An Experimental and Kinetic Modeling Study of the Reaction of CHF<sub>3</sub> with Methane

The gas-phase reaction of CHF<sub>3</sub> with CH<sub>4</sub> has been studied experimentally and computationally. The motivation behind the study is that reaction of CHF<sub>3</sub> with CH<sub>4</sub> provides a possible route for synthesis of CH<sub>2</sub>CF<sub>2</sub> (C<sub>2</sub>H<sub>2</sub>F<sub>2</sub>). Experiments are carried out in a plug flow, isothermal α-alumina reactor at atmospheric pressure over the temperature range of 973−1173 K. To assist in understanding the reaction mechanism and the role of the reactor material involved in the reaction of CHF<sub>3</sub> with CH<sub>4</sub>, the reaction of CHF<sub>3</sub> with CH<sub>4</sub>, pyrolysis of CH<sub>4</sub>, and pyrolysis of CHClF<sub>2</sub> have been studied in the presence of α-alumina or α-AlF<sub>3</sub> particles under various conditions. Under all conditions studied for the reaction of CHF<sub>3</sub> and CH<sub>4</sub>, the major products are C<sub>2</sub>F<sub>4</sub>, C<sub>2</sub>H<sub>2</sub>F<sub>2</sub>, and HF. Minor products include C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>, C<sub>2</sub>H<sub>3</sub>F, C<sub>2</sub>HF<sub>3</sub>, C<sub>3</sub>F<sub>6</sub>, CO<sub>2</sub>, and H<sub>2</sub>. C<sub>2</sub>H<sub>6</sub>, CH<sub>2</sub>F<sub>2</sub>, and CHF<sub>2</sub>CHF<sub>2</sub> are detected in trace amounts. The initial step is the gas-phase unimolecular decomposition of CHF<sub>3</sub>, producing CF<sub>2</sub> and HF. It is proposed that CF<sub>2</sub> decomposes on the surface of α-alumina, producing F radicals that are responsible for the activation of CH<sub>4</sub>. A reaction scheme developed on the basis of the existing NIST HFC and GRI-Mech 3.0 mechanisms is used to model the reaction of CHF<sub>3</sub> with CH<sub>4</sub>. Generally satisfactory agreement between experimental and modeling results is obtained on the conversion levels of CHF<sub>3</sub> and CH<sub>4</sub> and rates of formation of major products. Using the software package AURORA, the reaction pathways leading to the formation of major products are elucidated.