Salt Rejection of Non-Ionic Polymeric Membranes

A modified solution-diffusion model for the description of salt and water transport through homogeneous membranes is introduced. It is compared with the current solution-diffusion model and the combined flow-diffusion model for the description of transport under reverse osmosis conditions. The advantage of the modified description over the current solution-diffusion model is the inclusion of a salt-water coupling transport coefficient which allows the description to be extended to membranes of high water permeability (high water content). The advantage of the modified solution-diffusion model over the combined flow- diffusion model is that coupling is not introduced by a separate ad hoc assumption on the form of the coupling term, but it is an integral part of the transport description arising from a consideration of what is to be understood by diffusion as opposed to viscous flow. In applying the current and modified solution-diffusion models, extensive use is made of previously-published experimental data.