(691d) New Approaches to Forward Osmosis Membrane Design

Forward osmosis (FO) and pressure retarded osmosis (PRO) rely on salinity gradients to drive water across a membrane.  A major limitation to the widespread development and use of these technologies is the lack of an appropriately designed membrane.  Today’s thin film composite (TFC) membrane design consists of a three tiered structure consisting of a polyester (PET) nonwoven, an phase inversion precipitated polyethersulfone (PSu), and a polyamide selective layer.  While this design has yielded highly permselective membranes for hydraulically driven separations, they exhibit poor performance during osmotically driven processes due to the low porosity and intrinsic hydrophobicity of the PSu layer that limits pore wetting.  If the pore structure does not completely wet, the effective porosity of the support is reduced and internal concentration polarization is enhanced through a reduced solute diffusivity.

This paper will present two approaches to membrane design that aim to mitigate the impact of internal concentration polarization.  First, we are able to modify commercial TFC membrane support layers using polydopamine which chemically alter the hydrophobic support layers for increased hydrophilicity.  We are also building radically new TFC membrane support structures using electrospun nanofibers. Modification of TFC membranes has yielded a 5-12 fold increase in flux performance over the native membranes while our new membranes have exhibited a 2-5 fold improvement in flux over the best commercially available FO membranes.