Hydrogen fluoride handling

Hydrogen fluoride or compounds that can produce it and fluorine-containing oxidizers should be handled with adequate safety equipment and extreme care by weU-trained personnel. Often the effect of skin exposure is not immediately evident, especially when dilute solutions are handled. Pain may develop several hours later. 

Because hydrogen fluoride is extremely reactive, special materials are necessary for its handling and storage. Glass reacts with HF to produce SiF which leads to pressure buildup and potential mptures. Anhydrous hydrogen fluoride is produced and stored ia mild steel equipment. Teflon or polyethylene are frequently used for aqueous solutions. 

Aqueous hydrogen fluoride of greater than 60% maybe handled in steel up to 38°C, provided velocities are kept low (<0.3 m/s) and iron pickup in the process stream is acceptable. Otherwise, mbber or polytetrafluoroethylene (PTFE) linings are used. For all appHcations, PTFE or PTEE-lined materials are suitable up to the maximum use temperature of 200°C. PTEE is also the material of choice for gasketing. AHoy 20 or Monel is typically used for valve and pump appHcations. Materials unacceptable for use in HE include cast iron, type 400 stainless steel, hardened steels, titanium, glass, and siHcate ceramics. 

Although it is widely recognized as a hazardous substance, large volumes of HF are safely manufactured, shipped, and used, and have been for many years. Excellent manuals describing equipment and procedures for the safe handling of hydrogen fluoride are available from manufacturers (16,17,42). 

Experimentation with test animals and laboratory and plant experience indicate that the fluorophosphoric acids are less toxic and dangerous than hydrogen fluoride (58). However, they contain, or can hydrolyze to, hydrofluoric acid and must be treated with the same care as hydrofluoric acid. Rubber gloves and face shields are essential for all work with these acids, and full mbber dress is necessary for handling larger quantities. The fumes from these acids contain HF. 

Fluorides and dust are emitted to the air from the fertilizer plant. All aspects of phosphate rock processing and finished product handling generate dust, from grinders and pulverizers, pneumatic conveyors, and screens. The mixer/reactors and dens produce fumes that contain silicon tetrafluoride and hydrogen fluoride. A sulfuric acid plant has two principal air emissions sulfur dioxide and acid mist. If pyrite ore is roasted, there will also be particulates in air emissions that may contain heavy metals such as cadmium, mercury, and lead. 

Hydrogen fluoride is at present stored in bulk and used at only the Shellhaven refinery, bat future use is envisioned. Hydrogen fluoride boils point 19° C but stored and handled as a hq lie tied gas. Its vapor is highly irritating and toxic. A cold cloud will be denser than air in the early stages when released but wall become neutral or buoyant as it warms with dispersion. This r-sessment assumes negative buoyancy... 

A polymeric form of the reagent from hydrogen fluoride and poly(4-vinylpyndine) is especially easy to handle [I0 Other tertiary amines can also be employed [II], and a two-phase mixture of hydrogen fluoride-melamine-pentane hydrofluorinates cyclohexene to fluorocyclohexane m 98% yield [12]... 

The actual fluoride-forming reaction in the ammonium bifluoride route is hydro-fluorination. Hydrogen fluoride, which is present in chemical combination in the bifluoride, is readily released on heating. Bifluorides are easier to handle than hydrogen fluoride. The particular advantage of ammonium bifluoride over other alkali hydrogen fluorides is that it is volatile, and thus can be readily distilled out from the reaction mixture. 

The reaction gases (containing chlorodifluoramine) must be handled at below —5°C to avoid explosion. Ammonium hydrogen fluoride behaves similarly. 

Recently, a search has been conducted for solvents which are less hazardous to handle than halogen fluorides and hydrogen fluoride and which can be used to prepare solutions of the cationic species. Two have been found that are highly oxidation-resistant and suitable for this purpose 1,1,2-trichlorotrifluoroethane and... 

Hydrogen fluoride, HF, is a gas which, when dissolved in water, forms hydrofluoric acid. This acid is used to etch glass, and would quickly dissolve a glass bottle. It must therefore be kept in plastic bottles. Hydrofluoric acid is also very dangerous to handle, causing severe burns if it touches skin. 

Caution. Metal hexafluorides are volatile, toxic, corrosive, and highly hygroscopic materials. They must be handled in a very dry, clean, fluorine-preconditioned metal vacuum system. The vacuum system should be constructed from stainless steel or Monel materials (glass is not acceptable if pure products are desired). Hydrogen fluoride also is quite toxic and volatile. If only one metal... 

Time will show if there is need for desulfurization of high speed Diesel fuels. There is no doubt that many companies are actively studying desulfurization processes so as to be in a position to make the best choice. Of those for which published information is available for full scale operation, the most attractive seemed to be sulfur dioxide and furfural extraction, the latter having merit because it has successfully handled high sulfur catalytically cracked recycle stocks. The previously mentioned extraction process using anhydrous hydrogen fluoride also seems attractive because of the low treatment and high yield of refined product, but, until the results of commercial operation are fully known its merits cannot be established. 

More convenient for the formation of aryl fluorides 4 is the decomposition of triazenes with hydrogen fluoride/pyridine (70 30 w/w) mixture, easier to handle than pure hydrogen fluoride. In this case, decomposition is performed at a lower temperature (18-50°C) and acetic acid, for example, is a suitable solvent.299 However, radical side reactions can be more pronounced, especially with bromo-, iodo-, nitro- or 2-methoxy-subslituted substrates. 

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