Chlorine using Nafion, electrolysis

Later, Du Pont in America developed its own ionically conducting membrane, mainly for large-scale electrolysis of sodium chloride to manufacture chlorine, Nafion , (the US Navy also used it on board submarines to generate oxygen by electrolysis of water), while Dow Chemical, also in America, developed its own even more efficient version in the 1980s, while another version will be described below in connection with fuel cells. Meanwhile, Fenton et al. (1973) discovered the first of a... 

The monomer XXVIII is copolymerized with tetralluoroethylene to give a polymer-containing pendant fluorosulfonyl groups that are then hydrolyzed and acid exchanged to produce Nafion (XXIX) The resulting polymer combines the chemical, thermal, and oxidative stability of perfluorinated polymers such as polytetra-fluoroethy lene with the properties ofahighly acidic fluorinated sulfonic acid. Nafion is used in a variety of electrochemical applications such as the synthesis of chlorine and caustic and as the conductive membrane of many modern fuel cells. It has also been used in water electrolysis and as an acid catalyst in many proprietary commercial processes. 

MAJOR APPLICATIONS Nafion is the DuPont trademark for its family of perfluorinated ionomers, that is, resins and membranes. Asahi Chemical Industry Company produces Aciplex and Asahi Glass Company, Ltd., Japan, produces Flemion both are competitive products to Nafion in form and function. These perfluorinated ionomers are used in a variety of applications, the largest of which are as an ion exchange resin and in membrane separators in the commercial electrolysis of brine to produce caustic and chlorine. Nafion membranes are also being used in the development of fuel cells and as heterogeneous super acid catalysts in supported, cubed, or powdered form. 

The molecular structure of a conventional polymer used for a PFSA membrane is shown in Fig. 1. Membranes registered as Nafion (DuPont), Flemion , (Asahi Glass), and Aciplex (Asahi Chemical) have been commercialized for brine electrolysis and they are used in the form of alkali metal salt. Figure 4 shows a schematic illustration of a membrane for chlor-alkali electrolysis. The PFSA layer is laminated with a thin perfluorocarboxylic acid layer, and both sides of the composite membrane are hydrophilized to avoid the sticking of evolved hydrogen and chlorine. The membrane is reinforced with PTFE cloth. The technology was applied to PEFC membranes with thickness of over 50 xm [14]. 

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