Polymeric asymmetric membranes made from polyetherimide/polybenzimidazole/poly(ethylene glycol) (PEI/PBI/PEG) for oil-surfactant-water separation

Using polyetherimide (PEI) as the membrane material and polybenzimidazole (PBI) and poly(ethylene glycol) (PEG 600) as the additives, we have studied the asymmetric hollow fiber membranes prepared from wet-spun 25 wt% solids of 20:5:75 (wt ratio) PEI/PEG 600/DMAc and 19:1:5:75 PEI/PBI/PEG 600/DMAc solutions for oil-surfactant-water separation. We found that: (1) the addition of PBI in PEI/PEG dope solution resulted in the membrane morphology change from the fingerlike structure to the spongy structure, and (2) bore fluid chemistry significantly affect the membrane permeability. Pure water permeation fluxes of 19:1:5 PEI:PBI:PEG 600 hollow fibers which used 97:3 DMAc:water solution as bore fluid were about 30-fold of that used water as bore fluid (62.7-71.5 vs. 1.8 l/m(2) h bar). The former eliminated hydrodynamic resistance to water on the internal surface of hollow fiber membrane. For oil-surfactant-water emulsion systems (1600 ppm surfactant of sodium dodecylbenzenesulfonate and 2500 ppm oil of n-decane), experimental results illustrated that the rejection rates for surfactant, total organic carbon and oil were 51.4-79.1%, 83.1-92.7% and more than 99%, respectively. Based on the T-g data, PEG existed in hollow fiber membranes and increased the hydrophilicity of membranes because all T-g data were less than that of a neat PEI. In addition, using sodium hypochlorite (NaOCl) as a post-treatment agent for membranes did not show an improvement in membrane permeability, while the elongation at break of treated hollow fiber membranes decreased significantly. (C) 1999 Elsevier Science B.V. All rights reserved.