Charged polymer membranes are becoming increasingly important in water and industrial product purification, waste recovery and clean energy processes. Efforts by the scientific community to advance the understanding and performance of charged polymer membranes have historically treated ion exchange (IX) membranes used in electrically-driven processes and reverse osmosis (RO) membranes used in pressure-driven processes as two distinct classes of materials. However, our recent studies show that the water and salt transport properties of commercial IX membranes are generally independent of the membrane polymer type and on the same order of magnitude as those of other desalination polymers. This realization begs the question whether IX membrane polymers could be used in pressure-driven desalination membranes, or vice-versa, and invite further comparisons among different classes of membrane polymers. The combination of our IX membrane data and recently-published transport data for commercial RO active layers, as well as previous studies in the literature of other desalination polymers provide an opportunity to perform such a comparison. Accordingly, we compared the water and salt transport properties (i.e., permeability, partition and diffusion coefficients, water permeance, salt rejection) for twenty commercial IX membranes, four commercial RO active layers, and other desalination polymers. Our analysis shows that transport properties for all membranes fall within similar ranges, illustrating the fact that IX membrane and other desalination polymers are governed by similar ion exclusion and transport mechanisms. We also show that IX membranes have excellent water/salt partitioning selectivity, while RO active layers have exceptional diffusion selectivity. We propose an IX/RO composite structure that takes advantage of the relative strengths of IX and RO polymers to improve the water/salt selectivity of pressure-driven desalination membranes.

Comparison of water and salt transport properties in ion exchange and desalination membranes

2019 Fall National Meeting

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