Abstract
ABSTRACT
Dechlorinations of commercial PCB mixtures were conducted at temperatures from 200 to 400 °C over the solid base systems, CaO, Ca(OH)2, CaCO3, MgO, Mg(OH)2, BaO, Ba(OH)2, KOH, NaHCO3 and Na2CO3. Aroclor 1016 was reacted with excess solid base or their mixtures in sealed glass tubes. Organic residues containing only carbon, hydrogen and oxygen and inorganic chloride salts were formed. Dehalogenating ability depended on base strength (e.g., KOH > BaO/Ba(OH)2 > CaO/Ca(OH)2 > MgO/Mg(OH)2), temperature and surface area. Generating new surface area during dechlorination markedly increased the dechlorination rate but the addition of small amounts of NiCl2 and FeCl3 slowed the reaction. Carrying out the dechlorination in a closed hammer mill at 375° and 400°C increased the rate by more than 100 times that in static sealed tubes. The more highly chlorinated PCBs underwent dechlorination more rapidly over each of these base systems. 2-Chloro-and 2,2′-dichlorobiphenyl were the most resistant of the PCB congeners to dehalogenate. Dehalogenations of 4-chlorobiphenyl, 4,4′-dichlorobiphenyl and 4-chlorodiphenyl ether at 375 °C over CaO/Ca(OH)2 proceeded through benzyne intermediates as opposed to nucleophilic aromatic substitution. At 375°C, 4-chlorobenzophenone gave phenol and benzoic acid over CaO/Ca(OH)2.
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