Ion-exchange membrane systems—Electrodialysis and other electromembrane processes

This chapter describes electromembrane processes and how to model them in a basic way. Electrodialysis is taken as the starting point. Based on a description of the process as used in various applications, a viable modeling approach is developed. It is shown that electrodialysis is a complex process in terms of modeling, since three different driving forces are intrinsically present in the system: the electrical potential, which is the applied driving force, but due to the concentration changes related to the separation itself, concentration differences and (osmotic) pressure differences also occur as driving forces for transport through membranes. Aspects of ion permeation, water transport, and permselectivity are considered, as well as the efficiency of the process in terms of electrical energy use. The focus in this chapter is on macroscopic modeling, that is, understanding the process performance from an overall perspective. Microscopic modeling of pore potentials and electrical charge distribution on microscale is beyond the scope of this chapter. Various related processes are also described: diffusion dialysis, electro-electrodialysis, Donnan dialysis, continuous electrodeionization, membrane electrolysis, fuel cells, (membrane) capacitive deionization, electrodialysis with bipolar membranes, and reverse electrodialysis. Although a detailed modeling of these related processes is beyond the scope of this chapter, a concise introduction to process modeling is given where possible. In some cases, such as for fuel cells, this opens up a vast number of sources related to modeling, while for other processes there has been very limited development of models so far.