Pore radius estimation based on organic solute molecular shape and effects of pressure on pore radius for a reverse osmosis membrane

The pore radius of a reverse osmosis membrane was evaluated by considering the molecular shape of uncharged organic solutes. Molecular shape was approximated by a rectangular parallelepiped; molecular length (L) and molecular width (MWd) were used as shape parameters. The steric partition factor of a solute was calculated from L and MWd, and the Stokes radius and diffusivity were estimated from MWd. Twenty-four alcohols and polyhydric alcohols were used as probe solutes, and pore radius was estimated by both non-spherical and spherical models: a uniform pore-size model was used. The non-spherical model gave better correspondence between calculated and observed rejections for ES10 membrane, and the calculated pore radius (0.506 nm) was larger than that obtained by the spherical model (0.301 nm). The effect of applied pressure (0.2–1.0 MPa) on the pore radius was examined with the non-spherical model. The results indicated that the pore radius slightly increased with applied pressure, suggesting that the pore was slightly enlarged by increasing the applied pressure.