Computer modeling of water and salt transport in RO membrane active layers

Abstract

As part of a combined computational and experimental effort to develop new reverse osmosis desalination membrane materials, we have carried out detailed equilibrium and nonequilibrium molecular dynamics simulations of the aromatic polyamide active layers of reverse osmosis desalination membranes. Simulations carried out at low salt concentration yield hydraulic permeabilities in good agreement with experimental results for both traditional and novel membrane materials. The pressure and concentration profiles observed in nonequilibrium simulations support a solution-diffusion mechanism for water transport, even at the nanoscale. In the case of salt transport, our simulations reveal the critical role of charged groups in altering the uptake and diffusion of ions in the polymer. These results illustrate the emerging power of detailed computer simulations in the development of new materials.