How can osmosis and solute diffusion be coupled for the simultaneous measurement of the solvent and solute permeabilities of membranes?

• A novel method measures the membrane solvent and solute permeabilities concurrently.
• The method's underlying model is entirely based on osmosis and solute diffusion.
• Osmosis should not be neglected in the calculation of the solute permeability.
• Water and salt permeabilities depend to a large extent on the solution concentration.
• Salt permeabilities thus determined were able to simulate experimental RO rejections.

A novel experimental method and its associated model are proposed for the simultaneous determination of membrane solute and solvent permeabilities, which are essential transport parameters of reverse osmosis models used for process simulation. The method utilizes a single bench-scale batch apparatus consisting of two stirred half-cells containing solutions of different concentrations separated by a membrane across which coupled non-steady-state solute diffusion and solvent osmosis take place countercurrently in the absence of transmembrane pressure difference. Results are presented from days-long determinations of the water and sodium chloride permeabilities of Filmtec BW30 and NF270 membrane samples for initial transmembrane salt concentration differences ranging from 1 g L− 1 to 35 g L− 1. When used as input parameters for the simulation of pilot reverse osmosis desalination tests, the osmotic-diffusive salt permeabilities approximated the experimental rejection rates.

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