Salt-induced Compaction of Cellulose Acetate Reverse Osmosis Membranes

Abstract

In reverse osmosis, water flux.Jw is expressed as follows:
where A is a water permeation coefficient. Generally, the water permeation coefficient A is not constant, but it varies with applied pressure and feed concentration. This is due to "membrane compaction".
The purpose of this study is to investigate the effects of such membrane compaction phenomena, especially the effect of feed concentration on water permeation in cellulose acetate membranes.
Experimental data obtained and the values shown in the literatures were examined in detail, and a water permeation coefficient A was correlated to the following empirical equation which is analogous to the relation obtained by Kimura and Sourirajan for simple pressure compaction:
where A00 is a water permeability constant, a is a "pressure-induced compaction" factor, and b is a "salt-induced compaction" factor.
The effect of salt-induced compaction is more remarkably than that of pressure-induced compaction, and the value of "b" is greater than that of "a". The effect of salt-induced compaction was not recognized within the scope of this investigation.
And it was assumed that the salt-induced compaction is caused by the change in swelling pressure in the membrane.