Preparation And Application Of Positively Charged Composite Nanofiltration Hollow Fiber Membranes For Dye Purification

A positively charged composite nanofiltration(NF) hollow fiber membrane was prepared by interfacial polymerization using polyethyleneimine(PEI) and trimesoyl chloride(TMC) as the reactive monomers. The preparation conditions of NF membranes were optimized. Na3PO4 is not needed and the heat-treatment process can be omitted, which saves operation time and reduces cost. The surface morphology and chemical structure of the resulting composite NF membrane were characterized by scanning electron microscopy(SEM), attenuated total reflectance-Fourier transform infrared(ATR-FTIR), and X-ray photoelectron spectroscopy(XPS). Pure water flux, contact angle, molecular weight cutoff and surface zeta potential of the composite NF membrane were also evaluated. The rejection of the NF membrane for Mg Cl2(1 g/L aqueous solution at 0.4 MPa) was above 97.0%, and the permeate flux was approximately 35.3 L/m2 h. Furthermore, the NF membrane also showed excellent rejection performance for different dye molecules. The rejections of the NF membrane to brilliant blue KN-R, cationic red X-GTL, acid red B, rhodamine B and cationic gold yellow X-GL were 99.9%, 99.8%, 98.8%, 97.5% and 96.7%, respectively.The dye purification processes of cationic red X-GTL were studied using positively charged composite NF hollow fiber membranes. The impact of dye and Na Cl concentration on dye purification was studied. With the increase of Na Cl and dye concentrations, permeate flux and rejection rates of dye and Na Cl decreased, while the rejection rate of cationic red X-GTL was higher than 96% and the rejection rate of Na Cl was less than 20%. The simulated constant volume batch desalination process for dye purification was studied using hollow fiber NF membranes. Process 3 provided the best purification performance. The concentration of dye in the final solution reached 4.6 g/L, which was 4.6 times more concentrated than the original feed. Additionally, over 96.4% of the Na Cl was taken away from the solution. The results indicated that the higher of the concentration factor was, the better the concentration effect would be, and the less time would be needed.