Development of reverse osmosis low-pressure membranes.

Abstract

Thin film composite (TFC) membranes were developed for reverse osmosis (RO) under low pressure. Three commercial membranes, i.e. one type of polyvinylidene fluoride, namely AP-10, and two types of polyethersulfone, namely HW-18 and E-500, were used as substrate membranes. Sulfonated poly(2,6-dimethyl-1,4-phenyleneoxide), known as SPPO, was used as the ultrathin barrier layer of the composite membranes. The performances of the three substrate membranes were compared. The pore size and the pore size distribution of the substrate membranes were studied. Then the RO performances of the substrate membranes coated with SPPO were compared. It was observed that a high electrolyte separation without scarification of permeate flux was attained when membrane E-500 was used as the substrate membrane. Afterwards, the effects of the number of coating layers and the coating solution concentrations on RO performance of the TFC membranes, using E-500 membrane as the substrate membrane, were studied. The optimum coating solution concentration and the number of coating layers for maximum electrolyte separation were determined. The TFC membrane was then subjected to post-treatments, i.e. annealing and heat treatment under water, to improve the permeate flux. The final post-treated TFC membrane performance was concluded to be close to the targeted value.