Fluorine construction materials

Fluorinated polymers stand out sharply against other construction materials for their excellent corrosion resistance and high-temperature stability. In this respect they are not only superior to other plastics but also to platinum, gold, glass, enamel and special alloys. The fluorinated plastics used in process plants are polytetrafluorethylene (PTFE), fluorinated ethylene/ propylene (FEP), polytrifiuoromonochlorethylene (PTFCE) and polyvinyl fluoride (PVF). They are much more expensive than other polymers and so are only economical in special situations [59]. 

Sulfur tetrafluoride provides an inexpensive method for selectively converting a carbonyl to a difluoromethyl group. However, the reactions involving sulfur tetrafluoride, in general, require pressure equipment constructed of fluorine-resistant material such as Hastelloy-C bombs.8 Phenylsulfur trifluoride may be used to advantage for the same reaction, where small amounts are involved, since the reaction may be run at atmospheric pressure in glass, polyethylene, or metal containers. 

Screening tests were conducted on potential construction materials. The candidate materials evaluated included the following polytetrafluoroethylene (PTFE, TFE), fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy-alkanes (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), poly vinylidene fluoride (PVDF), polypropylene (PP), and polyvinyl chloride (PVC). These materials were chosen based on cost, availability, and information from manufacturers on compatibility with acid solutions. 

High yields of the monofluorinated product at short reaction times were obtained that exceeded the performance of standard batch laboratory processing [309]. Yields of 72% were achieved at 99% conversion [309,310], The metallic construction material interacts with the reaction and impacts the keto/enol equilibrium to the advantage of the enol species that is fluorinated faster. 

Hydrogenation process The high fluorine content of the residues leads to problems with construction materials. Elementary bromine is not recovered. Production of the hydrogen required for the process is energy intensive. 

ETFE-foils as a fluorine-polymer material differ fundamentally from textile membrane materials in terms of their thermal-mechanical as well as building-physics behaviour. This chapter first introduces the construction forms and variants of ETFE-foil structures and provides an overview of the development of ETFE-foil constructions from an architectural perspective. Subsequently, the morphological structure of ETFE and the manufacturing process as well as the material behaviour and load-bearing characteristics of ETFE-foils are outlined. The final section discusses future development potentials and the future use of ETFE-foil constructions in structural engineering. 

Stainless steel is used as a construction material for support plates for the membranes and for spacers. Chemically stable elastomeres, like EPDM or per-fluorinated polymers are used as gasket material, more widely used is expanded graphite, due to its excellent chemical and thermal resistance. Preferentially the... 

Most plastics react chemically with chlorine because of their hydrocarbon structural makeup. This reactivity is avoided with some plastics in which fluorine atoms nave been substituted into the hydrocarbon molecule. The Chlorine Institute recommends that hoses constructed with such an inner lining "have a structural layer braid of polyvinyli-dene fluoride (PVDF) monofilament material or a structural braid of Hastelloy C-276. An underlying lesson here is material compatibility. Material compatibility tables exist that engineers can consult, including in other sections within this volume. 

CAUTION. Fluorine is a strong oxidizer and a very corrosive material. An appropriate vacuum line made from copper or Monel in a well-ventilated area should be constructed for working with this element. The reactions themselves were carried out in Teflon vessels. If elementary precautions are taken, work with fluorine is relatively simple. 

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... 

The chemistry of fluorinated building blocks involves methods for the construction of fluorine-containing target molecules from fluorine-containing starting materials by carbon-carbon bond formation to the fluorinated fragment. Ideally, the fluorinated building block should be easy to handle and relatively readily available. This could mean that the material is available commercially, or can be synthesised from such a compound via a short reaction sequence. 

Fermenters with a capacity of over about 10 litres are too heavy to sterilise in autoclaves. Whilst they may still be laboratory-sized, they have to be constructed so that they may be sterilised in situ. They become, as a consequence, pressure vessels and the extensive use of glass becomes impractical and the preferred material of construction is a stainless steel. Seals are typically of silicone or other synthetic rubber or fluorinated plastics, with borosilicate glass being retained for sighting windows. This format is retained for vessels which are far larger than the laboratory scale, and Fig. 5.80 outlines the construction of a typical industrial deep tank fermenter. 

An enantioselective fluorination method with catalytic potential has not been realized until recently, when Takeuchi and Shibata and co-workers and the Cahard group independently demonstrated that asymmetric organocatalysis might be a suitable tool for catalytic enantioselective construction of C-F bonds [78-80]. This agent-controlled enantioselective fluorination concept, which requires the use of silyl enol ethers, 63, or active esters, e.g. 65, as starting material, is shown in Scheme 3.25. Cinchona alkaloids were found to be useful, re-usable organocata-lysts, although stoichiometric amounts were required. 

When constructing electrolyzers for this process it is rather difficult to find suitable materials which can resist the effects of fluorine as it attacks most metals even at normal temperature fortunately continuous fluoride coatings are formed on the surface of some metals which protects them against further corrosion at least to a certain extent. Such metals are iron, nickel, Monel metal, aluminium and its alloys, magnesium and especially electron one of its alloys. However, the protective films are only stable at lower temperatures. At elevated temperatures a violent reaction proceeds between the fluorine and the metal. Monel metal and copper have relatively the best resistance against fluorine at elevated temperatures. These metals, therefore, were widely used to construct electrolyzers. In more recent designs, copper was replaced by steel or electron. 

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