Environmental Science & Technology 2008-08-01

Conversion of CHF3 to CH2=CF2 via reaction with CH4 and CaBr2.

Wenfeng Han, Hai Yu, Eric M Kennedy, John C Mackie, Bogdan Z Dlugogorski

Index: Environ. Sci. Technol. 42(15) , 5795-9, (2008)

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Abstract

Reaction of CHF3 and CH4 over CaBr2 was investigated at 400-900 degrees C as a potential route for transforming the highly potent greenhouse gas, CHF3, into the valuable product CH2=CF2. The homogeneous reaction of CHF3 with CH4 was also studied to assist in understanding the chemistries involved. Compared to the gas phase reaction, the addition of CaBr2 as a reactant increases the conversion of CHF3 and CH4 significantly at low temperatures while to a lesser extent at higher temperatures. In the absence of CaBr2, besides the target product, CH2=CF2, a large amount of C2F4 forms. On addition of CaBr2, the rate of formation of C2F4 drops dramatically to near zero, while the rate of formation of CH2=CF2 increases considerably at temperatures below 880 degrees C. Experimental and theoretical studies suggest that CHF3 strongly interacts with CaBr2, resulting in the fluorination of CaBr2 to CaF2, the release of active Br species results in the selective formation of CBrF3. The subsequent reactions involving Br, methane, and CBrF3 play a major role in the observed enhanced yield of CH2=CF2.