Fowler process

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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.

Contents

Background

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). [1] 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, [2] at a pilot plant scale, in particular, perfluoro-n-heptane and perfluorodimethylcyclohexane (mixture of 1,3-isomer and 1,4 isomer), [3] and on an industrial scale by Du Pont. [4]

Chemistry

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

2 CoF2 + F2 → 2 CoF3

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.

C6H14 + 28 CoF3 → C6F14 + 14 HF + 28 CoF2

The reaction proceeds through a single electron transfer process, involving a carbocation. [5] This carbocation intermediate can readily undergo rearrangements, which can lead to a complex mixture of products.

Feedstocks

Typically hydrocarbon compounds are used as the feedstocks. For cyclic perfluorocarbon, the aromatic hydrocarbon is the preferred choice, so for example, toluene is the feedstock for perfluoromethylcyclohexane, rather than methylcyclohexane, as less fluorine is required. Often partially fluorinated feedstocks are used, for example, bis-1,3-(trifluoromethyl)benzene to make perfluoro-1,3-dimethylcyclohexane. Although these are considerably more expensive, they require less fluorine and more importantly, they generally give higher yields, as the carbocation rearrangements are much less likely.

Flutec perfluorocarbons

Cobalt(III) fluoride reactor at F2 Chemicals Ltd, Preston Cobalt fluoride reactor at F2 Chemicals Ltd.jpg
Cobalt(III) fluoride reactor at F2 Chemicals Ltd, Preston

In the UK, Imperial Chemical Industries Limited (later ICI) was also developing cobalt(III) fluoride technology during the war, prompted by the work in the US. [6] The process was later commercialized under the tradename Flutec by the Imperial Smelting Company (later ISC Chemicals) at Avonmouth near Bristol. Physical properties were determined by a company called G.V. Planer, under a project in 1965 called the Planar Project. Products were therefore designated PP1, PP2, PP3, etc. [7] The designation has remained to this day.

ISC Chemicals became part of RTZ in 1968, [8] and that part of the business was transferred to Rhone-Poulenc in 1988. [9] The Flutec business went into a decline, due to a drop in its main application, vapor phase reflow soldering (used in surface-mount technology, and six years later the Flutec business was purchased by BNFL Fluorochemicals Ltd and transferred to Preston, Lancashire, where it has been developed into several new applications. [10] BNFL Fluorochemicals Ltd became F2 Chemicals Ltd in 1998.

Related Research Articles

<span class="mw-page-title-main">Fluorocarbon</span> Class of chemical compounds

Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often have distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Several fluorocarbons and their derivatives are commercial polymers, refrigerants, drugs, and anesthetics.

<span class="mw-page-title-main">Manganese(III) fluoride</span> Chemical compound

Manganese(III) fluoride (also known as Manganese trifluoride) is the inorganic compound with the formula MnF3. This red/purplish solid is useful for converting hydrocarbons into fluorocarbons, i.e., it is a fluorination agent. It forms a hydrate and many derivatives.

<span class="mw-page-title-main">Nickel(II) fluoride</span> Chemical compound

Nickel(II) fluoride is the chemical compound with the formula NiF2. It is an ionic compound of nickel and fluorine and forms yellowish to green tetragonal crystals. Unlike many fluorides, NiF2 is stable in air.

<span class="mw-page-title-main">Bromine pentafluoride</span> Chemical compound

Bromine pentafluoride, BrF5, is an interhalogen compound and a fluoride of bromine. It is a strong fluorinating agent.

<span class="mw-page-title-main">Octafluoropropane</span> Chemical compound

Octafluoropropane (C3F8) is the perfluorocarbon counterpart to the hydrocarbon propane. This non-flammable and non-toxic synthetic substance has applications in semiconductor production and medicine. It is also an extremely potent greenhouse gas.

Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers.

<span class="mw-page-title-main">Cobalt(III) fluoride</span> Chemical compound

Cobalt(III) fluoride is the inorganic compound with the formula CoF3. Hydrates are also known. The anhydrous compound is a hygroscopic brown solid. It is used to synthesize organofluorine compounds.

Organofluorine chemistry describes the chemistry of organofluorine compounds, organic compounds that contain a carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil and water repellents to pharmaceuticals, refrigerants, and reagents in catalysis. In addition to these applications, some organofluorine compounds are pollutants because of their contributions to ozone depletion, global warming, bioaccumulation, and toxicity. The area of organofluorine chemistry often requires special techniques associated with the handling of fluorinating agents.

Perfluorodecalin is a fluorocarbon, a derivative of decalin in which all of the hydrogen atoms are replaced by fluorine atoms. It is chemically and biologically inert and stable up to 400 °C. Several applications make use of its ability to dissolve gases.

<span class="mw-page-title-main">Fluorine</span> Chemical element, symbol F and atomic number 9

Fluorine is a chemical element; it has symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. Fluorine is extremely reactive, as it reacts with all other elements except for the light inert gases.

<span class="mw-page-title-main">Perfluorooctane</span> Chemical compound

Perfluorooctane, also known as octadecafluorooctane, is a fluorocarbon liquid—a perfluorinated derivative of the hydrocarbon octane. It can be a good substitute for insulating oil in high voltage electronics. In addition to heat transfer applications, it has also been used as a breathable fluid in partial liquid ventilation.

A hexafluoride is a chemical compound with the general formula QXnF6, QXnF6m−, or QXnF6m+. Many molecules fit this formula. An important hexafluoride is hexafluorosilicic acid (H2SiF6), which is a byproduct of the mining of phosphate rock. In the nuclear industry, uranium hexafluoride (UF6) is an important intermediate in the purification of this element.

Electrochemical fluorination (ECF), or electrofluorination, is a foundational organofluorine chemistry method for the preparation of fluorocarbon-based organofluorine compounds. The general approach represents an application of electrosynthesis. The fluorinated chemical compounds produced by ECF are useful because of their distinctive solvation properties and the relative inertness of carbon–fluorine bonds. Two ECF synthesis routes are commercialized and commonly applied: the Simons process and the Phillips Petroleum process. It is also possible to electrofluorinate in various organic media. Prior to the development of these methods, fluorination with fluorine, a dangerous oxidizing agent, was a dangerous and wasteful process. ECF can be cost-effective, but it may also result in low yields.

<span class="mw-page-title-main">Neptunium(VI) fluoride</span> Chemical compound

Neptunium(VI) fluoride (NpF6) is the highest fluoride of neptunium, it is also one of seventeen known binary hexafluorides. It is an orange volatile crystalline solid. It is relatively hard to handle, being very corrosive, volatile and radioactive. Neptunium hexafluoride is stable in dry air but reacts vigorously with water.

Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding. Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others the highest oxidation states of oxides and fluorides are always equal.

<span class="mw-page-title-main">Fluorochemical industry</span> Industry dealing with chemicals from fluorine

The global market for chemicals from fluorine was about US$16 billion per year as of 2006. The industry was predicted to reach 2.6 million metric tons per year by 2015. The largest market is the United States. Western Europe is the second largest. Asia Pacific is the fastest growing region of production. China in particular has experienced significant growth as a fluorochemical market and is becoming a producer of them as well. Fluorite mining was estimated in 2003 to be a $550 million industry, extracting 4.5 million tons per year.

<span class="mw-page-title-main">Perfluoro-1,3-dimethylcyclohexane</span> Chemical compound

Perfluoro-1,3-dimethylcyclohexane is a fluorocarbon liquid—a perfluorinated derivative of the hydrocarbon 1,3-dimethylcyclohexane. It is chemically and biologically inert.

<span class="mw-page-title-main">Perfluoromethylcyclohexane</span> Chemical compound

Perfluoromethylcyclohexane is a fluorocarbon liquid—a perfluorinated derivative of the hydrocarbon methylcyclohexane. It is chemically and biologically inert.

Perfluoromethyldecalin is a fluorocarbon liquid—a perfluorinated derivative of the hydrocarbon methyldecalin. It is chemically and biologically inert. It is mainly of interest as a blood substitute, exploiting the high solubility of air in this solvent.

References

  1. ↑ Uranium Hexafluoride Archived 2007-12-20 at the Wayback Machine , International Chemical Safety Cards #1250.
  2. ↑ Fowler, R. D.; Burford, W. B., III; Hamilton, J. M., Jr.; Sweet, R. G.; Weber, C. E.; Kasper, J. S.; Litant, I. (1947). "Synthesis of Fluorocarbons." Ind. Eng. Chem.39: 292–298. doi : 10.1021/ie50447a612.
  3. ↑ Burford, W. B., III; Fowler, R, D.; Hamilton, J. M., Jr.; Anderson, H. C.; Weber, C. E.; Sweet, R. G. (1947). "Pilot Plant Syntheses - Perfluoro-n-heptane, perfluorodimethylcyclohexane, and high boiling fluorocarbon oils." Ind. Eng. Chem.39: 319–329. doi : 10.1021/ie50447a618.
  4. ↑ Benner, R. G; Benning, A. F.; Downing, F. B.; Irwin, C. F.; Johnson, K. C.; Linch, A. L.; Parmalee, H. M.; Wirth, W. V. (1947). "Fluorocarbons by Fluorination of Hydrocarbons with Cobalt Trifluoride." Ind. Eng. Chem.39: 329–333. doi : 10.1021/ie50447a619.
  5. ↑ Sandford, G. (2003). " Perfluoroalkanes." Tetrahedron59: 437–454. doi : 10.1016/S0040-4020(02)01568-5.
  6. ↑ Dawson, A. M. (1943). Imperial Chemical Industries Limited, General Chemical Division, Research Department Report R/GC/1685.
  7. ↑ M. Hill (1975). "Process and market development of fluorocarbon fluids". Chem. Ind.: 118–121.
  8. ↑ "Rio Tinto Co - Graces Guide".
  9. ↑ Rhodia website (obsolete link)
  10. ↑ website
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