MASS TRANSPORT OF BINARY ELECTROLYTES IN MEMBRANES - CONCENTRATION DEPENDENCE FOR SODIUM CHLORIDE TRANSPORT IN CELLULOSE ACETATE

Equations describing the transport of water and a binary salt through semipermeable membranes are presented. Methods of experimentally determining the resulting six independent transport parameters have been tested. Measurements of these parameters on Loeb-type membranes are presented for curing temperatures of 75°, 84°, and 95° C. If the membrane concentration is characterized by the geometric mean activities of adjacent solutions, the osmosis parameters as defined are concentration-independent up to 0.1M. They are also independent of the pressure difference across the membrane up to 600 p.s.i.g. Above 600 p.s.i.g. compaction causes a decrease in the transport parameters. Coupling between the different driving forces is quantitatively measured. During reverse osmosis the water flux is not influenced by coupling and can be described by one parameter. The salt flux shows coupling to the water flow and requires two parameters to describe its variations. The reciprocal relations are valid to within at least an order of magnitude. Since water flux coupling is small, the uncertainty in the magnitude of the corresponding coupling parameter is large. Electrical conductivity in a membrane is one third or one fourth of that in the adjacent solution. The transference number of the sodium ion decreases from 0.85 at 0.0035M to about 0.3 at 0.075M. © 1969, American Chemical Society. All rights reserved.