Characteristics of Cellulose Acetate Membranes used for the Reverse Osmosis Process:The Case of Symmetric Membranes

概要

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To investigate more clearly the nature of the dense layer of asymmetric membranes used in the previous paper, symmetric membranes that consist only of dense layer were made from casting solutions of 4 different compositions. The symmetry of membranes were checked by the reverse osmosis experiment facing both sides of membranes to the high pressure. Using these membranes their perMeabilities and distribution coefficients of NaCl, water contents and thicknesses were determined. These results were combined to give diffusivities of NaCl in membrane, which are highly sensitive to the change of-water content. Its twofold change gives 2 orders of magnitude change of diffusivity. According to the free volume theory of Yasuda based on the concept of homogeneous membrane, diffusivity is dependent on φw, water content, as Ds=Dso exp [-v*/vf, H2O (1/φw-1)] Also according to the pore size distribution theory of Glueckauf based on the porous membrane concept, Ds is given as Ds=Dso φ4w Ds values from both of these equations coincide well with the experimental results obtained here. More experimental results with different solutes are necessary to get more clearer insights and unified understandings of separation mechanism.
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