Preparation And Characterization Of Novel Solvents-resistant Nanofiltration Membrane Based On Polybenzimidazole

Solvent resistant nanafiltration(SRNF) membrane process possesses advantages, such as green, high efficiency, low energy consumption and simple operation. This process shows quite good usage in many fields, like the textile, paper, food, pharmaceutical, petrochemistry and biochemistry. Recently, developing high performance polymer solvent resistance nanofiltration membrane with low cost becomes a hot topic in the membrane separation. Polybenzimidazole(PBI) is one of thermoplastics, and possesses excellent mechanical stability, thermal stability and chemical stability. In this study, to improve the solvent stability of nanofiltration membrane materials in the solvent medium, especially in the polar solvent medium, high performance PBI solvent resistance nanofiltration membrane materials were developed by the method of molecular design. The relationship between membranes morphology and their performance was clarified by studying their forming process, crosslinking mechanism and microstructure. The structure, composition and preparation of high performance solvent resistance nanofiltraion membrane were established. The detailed work is as follows:(1) Design and fabrication of PBI membrane material with high performance and excellent solubility, and confirming its chemical structure via NMR and FTIR.(2) PBI solvent resistant nanofiltration membranes were prepared via phase inversion. Their structure is tuned by varying the polymer concentration and the evaporation time of volatile solvent. The relationship between membranes morphology and their SRNF performance was investigated. The experimental results show that with the increasing the PBI content in the cast solution, the number of large pores in the membrane support layer decreased and the surface layer became denser. Accordingly, the membranes selectivity increased and their flux declined.In addition, the morphology of PBI nanofiltration membranes can be tuned by controlling the evaporation time of co-solvent. With increasing the evaporation time of volatile solvent, the thickness of membrane surface layer increased. The membranes showed higher selectivity and lower flux. The prepared PBI solvent resistant nanofiltration membranes showed more than 95% retention on positive charge MB(MW=374) in alcohol based medium. No obvious change in the pure solvent flux of prepared PBI membrane was found after running for 20 hours.(3) To further enhance the solvent stability of PBI nanofiltration membrane, The effect of crosslinking time and the modified PBI membrane structure was investigated. The experimental results showed that the surface roughness of the modified PBI nanofiltration membranes increased, their solvent stability enhanced, and their membrane selectivity can be tuned by varying crosslinking time. Compared with the pristine PBI membrane, the higher selectivity of the modified PBI was obtained, showing more than 90%, even up to 99.9%, retention on rose red, bromothmol blue and crystal violet in the ethanol, isopropanol, ethyl acetate and tetrahydrofuran based medium.