Fowler process

The Fowler Process is an industry and laboratory route to fluorocarbons, by fluorinating hydrocarbons or their partially fluorinated derivatives in the vapor phase over cobalt(III) fluoride.

The Manhattan Project required the production and handling of uranium hexafluoride for uranium enrichment, whether by diffusion or centrifuge. Uranium hexafluoride is very corrosive, oxidising, volatile solid (sublimes at 56 °C). To handle this material, several new materials were required, including a coolant liquid that could survive contact with uranium hexafluoride. Perfluorocarbons were identified as ideal materials, but at that point no method was available to produce them in any significant quantity.

The problem is that fluorine gas is extremely reactive. Simply exposing a hydrocarbon to fluorine will cause the hydrocarbon to ignite. A way to moderate the reaction was required, and the method developed was to react the hydrocarbon with cobalt(III) fluoride, rather than fluorine itself.

After World War II, much of the technology that had been kept secret was released into the public domain. The March 1947 issue of Industrial and Engineering Chemistry presented a collection of articles about fluorine chemistry, starting with the generation and handling of fluorine, and going on to discuss the synthesis of organofluorides and related topics. In one of these articles Fowler et al. describe the laboratory preparation of numerous perfluorocarbons by the vapour phase reaction of a hydrocarbon with cobalt(III) fluoride, at a pilot plant scale, in particular, perfluoro-n-heptane and perfluorodimethylcyclohexane (mixture of 1,3-isomer and 1,4 isomer), and on an industrial scale by Du Pont.

The Fowler process is typically done in two stages, the first stage being fluorination of cobalt(II) fluoride to cobalt(III) fluoride.

During the second stage, in this instance to make perfluorohexane, the hydrocarbon feed is introduced and is fluorinated by the cobalt(III) fluoride, which is converted back to cobalt(II) fluoride for reuse. Both stages are performed at high temperature.

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