The fluorination of methane and related compounds by copper(II) fluoride and other metal fluorides

Abstract

Methane reacted with MnF 3 between 350-650°C affording hydrogen fluoride, MnF 2, the fluoromethanes CH 3F, CH 2F 2, CHF 3 and CF 4 and a complex mixture of less volatile fluorocarbons. Methane reacted with FeF 3 between 650-950°C giving the fluoromethenes CH 3F, CH 2F 2 and CHF 3, C 2H 4 and carbon, as well as hydrogen fluoride and FeF 2. A more detailed study of the CuF 2-CH 4 reaction between 600-850°C showed that copper metal, hydrogen fluoride and CH 3F were always obtained, other products including CH 2F 2, CHF 3, CF 4, C 2H 4, C 2H 6, C 2F 6 and carbon. Yields of the fluoromethanes were enhanced by using relatively large amount of CuF 2 and by adding CaF 2 as an inert support. A nearly constant reaction rate occurred at a fixed temperature. Dilution of methane with nitrogen decreased yields of carbon and CH 3F but increased yields of C 2H 4 and C 2H 6. A brief study of the reactions with CuF 2 and some of the CH 4-CuF 2 reaction products was also made. Ethane and ethene both afforded traces of trifluoromethane and relatively large yields of carbon and hydrogen fluoride. That the fluorination of methane to tetrafluoromethane could take place sequentially was demonstrated by reactions with CH 3F, CH 2F 2 and CHF 3. Some pyrolysis of CH 2F 2 and CHF 3 also occurred under the chosen reaction conditions. The CH 4-CuF 2 reaction was made part of a cyclic process in which generation of the CuF 2 in situ from copper metal by successive reaction with oxygen at 400°C and hydrogen fluoride at temperatures rising to 600°C was followed by reaction with methane; 68% coversion to fluorinated products occurred. The cycle was completed by re-conversion of the copper metal residue back to CuF 2 and further reaction with methane when almost identical yields of fluorocarbons and hydrogen fluoride were obtained.