Fluorine manufacture

The fluorine thereby obtained is directly processed further (to uranium hexafluoride, sulfur hexafluoride) or liquefied (b.p. -188°C) and filled into pressure cylinders. Pressure cylinders with mixtures of fluorine and nitrogen, with 10 or 20% by volume of fluorine, are widely marketed (utilized, for example, for the surface fluorination of vehicle fuel tanks). The worldwide fluorine capacity is estimated to be ca. 7.5 10 t/a, of which 60% is in the USA, 25% in Europe and 15% in Japan. Ca. 75% of the fluorine manufactured is utilized in the manufacture of uranium hexafluoride, 22.5% in the manufacture of sulfur hexafluoride and 2.5% in the manufacture of tetrafluoromethane. In 1986 ca. 100 t of fluorine was utilized in the manufacture of fluorographite (high conductivity) for use in batteries. 

Electrochemical fluorination manufacture of perfluoro- compounds with functional groups by electrolysis of the corresponding nonfluorinated compounds in liquid hydrogen fluoride... 

Polarization can be controlled to some extent, but it is never fully overcome and this, combined with the anode- thode gap of about 5 cm necessary to avoid reactions between the electrolysis products in undivided cells, causes the cell voltage to be from —8.5 to —13 V for the working current density of 70-200 mA cm (Table 5.2). This compares with the calculated reversible cell voltage of — 2.9 V so it is clear that fluorine manufacture cannot be described as energy-efficient The total energy consumption for a cell with a 95% current efficiency (Ic. with a small amount of back chemical reaction between and Hj)... 

Vinyl Fluoride. Vinyl fluoride [75-02-5] C2H2F, the monomer for poly(vinyl fluoride), is manufactured by addition of hydrogen fluoride to acetylene (see Fluorine COMPOUNDS, ORGANIC, POLY(viNYL FLUORIDE)). 

Manufacturers. Besides manufacturers in the United States, commercial fluorine plants are operating in Canada, France, Germany, Italy, Japan, and the United Kingdom (see Table 5). Fluorine is also produced in the Commonwealth of Independent States (former Soviet Union) however, details regarding its manufacture, production volumes, etc, are regarded as secret information. The total commercial production capacity of fluorine in the United States and Canada is estimated at over 5000 t/yr, of which 70—80% is devoted to uranium hexafluoride production. Most of the gas is used in captive uranium-processing operations. 

Elemental fluorine is used captively by most manufacturers for the production of various inorganic fluorides (Table 5). The market for gaseous fluorine is small, but growing. The main use of fluorine is in the manufacture of uranium hexafluoride, UF, by... 

J. Dykstrra, A. P. Huber, and B. H. Thompson, "Multi-Ton Production of Fluorine for Manufacture of Uranium Hexaduoride," paper presented... 

In addition, there are other methods of manufacture of cryoHte from low fluorine value sources, eg, the effluent gases from phosphate plants or from low grade fluorspar. In the former case, making use of the fluorosiHcic acid, the siHca is separated by precipitation with ammonia, and the ammonium fluoride solution is added to a solution of sodium sulfate and aluminum sulfate at 60—90°C to precipitate cryoHte (26,27) ... 

Significant amounts of cryoHte are also recovered from waste material ia the manufacture of aluminum. The carbon lining of the electrolysis ceUs, which may contain 10—30% by weight of cryoHte, is extracted with sodium hydroxide or sodium carbonate solution and the cryoHte precipitated with carbon dioxide (28). Gases from operating ceUs containing HF, CO2, and fluorine-containing dusts may be used for the carbonation (29). 

It is used as a fluorinating reagent in semiconductor doping, to synthesi2e some hexafluoroarsenate compounds, and in the manufacture of graphite intercalated compounds (10) (see Semiconductors). AsF has been used to achieve >8% total area simulated air-mass 1 power conversion efficiencies in Si p-n junction solar cells (11) (see Solarenergy). It is commercially produced, but usage is estimated to be less than 100 kg/yr. 

Manufacture. Boron trifluoride is prepared by the reaction of a boron-containing material and a fluorine-containing substance in the presence of an acid. The traditional method used borax, fluorspar, and sulfuric acid. 

The large amount of fluorine values released from phosphate rock in the manufacture of fertilisers (qv) gives a strong impetus to develop fluorine chemicals production from this source (see Phosphoric acid and the phosphates). Additional incentive comes from the need to control the emission of fluorine-containing gases. Most of the fluorine values are scmbbed out as fluorosiUcic acid, H2SiPg, which has limited useflilness. A procedure to convert fluorosihcic acid to calcium fluoride is available (61). 

CoF is used for the replacement of hydrogen with fluorine in halocarbons (5) for fluorination of xylylalkanes, used in vapor-phase soldering fluxes (6) formation of dibutyl decalins (7) fluorination of alkynes (8) synthesis of unsaturated or partially fluorinated compounds (9—11) and conversion of aromatic compounds to perfluorocycHc compounds (see Fluorine compounds, organic). CoF rarely causes polymerization of hydrocarbons. CoF is also used for the conversion of metal oxides to higher valency metal fluorides, eg, in the assay of uranium ore (12). It is also used in the manufacture of nitrogen fluoride, NF, from ammonia (13). 

Most of the acid-grade spar used for HF production ia the United States is imported. More than two-thkds of the fluorspar consumed ia the United States goes iato production of HF nearly 30% is consumed as a flux ia steelmaking and the remainder is consumed ia glass manufacture, enamels, welding rod coatings, and other end uses or products (see Fluorine compounds, inorganic-calcium). 

It appears that the ultimate replacements for the high volume chlorofluorocarbon products are to be more highly fluorinated organic chemicals, thus requiring significantly higher volumes of HF in thek manufacture. 

Chemicals. Both organic and inorganic fluorine-containing compounds, most of which have highly speciali2ed and valuable properties, are produced from HF. Typically these fluorinated chemicals are relatively complex, sometimes difficult to manufacture, and of high value. These materials include products used as fabric and fiber treatments, herbicide and pharmaceutical intermediates, fluoroelastomers, and fluorinated inert Hquids. Other products include BF, SF, and fluoborates. 

Many different processes using HF as a reactant or source of fluorine are employed in the manufacture of fluorinated chemical derivatives. In many cases the chemistry employed is complex and in some cases proprietary. Electrochemical fluorination techniques and gaseous fluorine derived from HF are used in some of these appHcations. 

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