Decomposition of tetrafluoromethane by reaction with CaO-enhanced zeolite

Abstract

Tetrafluoromethane (CF4), the most stable perfluorocarbon, has a high global warming potential and high chemical stability. Various methods, including rotary kiln processing, plasma decomposition, and catalysts, are used to decompose CF4 before discharge to the atmosphere. However, these processes typically use a hydrolysis reaction to produce hydrogen fluoride (HF) and carbon dioxide, and the reactor needs to be made of specific materials to avoid corrosion from HF. In addition, adsorption or absorption of HF is required to render it harmless. Therefore, a dry process without HF production is desirable to decompose CF4.In this study, we investigated zeolite as a catalyst to promote the reaction between CaO and CF4. The effects of the zeolite type and mass fraction on CF4 decomposition were investigated. The catalytic activity of zeolite was in the order of mordenite (MOR) > ZSM-5 > Beta > Y. Ammonia temperature programmed desorption of the zeolites showed the order of the ratio of strong acid strength to weak acid strength agreed with the catalytic activity.A higher CaO mass fraction in the mixture meant the reaction could be carried out for longer. The optimum zeolite mass fraction and type were 10 % and MOR, respectively. This gave CF4 decomposition of > 90 % for about 5 h. The effect of the decomposition temperature was investigated at 923 and 973 K. Although the temperature did not affect CF4 decomposition, the CO2 selectivity changed greatly.