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Abstract

Using modified cellulose acetate membranes, the dependence of volume flow density and salt rejection on pressure was measured in a hyperfiltration apparatus: (1) when the air-dried surface of the membrane is juxtaposed with the brine, and (2) when the bottom surface is juxtaposed with the brine. The thickness of the unstirred boundary layer at the air-dried surface was increased by placing suitable supporting membranes on this surface. These experiments proved that the asymmetric behaviour of modified cellulose acetate membranes is the result of concentration polarization. It was also proved that the film-diffusion-theory model predicts salt rejection behaviour. The studies were completed by electron photo micrographs of the supporting membranes.