General Applications of Perfluorinated Ionomer Membranes

Abstract

Described here are applications other than industrial chloralkali, water electrolysis and fuel cells. The applications are divided into six general classes. SeparatorsThe use of Nafion as a separator in cells for chloralkali electrolysis is described elsewhere. The exceptional chemical inertness and thermal stability coupled with favourable electrical conductivity being of particular advantage in this application. These properties have been exploited in a number of other electrochemical applications.The RAI Research Corporation also offers a range of battery separators under the name of Permion (1) . These membranes are made by radiation grafting of a suitably active group onto an inert base film. The active groups include weak acids such as acrylic and substituted acrylic acid and stronger acidic groups such as sulfonated styrene. The base film can be Teflon R, polyethylene or polypropylene. They are thus not strictly perfluorinated membranes as is Nafion, but in chemical inertness and in many physical properties such as electrical conductivity and ion flux are useful as separators in batteries.Grot (2, 3, 4) has summarized the properties of some perfluorinated membranes used as separators, mainly for chloralkali electrolysis, and also described regeneration of chromic acid solutions. Solutions of chromium(VI) in sulfuric acid are used in a number of industrial processes. For example in etching plastics prior to metallizing. The used solution contains chromium(III) which can be electrolytically reoxidized to chromium(VI) using lead anodes. Nafion in tubular form (80 mm diameter) is used as the separator in cylindrical cells. Sulfuric acid is used as the catholyte, the permselectivity of the Nafion ensuring that little sulfate ion migrates to the chromium(VI) solution. In the regeneration of chrome plating solutions even small amounts of sulfate migrating across the separator would upset the critical ratio 0097-6156/82/0180-0475$05.00/0

State of Understanding of Nafion

“…Membranes in H 2 −O 2 fuel cells are of great current interest in this regard. These molecular events also underlie the function of membranes in the arena of membranes in chlor-alkali electrolytic cells, water electrolyzers for the production of H 2 , and membranes used in Donnan dialysis processes that are used to strip metal ions, such as those of copper and nickel, from electroplating waste solutions . Yeager and Gronowski provide a good listing of such applications, a number of which involve Nafion .…”

“…These molecular events also underlie the function of membranes in the arena of membranes in chlor-alkali electrolytic cells, 163 water electrolyzers for the production of H 2 , 164 and membranes used in Donnan dialysis processes that are used to strip metal ions, such as those of copper and nickel, from electroplating waste solutions. 165 Yeager and Gronowski provide a good listing of such applications, a number of which involve Nafion. 166 Related to this is the strong acidity of Nafion in the protonated form and its use as a solid substrate in organic synthesis as a superacid catalyst.…”

Efficiency and Temperature Dependence of Water Removal by Membrane Dryers

“…The resulting gradient in the vapor pressure of water across the membrane drives the transfer of water from the carrier to the purge gas. 4,5 In an alternative "static" arrangement, the Nafion tube can be enclosed in a container packed with desiccant, 6,7 eliminating the need for purge gas but limiting the efficiency and lifetime of the dryer. 7 Nafion dryers are highly selective for water, resistant to chemical degradation, and impermeable to many analytes, excepting low-molecular-weight, polar, oxygenated compounds including some ketones, alcohols, aldehydes, and water-soluble ethers.…”

“…In Nafion-based tubular dryers (Figure ), carrier gas is passed through one or more Nafion tubes mounted coaxially inside a second tube or sheath which is continuously purged with a countercurrent flow of dry gas. The resulting gradient in the vapor pressure of water across the membrane drives the transfer of water from the carrier to the purge gas. , In an alternative “static” arrangement, the Nafion tube can be enclosed in a container packed with desiccant, , eliminating the need for purge gas but limiting the efficiency and lifetime of the dryer 1 Chemical structure of Nafion, where a = 5−11, b = 1−3, c ≈ 1000, and n = 1−13.…”

Conductance Measurements in an Electrolytic Membrane Cell at Elevated Temperatures and Pressures

“…Nation| perfluorinated sulfonate ionomer of 1150 equiv, wt was used to test the method. This type of membrane shows promise in a number of electrochemical applications with corrosive environments because of its exceptional chemical inertness and thermal stability (11). The conductivities of Nation membranes of various equivalent weights have been studied by several investigators.…”