Nernst-Planck transport theory for (reverse) electrodialysis: III. Optimal membrane thickness for enhanced process performance
arXiv:2003.07571 · doi:10.1016/j.memsci.2018.07.090
Abstract
The effect of the thickness of ion exchange membranes has been investigated for electrodialysis (ED) and reverse electrodialysis (RED), both experimentally and through theoretical modeling. By developing a two-dimensional model based on Nernst-Planck theory, we theoretically find that reducing the membrane thickness benefits process performance only until a certain value, below which performance drops. For ED, an optimum thickness can be identified in the range of 10-20 microns, while for RED the maximum power density is found for membranes that are three times as thick. Model calculations compare well with experimental data collected with a series of homogeneous membranes with the same chemical composition and a thickness in the range of 10-75 microns. Our results show that the classical picture that membranes should be as thin as possible (as long as they remain pinhole-free and structurally stable) is insufficient, and must be replaced by a more accurate theoretical framework.