Preparation And Application Of Nanofiltration Membrane Based On Nanomaterials And Fluorinated Monomer

Nanofiltration technology has been widely used in biochemical, pharmaceutical, food and dye areas. How to improve the permeability of the NF membrane has become one of the hottest topics. In this paper, composite NF membranes were prepared by interfacial polymerization. In the preparation process of the NF membrane, the permeability of NF membranes had been optimization by added inorganic or organic materials in the polymerizable monomer solution or selected a new polymerization monomer. The optimization NF membranes were used in the dye wastewater treatment and reverse osmosis concentrated water softening. The conclusions were as follows:Firstly, silica-polypiperazine-amide nanofiltration (NF) membranes were prepared by interfacial polymerization on polyethersulfone (PES) supporting membrane. Different preparation conditions and NF membrane performances were discussed, including silica concentrations, monomer concentrations, reaction time and salt rejections. The chemical structure characterizations of polyamide composite membrane were carried out by attenuated total reflectance infrared (ATR-IR). The surface images and cross sections were observed by scanning electron microscope (SEM) and atomic force microscopy (AFM). The results showed that polypiperazine-amide NF membrane prepared under the optimum conditions exhibited Na2SO4rejection of97.4%and water flux of46.8L·m-2·h-1. After added silica sol in the aqueous phase, the rejection of the resulting membrane changed slightly, but the water flux increased21.1%than polypiperazine-amide NF membrane. According to the rejection of polyethylene glycols (PEGs), the molecular weigh cut-off (MWCO) of the resulting membrane was under600Da. When the nanoparticles of SiO2, TiO2and Al2O3added in aqueous phase and organic phase respectively, the nanoparticles added in organic phase exhibited better performance than in aqueous phase. When the hydrophilic polymer compound of Poly(styrene sulfonic acid) sodium salt (PSSS) in the aqueous phase, the water flux was increased but the salt rejection was changed slightly.Secondly, a novel composite nanofiltration (NF) membrane was prepared by interfacial polymerization of2,2’-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-trifluoroethyl)-4,4’-methylene-dianiline (BHTTM) and trimesoyl chloride (TMC). Different preparation conditions and NF membrane performances were discussed. The membrane structures of composite NF membranes were characterized by ATR-IR, SEM and AFM. The BHTTM-TMC composite NF membrane was prepared under the condition:1%(w/v) BHTTM in the aqueous phase;0.15%TMC in the organic phase; reaction time for10s and curing temperature at80℃for5min. The optimum condition exhibited Na2SO4rejection of85.3%and the water flux of10.1L·m-2·h-1under0.6MPa. The NF membrane was treated by5000ppm chlorine solution for1h. The salt rejection and water flux of the treated membrane reached to94.5%and94.8L·m-2·h-1. The rejection of two NF membranes for inorganic electrolyte solutions decreased in the order of Na2SO4, MgSO4, MgCl2, NaCl, which were typical characteristics of negatively charged membranes.The main objective of the research was to investigate the possibility of obtaining a membrane with high water flux. The composite polyamide NF membranes were prepared by interfacial polymerization of BHTTM and TMC with adding silica sol in aqueous phase. The performances of NF membranes were optimized by studying the preparation conditions. The results showed that the NF mrnbrane prepared under the optimum condition exhibited Na2SO4rejection of85.0%and the water flux of15.2L·m-2h-1under0.6MPa. Compared with the membrane not added nanoparticle in the aqueous phase, the permeability of silica-BHTTM-TMC NF membrane has improved. The NF membrane was treated by5000ppm chlorine solution for1h. The salt rejection and water flux of the treated membrane reached to94.0%and105L·m-2·h-1under0.6MPa (17.5L·m-2·h-1·bar-1). Compared to most other NF membrane water flux (5-10L·m-2·h-1·bar-1), the pure water flux has been greatly improved.Then, the hollow fiber NF membranes were prepared according to the preparation conditions of the flat NF membranes. PVC-silica-polypiperazine-amide NF membranes were prepared by interfacial polymerization of PIP and TMC with adding silica nanoparticle in organic phase. The salt rejection decreased whereas water flux increased with the increased of silica concentration. As the reaction time increased, the water flux decreased and the rejection increased. On the basis of the fluoride flat NF Membrane, the fluoride hollow fiber NF membranes were prepared by interfacial polymerization of1%(w/v) BHTTM in the aqueous phase;0.30%TMC in the organic phase on PVDF hollow fiber ultrafiltration membrane. The hollow fiber NF membrane had a good rejection after treated by500ppm chlorine solution for1h. When the concentration of chlorine solution increased to3000ppm, the rejiection of NF membrane changed slightly, but the permeate flux increased very obviously. PSf-silica-polypiperazine-amide hollow fiber NF membranes were successfully prepared by added silica sol into the aqueous solution.Finally, the reactive brilliant blue X-BR dye wastewater was treated by silica-polypiperazine-amide NF membranes, different operation conditions were discussed. With the increase of operation pressure, the permeate flux increased and the rejection of dye was above99.5%. When the feed dye concentration increased, the permeate flux decreased, but the rejection kept slightly increased. The NF membranes maintain permeability and selectivity after over10days of test, which showed excellent stability during the testing period. In addition, the RO concentrated water was treated by PSSS-polypiperazine-amide NF membranes. Different operation conditions and NF membrane performances were discussed, including operation pressure, temperature and salt concentrations. In different RO concentrated water concentration, the rejection of three kinds of ions decreased as per the order of SO42-, Mg2+and Ca2+. The salt rejection of Ca2+, Mg2+and SO42-kept on decreasing when the feed temperature was increased from25℃to40℃, while the permeate flux was increased. The salt rejection and permeate flux decreased with the increased of RO concentrated water concentration. Generally speaking, the NF membranes had a better treatment effect of dye wastewater and RO concentrated water.