| Abstract: | Cellulose acetate butyrate (CAB) membranes gave high salt and urea rejection with a water flux of about 3 gfd (gallons/ft2 · day) during hyperfiltration at 600 psig. Evidence was obtained which indicated that the CAB membranes used in this work were asymmetric. Membrane heat treatment increased urea rejection significantly while salt rejection was invariant, and water flux decreased. An increase in feed solution temperature caused a significant increase in water flux and a small decrease in urea and salt rejection. Increasing the pressure increased water flux and urea and salt rejection. During a 400-hr life test, the water flux decreased by about 25% while urea rejection increased and salt rejection was invariant. The influence of pressure, membrane heat treatment, and compaction during CAB membranes life testing on urea and salt rejection provided evidence that these two solutes were rejected by somewhat different mechanisms. Salt rejection was consistent with a solution–diffusion mechanism for membrane transport and uncoupled flow while changes in urea rejection with pressure, membrane heat treatment, and compaction during life testing suggested that urea was at least partially rejected by membrane exclusion resulting from geometric factors. |
