Effect of Pore Size and Charge of Ultrafiltration Membranes on Flux and Rejection

Abstract

This research aimed to synthesize two types of asymmetric cation exchange membranes and to study the effects of pore size and charge on flux and rejection. Crosslinked poly(styrene—co—divinylbenzene), CPS, membranes were prepared by the combination of polymerization and phase inversion, while non—crosslinked polystyrene, NCPS, membranes were prepared by phase inversion. Then, the films were sulfonated with 50 percent by volume sulfuric acid to provide the membranes with ion—exchange Capacity (IEC) of 0.5 meq/g. The sulfonation was characterized by infrared spectroscopy and IEC. To obtain the desired IEC sulfonation time of the NCPS membranes was 48 hrs, while that of the CPS membranes was 24 hrs.

Morphology of CPS and NCPS membranes was studied by Scanning Electron Microscope. It was found that these membranes were asymmetric and the location of the dense skin was always at the solution/glass interface. In comparison with NCPS membranes. CPS membranes possessed the higher number of pores, but the pore size was smaller. The flux and rejection of the membranes

were determined at the feed pressure of 10 bar. It was found that pure water flux increased about 50 percent after sulfonation. Rejection of dye and BSA and permeation flux increased as well, especially for NCPS membranes that have larger pore size.