A New Structure-Performance Model to Understand and Improve Neutral Solute Removal by RO/NF Membranes

We have developed a new structure-performance model relating solvent and (uncharged) solute transport through reverse osmosis (RO) and nanofiltration (NF) membranes. The transport model accounts for hindered diffusion, hindered convection, and solvent/solute-membrane affinity with only parameters unknown (i.e., not directly measureable) –membrane effective pore size and structure factor (ratio of porosity/thickness). To elucidate the two unknowns, membranes need only be characterized by pure water flux and a single neutral solute rejection experiment. Several neutral organic solutes and three commercial NF/RO membranes were characterized to determine relevant physical-chemical parameters (model inputs); subsequent model predictions of uncharged solute transport match experimental data very well. After validating the new model we used it to predict rejection of several representative neutral organic pollutants by commercially available NF/RO membranes and the results suggested that new combinations of membrane chemistry and structure might be required to sufficiently remove such solutes. A series of new membranes were prepared targeting such new membrane structures with satisfying results. We will present the model development, validation, and application.