title: Permeability of uncharged organic molecules in reverse osmosis desalination membranes.
abstract: Reverse osmosis (RO) membranes are primarily designed for removal of salts i.e. for desalination of brackish and seawater, but they have also found applications in removal of organic molecules. While it is clear that steric exclusion is the dominant removal mechanism, the fundamental explanation for how and why the separation occurs remains elusive. Until recently there was no strong microscopic evidences elucidating the structure of the active polyamide layers of RO membranes, and thus they have been conceived as "black boxes"; or as an array of straight capillaries with a distribution of radii; or as polymers with a small amount of polymer free domains. The knowledge of diffusion and sorption coefficients is a prerequisite for understanding the intrinsic permeability of any organic solute in any polymer. At the same time, it is technically challenging to accurately measure these two fundamental parameters in very thin (20-300 nm) water-swollen active layers. In this work we have measured partition and diffusion coefficients and RO permeabilities of ten organic solutes in water-swollen active layers of two types of RO membranes, low (SWC4+) and high flux (XLE). We deduced from our results and recent microscopic studies that the solute flux of organic molecules in polyamide layer of RO membranes occurs in two domains, dense polymer (the key barrier layer) and the water filled domains.
authors.affiliation: Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, 10000 Zagreb, Croatia; Department of Engineering, Aarhus University, Hangoevej 2, 8200 Aarhus N, Denmark. Electronic address: edrazevic@eng.au.dk.
authors.forename: Emil
authors.initials: E
authors.lastname: Dražević
authors.affiliation: Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, 10000 Zagreb, Croatia.
authors.forename: Krešimir
authors.initials: K
authors.lastname: Košutić
authors.affiliation: Pliva Croatia TAPI, Prilaz Baruna Filipovica 25, 10000 Zagreb, Croatia.
authors.forename: Marin
authors.initials: M
authors.lastname: Svalina
authors.affiliation: Department of Engineering, Aarhus University, Hangoevej 2, 8200 Aarhus N, Denmark.
authors.forename: Jacopo
authors.initials: J
authors.lastname: Catalano
mesh_terms: D005374:Filtration; D008567:Membranes, Artificial; D009995:Osmosis; D010539:Permeability; D018508:Water Purification
chemical_list: D008567:Membranes, Artificial
keywords: Desalination; Diffusivity; Organics; Partitioning; Permeability; Reverse osmosis