Reverse Osmosis Separations of Organic Solvent Mixtures and Nanofiltration Separations of Organic Solutions By Perfluoropolymer Membranes

There are very few published articles on reverse osmosis (RO) based separations of organic solvent mixtures where the molecular weights of constituent solvents are less than 100 Da. This problem becomes acute when the solvents are powerful and can swell most of the polymers. To avoid swelling, we are studying particular classes of fluoropolymers which are extremely inert. Various combinations of solvents of interest for separation include aromatic-polar aprotic solvents, polar protic-polar aprotic solvents, polar protic 1-polar protic 2 solvents, polar protic-nonpolar solvents etc. We will illustrate the reverse osmosis separation behavior of such solvent mixtures through novel flat composite perfluoropolymer-based membranes and show remarkably selective permeation-based separations of organic solvent mixtures achieved at room temperature. We will deliberate on the basis for such separations based on solvent properties, solvent-polymer interactions, and the free volume dimensions of such polymers. The solvent sorption properties of the polymer are of significant interest in such a context. This presentation will also focus on organic solvent nanofiltration-based rejection of larger solutes of molecular weight >300 Da from a variety of solvents through particular fluoropolymer membranes. Performance data will be provided for two dye solutes. These data provide a useful backdrop also for the reverse osmosis separation described earlier.