EFFECT OF POROUS SUPPORT FABRIC ON OSMOSIS THROUGH A LOEB-SOURIRAJAN TYPE ASYMMETRIC MEMBRANE

Commercially available asymmetric membranes of the Loeb-Sourirajan (L- S) type comprise a support fabric, bonded to the porous substructure. The influence of this fabric on osmotic permeation flux was examined, mostly with a Toray CA-3000 membrane from which, with care, it was pos sible to remove the support fabric. In osmosis experiments with 12% Mg Cl2 solution on one side (either side) and 6% solution on the other, t he permeation flux (J(1)) was of the order of 0.01 and 0.06 m(3)/m(2) d with and without fabric, respectively. These results could be genera lized by considering the resistivity to solute diffusion in the non-sk in part of the membrane. This resistivity term averaged 104 and 17 d/m for membranes with and without fabric, respectively, and in further t ests without fabric, it was between 15 and 25 d/m over a wide range of MgCl2 concentrations. Four other L-S membranes, all with support fabr ic, were tested in osmosis experiments. Their resistivity values were similar to or higher than those of the Toray membrane with fabric, but , with one of the four, the results were affected by switching the loc ation of the high and low concentration solutions. It was concluded th at existing commercially available L-S membranes are not appropriate f or large-scale osmosis applications because their support fabric decre ases permeation flux excessively.