Sulphonated PTFE

The PTFE is further sulphonated i.e., a side chain ending with sulphonic acid HSO3 is added. The HSO3 group is ionically bonded and hence, the end of the side chain becomes the S03 ion. The sulphonated PTFE is also known as perlluorosulphonic acid PTFE copolymer. PTFE has the following remarkable properties ... 

PTFE is a very chemically resistant material which is very hydrophobic (repels water) but does not have inherent ion exchange capabilities. Thus to convert this material into an ion-exchange material further processing is required. This requires the introduction of a side-chain which is then sulphonated. The classic side chain, used by DuPont, consists of a vinyl ether to which sulphonic acid is chemically bonded (Fig. 13.2). 

For sulphonation plants without an SO3 absorber the following system is recommended via gravity flow, sulphuric acid/oleum from the various parts of the gas raising plant is collected in an intermediate tank with level control. The intermediate tank should be sufficiently large to contain about one week s production of acid. The collected acid is discharged intermittently (say once a week) with a membrane pump and is sent to a PTFE lined mixer, which is filled with glass balls. Here acid dilution with water takes place using an acid to water ratio of 1 10, so as to maintain the resultant sulphuric acid temperature below 50°C. 

The cross-sectional area of the separator should be 1 m per ton AD/h. To ensure good separation, the sulphonic acid phase should remain in the separator for about 60 minutes. All the pipework should preferably be made of mild steel lined with PTFE. 

Figure 4.4 Example structure of a sulphonated fluoroethylene (also called perfluorosulphonic acid PTFE copolymer).

High-performance engineering thermoplastics Fluoropolymers (PTFE, FEP, PVDF), liquid crystal polymers (LCP), polyphenylene oxides or ethers (PPO, PPE), aromatic polyketones (PEEK, PAEK), polyphenylene sulphides (PPS), polysulphones (PSU), polyether sulphones (PES), polyamideimides (PAI), polyetherimides (PEI), polyimides (TPI). 

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