Bipolar ion exchange membranes

Consider the following simplest prototype problem for stationary electrodiffusion of a univalent symmetric electrolyte through a bipolar ion-exchange membrane with an antisymmetric piecewise constant fixed charge density XN(x). 

Bipolar ED. Bipolar ion-exchange membranes have one surface consisting of CX resin and the opposite surface of AX resin. The interface between the CX and AX resins may be regarded as a zero gap ED compartment. When a direct current is passed through such a membrane in a direction to pull anions out of such interlace and through the AX resin, the interface rapidly becomes depleted of all ions other than those resulting from the dissociation of water. Dilute alkali can therefore be produced at the outer surface of the AX region and dilute acid at Ihc outer surface of the CX layer. 

A review has been published on the application of ion-exchange membranes as separators in electrolytic reactions [13] and on bipolar ion-exchange membranes for the production of acids and bases from neutral salts [13,14]. 

Ion-exchange membranes are classified according their function as follows cation exchange membrane, anion exchange membrane, amphoteric ion exchange membrane, bipolar ion exchange membrane, and mosaic ion exchange membrane. 

Sensing membrane-.oHgo-probes immobilized pH control membrane bipolar ion-exchange membrane... 

Ion conductivity Electrodialysis Concentration or desalination of electrolytes, separation between electrolyte and non-electrolyte, bipolar ion exchange membrane process to produce acid and alkali, ion-exchange reaction across the membrane, electro-deionization (EDI, CDI), etc. 

A composite membrane prepared, e.g., by lamination of a cation exchange membrane with an anion exchange membrane, called a bipolar ion exchange membrane, shows interesting properties, for example water splitting to generate hydrogen ions and hydroxide ions at the interface of both membranes in electrodialysis, or a rectifier effect.110 When the current is passed from one direction. 

Figure 6.4 Acid and base production by water splitting using a bipolar ion exchange membrane. C Cation exchange membrane A Anion exchange membrane CA Bipolar ion exchange membrane.

Chemical Separation of oxalic acid from glyoxal,44 separation of sodium formate from pentaerythritol,45 preparation of aminoethane sulfonic acid (taurine),46 production of acids and alkalis from neutral salts by water-splitting using a bipolar ion exchange membrane,47 production of pure water by electro-deionization,48 utilization of double decomposition of salt49... 

Figure 6.19 Change in current efficiency of caustic soda production and concentration of caustic soda produced with cation exchange membrane material ( ) generation efficiency of H+ by bipolar ion exchange membrane current efficiency ( ) Nafion 324 (A) Nafion 110 (X) Aquatech membrane.

Today, most bipolar ion exchange membranes are industrially used in continuous ion exchange reactions across the membrane by the use of H+ and OH-generated from the bipolar ion exchange membrane. Examples include separation of gluconic acid from gluconate,28 production of amino acids from amino acid salts,29 separation of citric acid from citrate,101 ion exchange of soybean protein,102 and conversion of lactate into lactic acid.82... 

Fe(CN)6]3-.332 Another case to obtain quinone and hydroquinone by electrochemical oxidation of benzene with a high current efficiency, an anode modified by a bipolar ion exchange membrane, composed of a protonated poly-4-vinylpyridine layer and a perfluorocarbon sulfonic acid layer, is used. [Fe(CN)6]3 is incorporated in the inner layer (protonated poly-4-vinylpyridine) and is not contained in the solution. Release of [Fe(CN)6]3 from the inner layer is prevented by the outer layer. As a result, redox catalysts, i.e., Cr6+/Cr3+, or [Fe(CN)6]4-/ [Fe(CN)6]3 incorporated in the bipolar ion exchange membrane on the electrode surface accomplish catalysis more efficiently than if they were dissolved in the electrolyte solution.333... 

VJ. Frilette, Preparation and characteristics of bipolar ion-exchange membrane, J. Phys. Chem., 1956, 60, 432. 

Harnisch, F., Schroder, U., and Scholz, F. (2008) The suitability of monopolar and bipolar ion exchange membranes as separators for biological... 

J.J. Krol, Monopolar and Bipolar Ion Exchange Membranes. Universiteit Twente, Enschede, 1997. 

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