Membrane perfluorocarboxylic

Membrane cells are the state of the art chlor-alkah technology as of this writing. There are about 14 different membrane cell designs in use worldwide (34). The operating characteristics of some membrane cells are given in Table 3. The membranes are perfluorosulfonate polymers, perfluorocarboxylate polymers, and combinations of these polymers. Membranes are usually reinforced with a Teflon fabric. Many improvements have been made in membrane cell designs to accommodate membranes in recent years (35,36). 

Figure 9. Membrane self-diffusion coefficients vs. the reciprocal of absolute temperature for perfluorocarboxylate (light symbols) and perfluorosulfonate (dark symbols) polymers (A, A) H2O, (O, ), Na and ( , ) Cs. (Ref. 165 reprinted by permission of the publisher, The Electrochemical Society, Inc.)...

The self-diffusion coefficient of sodium ion is plotted in Fig. 11 vs. the reciprocal of absolute temperature for the perfluorosulfo-nate and perfluorocarboxylate membranes which were discussed in Section Here though, the membrane environment con-... 

Thus all successful chlor-alkali membranes currently employ a perfluorocarboxylate polymer to lower the rate of hydroxide ion transport. The sulfonate portion of some of these membranes is present mainly to add strength to the thinner carboxylate barrier layer. Fabric backing is also used in some cases to improve physical strength. 

In Figure 17, sodium ion transport number is plotted vs, catholyte concentration for a homogeneous perfluorocarboxylate film. The current efficiency is now higher than 90% over the entire caustic concentration region studied, although a minimum and maximum in performance is again observed. These features are shifted to lower concentration compared to perfluorosulfonate behavior though. Finally, the performance of a sulfonate-carbox-ylate bilayer membrane, Nafion 901, is plotted in Fig. 18. For such... 

Perfluorocarboxylate Ionomers Flexion Asahi Glass Chloral kali Membrane... 

The Asahi Chemical Company of Japan has developed a perfluorocarboxylic acid membrane (54) (55) (56). It is reported to be formed from Nafion films wherein the SO3H groups on the cathode surface are split off and the adjacent CF2 groups thereafter oxidized to carboxylic acid groups. 

Perfluorocarboxylic Acid Membrane and Membrane Chlor-Alkali Process Developed by Asahi Chemical Industry... 

In April 1975, Asahi Chemical started operation of a membrane chlor-alkali plant with a capacity of 40,000 MT/Y of caustic soda using Nafion perfluorosulfonic acid membrane. In 1976, this membrane was replaced by perfluorocarboxylic acid membrane developed by Asahi Chemical. The total caustic production capacity of plants based on Asahi Chemical s membrane chlor-alkali technology using perfluorocarboxylic acid membrane will reach 520,000 MT/Y in 1982, at seven locations in various countries. 

The weak acidity and relatively low hydrophilicity of the perfluorocarboxylic acid group results in a very high current efficiency of over 96%, although its electric resistance is high (1, 3, 5, T y 10, 26-29). The membrane can be exposed to fairly acidic solution as the pKa value is around 2. Its chemical stability is quite good under electrolysis conditions. 

Figure 1 shows the general methods for preparation of perfluorocarboxylic acid monolayer and multilayer membranes. 

The monolayer perfluorocarboxylic acid membrane can be prepared, if necessary, by chemical treatment which causes the chemical reaction throughout the membrane. 

Figure 2. The thickness of CO OH layer, current efficiency, and electric resistance of a multilayer perfluorocarboxylic and sulfonic acid membrane prepared by chemical treatment (COOH/SOsH).

Type of membrane Monolayer perfluorocarboxylic acid membrane (COOH) Multilayer membrane of perfluorocarboxylic and sulfonic acid by lamination or coating (C00H S03H) Multilayer membrane of perfluorocarboxylic and sulfonic acid by chemical treatment (COOH/SO3H)... 

Water Content. Figure 4 shows the relation between the water content of perfluorocarboxylic acid membrane prepared by chemical treatment and the ion exchange capacity with varying external solution concentration. As the concentration of the external solution increases, the membrane shrinkage increases and the water content is therefore decreased. The influence of... 

Water content in Figure 4 can be expressed as a function of ion exchange capacity and external solution concentration by the following empirical equation, which is similar to that proposed for perfluorosulfonic acid membranes by W.G.F. Grot in 1972 (44). The water content of perfluorocarboxylic acid membrane is much lower than that of perfluorosulfonic acid membrane. 

Figure 9. Electric resistance, ion exchange capacity (meq/g dry resin) and concentration of NaOH, for perfluorocarboxylic acid membrane prepared by chemical...

Table III shows the mechanical properties of perfluorocarboxylic acid membrane prepared by chemical treatment and perfluorosulfonic acid membrane.

Perfluorocarboxylic acid membrane prepared by chemical treatment... 

Table V. PVEX Monomer Appropriate for Perfluorocarboxylic Acid Membrane.

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