Preparation Of Ployimide Solvent Resistance Nanofiltration Membrane

In this research, polyimide solvent-resistant nanofiltration membranes were prepared. Polyamic acid was synthesized using Pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) as raw mateials, and then the polyamic acid was thermal imidized to form polyimide (PI) nanofiltration membranes. The main performance parameters of PI nanofiltration membranes were measured, the main factors affecting the properties of the membranes were studied, and the thermal imidization conditions were optimized.The results showed that the solid content, the thickness of the membrane, the evaporation time, the process of imidization and the time of the coagulating bath greatly affect the Fast Green FCF retention and the flux of the PI membrane. As the PAA concentration increased, the permeation of PI membrane reduced, but the FCF rejections increased. As the heat temperature increased, the permeation increased, but the FCF rejections reduced. Before the phase inversion time of 60 mins, the flux reduced and the rejection rate increased slightly as the phase inversion time increased; but after the phase inversion time reached 90 min, the flux increased greatly, and the rejection rate reduced apparently. The membrane with the highest rejection rate (98%) of Fast Green FCF (MW808.86) and water permeate flux 24.5L/(m2·h)was prepared in the following conditions:polymer concentration was 13%, phase inversion time was 1h, the evaporation time was 5s, and the imidization temperature was 200℃for 2.5h,250℃for 2h, and 300℃for 2h in nitrogen environment, the heating rate was 5℃/min. The filtration conditions:10mg/L FCF in water,20bar, room temperature.The SEM micrographs showed that defects developped after PI membranes were immersed in strong protic solvent (e.g. DMF) for a long time. Infrared spectra results indicated that the solid content had no effect on imidation, and that the starting temperature of thermal imidation was 170℃.