8000,000 g g-1 PCB (17.7 mol L-1 chlorine) requires an additional solvent to prevent solidification and to improve radiolytic yields. When this oil is diluted with 2-propanol (2-PrOH) and TEA (v/v/v, 1/17/20), complete dechlorination is achieved with a dose of 2500 kGy (initial radiolytic yield 0.23 mol J-1). The initial radiolytic yield for dechlorination is higher in 1/1 oil/TEA mixtures (0.50 mol J-1) but the dechlorination process is incomplete due to solidification. No dose-rate effect is observed upon comparing the results from electron-beam and gamma radiation. Ultraviolet photolysis also leads to the dechlorination of PCBs in transformer oils. Photolytic dechlorination of the oil/2-PrOH/TEA (1/79/20) solutions approached 90% after an exposure time of 120 hours in our experimental setup. Such yields were obtained by radiolysis with a dose of 2000 kGy (300 hours in our Gammacell). Replacing TEA with KOH in 20PrOH solutions greatly increases the yield of dechlorination both in the radiolytic and the photolytic experiments, demonstrating that the well-known chain reaction plays a role in both of these treatment methods.
, Silverman, J.
, Al-Sheikhly, M.
, Neta, P.
and Poster, D.
Dechlorination of Polychlorinated Biphenyls in Industrial Transformer Oil by Radiolytic and Photolytic Methods, Environmental Science & Technology
(Accessed May 28, 2023)