Electrodialysis theory

After the treatment of the theory and its experimental verifications in the chapters 3 and 4 respectively, chapter 5 will deal with the application of the selective membranes in electrodialysis and related fields. 

Advantages to Membrane Separation This subsection covers the commercially important membrane applications. All except electrodialysis are pressure driven. All except pervaporation involve no phase change. All tend to be inherently low-energy consumers in theory if not in practice. They operate by a different mechanism than do other separation methods, so they have a unique profile of strengths and weaknesses. In some cases they provide unusual sharpness of separation, but in most cases they perform a separation at lower cost, provide more valuable products, and do so with fewer undesirable side effects than older separations methods. The membrane interposes a new phase between feed and product. It controls the transfer of mass between feed and product. It is a kinetic, not an equilibrium process. In a separation, a membrane will be selective because it passes some components much more rapidly than others. Many membranes are very selective. Membrane separations are often simpler than the alternatives. 

As membranes employed in the chlor-alkali industry are generally of the non-crosslinked type, their properties are influenced significantly by the conditions in which they are utilized. The extreme temperature, concentration and current density to which they are subjected in the chlor-alkali process are not encountered in other applications such as electrodialysis. Clarification of the membrane properties is therefore both practically necessary and theoretically interesting, and application of ion cluster theory has been attempted (42, 43). 

A. Sonin and R, F, Probestein. Hydrodynamics—Theory of Desalinarion by Electrodialysis,... 

H.P. Rapp, G. Eigenberger and H. Strathmann, Electrodialysis with bipolar membranes - theory and application , Proc. of ICOM 96 The 1996 International Congress on Membranes and Membrane Processes), Yokohama, Aug. 18-23, p. 506-507. 

Emphasis is on rational theory and its consequences, with the purpose of showing the underlying unity of PCH, in which diverse phenomena can be described in physically and mathematically similar ways. The magic of this unity is shown in the similar manner in which solutes concentrate in a flow containing chemically reacting surfaces, reverse osmosis membranes, and electrodialysis membranes or the similarity of particle motions in sedimentation, centrifugation, ultrafiltration, and electrophoresis. Experimental results, numerical solutions, and reference to topics not covered are noted where they serve to illustrate a concept, result, or limitation of what has been presented. Empiricism is not eschewed, but only limited use is made of it and then only when it contributes to a better understanding of an idea or phenomenon. 

---