Determination of transport properties and limiting current densities of ion exchange membrane stacks

For the economy of electrodialysis desalination plants it is important to know the permselectivities and permeabilities of the ion exchange membranes used. In particular, when dealing with high salt contents the permeabilities should be small. The relationship between ion flux density and current density was measured with a membrane stack. The experimental data are reasonably accurate, however only as obtained for a combination of an anion exchange membrane with a cation exchange membrane.The permselectivities are compared with data of the apparent permselectivities as obtained from measurements of the membrane potential. In addition, permeabilities were calculated from data of tracer experiments as well as from electrochemical membrane data.Economic assessments also require a knowledge of the limiting current density of the combination of a cation- and an anion exchange membrane, for at higher current densities there will be a loss of both energy and product water.The limiting current density was determined for various membrane combinations as a function of liquid flow.