Industrial Synthesis of Tetrafluoroethylene

The manufacturing process of TFE consists of the following four steps  

The first step is set up to produce hydrogen fluoride (FtF), and the second yields trichloromethane (chloroform). Chloroform is then partially fluorinated with hydrogen fluoride to chlorodifluoromethane using antimony fluoride (SbFj) as a catalyst in the third step. Finally, in the fourth step, chlorodifluoromethane is subjected to pyrolysis, in which it is converted to tetrafluoroethylene. The pyrolysis is a non-catalytic gas-phase process carried out in a flow reactor at atmospheric or subatmo-spheric pressure and at temperatures 590°C to 900°C (1094°F to 1652°F) with yields as high as 95%. This last step is often conducted at the manufacturing site for PTFE because of the difficulty of handling the monomer [9]. 

TEE (molecular weight 100.02) is a colorless, tasteless, odorless nontoxic gas [11]. It is stored as a liquid (its vapor pressure at -20°C is 1 MPa) and polymerized usually above its critical temperature of 33.3°C (91.9°E) and below its critical pressure 3.94 MPa (571 psi). The polymerization reaction is exothermic. In the absence of air it disproportionates violently to yield carbon and carbon tetrafluoride. This reaction generates the same amount of energy as an explosion of black powder. The decomposition is initiated thermally therefore, the equipment used in handling and polymerization of TFE has to be without hot spots. The flammability limits are 14% to 43% TFE burns when mixed with air and forms explosive mixtures with air and oxygen. The ignition temperature is 600°C to 800°C (1112°F to 1472°F) [12]. When stored in a steel cylinder it has to be under controlled conditions and with a suit- 

The largest proportion of TEE is used for the polymerization into a variety of PTFE homopolymers, modihed PTFE, and micropowders. It is also used as comonomer in the copolymerization with hexafluoropropylene, ethylene, perfluorinated ether, and other monomers and also as a comonomer in a variety of terpolymers. Other uses of TEE are to prepare low-molecular-weight polyfluorocarbons and carbonyl fluoride oils as well as to form PTFE in situ on metal surfaces [14] and in the synthesis of hexafluoropropylene, perfluorinated ethers, and other oligomers [15]. 

Essentially, TFE in its gaseous state is polymerized via a free radical addition mechanism in aqueous medium with water-soluble free radical initiators, such as per-oxydisulfates, organic peroxides, or reduction-activation systems [16]. The additives have to be selected very carefully since they may interfere with the polymerization. They may either inhibit the process or cause a chain transfer that leads to inferior products. When producing aqueous dispersions, highly halogenated emulsifiers, such as fully fluorinated acids [17], are used. If the process requires normal emulsifiers, these have to be injected only after the polymerization has started [18]. TFE polymerizes readily at moderate temperatures (40°C to 80°C, or 104°F to 176°F) and moderate pressnres (0.7 to 2.8 MPa, or 102 to 406 psi). The reaction is extremely exothermic (the heat of polymerization is 41 kcal/mol). 

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