Development of the technology for detoxification of Freons by using oxidative and reductive methods

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Catalytic decomposition of Freon 12 (a model compound) on PO_4/ZrO_2 was carried out. Superacid PO_4/ZrO_2 whose Hammett acidity coefficient was lower than -12.14 was prepared by precipitation from zirconium (IV) oxynitrate followed by impregnation of PO_4 anion. Freon 12 was completely decomposed on this catalyst at a temperature as low as 300 ﾟC. Although this catalyst was comparatively robust against inorganic fluorine produced during the reaction, it deactivated during prolonged use. In order to prolong the lifetime of this catalyst, water (1%, 4%) was added in the reaction mixture. Water helped maintain the activity of PO_4/ZrO_2, and more than 60% of Freon 12 was decomposed even after 30 h; inorganic fluorine accumulated on the surface of the catalyst was removed by hydrogen from water as HF. This result suggested the possibility of developing practical catalytic decomposition process for Freons.Reductive method employed sodium and lithium dihydronaphthylides as reducing agents and Freon 113 as a model compound for Freons. Halogen atoms were effectively removed as sodium chloride and fluoride. The rate of defluorination was accelerated remarkably under UV irradiation, thus the defluorination was completed at a room temperature within 100 min. Analysis of the reaction intermediates suggested that the major intermediates were produced by the coupling between dihydronaphthylide and two-carbon unit of Freon 113. As the reducing ability of lithium is lower than that of sodium, ratio of dechlorination to defluorination increased by using lithium. This ratio was also increased by using diethyl ether as a solvent. These results suggested the possibility of transforming used Freons to useful fluorinated compounds.