Catalytic Conversion of Hazardous and Toxic Chemicals:Catalytic Hydrodechlorination of Polychlorinated Pesticides and Related Substances.

摘要

A study has been undertaken of the catalytic conversion of chlorinated pesticides and other environmentally undesirable chlorinated materials into acceptable compounds. The results of this study show that chlorine can be catalytically removed and replaced by hydrogen to produce relatively nontoxic hydrocarbons which may either be useful as items of commerce or which may be easily combusted. The experimental foundation for a large scale hydrodechlorination process has been laid. The Process involves the use of a supported nickel catalyst in a batch process using ethanol as a solvent and sodium hydroxide as an acid acceptor of the hydrogen chloride byproduct. Temperatures of less than 150C and hydrogen pressures of less than 50atmospheres are required for most classes of chlorinated pesticides and related substances. Palladium as a catalyst did not give results which were significantly better than nickel. A reactivity sequence has been established based on carbon chlorine bonding,wherein olefinic chlorine is most reactive,aromatic chlorine is less reactive and aliphatic chlorine is least reactive. Reaction models have been proposed and the relative rates of parallel and consecutive hydrodechlorination steps have been determined for Aroclor and DDE under various process conditions. Removal of ortho substituted chlorine is the limiting reaction in hydrodechlorination of Polychlorinated Biphenyls (PCB's). Highly bridged and nonplanar molecules such as Aldrin and Dieldrin are the most difficult compounds to hydrodechlorinate due to steric effects. Removal of aromatic chlorine is the limiting reactor in the hydrodechlorination of DDT and DDE. The hydrodechlorination process as described should be applicable to other classes of pesticides such as the isomeric hexachlorocyclohexanes (e.g., Lindane),and the Methanoindenes (e.g., Chlordane). Due to steric effects chlordane should have a reactivity similar to that of Aldrin.