Modified poly-2-vinylimidazoline reverse osmosis membranes. II
The RO performances of novel composite RO membranes made from poly-2-vinylimidazoline (PVI) precursors and crosslinked with 3-(chlorosulphonyl)benzoyl chloride (A) have been described in an earlier paper . Modifications were made to these membranes in efforts to improve their RO performances by improving the rate of water transport (flux) through the membranes without adversely affecting their salt-retention properties. Two approaches were used. First, the compositions of the PVI precursor solutions were modified to include selected hydrophilic additives: piperazine, polyvinylalcohol or HA-1 (a proprietary copolymer). The average fluxes of membranes made from precursors comprising PVI I + polyvinylalcohol and PVI I + piperazine were higher than that of the control PVI I/A membrane. Membranes made from precursors comprising PVI II + polyvinylalcohol and PVI II + HA-1 gave good performances at an operating pressure of 500 kPa (average of 90% retention and 200 lmd flux). Second, membranes were post-treated, post-reacted or stored in various ways. This approach was used in efforts to also improve the storage life of the membranes. (Dry storage of PVI/A membranes for about one week had led to a decline in their salt retention.) Good RO test results were recorded for a set of PVI I/A membranes which had been stored in a pH 11 buffer solution for one week (99.1±0.3% retention and 540±88 lmd flux). Post-treatment of PVI I/A membranes with glycerol or polyvinylalcohol also resulted in improved fluxes and storage life of the membranes. © 1992.