Understanding membrane parameters of a forward osmosis membrane based on nonequilibrium thermodynamics

Transport phenomena of solvent and solute through a membrane in hydraulic and osmotic pressure driven membrane processes were analyzed on the basis of nonequilibrium thermodynamics with three independent membrane parameters (water permeability, reflection coefficient, and solute permeability). Transport equations describing the flows of solvent and solute through a membrane were derived from general linear differential equations. To examine the uniformity of these parameters in membrane processes operated by the two driving forces, we determined the membrane parameters related to active layer of the same membrane using two methods. First, membrane parameters were determined from rejection data of several neutral solutes in hydraulic pressure driven mode experiments. Second, volumetric flux of solvent and molar flux of solute generated by the same neutral draw solutes were investigated in osmotic pressure driven mode experiments. Membrane parameters for these solutes were obtained based on experimental data and the nonequilibrium thermodynamic model. The results revealed good agreement between the two methods, which demonstrated that hydraulic and osmotic driving force were equivalent in relation to transport behavior within the membrane active layer. This contributed to further understanding of the transport phenomenon in osmotic pressure driven membrane processes and its similarities and differences with that in hydraulic pressure driven membrane processes.

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► Analyzing the performance of an FO membrane based on nonequilibrium thermodynamics.
► The membrane parameters obtained from different modes of experiments were uniform.
► A unique meaning was given for each membrane parameter.