Dechlorination of Polychlorinated Biphenyl by UV-Irradiation -Influence of Sodium Chloride Deposition on a Lamp Wall on the Decomposition Yield of PCB-

Abstract

The dechlorination of concentrated (4.4 X 10^-1 mol/l) PCB solution in alkaline 2-propanol by UV-irradiation brought about white deposition of sodium chloride on the surface of quartz jacket contacting the PCB solution. Consequently, penetration of light into the reaction mixture greatly decreased, whereas such deposition was not observed in the case of PCB concentration less than 4.6 X 10^-2 mol/l. From the discussions of the output characteristics of light source (100 W high pressure mercury lamp), the molecular extinction coefficient of PBC, and the wavelength dependence of the quantum yield of dechlorination, it was found that dechlorination occurred in the neighbourhood of less than O.92 mm and 8.00 mm from the jacket wall in 4.4 x 10^-1 mol/l and 4.6 X 10^-2 mol/l of PCB solution, respectively. Several attempts were made to allow the photodechlorination of an increased amount of PCB without the growth of deposition on the jacket. By supplying PCB step by step or continuously into the alkaline alcoholic solution from outside of the reactor under irradiation, 8 times of PCB by weight could be successfully dechlorinated (99.5%) with the rate acceleration by a factor of 1.6 in comparison with those of the reaction of PCB (4.6 X 10^-2 mol/l) in a batch.