Study On Preparation And Performance Of Anti-fouling Composite Nanofiltration Membrane

Nanofiltration (NF) is a new type of membrane seperation technique, whose pore sizes range is between that of reverse osmosis and ultrafiltration membranes. NF membranes possess low operation pressure, energy saving, environmental friendly and other series of features. NF membranes are widely applied in food industry, water treatment, pharmaceutical industry and other industries. However, there are still some problems of NF membranes, such as low flux, membrane fouling and poor durability which limit their large-scale applications. This paper aims to improve the flux and antifouling of composite NF membranes by introducing the well membrane-forming and highly hydrophilic polyvinyl alcohol (PVA) into the interfacial polymerization process for preparing NF membranes.The effect of monomer concentration, treating temperature and aqueous phase pH on the performance of NF membrane was studied to determine the best conditions for preparing composite NF membranes. It was found that the optimum monomer concentrations of TMC and PIP are 0.2% and 0.35 wt%. The optimum post-processing temperature and aqueous pH are 50℃and 12.Furthermore, polyvinyl alcohol (PVA) was successfully introduced into the interfacial polymerization process and PVA composite NF membranes have been prepared by varying the ratio of PVA to PIP. Effects of PVA on the formation, structure and separation performance of composite NF membrane were investigated. The results showed that the addition of PVA effectively reduced the Root Mean Squared Roughness (RMS). As the ratio of PVA/PIP increased from 0% to 16%, the RMS of the membrane decreased from 110.7 nm to 41.6 nm. In addition, the presence of PVA improved the hydrophilicity and flux of the membrane while maintaining their rejection performance. For example, the flux was increased by 80% in average when the w/w of PVA/PIP was increased from 0% to 16%. Due to the larger RMS and hydrophilicity, the modified PVA composite NF membranes show better anti-fouling and recovering performance.Finally, PVA composite NF membranes were used in separation of organic compounds. It was found that composite NF membranes are more effective in retenting charged organic compounds than retenting non-charge molecules with molecular weight below 100. For example, the rejections of tyrosine, salicylic acid, and terephthalic acid were 63%,77% and 97%, respectively. Effects of operating conditions on membrane performance were also invetegated.