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Abstract
In this research, a method based on base-catalysed decomposition (BCD) was developed using sodium hydroxide and glycerol for dechlorination of transformer oils with low levels of polychlorinated biphenyls (PCBs). PCB removal and dechlorination efficiencies were measured by gas chromatography and the silver nitrate titration method, respectively. PCB dechlorination and removal efficiencies after 4 h at 250°C and in the presence of iron were 97.4% and 99.8%, respectively. However, in the absence of iron the same efficiencies were calculated to be 79.4 and 99.7%, respectively. The dielectric loss factor of oil refined at 250°C was 0.0064 and did not meet the required standards to be reused in the transformers. However, that refined at 200°C satisfied the standards with acceptable conversion rates. Use of iron, besides increasing conversion rates, changed the mechanism of the reaction from nucleophilic substitution to a combination of hydrodechlorination and nucleophilic substitution. In the presence of iron, highly chlorinated PCBs were converted to less chlorinated PCBs, and this caused the concentration of less chlorinated PCBs to reach a peak and then decline thereafter. The production of PCB 36 confirmed this. However, in the absence of iron particles, all changes in the PCB concentration curves were downward.
Highlights
More than four decades have passed since the production and use of polychlorinated biphenyls (PCBs) were banned, but theyThe Authors
One of the practical and relatively inexpensive methods of purifying transformer oils and treating soil polluted with PCBs that is mostly used in developed countries is base-catalysed decomposition (BCD) [14,15]
The chromatograms of the initial untreated oil, and oil treated with a mixture of glycerol, sodium hydroxide and iron after 1 and 4 h are compared in figure 2
Summary
More than four decades have passed since the production and use of polychlorinated biphenyls (PCBs) were banned, but theyThe Authors. PCBs were mainly used in the production of Askarel, which was produced in the reaction between Arochlor, a trade name for a mixture of PCBs in the USA, and trichlorobenzene They were used as the dielectric fluid in capacitors, transformer oils, hydraulic fluids, etc. One of the practical and relatively inexpensive methods of purifying transformer oils and treating soil polluted with PCBs that is mostly used in developed countries is base-catalysed decomposition (BCD) [14,15]. In this method, PCBs are dechlorinated by using a high-boiling-point hydrocarbon, base and metal catalyst. Xiao et al [20] proposed a combination of mechanisms in which nucleophilic substitution was the major mechanism and hydrodechlorination was the minor mechanism of PCB decomposition
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