Studies on a Mechanism for Salt Rejection in Reverse Osmosis Membranes as a Guide to Improved Materials for Desalination of Sea Water.

摘要

This report is presented in two parts which describe studies of the interactions of ions with water in nonaqueous systems in general and in reverse osmosis membranes in particular. The first part describes studies of cellulose acetate membranes which have been treated with aqueous salt solutions. The membranes were studied by ESCA (Electron Spectroscopy for Chemical Analysis) and by Flame Emission Spectroscopy. It is shown that sodium ions penetrate and are retained in the membranes,even after rinsing and that their interaction appears to be particularly strong in the active side of the asymmetrical membranes. An attempt was also made to prepare an effective phosphorylated cellulose acetate membrane which should show superior resistance to hydrolysis at high pH. This phase of the project was not completed,but a recent Japanese patent shows that such membranes may be operable. Further development of such membranes is recommended. The second part of the report describes studies of the hydration of anions in non-polar non-hydrolysis solvents. The resulting free energies of hydration are related to a large number of other water-ion interactions. It is suggested that ion separation by membranes can be profitably regarded in terms of the energy required for dehydration rather than as the consequence of some kind of ion-rejection by the membrane.