Effects of the polyamide molecular structure on the performance of reverse osmosis membranes

Abstract

Thin-film composite reverse osmosis membranes of polyamides were prepared by interfacial polymerization. Various benzenediamines and poly( aminostyrene) were interfacially reacted with various acyl chlorides to prepare a skin layer of composite membranes. Among the membranes prepared from the structural isomeric monomers of benzenediamines and acyl chlorides, i.e., the same chemical composition but different in the position of functional groups on the aromatic ring, the membrane with the best salt rejection was obtained when the reacting groups forming amide are located at the same position on the aromatic ring. Membranes prepared by interfacially reacting various diamines with trimesoyl chloride revealed that the salt rejection depends on the linear chain structure of polyamides and network formed by crosslinking. Membranes obtained by interfacial polymerization of poly(aminostyrene) with trimesoyl chloride showed higher water flux but lower salt rejection than those obtained by interfacial polymerization of various benzenediamines with trimesoyl chloride. Membranes obtained here showed the typical trade-off behavior between salt rejection and water flux. However, membranes prepared by interfacially reacting trimesoyl chloride with a mixture of poly(aminostyrene) and m-phenylenediamine or a mixture of poly(aminostyrene), m-phenylenediamine, and diaminobenzoic acid showed a performance advantage over usual membranes, i.e,, a large positive deviation from the usual trade-off trend. (C) 1998 John Wiley & Sons, Inc.