Ion exchangers Nafion

The alcohol tolerance of O2 reduction by bilirubin oxidase means that membraneless designs should be possible provided that the enzymes and mediators (if required) are immoblized at the electrodes. Minteer and co-workers have made use of NAD -dependent alcohol dehydrogenase enzymes trapped within a tetraaUcylammonium ion-exchanged Nafion film incorporating NAD+/NADH for oxidation of methanol or ethanol [Akers et al., 2005 Topcagic and Minteer, 2006]. The polymer is coated onto an electrode modified with polymethylene green, which acts as an electrocatalyst... 

Ethylene has been separated from ethane by a silver nitrate solution passing countercurrent in a hollow fiber poly-sulfone.165 This separation has also been performed with the silver nitrate solution between two sheets of a polysilox-ane.166 A hydrated silver ion-exchanged Nafion film separated 1,5-hexadiene from 1-hexene with separation factors of 50-80.167 Polyethylene, graft-polymerized with acrylic acid, then converted to its silver salt, favored isobutylene over isobutane by a factor of 10. Olefins, such as ethylene, can be separated from paraffins by electroinduced facilitated transport using a Nafion membrane containing copper ions and platinum.168 A carbon molecular sieve made by pyrolysis of a polyimide, followed by enlargement of the pores with water at 400 C selected propylene over propane with an a-valve greater than 100 at 35°C.169... 

In Chapter 20, Koval et al briefly review reports of the use of silver ion-exchanged membranes for separations of unsaturated hydrocarbons. Interesting properties of silver ion-exchanged Nafion are summarized and equations which define common transport performance parameters are presented. New performance data for liquid-phase separations of close boiling alkene/alkane mixtures and a variety of separations involving aromatic compounds are presented. 

Facilitated Transport Membranes Separation of Ethene from Ethane with Silver Ion-Exchanged Nafion Hollow Fibers... 

To test the stability of silver ion-exchanged Nafion hollow fibers for olefin separation, a 50 fiber module was prepared and tested. The observed and calculated ethene flux as a function of the driving pressure is shown in Figure 4. 

Iwai, Y, Yamanishi, T., Thermal stability of ion-exchange Nafion N117CS membranes. Polym. Degrad. Stab. 2009, 94 (4), 679-687. 

Films of the copolymers are, as with Nafion, saponified and used for permselective membranes. They have a much higher tensile strength than the Du Pont material and are also claimed to have a higher ion exchange capacity. 

A very similar idea is the use of ion exchanging polymers into which redox active ions can be incorporated by equilibration with an adherent solution. Sulfonated perfluoro polymers (Nafion), polyvinylsulfonic acid , and polystyrene... 

To keep the consumption of the valuable platinum low, thin foils have been glued to a graphite support [34] or thin-layers of platinum have been sputtered on to a glass base [59]. Platinum can be used in a particle electrode by plating silica gel with platinum [60], or in a solid polymer electrolyte where platinum is incorporated into a nafion ion exchange membrane [61]. 

In the membrane-cell process, highly selective ion-exchange membranes of Du Font s Nation type are used which allow only the sodium ions to pass. Thus, in the anode compartment an alkali solution of high purity is produced. The introduction of Nafion-type membranes in chlor-alkali electrolyzers led to a significant improvement in their efficiency. Today, most new chlor-alkafi installations use the membrane technology. Unfortunately, the cost of Nafion-type membranes is still very high. 

Fischer and Holderich (1999) have shown that Bayer-Villiger reaction of cyclopentanone with aqueous 30 % H2O2, to give delta-valerolactone, is amenable to catalysis with cationic ion-exchange resin (CIER), Amberlyst-I5 without cataly.sts the conversion and the yield of the product are poor. Nafion on silica also works but was found to be poor compared to Amberlyst-15. Beta zeolite also works but was found to be inferior to Amberlyst-I5. 

Klotzbach T, WattM, Ansari Y, Minteer SD. 2006. Effects of hydrophobic modification of chit-osan and Nafion on transport properties, ion-exchange capacities, and enzyme immobilization. J Membrane Sci 282 276-283. 

An improvement in this process was shown by Fujita [17] among others [e.g. 18] who used an ion-exchange membrane such as Nafion as the electrolyte. The cathode... 

Nafion, a perfluorinated sulfonated polymer, is a typical example of an ion-exchangeable resin with high promise as a catalyst support. Its properties are significantly different from those of common polymers (stability towards strong bases, and strong oxidizing and reducing acids and thermal stability up to at least 120 °C if the counter ion is a proton, and up to 200-235 °C if it is a... 

Several strategies to immobilize the p-oxo catalysts on an electrode surface or in a membrane have been employed. However, no available data about their efficiency as modified electrodes for water oxidation have been given.482-486 It should be noted that [ (bpy)2RuIII(OH2) 2(M C))]4+ is also an excellent electrocatalyst for oxidation of chloride to chlorine (better than for the oxidation of H20 into 02) at 1.20 V vs. SCE in 0.05 M HC1 solution,487 or at a modified electrode prepared by incorporation of the complex by ion-exchange into polystyrene sulfonate or Nafion films.482,4 8... 

We have found that similar behavior occurs when the column is packed with other salts of Group I elements, such as NaSbF Na AlF, or NiF, or with Nafion ion-exchange resins (H or K forms). In batch equilibration experiments, using 1 g amounts of solids stirred with 5-15 ml volumes of solutions, we have found that the radon ions can also be collected on the compounds CsBrF, Ca(BrF )2, and Ba(BrF )2. Thus it is apparent that, in its oxidized state, radon can displace H, Na, K, Cs, Caz, and Baz ions from a number of solid materials. 

Because Nafion film can preconcentrate organic cations at a substrate electrode surface, Nafion-coated electrodes can be used as sensitive and selective sensors for electroactive organic cations. The film-entrapped ion is then either oxidized or reduced and the resulting current is recorded and related to the concentration of ions in the aqueous solution (qualitatively similar to anodic stripping voltammetry). It was shown that ion-exchange voltammetric determination of the dication methyl viologen at a Nafion-film-coated electrode results in an improvement of three orders of magnitude in detection limit relative to an uncoated electrode.46... 

The reason for Nafion LB-film fabrication was the wish to obtain the highly ordered systems from perfluorinated ion exchange polymer with multilayered structure, where the ionic layers (conductors) would alternate with fluorocarbon polymer layers (insulators), and to investigate the properties of such films.74 This polymer contains a hydrophobic fluorocarbon polymeric chain and hydrophilic ionic groups, so it is sufficiently amphiphilic it has a comblike structure that makes it a suitable polymer for LB-film deposition. 

---