Preparation And Characterization Of Polyacrylonitrile-based Solvent-resistant Nanofiltration Membranes

Nanofiltration membrane, a kind of pressure-driven membrane, is a new kind of separation membrane which has been applied in many fields such as foods, medicine, and chemical industry etc. Recently, the application of nanofiltration membrane in organic solution has attracted great attention. In general, the solvent resistance performance of polymeric nanofiltraion membrane is inferior to inorganic nanofiltration membrane, however, it has superior formability. So many researches have been focused on the preparation, characterization, modification and application of solvent resistant polymeric nanofiltration membrane. In this experiment, a series of solvent resistant polyacrylonitrile(PAN)-based nanofiltration membranes were prepared by different methods as alkali-modification, doping with carbon nanotube and interfacial polymerization etc. The main results are as follows.(1) Improving the solvent resistant performance of PAN membrane by alkali modification. The effects of alkali concentration, reaction time and reaction temperature on the membrane performances were investigated. The results indicated that moderate modification is favor for improving the solvent resistant performance. However, excessive modification would destroy the membrane structure. The appropriate modification conditions are as follows: reaction temperature is 45℃,reaction time is 3h and alkali concentration is 2M.(2) A series of solvent resistant CNTs/PAN nanofiltration membranes were prepared by phase inversion and then treated by NaOH and ZnCl2 solution which showed moderate high retention of Rhodamin B in isopropanol. The effects of concentration of NaOH and ZnCl2 solution, time of NaOH treatment and the amount of carbon nanotubes were investigated. The results demostrated that solvent resistance first increased and then decreased with concentration of NaOH&ZnCl2, time of NaOH treatment. SEM, IR analysis and filtration results indicated that the carbon nanotubes were successfully incorporated into PAN matrix. Adding carbon nanotubes can increased the Rhodamin B rejection efficient and flux. However, there was no obvious difference between membranes prepared by adding different dosage of carbonnanotubes.. The highest Rhodamin B retention in isopropyl alcohol is 73.0%, flux of isopropyl alcohol at 0.3MPa is 4.0 L/(m2h). Besides, the mechanical property of membranes with different dosage of carbon nanotubes was also investigated. It seems the fracture strength of the membrane can be improved by adding appropriate amount of carbon nanotubes. Adding some carbon nanotube can also improve the membrane’s heat stability.(3) A series of ZnO/PAMAM/PAN composed solvent resistant nanofiltration membranes were prepared by interfacial polymerization of PAMAMM with isophthaloyl dichloride. The effects of dosage of nano ZnO and concentration of PAMAM were investigated. The SEM images showed that a layer of PAMAM was formed on the surface of PAN membrane. The results showed that Rhodamin B retention first increased and then decreased by increasing the dosage of ZnO particle. While Rhodamin B retention efficient first increased and then leveled off by increasing the concentration of PAMAM, while nano ZnO addition can promote the formation of nodular structure on the polymer layer which can reduce the polymer chain movement so as to improve the solvent resistance of the membrane. The highest retention of Rhodamin B in isopropyl alcohol is 54.8%.