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

研究了模型化合物氟里昂12在PO4/ZrO2上的催化裂解反应。以硝酸锆(IV)为原料，经沉淀后浸渍PO4阴离子，制备了Hammett酸度系数小于-12.14的超强酸PO4/ZrO2。氟里昂12在该催化剂上完全分解，反应温度低至300ﾟC。虽然该催化剂对反应过程中产生的无机氟有较强的抵抗力，但在长时间使用时会失活。为了延长催化剂的使用寿命，在反应混合物中加入水(1%、4%)。水有助于保持PO4/ZrO2的活性，30h后仍有60%以上的氟里昂被分解，催化剂表面的无机氟被氢气以HF的形式脱除。这一结果表明了开发实用的氟里昂催化分解工艺的可能性。还原法以二氢萘基钠和锂为还原剂，以氟里昂113为模型化合物。卤素原子以氯化钠和氟化物的形式被有效去除。在紫外光照射下，脱氟速度显著加快，室温下100min即可完成脱氟。对反应中间体的分析表明，主要中间体是二氢萘烷与氟里昂113的两碳单元偶联生成的。由于锂的还原能力低于钠，因此锂的脱氯/脱氟比增大。用乙醚作溶剂也能提高这一比例。这些结果表明了将用过的氟里昂转化为有用的含氟化合物的可能性。

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.