Preparation Of Polyetherimide Flat Ultrafiltration Membranes

Polyetherimide(PEI) has many advantages in dealing with oil containing solutions, because of its high glass-transition temperature, good thermal stability, corrosion resistance, chemical stability, permeability and selectivity, compared with the present industrialized membrane material for ultrafiltration. However, the research of its application in ultrafiltration has rarely been reported for its late commerial production. This paper is focus on the preparation of PEI ultrafiltration membrane.The effects of different nonsolvents (H₂O, polyethylene glycol 400 (PEG400), n-butanol (BuOH) andγ-butyrolactone (γ-GBL)) on the behavior of phase separation of PEI casting solution were studied at different operating temperature according to the linerized cloud point (LCP) correlation. It was found that the behavior of phase separation of PEI/DMAc/NSA (nonsolvent additive) mentioned above all agreed well with the LCP correlation. The binodal lines of the four systems were calculated according to the LCP correlation linear regression results. Therefore, the maximum content of NSA in casting solution could be known according to the binodal line of the system, which provided scientific basis for the composition of casting solution. It could be seen that the larger the intercept |a| was the stronger NSA coagulation ability was when the slope of the simulated LCP line was the same. The sequence of NSA coagulation ability was as follows:γ-GBL＜PEG400＜BuOH＜H₂O.Flat Polyetherimide (PEI) ultrafiltration (UF) membranes were prepared by the dry/wet phase inversion method with N, N-dimethyl-acetamide (DMAc) as a solvent, and water as a coagulant. PVP, Ether,γ-GBL, BuOH, and PEG400 were chosen as additives for membrane preparation. The effects of PEI concentration, the types of additives and their contents in casting solutions on membrane structures and performances were investigated, respectively. A series of flat UF membranes with different performances and structures were successfully prepared with the home-made miniature membrane casting machine. The UF membranes prepared in experiment showed that the pure water fluxes (PWF) were from 130 to 1448 L·m^-2·h^-1, and the Bovine Serum Albumin (BSA) rejection ratios were from 30.3% to 99.8% under the operating parameters of 0.1MPa and 20℃.In addition, the effects of coagulant temperature and evaporation time on UF membrane performance were also researched. As the increase of coagulant temperature, the PWF of membranes prepared from PEI/DMAc/BuOH casting solution increased and their rejection decreased. The PWF of membranes prepared from PEI/DMAc/γ-GBL casting solution increased and their rejection changed little with the increase of coagulant temperature. As the increase of evaporation time, the PWF of membranes with ether as an additive decreased and their rejection increased. The PWF of membranes withγ-GBL as an additive increased first and then decreased with the increase of evaporation time, while their rejection showed the opposite trend.