Composite Polyvinyl Alcohol Nanofiltration Membranes Developed

As a new separation membrane technology developed in recent years, nanofiltration membrane is the most appealing field of membrane science and technology Compared with those traditional membranes, the advantages of nanofiltration membranes are as follows:(1) Having hole diameters of nanometers;(2) Low operation pressure;(3) Economic for it can replace many procedures in traditional process and separation technology,(4) Having high selectivity to different irons.Now the demands for nanofiltrations membrane in those medicine and food industries increase dramatically. Among them, to develop nanofiltration membranes which have low cost, high stability to heat and good performances is a very important task.Poly(vinyl alcohol) is material that becoming more and more appealing to thin film composite nanofiltration membrane.Having poly(vinyl alcohol) as membrane material, malic acid and 5-sulfosalicylic acid as crosslinking agents, this research aims at developing a nanofiltration membrane, which is chlorine-resistant and have good performance.Thin film composite nanofiltration membranes were prepared by coating porous polysulfone membranes with a polyvinyl alcohol layer and further cross-linking its surface. Under the conditions of operation pressure about 0.75 MPa and feed temperature 25℃, the rejection performance of NaCl feed solution (500ppm), is about 35%, while the flux is about 2.5m3/m2d, which is relatively high compared with thosecommercial nanofiltraion membranes having the same rejection characteristics.Serving as support membranes, polysulfone ultrafiltrtion membranes were prepared in advance by phase conversion methods, of which the average hole diameters were about 600 A. The influences of the kind and concentration of additive in the casting solutions were discussed, and NMP was the one that can result in better performance, while the mixture of NMP and PEG would broaden the scope of average diameters.In the preparation of the barrier of composite nanofiltration , the malic acid and the 5-sulfosalicylic acid were proved to be effective, resulting in a relative high flux without rejection decrease. And the experiments showed us that, those factors which could make impacts on the membrane performances included the concentrations of reactant, catalyst, the time and temperature of crosslinking, and testing conditions, such as the operation pressure, concentration of feed solution etc..