Handling of hydrogen fluoride

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). 

For the safe handling of hydrogen fluoride, fluorine/helium. and trifluoromethyl hypo-fluorite the use of a specific apparatus has been proposed (Figure 1). 

Since anhydrous hydrogen fluoride serves as the reaction medium, special equipment is needed. An efficient fume hood is absolutely necessary. Care must be exercised in the handling of hydrogen fluoride to avoid injury to the operator. 

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. 

Handling precautions for the gas or anhydrous liquid have been detailed.8 A polythene condenser for disposal of hydrogen fluoride has been described.8,9... 

Incidentally, the handling of the melt of hydrogen fluoride and of course fluorine itself is somewhat problematic, but the precautionary measures are well known (for instance, grease must be kept out of the system, because otherwise highly exothermic combustions will take place, melting or bursting piping or valves). 

Plutonium hexafluoride is a reddish-brown solid, and like neptunium hexafluoride, is light sensitive. Again, as in the case of uranium and neptunium hexafluorides, plutonium hexafluoride may be handled and stored in quartz or Pyrex equipment with no sign of decomposition provided the glass has been thoroughly outgassed and the hexafluoride is completely free of hydrogen fluoride. Any of the actinide hexafluorides may be heated to 200° in quartz apparatus with little if any attack on the container. 

Several breakdown processes have been used in which the ore is reacted with a fused or sintered fluorinating agent such as potassium hydrogen fluoride or sodium silicofluoride. The most important of these is the Copaux-Kawecki process for opening beryl ore. This is in many ways a unique process and other processes are unlikely to have many features in common with it apart from the problems associated with the handling of toxic fluorides. Since the fluorine is in combination with sodium, as the simple fluoride or as stable complexes with silicon and iron, the severe corrosion conditions inherent in many other fluorination reactions are almost absent in this case. 

Hydrogen fluoride is a powerful solvent but its use has been severly restricted both by its reactivity towards glass and silica and by its physiological properties. Experimental techniques have, however, been developed which allow the more widespread use of this interesting solvent. Polytetrafluoroethylene and poly-chlorotrifluoroethylene (the latter being transparent) are now available to handle liquid hydrogen fluoride. Some details have been given in a recent review article. ... 

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. 

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. 

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. 

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