Hydrogen fluoride construction materials

As the large scale commercial use of hydrogen fluoride is now well established, particularly in the petroleum industry, the techniques of the use of large size equipment is well known. Reports are available on various aspects of industrial use. A book has been published with particular reference to paraffin alkylation (Phillips Petroleum Company, 13). Corrosion, instrumentation, materials of construction, safety measures, etc., are included. The following journal articles also contain material of interest on large scale technique (Holmberg and Prange, 17, Frey, 18, Fehr, 19). There are certain features that need to be watched, such as corrosion, embrittlement, etc., but the above references deal with these subjects. Corrosion is not particularly serious in properly constructed equipment except where air enters. 

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... 

Hydrogen Fluoride.31 The acid HF is made by the action of concentrated H2S04 on CaF2 and is the principal source of fluorine compounds (Chapter 16). It is commercially available in steel cylinders, with purity approximately 99.5% it can be purified further by distillation. Although liquid HF attacks glass rapidly it can be handled conveniently in apparatus constructed either of copper or Monel metal or of materials such as polytetrafluoroethylene (Teflon or PTFE), Kel-F (a chlorofluoro polymer), etc. 

Materials of Construction. In a great many cases, steel is suitable for the construction of alkylating equipment, even in the presence of the strong acid catalysts, as their corrosive effect is greatly lessened by the formation of esters as catalytic intermediate products. In the petroleum industry, sulfuric acid and hydrogen fluoride are employed on a very large scale as alkylation catalysts however, these must be substantially anhydrous to be effective so steel equipment is satisfactory. Where conditions are not anhydrous, lead-lined, Monel-lined, or enamel-lined equipment is satisfactory. In a few cases, copper or tinned copper is still used, as in the manufacture of pharmaceutical and photographic products, to lessen contamination with metals. 

Materials of construction for the dry way plant are selected to be resistant to corrosion by hydrogen fluoride at the last stage, since these conditions... 

The traditional catalyst hydrogen fluoride, an extremely corrosive, hazardous and toxic chemical used in the production of linear alkylbenzenes (LAB s), has been successfully replaced by a solid acid catalyst, viz. fluorided silica-alumina catalyst, which does not require special material of construction (of the container), involves lower operating costs and obviates the need for an acid scrubbing system and waste disposal of calcium fluoride. ... 

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