The changes of membrane performance with polyamide molecular structure in the reverse osmosis process

In order to develop high performance membranes for the reverse osmosis process, thin film composite membranes were prepared by the interfacial polymerization with various acyl chloride solutions and amine solutions containing poly(m- aminostyrene), (PmAS). PmAS was prepared by reducing poly(m-nitrostyrene) that was obtained by the free radical polymerization of 3-nitrostyrene. The results related to changes in the membrane performance with interfacial reaction time and thickness measured with ESCA indicate that the thickness of the skin layer obtained from various reactants is nearly constant. Membranes obtained by the reaction of trimesoyl chloride (TMC) with various amines, i.e. aromatic diamines and polyaminostyrenes showed performance advantage over those obtained from the difunctional acyl chlorides and amines. Membranes prepared by the reaction of TMC with aromatic diamines, PmAS, or poly(p-aminostyrene) exhibited a trade-off trend between salt rejection and water flux. Membranes prepared by the reaction of TMC with a mixture solution of PmAS and aromatic diamines showed performance advantage over the trade-off trend. Membranes prepared from PmAS and a mixed solution of TMC and benzoyl chloride (BC) also exhibited a performance advantage. The active skin layer of thin film composite membrane, which showed the best performance in the reverse osmosis process could be obtained by reacting mixed amine solution containing PmAS and m-phenylenediamin (MPDA) with mixed acyl chloride solution containing TMC and BC. Membranes having a continuous range of properties as well as a performance advantage over usual membranes could be developed by blending the reactants or by controlling the polyamide chain structure. (C)2000 Elsevier Science B.V. All rights reserved.