(54a) Fundamentals Of Gas and Water Purification Using Polymer Membranes

Polymer membranes are critically important in addressing urgent global needs in the 21^st century for energy efficient gas separations as well as reliable, sustainable, efficient access to clean energy and clean water.  In the gas separation field, polymer membranes are now well established for air separation, hydrogen purification, and, increasingly, natural gas processing.  Polymer membranes have also emerged as a leading technology to desalination water (e.g., reverse osmosis) and are being explored for energy generation in applications such as reverse electrodialysis and pressure retarded osmosis.  Furthermore, efforts are under way to develop additional applications of membranes for water purification, such as forward osmosis and membrane-assisted capacitive deionization.  In each of these applications, control of small molecule transport (gases, water and ions) across polymer membranes is critically important for optimizing performance of such membranes.  This presentation focuses on the fundamentals of small molecule transport in polymers obeying the solution/diffusion model.  Structure/property correlations are shown for a variety of polymers, including uncharged and charged materials.  The role of free volume in governing diffusion of solutes through polymers is explored.  Consistent with the so-called upper bound relations in gas separation membrane materials, the existence of a water-salt permeability/selectivity tradeoff relation is observed for polymers being considered for water purification and energy generation applications.  Areas where the physics of water and ion transport are both similar to and different from those of gas transport in polymers are highlighted.