Fabrication of multi-layer composite hollow fiber membranes for gas separation

Using multilayer composite hollow fiber membranes consisting of a sealing l ayer (silicone rubber), a selective layer (poly(4-vinylpyridine)), and a su pport substrate (polysulfone), we have determined the key parameters for fa bricating highperformance multilayer hollow fiber composite membranes for g as separation. Surface roughness and surface porosity of the support substr ate play two crucial roles in successful membrane fabrication. Substrates w ith smooth surfaces tend to reduce defects in the selective layer to yield composite membranes of better separation performance. Substrates with a hig h surface porosity can enhance the permeance of composite membranes. Howeve r, SEM micrographs show that, when preparing an asymmetric microporous memb rane substrate using a phase-inversion process, the higher the surface poro sity, the greater the surface roughness. How to optimize and compromise the effect of both factors with respect to permselectivity is a critical issue for the selection of support substrates to fabricate high-performance mult ilayer composite membranes. For a highly permeable support substrate, pre-w etting shows no significant improvement in membrane performance. Composite hollow fiber membranes made from a composition of silicone rubber/0.1-0.5 w t% poly(4-vinylpyridine)/25 wt% polysulfone show impressive separation perf ormance. Gas permeances of around 100 GPU for H-2, 40 GPU for CO2, and 8 GP U for O-2 with selectivities of around 100 for H-2/N-2, 50 for CO2/CH4, and 7 for O-2/N-2 were obtained. (C) 1999 Elsevier Science B.V. All rights res erved.