(469e) RO Membrane Characterization and Modeling Under High Pressure

High pressure reverse osmosis (HPRO) is an alternative to energy intensive thermal desalination technologies for brine concentration. HPRO can potentially reduce the energy consumption of brine concentration by 90% over thermal desalination systems. Operating HPRO is challenging as state of the art thin film composite (TFC) reverse osmosis (RO) membranes do not perform well at excessively high pressures. These membranes can undergo changes when exposed to excessively high pressure. These changes can be modeled and observed in the different layers of the TFC membrane. We break down our work by layer

The polyamide selective layer – This layer is ultra-thin to enable fast water transport but highly crosslinked to restrict solute transport. Under excessive pressure, this layer may undergo microstructure changes. In this work, we valuate the microstructure changes and quantify impacts on permeance and selectivity using molecular dynamics simulations.

Porous support layer - The support layer is typically comprised of that is formed onto a nonwoven polyester scrim layer. Under high pressure, these layers will compress, leading to a reduction in support layer permeance. We use X-ray microscopy to quantify features of compressed membranes (porosity, tortuosity) and to measure the individual permeance of each part of the support layer.

Our findings indicate that polyamide layers do exhibit microstructure changes and a narrowing of the free volume element sizes when under extreme pressures. We also show substantial compression in an RO membrane support layer under higher pressures with more compaction occurring in the polysulfone layer than in the polyester layer. We conduct some tests in the presence of a spacer and find that compression is more severe where the permeate spacer presses against the membrane. Such findings provide critical insight into the future design of HPRO membranes, spacers, and modules.