:The Case of Asymmetric Membranes

概要

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Loeb-Sourirajan type cellulose acetate membrane developed for the reverse osmosis process has the asymmetric structure, that is composed of a thin dense layer and remaining porous substrate. Characteristics of each layer were separately determined in this experiment using membranes, whose reverse osmosis characteristics had already been determined. First the diffusivity of NaCl in the porous layer (B) was determined by measuring the release rate of NaCl into water through it after equilibrating the membrane with the solution of certain NaC1 concentrationn Next the permeability of the dense layer (A) was determined by the same procedure except for diffusing through both A and B. Other properties, such as distribution coefficients, water contents and layer thicknesses were determined for B. Those for A could not be determined because of its thinness. Though B layer has no relation with the reverse osmosis separation, its properties are interesting to show the general characters of porous cellulose acetate membranes. With the increase of heat-treatment temperature, water contents decrease, distribution coefficients increase and diffusivities remain constant. Solute permeability of A layer agreed well with that obtained from the reverse osmosis experiment except for membranes with large permeabilities. These results show that transport equations and experimental methods used are correct.
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